Shriver, the Manipulation of Air-Sensitive Compounds.Pdf

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scNnodr[ocl^tilsN]s-dtv JONO|rytndrNVlN lHl THEMANIPULATION OF AIR.SENSITIVECOMPOUNDS

SECOND EDITION

D. F.SHRIVER

Nort hu'est ertt U tt i versi I v Evonstott. Illinois M. A. DREZDZON

Antoco C hetn icu ls Contpurty, Nuperville, Illittois

A Wiley-lnfersciencePublicotion JOHNWITEY & SONS New York / Chichester / Brisbqne / Toronlo / Singopore

I- Copvright i' 1986bv John Wilel ct Sons.Inc.

All rightsreserve'd. Published sinrultaneouslt in Canada.

Reproductionor translationof anv part of thrs u ork be1'ondthat pernrittedb1'Section 107 or l0U of the 1976United StatesCopl'right Acr \\'ithoutthe pcrnrission of the copl'rightouncr is unlauful.Ilcqucsts for pcrnrissionor further in{ornrationshould bc addressedtt, the PermissionsDepartmcnl. John Wilo & Sons.Inc.

Libru4' td Congre.ssCutaloging in Publication Data:

Shriver,D. F'.(Du*'ard F.). 193.1- The manipulationof air-sensitiveconrpounds.

"A Wile-,--lntersciencepublication. " lncludesbibliographical references and index. l. Chemistrv-Manipulation. 2. Vacuumtechnology. 3. Protectiveatmospheres.,{. Air-sensitivecontpounds. I. Drezdzon.M. A. (Mark A.) II. Title.

QD6l.557 l9rJ6 542 86-1l0l2 lsBN0-.171-86773-X

Printed in the United Statesof America r0 9 8 7 6 5 ,1 3 2 I PREFACE

The continuedimportance of researchand developmentwith air-sensitivecompounds,coupled with the generallack of publicationsor undergraduateinstruc- tion on the techniquesused in this area, prompted us to revisethis monograph. The levelof presentationis designedto make the book usefulto the chemistwho is beginningwork in the field. In addition, considerabletechnical data and information are given that should aid chemistsat all levelsof proficiencyin the designof experiments. In the belief that the beginnerneeds a selectiveapproach and the more sea- sonedworker will exercisehis ingenuity,we haverefrained from presentingbrief referencesto many similar items of equipment, but have attemptedto present rational approachesto the common operationsinvolved in the synthesis,separation, and characterizationof air-sensitivematerials, and to illustratethese with typical apparatus.Whenever possible, these examples are basedon equipment with which we havehad experienceor on firsthand observationof the equipment usedby others.This has resultedin a somewhatpersonalized account, which we hope will ensurereliability without being objectionableto establishedworkers with different preferencesin equipment design.The techniquesdiscussed here were largelydeveloped for use with inorganic and organometalliccompounds; however,they are generallyuseful for problens involvinggases and air-sensitive solidsor liquids, so they find application in all areasof chemistry,as well as biology and physics. We had two goals in mind while writing this secondedition. The first was to bring the text up to date. Although there have been no radical new develop- ments,there has beena steadyimprovement in technique.Our secondobjective wasto make the book more accessibleto the readerinterested in a specifictech- nique. Thus more sectionheadings are used and more detailedexamples are given. PREFACE

The continuedimportance of researchand developmentwith air-sensitivecompounds,coupled with the generallack of publicationsor undergraduateinstruc- tion on the techniquesused in this area, prompted us to revisethis monograph. The levelof presentationis designedto make the book usefulto the chemistwho is beginningwork in the field. In addition, considerabletechnical data and information are given that should aid chemistsat all levelsof proficiencyin the designof experiments. In the belief that the beginnerneeds a selectiveapproach and the more sea- sonedworker will exercisehis ingenuity,we haverefrained from presentingbrief referencesto many similar items of equipment, but have attemptedto present rational approachesto the common operationsinvolved in the synthesis.separation, and characterizationof air-sensitivematerials, and to illustratethese with typical apparatus.Whenever possible, these examples are basedon equipment with which we havehad experienceor on firsthand observationof the equipment usedby others.This has resultedin a somewhatpersonalized account, which we hope will ensurereliability without being objectionableto establishedworkers with different preferencesin equipment design.The techniquesdiscussed here were largely developedfor use with inorganic and organometalliccompounds; however,they are generallyuseful for problemsinvolving gases and air-sensitive solids or liquids, so they find application in all areasof chemistry,as well as biology and physics. We had two goalsin mind while writing this secondedition. The first was to bring the text up to date. Although there have been no radical new develop- ments,there has beena steadyimprovement in technique.Our secondobjective wasto make the book more accessibleto the readerinterested in a specifictech- nique. Thus more sectionheadings are used and more detailedexamples are given. PREFACE

In the preparationof the first editionof this book aid u'asreceived from nrany people:A. L. Allred, F. Basolo,R. L. Burwell,Jr.,E. W. Schlag,Paul Treichel, R. W. Fowells,and Shirley Shriver. Useful suggestionsfor the secondedition were provided by L. Aspry, R. L. Burwell, Jr., P. Bogdan. N. J. Cooper, D. Kurtz. J. Malm, and S. H. Strauss.For aid in proofreadingwe appreciate the help of Ann Crespi, CynthiaSchauer, Daniel Shriverand Ralph Spindler.

D. F. Ssnrvrn M. A. DnpzpzoN

Evanston. Illinois Nuperville. Illinois Februum, I986 CONTENTS

INTRODUCTION

PART4 INERT-ATMOSPHERETECHNIOUES 'l grNcx-roprNERT-ATMospHERETEcHNToUES l.l Techniquesfor Purgingand Drying Apparatus,7 1.2 Adaptationsof StandardGlassware, I I 1.3 Syringeand CannulaTechniques, l3 1.4 QuantitativeGas Manipulation,24 -Iechniques, I .5 Schlenk 30 1.6 CappablePressure Reactors,4l l 7 Hot Tube and SealedTube Technioues.42 GeneralReferences.44

2 INERT-ATMosPHEREGLovEBoxEs 45 2.1 GeneralDesign and Applications,45 2.2 Replacementof Air by an Inert Atmosphere.47 2.3 Sourcesof and Reductionof Impurities in Glove Box Atmospheres.51 2.4 Glove Box Hardware and Procedures,59 2.5 Typical Glove Box Systems,62 2.6 Equipmentand Operations,64 General References.66

3 INERTGASES AND THErR puRrFrcATroN 68 3.1 Sourcesand Purity,68 3.2 Purificationof Gases.69

vll r viii CONTENTS

3.3 Inert-GasPurification Systems, 80 3.4 Detectionof Impurities,83 General References.83

4 puRrFrcATroNoF sotvENTs AND REAGENTS 84 4.1 SolventPurification. 84 4.2 SolventStorage, 89 4.3 DetectingImpurities, 89 4.4 Purificationof SpecificSolvents, 90 4.5 Purificationof SomeCommonly Used Gases, 92 4.6 AnhydrousMetal Halides,95 GeneralReferences.96

PART2 VACUUM LINEMANIPULATIONS

5 vAcuuM LINEDESTeN AND oPERAIToN 99 5.1 GeneralDesign, 99 5.2 Initial Evacuation.103 5.3 Manipulationof VolatileLiquids and CondensableGases. 104 5.4 Lorv-TenrperatureBaths. 109 5.5 Vapor Pressureas a CharacteristicProperty, I l3 5.6 Manipulationof NoncondensableGases, I l3 5.7 Safety,116 GeneralReferences. ll7

6 PUMPsFoR RoUGH AND HIGH vAcuuM .t.t8 6.1 Rough-VacuunlSystems, l l8 6.2 High-VacuumPumping Systems, I l9 General References.128

7 PRESsUREAND FLOw MEAsUREMENT AND IEAKDETECTION t29 7.1 Manometry(l-760 torr), 129 7.2 Medium-and High-Vacuum Measurements(10 r-10 6 torr). 137 7.3 Leak Detection.143 7.4 Flow Measurement.146 7.5 Flow Control. 149 GeneralReferences. 150 CONTENTS IX

8 JorNTs,sToPcocKs, AND vALVES 152 8.1 Joints,152 8.2 Stopcocks,161 8.3 Valves.164

9 spEcrALrzEDvAcuuM LINE EeutpMENT AND opERATtoNs .r68 9.1 Characterization.168 9.2 Separations,190 9.3 Storageof Gasesand Solvents,200 9.4 SealedTube Reactions.202 9.5 MiscellaneousTechniques, 206 General References.208 '10 MEIALsYsTEMS 210 l0.l CompressedGases, 210 10.2 Cutting and BendingTubing, 214 10.3 Tubing, Joints,and Fittings,215 10.4 Heavy-WalledTubing and PipeJoints, 219 10.5 Valves.222 10.6 PressureGauges, 227 10.7 TypicalMetal Systems,227 General References.236

APPENDIXI SAFETY 237 I.l Combustibles,237 I.2 UnstableCompounds, 238 I.3 SomeDangerous Mixtures, 238 L4 Disposalof ReactiveWastes, 239 I.5 High-PressureGas Cylinders.240 I.6 Asphyxiationby Inert Gases,240 I.7 ExtinguishingFires, 240 General References.241

APPENDIXII GLASSAND GLASSBLOWING 242 II.l Propertiesof Glasses,242 IL2 Equipmentand Materials,245 II.3 Sequenceof Operations.247 II.4 Annealing,247 ll.5 Cutting GlassTubing,248 IL6 BendingGlass Tubing,249 II.7 Test-TubeEnds and Fire Cutoffs.249

I- CONTENTS

II.8 End-to-EndSeals. 251 IL9 T-Seals.253 II.l0 RingSeals. 253 I I. I I ClosedCircuits. 255 II.l2 Metal-to-GlassSeals. 255 II.l3 HealingCracks and Pin Holes,256 IL14 SealingTubing under Vacuum,257 General References.258

APPENDIXIII PLASTICSAND ELASTOMERS 259 III.I Plastics:General Properties and Fabrication.260 IlL2 CellularPlastics. 265 III.3 Propertiesof SpecificPlastics, 267 III.4 Elastomers.272 lll.5 Propertiesof SpecificElastonrers, 272 General References.274

APPENDIXIV METATS 275 IV.l Propertiesof SpecificMetals, 276 General References.280

APPENDIXV VAPOR PRESSURESOF PURESUBSTANCES 28tl V.l Analy'ticalRepresentation of Vapor PressureData. 281 V.2 Least-SquaresFitting Procedurefor the AntoineEquation, 28.1 V.3 Correlationand Estimationof Vapor Pressures,286 V.4 Tableof Vapor Pressures.289 V.5 Sourcesof Vapor PressureData. 313

APPENDIXVI PRESSUREAND FLOW CONVERSIONS 3,15

INDEX 3.19 INTRODUCTION

A. Generol Mefhods. The mostwidely used methods for handlingair-sensitivecompounds are basedon the useof an inert gasatmosphere to excludeair. This approachmay be further subdividedinto ( 1)those techniques which involve bench-topoperations with specialglassware (often called Schlenktechniques, Chapter 1) and (2) glove box techniquesin which conventionalmanipulations are perfornredin an inert-atmospherebox (Chapter 2). Both of thesemethods may be usedto handle large quantitiesof solidsand liquids; however,the Sch- lenk type equipmentis generallymuch more efficientand more securefrom the atmospherethan the dry box. The principal advantagesof the dry box lie in its usefor intricate manipulationsof solidsand for the containmentof radioactive and/ or highly poisonoussubstances. More rigorousexclusion of air and the quantitativemanipulation of gasesis achievedin a previouslyevacuated apparatus. This vacuum line method is outlined in Chapter5, wherethe basicoperations are described,such as quantitative transferand pressure-volume-temperaturemeasurement of gases,trap-to- trap separations of volatile materials, and the use of vapor pressuresto characterizesubstances. Succeeding chapters (6-8) describein detail the individual vacuum line componentssuch as stopcocks,joints, diffusionpumps, and manometers.Many accessoryitems such as spectroscopycells, vapor-pressure thermometers,and gas-chromatographyapparatus are describedin Chapter9. This set of chapters,plus supplementarymaterial in the Appendixes,form a guide to modern glassvacuum line practice.This techniquehas beenused suc- cessfullyin the synthesisand manipulationof hydrides,halides, and many other volatile substances.However, glass vacuum systemsare not appropriate for hydrogenfluoride and someother reactivefluorides. These are best handled in the metal or fluorocarbonapparatus described in Chapter 10. The strengthsof thesevarious techniques for handling air-sensitivematerials are summarizedin Table l

f z INTRODUCTION

Toble'1 . Comporisonof lnert-Almosphereond Vocuum LineTechniques

Technique Exclusionof Air Quantities" OutstandingFeatures

Schlenkand Good to very Medium to Rapid and easymanipulation syringe good large of solutions;simple fansfer of solids Glovebox Poor to very Small to very lntricate transferoperations; good large containmentof poisonousand radioactivesubstances Vacuumline Very good to Very small to Quantitativegas handling; excellent medium transferand storageof volatile solventss ithout contaminalion

"Very small, about I mgl small. about 100mgl medium, severalgramsl large,hundreds of grams; very large. kilogranrs.

B. Plonning lhe Expeliment. Whatevergeneral technique is used,it is important to plan each new experiment in detail. Impassescan be avoided b1' sketchingthe setupat eachstep with due attentionpaid to the methodfor transferring materials.If measurementsare involved,a simpleestimate of the potential errors should precedethe newly planned experimentto ensurethat results will be determinedwith meaningfulaccuracv. Frequently. such an estimatewill suggestconditions and apparatusdesigns which will minimizethe errorswithout introducingany new complications.

C. Appololus Design. Sometimesit is necessaryto designand construct specialapparatus. Three criteria for a good designare: (1) Is it the sinrplest designconsistent with its intended purpose?(2) Is it robust? (3) Is it easyto clean?To ensurethat an item is sturdy it shouldbe designedso that stressesare not concentratedin small sectionsof glass.For pernranentinstallations, such as a vacuumline. all heavyitents are individually supported. rvhile the lightersec- tions are clampedat the minimum number of pointsu'hich suffice to supportthe apparatusand avoid leverage.Generall,v. portable glass\Ä'are should be designed as one strong, compact unit \r'hich may be supportednear a point of balance. Finally,the materialsof constructionmust rvithstand the chemicalsand solvents which are to be handled. The most frequent problemsarise with stopcock greases,\\'axes, rubbers, and plastics.These problen'ls may be minimizedby se- lectingmaterials on the basisof the information on chemicaland solventresistance which is preserrtedin Chapter 8 and Appendix IIl. To aid in the proper choiceof metals,information on their corrosionresistance is givenin Chapter10 and AppendixIV. I

's{?OJ JoJxoq e^oJ8Jo snlsJpddelunnJe^ ^rau e '{JJn;e;eco1 ,{resseceu 'elduexe .epe.,, rraqJ sr 1r Joc ueeq seq aEueqce ra,ra -ueq,t sllneJ JoJIJer{c o1pa;eda.rd aq lsntu 1sr;elueulradxeaq} .eJoJereql .snl€r -edde pa'ra1yero pelJnJrsuoc Ä1meue uorJ drqru".ulro^ ur srJeJap e^ouar 'pau8rsap ll'.us o1dressecau dJJensn sr 1r rJradoid luerudrnbaeqr'pu' i.n,äruo" lle,r aq Äeruluauuedxa ue q8noql ue,rE .Ou;looqselqnotl .o puo InO-IcaqC

NO[CnooölNl

A PARII Inert-Atmosphere Techniques 8 eENcH-TopTNERI-ATMoSpHERE TEcHNtoUES evacuationofthe apparatus,and ifthere areno leaksin the apparatus,n repeti- tions of the pump-and-fill processwill reducethe fraction of atmosphericgases A, to (l)

The secondmethod for removingatmospheric gases involves sweeping air out of the apparatusby a flush of inert gas. The factorswhich influencethis type of processare discussedin detail in Chapter 2. For the present.it is adequateto note that a continuousflush of inert gas, u'hich pushesthe atmosphericgases from one extremeof the apparatusto an outlet on anotherextreme, as in Fig. 1.1,is mostefficient. This so-calledplug flow is difficultto achievewith single- neckflasks and similar apparatus.A flow of inert gaswhich bypassespart of the apparatusis relativelyinefficient.

B. Purging on Open Vessel. In many operationsdescribed in this chapter, it is necessaryto open the apparatusbriefly while an inert-atmosphereflush is maintained out of the openingto minimize the entranceof air. Even under conditionsin which there is little turbulence in the flowing inert gas stream,

Inerl-gas rnlet2 +

To nooo --\ + water \

Mineral oil bubbler

Fig. l.l. Three-neckedreaction flask with dropping funnel. stirrer, and reflux condenser.With the droppingfunnel stopcockin the open position.a flou of inert gasfrom inlet I through the mineral oil bubbler efficientlypurges the apparatusof atmosphericgases. During reactionand subsequent coolingof the reactionmixture. a slow flow of inen gasfronr inlet 2 through the mineral oil bubbler preventsatmospheric gases from backing up into the system.and this configurationmini- mizesexposure of the reactionmixture to impuritiesin thc-inert gas. TECHNIOUESFOR PURGING AND DRYINGAPPARATUS I therewill be countercurrentdiffusion of atmosphericgases. An estimateof the flow rateI necessaryto maintain the partial pressureP11 of an atmosphericcom- ponent at some desiredpartial pressureP inside the apparatusis given by the equationl - -(ADt.2/X)ln(P/Po) L Q) where,4is the cross-sectionalarea of the tube through which the gasis issuing,X is the lengthof this tube, and D1.2is the diffusioncoefficient of the impurity gas I in the inert gas 2. In round numbers, the diffusion coefficientof oxygenin nitrogenis 0.2 cm2ls at I atm total pressure,and a desirablepartial pressurefor oxygenwithin the apparatusmight be 10-rtorr. If we assumethat the neck of a flask is 1.5 cm in diameterand 5 cm long. Eq. (2) indicatesthat a nitrogenflow rate of only 50 cm3/min would be requiredto maintain this low levelof oxygen. Experienceteaches us that far larger flow ratesare required; somethingon the order of severalliters per minute would be typical under theseconditions. Even though Eq. (2) doesnot appearto apply to the rather largeopenings common to many preparative-scaleapparatus designs, it is probably much more accurate for the lessturbulent flow of gas from smaller-diametertubing. The general form of the equationis sensible,suggesting that the entranceof air is reducedby a long-neckedflask with a small crosssection for this neck.

C. Monifold fot Inert Gos ond Vocuum. Pureinert gas.generally nitrogen but sometimesargon or helium, is requiredfor the operationsdescribed in this chapter. As describedearlier, equipment is filled with the gas by purging with a large volume of gas, or evacuationfollowed by filling with the gas. To accomplishthese purging operationsin an efficientmanner it is handy to have an inert-gasmanifold with severalheavy-walled flexible vinyl or rubber tubes attachedto provideinert gasto separatepieces of apparatus.A mineraloil bubbler, or occasionallya mercurybubbler, is attachedto the gasoutlet on the apparatusto protect againstexcessive pressure. When the pump-and-fill techniqueis used,a more complexmanifold for the distributionof inert gas and vacuunl is generallyemployed, in conjunctionwith a liquid nitrogen-cooledtrap, mechanicalvacuum pump, and pressurerelease bubblers(Fig. 1.2). This manifold can be usedto purge severalpieces of apparatusat once, and the two-way stopcocksor valvesprovide a ready means of switching betweenin- ert gas and vacuum. Sourcesof purified inert gas and vacuum are attachedto this manifold. An oil bubbler on the inert gasinlet servesas an approximateflow indicator. The inert gas is controlledat the tank with a high-qualitydual-stage diaphragm regulatorwhich is designedfor good regulationaround 3 psig (915 torr). A pressurerelease bubbler is often included on the inert gas line. Glass stopcocksattached to thesemanifolds will becomedislodged by the small positive pressureof inert gas.Therefore, it is essentialto securethese stopcocks, and rG. Antos. Ph.D. Thesis,Northwestern Universitv. 1973. ,10 BENCH.TOPINERT-ATMOSPHERE TECHNIQUES

To vacuum pump

Pressurerelease bubbler .r'

To apparatus Low-temoerature trao

Fig. 1.2. Manifold for medium vacuumand inert gas.A low-temperaturetrap, on the right sideof the figure,is usedin the vacuumline to protectthe pump from harmful vapors.When the apparatus is being filled u'ith gas or purged *'ith inert gas. the valveon the pressurerelease bubbler (uhich containsa checkvalve to preventoil from backingup into the line)is openedto avoidexcess pressure u'hichwould blo* the apparatusapärt. Oflen a mineraloil bubbler(nol shownhere) is connectedin line u'ith the inert-gassource to providevisual indication of the inert-gasflow.

all others used on inert-atmosphereequipment, with high-quality plug retainers.2 Details on the purification of inert gasescan be found in Chapter 3. The sourceof vacuum is generallya rotary mechanicalvacuum pump. The pump is protectedfrom chemicalsand solventvapor by meansof a trap cooledby Dry Ice or, preferably,liquid nitrogen.CAUTION: A liquid nitrogentrap must neverbe connectedto a manifold where the vacuum sourcehas been turned off. Failure to removea liquid nitrogen trap from a manifold after shutting off the vacuum will result in the condensationof liquid air in the trap. If warmed up, this liquid air will evaporateand may pressurizethe apparatus, presentingan extreme explosion hazard. It is desirablefor this trap to be deepenough to extendto the bottom of a l-L Dewar, thus permitting long-termcooling. The trap shouldbe easily removedso that accumulatedcondensables can be readily (and frequently) discarded.

D. PUrging Sylinges. Syringesare conveniently purged from an inert-gas sourcesuch as a tubewith a rapidlyflowing inert-gas stream or a specialseptum attachedto the inert-gasmanifold. Two or threecycles of filling,removing the

'Excellent retainers(K-809000). which must be usedu'ith stopcockplugs front the sanremanufac turer, are availablefronr KontesGlass Co. Vineland NJ. ADAPTATIONSOF STANDARDGLASSWARE 11

needlefrom the inert-gassource, and expellingthe gas are sufficient.If the syringe is going to be used to removeliquid fronr a flask which is being rapidly flushed,the inert gas may be drawn from the flask and expelledoutside of the flask to purge the syringe.When highly moisture-sensitivematerials, such as aluminum alkyls and activeborohydrides, are being handled,the syringeparts should be stored in a drying oven around 130"C and removedjust prior to purging.

E. Drying Glosswore. The purging proceduresdescribed thus far remove relativelylittle of the moisturewhich is adsorbedon glasssurfaces. When handling compoundswhich are highly moisture sensitive.such as aluminum hydrides.borane adducts, and lithiunr alkyls, it is often in'rportantto employspe- cial drying procedures.A drying ovenset at around l30oC can be usedto bake out glasswarefor severalhours prior to use. This glasswareshould be flushed with dry inert gasas it cools.To preventapparatus from stickingtogether, standard taper joints, stopcocks,and syringesshould be completelydisassenrbled beforethey are placedin the oven. Alternatively,the glasswaremay be flushed while it is being heatedwith a Bunsenburner or heat gun. CAUTION: When using a Bunsenburner or heat gun to dry glassware,all flammable materials must be removedfrom the area. If the glasswarehas been rinsed with a volatile solvent, such as acetoneor methanol, to aid the drying process, the residual solvent vapors should be removed from the glasswareprior to drying by purging severalminutes with inert gas. The heatingis startednear the inert-gasinlet and carriedalong the apparatustou'ard the gasoutlet. Silylatingagents have also been used to treat glassrvarebefore handling nrttis- ture-sensitivecompounds. For example,a chlorine-ternrinatedpol-ydinteth-yl si- -lhese loxaneis availablecontntercially.r reagentssuppress the basicitl'ofthe glassand providea hydrophobicsurface.

4.2 ADAprATroNsoFsTANDARD GrAsswARE

Many operationsrvith air-sensitiveliquids can be perfornredin standardtaper glasswarefitted with a bubbler and inert-gassource. NOTE: To avoid blowing apparatus apart, stills and reaction pots should be vented to a bubbler before they are heated.Figure I . I illustratesa typical setup for a three-neckreaction flask equippedrvith a dropping funnel, stirrer, and reflux condenser.This ar- rangementprovides several important featuresfor safeand efficientoperation. Inert-gasinlet I and the oulet through the mineral oil bubbler are positionedfor efficientinitial purge. Pressurebuildup, especiallyduring heating,is avoidedby allowingpressure release through the bubbler. A constantslow flow of inert gas rThis nraterialis sold under the nanreGlassclad bv PetrarchSlstcms. Inc.. BartranrRoad. Bristol. PA 19007. o HJ

StrIl-head thermometer

Insulated to v rgeraux nooo column Inerl-ga s inlet 3 Mrneral oil bubbler

Receiver

Heatrng mantle

Fig. 1.3. Distillation under inert atnrosphereusing modifiedstandard taper \r'are.Note the sidearnr addedto the standardsingle-necked still pot and receiver.The sidearmon the still pot allows efficientinitial purging of the apparatus,while the sidearmon the receiverallou's one to maintain a brisk inert-gasflow over the distilledsolvent when the receiveris renrovedfrom the still. The apparatusis initialll'purged as follons: ( I ) The entireapparatus, except for the receiver.is assembled.(2) Inert-gasinlet I is openeduhich purgesthe still pot. colunrn, and condenser.(3) The receiveris attachedto inen-gasinlet 3 and purgedseparately. (4) After both the receiverand the main pan of the apparatushave been sufficientlypurged (about 3-5 min), the receiveris attachedto the main apparatuss'hile maintaining the inert-gasflow fronr both inlets I and 3. When the receiveris attached,there will be a vigorousinert-gas flou' through the mineral oil bubbler. (5) A slowflow of inert gasis startedfrom inlet 2. The inert-gasflou'from inletsI and 3 is nou terminated.Distillation may nou begin.The slo* flo* of inert-gasfrom inlet 2 through the mineraloil bubbler will prevent air from backing up into the apparatusuhile minimizing exposureof the solventto any impurities presentin the inert gas. If the inert-gasflou is maintainedthrough the still pot during the distillation, the efficiencyof the separationwould be degraded.When the distillationis complete.the inert- gasflow from inlet J is resunredbefore disconnecting the receiverfrom the apparatus.

12 SYRINGEAND CANNULATECHNIOUES 43

:hroughinlet 2, with no flow from inlet 1, preventsair contaminationduring the .rru15.o* the reactionwhile not exposingthe entire systemto any impuritiesthat :rav be presentin the inert-gasstream. This slowinert-gas flow from inlet 2 also rreventsair from being suckedin while the apparatusis cooling after the reac- :ron l'lasbeen completed. Finally, this arrangementprevents the depletionof : iqhly volatilesolvents. An apparatusfor distillation under inert atmosphere,illustrated in Fig. 1.3, :ncorporatesthe samefeatures seen in the inert-atmospherereaction apparatus Fig. l.l). The distillation apparatusalso containssome slightly modified round-bottomflasks for more efficientinitial purging. Thesemodifications will re discussedin greaterdetail in the following section. To minimize leakage,joints areeither lightly greasedor equippedwith Teflon .lc-eves,and are held togetherwith springs,special clips, or rubber bands.When rr can be used,grease provides the tightestseal; however, Teflon sleevesare gen- .:rally used for connectionsto still pots and similar harsh environnents. The rarious types of stopcockgrease, including the new solvent-resistantTeflon- hasedlubricants, are summarizedin Chapter 8. Greasedstandard taper joints rre readilyavailable and are adequatefor most purposes;however, O-ring joints .rresuperior for most inert-atmosphereapparatus. The advantagesof O-joints arethat they are resistantto solvents,and the clampsused with thesejoints hold rhe apparatustogether much more positivelythan do the springsand other de- ricesused on standardtaper joints. Very satisfactoryoperation is possiblewith either standard O-joints or the Teflon-supportedO-ring joints (Solv-Seals). Thesetypes of joints are describedfurther in Chapter8. If standardO-joints are used, the O-ring material should match the solventsbeing handled; again, Chapter8 should be consultedfor details. The principal drawbacksof the standard apparatusis that it is difficult to flush efficiently and liquid transfer operationsare awkward. With little addi- rional complexity,the apparatuscan be adaptedfor efficientpurging and solution transferby syringeor cannula.

{ ,3 syRrNeEAND cANNULA TEcHNrouEs

A. TypicolAppololus. A simplemodification which improvesthe utility of a one-neckstill pot or solventreceiver is a sidearm,which can be usedfor flushing the flask. This simple modificationfacilitates the initial flush of the apparatus shownin Fig. 1.3. Furthermore,the sidearmprovides several alternatives for the removalof solventsfrom a receiver,such as flushing the flask while solvent is removedthrough the standardtaperjoint, or removalof solventthrough the sidearm,as illustratedin Fig. 1.4. The sidearmalso permits the flask to be maintainedunder a constantflush of inert gas when it is attachedto another pieceof apparatus(Fig. 1.5). BENCH.IOPINERT.ATMOSPHERE TECHNIOUES

(b)

Fig. 1.4. Transferof solventby syringefrom a storageflask u'ith lhe exclusionof air. (a) Solvenlis removedthrough the neck of the storageflask while maintaininga brisk florvof inert gasfrom the sidearnt.(6) Solventalso may be removedthrough the sidearmwhile rraintaining I atm of pressure in the flask by admitting inert gasthrough the inlet. In both (a) and (b), the syringeis initiallypurged by samplinginert gasfrom the storageflask and expellingthis gasoutside the storageflask.

B. Septo ond Olher Closules. Rubber septamay be attachedin a variety of ways,as illustratedin Fig. 1.6. The flat varietyis held in placeby screwcaps, crinped caps, or beveledholders. Various manufacturersprovide apparatus with thesetypes of septumclosures.a Of greaterversatility are the sleeveseptum stoppers(Fig. 1.7), which can be attachedto straight tubes or standardtaper joints without any specialfixtures.s Two problemswith all septaare their sensitivityto solventsand chemicalsand leakagethrough the punctured septum. Flat compositesepta minimize these problenrs.These consist of a central core of a compliant rubber, such as a soft

aSpecialseptum closuresand apparatuswith theseclosures are manufacturedby Ace GlassCo., Aldrich ChenricalCo.. KontesGlass Co., and WheatonGlass Co. in the United States,and Sovirel in France. sSleeve-typeseptunr closures are u'idelyavailable from chemicaland hospitalsupply houses.An excellentsleeve septunr stopper, produced by the SubaSeal Co. in the United Kingdom,is available therefrom Gallenkampsand from Strem ChemicalCo. in the United States. SYRINGEAND CANNUTATECHNIOUES ,15

Fig. 1.5. Joiningtwo piecesof equipmentunder inert-gasflush. Both piecesare initially purged with inert gas separately before joining. Note the use of wire hooks and rubber bands to secure individual piecesof glassware.If the glasswareis constructedusing O-ring joints, the O-ring joint clampshold the apparatustogether.

siliconerubber, sandwichedbetween thin sheetsof Teflon. The siliconerubber imparts goodsealing action, and the Teflon is highly resistantto solventsand to permeationby atmosphericgases. Direct contactof solventswith septashould be minimized and septa should be replacedoften. When organic solventsare being used, one must be wary of impurities extractedfrom septa,joints, and tubing. Theseextracted impurities may foul reactionsand causeconsiderable confusionin the interpretationof IR and NMR spectra.The prime offendersare hydrocarbonand siliconestopcock greases, dibutyl phthalateand similar plasti- cizersfrom Tygon tubing, and variousextracts from rubber goods.Some spec- tral methodsfor identificationof thesenuisances are collectedin Table 1.1. The pickup of impurities from septacan be greatly minimized by prior extraction with an appropriate hot solvent followed by pumping off the absorbed solvent beforeuse. Septa make poor closuresfor containersused for the long-termstorage of highly air-sensitivematerials, since atmosphericgases diffuse through RubbersePtum -

\_ /@\ t_lTl ltt Itl U/r (b)

Gloss

To ooDorotus (o)

Fig. 1.6. Methods for attachingrubber septato glassapparatus. (a) A modified Swagelok-type fitting. The lip on one end of the fitting is turned dorvnon a lathe, and the septum replacesthe ferrules.On the otherend, a Teflonfront ferruleis usedto nrakethe connectionu ith a glasstube. (ä) An all-glassseptunr holder. (c) Crosssection of a plasticthreaded cap septumholder on a threaded glasssidearm (manufactured by Wheaton GlassCo.). nn W NN \trN (a) (b)

Fig, 1.7. Securinga Suba-sealinto a glasstube. (a) Crosssection of Suba-sealas it is insertedinto a glasstube. (b) After inserting.the flap on the Suba-sealis foldedover the tube. (c) The flap may be securedto the tube by wirc.

Ioble '1.'l SpeclrolSignolures of lmpuriliesfrom SfopcockGreose ond Rubberond Plosliclfems

Source Nirtureof Inrpurit! SpectroscopicIdentif ication

Rubber septa Dyes.antioxidants, Vis-UVabsorption or tubing etc.

T_vgonand other Dibutyl phthalateand NMR:Mult. 7.5. dub. 4.5 flexiblepoly(vinyl other plasticizers Mult.l.l-1.9, chloride)tubing Mult.0.92 ppm

Stopcocksand Siliconegrease NMR:ca. 0.1 ppm joints ApiezonL NMR:ca. 1.25, 0.9 ppm

ti6 SYRINGEAND CANNULATECHNIOUES 17

\cpta and the rubber is likely to undergo chemical breakdown. One possible .:rceptionto this statementis the use of unpunctured Teflon-coatedsepta as >c'als;but evenhere one is better off using sealedglass ampules for storage.

C. Syringes. The principal variationsin availablesyringes are in the design ,rf the tips and plungers.For most preparative-scalework, syringeswith remov- able needlesare employed.The removableneedle with a femalejoint hub is at- rachedto a male tapered joint on the syringe.This male Luer tip may be a straightinner joint fashionedfrom glassor metal or a metaljoint with surrounding locking devicewhich holds the needlesecurely in place.The metal locking variety is preferable because it prevents the detachment of the needle during critical transfer operationsand the metal tip is more robust than a glasstip. Glasstips are desirablewhen highly corrosiveliquids are handled. The Luer taper joints are widely adopted but not universal.Nonstandard tapers do not sivean air tight sealif mixed with a Luer component.Microliter syringes,which are usefulfor sampling small volumesof liquids, often have needleswhich are permanentlyattached to the barrels. The standard small syringesare often constructedwith individually matched plungersand barrels which are given matching codenumbers. These plungers and barrels are not interchangeablewith those from other syringes.Larger syringes often have interchangeable parts. Leakage of air past the plunger is a constantproblem with thesetypes of syringes.When a light coatingof mineral ,ril on the plunger can be tolerated,this providesan effectivemeans of reducing the leakage.It also is possibleto reducethe entranceof air past the plunger by forcing the solution into the syringewith a small positivepressure rather than suckingthe materialinto the syringeby pulling on the plunger.For example,the three-needletechnique illustrated in Fig. 1.8 may be usedto fill a syringeunder controlledpositive pressure. The variousmethods of forcingthe solutioninto the svringeare done with the greatestcontrol by using a metal syringeholder which limits plungertravel and thus avoidsthe possibilityof the plungerpopping out of the syringe(one such holder is illustratedin Fig. 1.9). It is especiallyhelpfulto usea metal syringeholder when pyrophoricmaterials, such as neat aluminum alkyls,are transferredby syringe.The metal holder alsohas the convenienceof permitting one-handedoperation of the syringe. Tighter sealsbetween the plunger and barrel are achievedwith so-calledgas tight syringesin which a Teflon-tippedplunger or an O-ring-equippedplunger is employed.Very good leak resistanceis also displayedby the inexpensive"disposablesyringes," which consistof a polypropyleneshell and a rubber-tipped plunger. Unfortunately, the rubber swellsand sticks in the barrel when most organic solventsare transferred; but these disposablesyringes are excellentfor work with aqueoussolutions.

D. Sytinge Needles. Syringecannulae, which will be referredto asneedles throughoutthis discussion,are most commonlyconstructed from stainlesssteel tubing fitted to a metal or plastichub. Chromium-platedbrass hubs areperhaps Ne --r

Vent

Serum bottle cop

\wirs

Fig, l.E. The three-needletechnique for uithdrau'ing liquid from a storagetube. The syringeis initiallypurged by samplinginert gasfrom the tube and expellingthe gasoutside the tube. To fill the syringe, the vent is briefly coveredwith a finger, forcing the solution into the syringe.

B-D Cornwollmetol holder Luer-Lok volve /,prPettrng 1CC stze 8-D NoMS09 l/

B-D Yoleregulor porn 20 gouge hypodermicneedle (Luer-Lok)1 jn. long

Assembledhypodermrc syringe in metol prpefting holder

Plunger

-oooo oooSN\ '\ Tensronsprrng ooooo B-D CornwolJsyrrnge (Luer-Lok) Reto ne. wosher Groduotions,cc t cc sjze

Plungerossembly

Fig. 1.9. Assembled hypodermic syringe in metal pipette holder.

,t8 SYRINGEAND CANNUTATECHNIQUES 19

rhe most common variety.Leaks in the Luer taperjoint betweenthe needleand svringebody nraybe minimized by the useof a small amount of stopcockgrease on the syringejoint. A checkfor grossleaks is performedby pulling air into the svringe,inserting the needle into a rubber stopper, compressingthe syringe plunger to about half of the original volume, and noting whetherthe plunger returnsto its original volume mark when released.Poorly fitting needlesor syringe parts shouldbe discarded.Needle tips are easilyblunted and bent over in rhecourse of laboratorywork, so a small, fine-grainedwhetstone should be kept handy to resharpenthe point. A needletip that is curled back or has a burr on rhe point is especiallydamaging to septa.A sharp needlenot only makesinser- tion easierbut also reducesleakage through the punctured septum. The so- callednoncoring or deflectingtip, which hasa sideopening or a l2o beveledtip, is preferredover other typesof needlesbecause it doesthe leastdamage to septa. A flat-cut point shouldbe avoided.When working with unstableor reactivesubstances,it is important to flush a needleand syringewith pure solventimntedi- ately after use. Stiff metal cleaningrvires are often providedwith neu' needles and are usefulfor removingdeposits from the interior of the needle. The outsidediameter of the needleis generallyspecified in the United States by its wire gauge. Table 1.2 presentsthe metric equivalentof comnron wire gaugesand the sizesof matching syringes.The latter are providedas a convenient guide and not as a setof rules. Teflon needlesare convenientfor transferring highly corrosivematerials; however. these are not generalsubstitutes for metal syringesbecause they cannot penetratesepta. A rangeof specialsyringe fittings is available.such as crosses,filters, T's. and stopcocks.bThe small stopcocksor valvesfind usein retainingliquids in syringes.These are especially useful in conjunction with large-volumesyringes or u'hen handling highly pyrophoricmaterials, such as aluminum alkyls.A setupincluding a syringe stopcockalong with a syringeholder has already been illustrated (Fig. 1.9).An- other applicationof theseitems is the adapterfor the removalof aluminum alkyls and other reactiveliquids from a small cylinderdescribed in the following example.

Ioble '1.2.Needle Sizesond Molching syringes

Gauge o.d. (nrnr) ApproxirrrateVolunre of MatchingSvlinge

25 0.46 Microliters 23 0.57 0.2-2nL 20 0.81 l-5 mL l8 1.02 5-50nrl l4 r.63 50-100nrL

'The constructionof a large syringefor dispensingqases is desclibedb1'G. W. Kranter,J. Chcm' Edac..50. 221 \1973). SyringeT's, stopcocks.and needlestock for cannulaeare availablcfrom AldrichChenrical Co.. P.O. Box 355.Miluaukcc. Wl 53201.

r 20 BENCH.TOPINERT-ATMOSPHERE IECHNIQUES

Metalcylrnder

Lead gaskel @' 5 32thread Wrenchfor l6 valve {u---' t fl-ll n Ht/ Inert gas Three way r-1\l/ Stopcock Luer-lok @iM l+J' Lue r-lo k Syringeneedle V

E. Exomple:Wifhdrowol of Highly Reoclive liquids from Mefol Tonks. Highly reactiveliquids such as aluminum alkyls can be withdrawn from a low-pressurecylinder using the apparatusshown in Fig. l.l0a. CAU- TION: Highly reactive liquids should be handled in a hood which contains a minimum of flammable material or chemicals.After attaching the syringeapparatus to the cylinder, the needleis purged with inert gas for severalminutes. While purging, the needleis insertedthrough the septuminto the reactionflask. 'QINGEAND CANNULA TECHNIOUES 24

Fig. 1.10, Transfer of air-sensitiveliquids from metal cylinders.(a) A three-waymetal stopcock .,'nstructedfor usewith syringesmay be modified by the addition of a threadedfitting so that it :rateswith a lecturebottle. The sideinlet is usedto purgethe apparatusinitially and to blou,liquid ,utof the syringeneedle at the completionof the transfer.The cylinderis put under a lou'pressure oI :ncrt gas beforethe transfer is begun. (ö) Sometimesair-sensitive liquids are sold in siphon-type ;rlinders, and the liquid fronr such a cylindercan be dispensedas shownhere. As with the previous rrample, inert gas is usedto forcethe liquid out of the cylinder.

The three-wayvalve is then switchedto allow liquid dispensing.When the desired quantity of liquid has been removed from the cylinder, the cylinder is closedand the three-wayvalve switched back to inert gas, so that the needleis purged by inert gas before it is removed from the reaction flask. An apparatusfor the withdrawalof reactiveliquids from metal cylindershav- ing a siphon tube is shown in Fig. 1.10ä. This setup is operatedin much the sameway asthe syringeapparatus, the main differencebeing the useof inert gas to force the liquid out of the cylindercontaining the siphon tube.

r 22 BENCH.TOPINERT.AIMOSPHERE TECHNIQUES

F. Liquid llonsfer Connuloe. The transferof liquids betweentwo flasks may be accomplishedwith a cannulaalone (Fig. 1.11).These cannulae usually are constructedfrom syringeneedle stock which is commerciallyavailable in convenientlengths.6 In addition to simpleliquid transfer,special filtration can- nulaecan be constructed.In a recentdesign by M. L. H. Green,a stainless-steel cannula is cementedwith epoxy resin to a short length of heavy-walledglass capillary tubing which has a slightly flared and fire-polishedopening (Fig. l.l2a). This opening is coveredby hardenedfilter paper which is neatlyfolded back on the glassfitting and wired in place,as illustrated in Fig. |.l2b . A sleeve- type septum stopperis pushedonto this filter apparatus,with the stopperend toward the filter. This assemblymay then be attachedto a receiverand flask as illustratedin Fig. 1.11. Filtrationwith more conventionalequipment is illustratedin Fig. 1.13. In comparisonwith syringetechniques, the use of cannulaeprovides better air exclusionand greaterconvenience for the transferof largevolumes of solution. However,syringe techniques are much better suited for the quantitative dispensingof Iiquids, as demonstratedin the following example.

G. Exomple: Quonlitotive Dispensing of Liquids. Moderate accuracy in liquid-transfer operationscan be achievedusing syringegraduations. Air should first be expelledfrom the filled syringeby pointing the needleup and squirtingout all bubbles.Higher accuracycan be achievedby weighingthe dis- pensedliquid. The syringeis filled and the needletip is stopperedby insertion into a small rubber stopper.This assemblyis weighed,the liquid dispensed,and the syringeplus rubber stopperis reweighed.If the syringeis not goingto be re-

Fig. Lll. Solutionttansfer using a stainlesssteel cannula. The solutionis forcedthrough the needle by meansof the pressutedifferential createdby opening the inert gas inlet, which pressurizesthe right-hand flask. The receivingflask is either maintainedat I atm by opening the sidearmto a bubbler, or is maintainedat slightlyless than I atm by openingthe sidearmbriefly to a vacuum source. fUES SYRINGEAND CANNULATECHNIQLJES 23 asks tally lr rt ein llurallLösausecanr lan- lf | | iteel | | ,-Eporv cement | | lass 11 K /-t\ -wrretre.down Fig. llll,-Grassrttng W^ ded ä5 )ve- @FrterPaPer (4.) (D) :nd ias Fig. 1.12. Assenrblyof a filter cannula or "Green filter." (a) A pieceof glasscapillary tubing, us- u hich hasbeen blou'n open and fire-polishedto form a lip on oneend. is attachedto the cannulau ith cpoxycement. (ä) Filtcr paper is folded over the glasscapillarl and secured*ith u'ire. ter lu- ive Inertgas To bubbler rcy \ir nd is- f,n :td 'e-

t ig. 1.13. Variationon thecannula techniquc. The glass tubc uith frittedfilter and theglass delir- -:\ 1ubesareattachedtotheglassstandardtaperjointsbJ'meansofplasticadaptors(e.g.,KontesK- I-'rE00). The flexiblc plastic tubing connectingthe t$o parts should be inrperi'iousto solvents. I rilon tubing is bestand. to prcvcntcontamination of thc filtrate, T1'gontubing shouldbe avoided rrr'll',rganic solverrts arc used.

usedimnlediately, it should be rinsed u'ith degassedsolvent immediately after use, to avoid the buildup of depositsof decompositionproducts in the syringe and needle.However, if it is to be re-usedsoon with the samesolution, the stopper may be left on the needletip and both rinsing and inert-gasflush may be omitted beforethe syringeis filled again.

H. Specfloscopic Meosuremenls. The samplingof air-sensitiveliquids for NMR and IR spectroscopyis often most convenientlyperformed by syringe. Smallrubber septaare availablewhich fit 5-mm and other sn.rallNMR tubesand

I_ 2A BENCH-TOPINERT-ATMOSPHERE IECHNISUES alsofit the Luer inletson IR cells.The NMR tubemay be purgedby purnp-and- fill operations,u'hereas IR cellsare easily flushed by inertgas. The filling of the IR cell is accornplishedby insertingthe syringeneedle into the septumon the cell inlet.and the outletseptum is piercedrvith a smallneedle. An excessof liquid is flushedthrough the cellto excludegas bubbles. A somewhatless air-free operation is achievedby flushingthe celland then attachinea svringecontaining the liquid by joining the Luer fittingson the syringeand cell. An emptysyringe is attachedto the cell exit to serveas a reservoirfor excessliquid u'hich is forced through the cell. Once the cell is filled. the inlet and outlet are cappedrvith Teflon stoppers.Conventional visible-UV cells can also be fitted rvith syringe caps for air-free spectroscopy.A visible-UV cell that has been usedfor a u'ide varietyof air-sensitiveinorganic and biologicalcon.rpounds is illustratedin Fig. 1.14.More sophisticatedspectroscopic cells. some of rvhichare suitable for use in conjunctionwith syringetechniques. are describedin Chapter9.

4 ,4 euANTrTATrvEGAS MANIPULATToN

A. Dispensing Goses. The dispensingof gasto a solutioncan be accomplishedin severalu'ays. For example,a solutionmay be saturatedby bubbling

Needle - volve

l-cm ,single- piece CUVCTTE ReseTvorr':

Fig. Ll4. Evacuablecell lor UV-r'isiblespectra.'I'his cell is evacuatedand then flushedthrough ar 'l'he inert-gasinlct attachedto thc O-ring joint. Teflon stenrof the valvc is removedunder flush solutionsare introducr-dthrough this opening.and then tipped over into the culette after the valrr stem has bcen replaced.Altcrnativell. ct>ndensablest>lve'nts and solutcsma1' be condensedinto th reservoiron a vacuunrIine. ,ES :, ANIITAIIVEGAS MANIPULAIION

U- -:: through it from a syringeneedle attached to a tube and low pressuregas he urce(Fig. 1.15). 'f ell he quantitativedelivery of a gasis somewhatmore involved.While it is true is '- JI a vacuumsystem often permitsthe mostsatisfactory method of quantitative 'a- -,,: handling, someadequate procedures exist which are basedon simple, con- he : ntionalinert-atmosphere apparatus. A largegastight syringe is oneof the most is rvious devicesfor the measurementof an aliquot of gas.bA sampleof gas may :d ^.:drawn into the syringefrom a streamof the gasconnected to an exit bubbler. rh \nother method for dispensinggiven quantitiesof gas is a gasburet, similar to i! re describedlater in connectionwith the measurementof evolvedgases.T Still le i:r()thersimple scheme is to flush a bulb of known volumewith the desiredgas, ] ,nd then bubble this gas into the reactionflask by meansof a slow inert-gas .:ream(Fig 1.16).Condensable gases may be trapped.measured by volumeof '.reliquid, and dispensedby controlledwarming of the gas.A suitableapparatus ',r this purposeis illustrated in Fig 1.17. Gaseswhich are condensableat Dry :re temperature,-78oC, can be handledby this technique. Finally, it is often possibleto generatequantitatively the desiredgas from :reasuredamounts of liquid or solidreagents. The generatedgas is then quanti- :.ltivelytransferred by inert-gasflush into a reaction mixture. The automatic :lsimeter developedby C. S. Brown and H. C. Brown is usefulwhen it is neces- .rrv to know the quantity of gas consumedin the courseof a reaction.sThis rpparatus can be applied to the generationof a varietyof gases,such as H2,E

Tobubbler _>

To hood

Fig. 1.15. Dispensinggas directly from a tank. l-he needlevalve is usedto controlthe gasflow into thc solution,and a mercury-filledbubbler preventsexcessive pressure buildup.

T. N. Sorrelland M. R. Malachou'ski,Inorg. Chem., 22. l88J (1983),provide a recentdescription ,,f gasuptake experimentswith a gasburet. 'C. A. Brownand H. C. Bro$'n,./.Orp. Chem..31.3989(196b). r 26 BENCH.TOPINERT.ATMOSPHERE TECHNIOUES

Reagentgas To reactron Calibratedvolume rnleI vesseI --.>

t V Inert gas Tobubbler In hood

Fig. 1.16, Gas-samplingtube. The tube is flushedwith the reagentgas by openingto the reagent gasinlet and ventingto a mineraloil bubbler. After severalminutes, the flush is terminatedby first closingthe inlet stopcock,then the outlet stopcock.(This ensuresthat the pressureinside the (ube equals thr- laboratoryatmospheric pressure.) The laboratorJteniperature and pressureare then measuredfor usein calculatingthe anount of gasdispensed. Finaiiy. the known quantit]'of reagent gasis dispensedto the reactionvessel by openingthe inlet stopcockto inert gas.the outlet stopcock to the reactionvessel, and flushingthe tube rvith inert gasfor seYeralnrinutes.

CO,ehydrogen halides,r0'r I 02, r2 ethylene,rr and SOt,rr but notgases which react with mercury. By meansof a cleverliquid inlet device,gas is producedin the generatorin responseto the amount consumedin an attachedreactor. This liquid inlet valve(Fig. 1.18),consists of a tube partiallyfilled u'ith mercury.The tube hasprovision for the inlet of liquid from a needleattached to a buret and for the controlledflor.r' of this liquid into the reactionvessel via severalsmall holes abovethe mercury level.Liquid from this inlet valvedrops into the gasgenerator, and the evolvedgas is conductedfrom thereto a reactionflask. The flou'of liquid can be initially adjustedby the depthto which the needleprojects into the mercury pool of the valve.When the systemis properlybalanced. the pressure drop causedby gas consumptionin the reactorpulls the reagentfor gasgenera- tion in through the liquid control valve.As the pressurebuilds up, this flow of reagentstops, only to resumeagain when the reactionconsumes some of the generatedgas. When the quantitativemeasurement of gas consumptionis required, the exit bubbler servesonly as a safetydevice and the systemmust be set up so that there is no gasexpelled through the bubbler during the courseof the reaction.

B. Meosuremenf of Evolved Goses. The measurementof evolvedgases providesa readymeans of conductingcertain analyses and followingthe course

'qM.W. Rathkeand H. C. Broun.,/.Ant. Chent.Soc..88.2606 (1966). l"H. C. Bro*'nand N.-H. Rei,"/.Ore. Chent.,31,1090 (19b6). IrG. W. Kranter. A. B. Levv,and M. M. Midland. in H. C. Brorvn,Organr'c.i.r'rr/ltcses via Borunes, Nel'Yorkl Wiley, 1973,p. 218. r2H.C. Brown.M. M. Midland,and G. W. Kabalka,J. Ant. Chent.Soc..93, 1024 (1971). OUANIITATIVE GAS MANIPULAIION 27

Inert'gasInlet ,1, To reactron VESSCI

Ar.rtrDackup To gas absorber trap or hood

Mercury bubbler

Calrbratedlow temperature trap tor ltqurttedgas

Fig. 1.17. Apparatusfor dispensingknoun quantitiesof condensablegases. The trap may be cali- 'orated by using water (for large volumes)or mercury(for small volumes).A nrercurybubbler is rncludedto pre\ent blowing the apparatusapart. After assemblingthe apparatus,the entiresystem is thoroughlypurgcd uith inert gas.Stopcock B is then turned to route gasto a hood or gasabsorber, the inert-gasflow is ternrinated,and a slou flou of the desiredgas is adnrittedfronr a cylinderequipped with a pressureregulator and needle ralvefor flou'control.A Deuarcontainingrefrigerant capable of liquifvingthe gas(see Table 5.I) is then raisedaround the trap. After the desiredvolume of liquid is collected,the reagentgas flou is terminated,stopcock A is closed,and stopcockB is turned to direct gasto the reactionvessel. The Dewaris then loweredfrom the trap. allorvingthe collectedgas to boil off. The rate of vaporization mayby controlledby raisingand loweringthe Deuar. When the trap appearsto havebeen emptied. a flush of inert gas nray be usedto flush out remainingreagent vapor.

of a reaction.For example,the analysisof activehydrides and alkyl compounds can often be conductedby quantitativehydrolysis to produce hydrogenor al- kane. A simplegas buret system,illustrated in Fig. 1.19,is usefulfor thesetypes of measurements.It alsomay be usedto dispensespecific quantities of gasto an inert-gasstream for introduction into a reactionmixture. The procedurefor using this gas buret apparatusfor the analysisof active hydridesor alkyl com- poundsby hydrolysisis describedin the following example.

C. Exomple:Anolysisof AcfiveHydrides or AlkylCompoundsUsing o Gos Burel. This procedureutilizes the gasburet illustratedin Fig. l.l9 to analyzeactive hydrides or alkyls.First, the water levelsin the reservoirand buret sidesare adjusted to equalheight and an initialburet reading is taken. A sample of known weightis introducedinto the hydrolysisflask usinga syringe.After gas Reagentinlet trom buret

Reagentoverflow to generatorflask

Reactionvessel

Fig. I.18. Bro*nl gasgenerator ancl apparatus for reactionswith gases.Reagents are mixed in the gasgenerator and the resulringgases are passedinto the reactionvessel. The nrercurvbubbler on the far left has a float check valYervhich preventsnrcrcury and air fronr being suckedback into the reactionvessel. The key to this apparatusis the automaticIiquid intetvalve, shou'n in detail on the right. A drop in gas pressurervithin the apparatuspulls liquid fronr the buret through the syringe needleand the ntercurv.The rate of delivertof reagentis adjustedby raisingor loweringthe buret and attacheds-yringe needle.

28 tig. 1.19. A gas buret for the measurementor deliveryof gases.When the elbou (on ''rrhed left) is at- to the top of the buret, gas is collectedand its volumeis measuredafter equalizingthe mer- 'urrlevcls.Forexanrple,ahydrolysisflasksinrilartothereactionflaskinFig.l.l8maybeattached ' ' lhls elbow.When the stopcockassembly is used(ar the right), the buret can be filled uith sasand , n)easuredvoluntc of this gas can be injectedinto a streamof flou,inginert gas.

29 r_ 30 BENCH.TOPINERT.AIMOSPHERE IECHNIQUES evolutionhas ceased.the water levelsare again matched.and both a buret and barometricpressure measurement are taken. A correctionmust be madefor the vapor pressureof the solventused in the system,especially if the solventis very volatile.

'1,5 scHLENKTEcHNToUES

A. Bosic Apporolus. The original Schlenktube consistedof a long tube with a sidearmnear the top which permitted the removalof air by evacuation and filling rvith inert gas. A completemethodology for rvork with air-sensitive liquids has evolvedfrom the original Schlenktube. The Schlenktube described here has a teardrop shapeto facilitatethe stirring of reactionmixtures and the vacuum evaporationof solvents,while still maintaining easeof pouring and scrapingsolids from the Schlenktube. The currentlypopular Schlenkware permits the transfer of liquids or solids by pouring within a closedapparatus or under an inert-gasflush. Since it is possibleto perform fairly complex solids transferu'ith this type of apparatus.the needfor glovebox opetationsis minimized. Someof the basic items of equipmentinclude a Schlenktube (which is usedas a reactionflask), a fritted funnel, a dropping funnel, and a solidscontainer(Fig. 1.20).Most Schlenkware pieces are fitted u'ith a sidearmthrough which the apparatuscan be evacuatedand filled with inert gas.Some basic oper- ationsusing severalof thesepieces are describedbelow.

it- / \, 1 trrW\ l"\ (\, V/'

Fig. 1.20. Basicpieces of inert-almosphereSchlenk-typc apparatus. (r) Schlenktube. This is useful as a reactionvessel and filtrate receiver.The pear shapeof the vesselfacilitates stirring the con- tentswith a stirbar and magneticstirrer, and removingsolids. (b) Fritte or fritted funnel. This is usedfor filtrations.The Teflon valveis usefulwhen contaminationby stopcockgrease is objectionable.Double-ended frittes (Fig. 1.5)are also useful. (c) Droppingfunnel. As in the caseof the fritted funnel,the Teflon valveis usedto avoidcontamination of the solutiorrby stopcockgrease. (2./) Solids container.This is usedfor adding, receiving.and storingair-sensitive solids. (Reproduced by pernrissionof the copyrighto*ner, KontesGlass Co.) SCHLENKTECHNIQUES 31

B. Exomple: Purging Schlenk Wore. In general,a high vacuumis not requiredfor the pump-and-fill typeof purgeused in Schlenktechniques. Sev- cral cyclesof pumping and filling rvith inert gasare sufficientto reducethe oxygen and other atmosphericgases to very low levels.For example.suppose the \\'stemis evacuatedto 2 torr. ApplyingEq.(1), afterthe secondpumping and rillingthe pressureof residualair is 2 x 2i760 torr, and afterthe third it is 2 X I 160)2torr, or approximatelyl0'i torr. Becauseof the frequencywith which :hcsepump-and-fill cyclesare performed,it is usefulto ernploya manifold for 'hcdistributionofvacuumandinertgas,suchastheunitillustratedinFig. 1.2.

C. Exomple: Joining Two Pieces of Schlenk Wore. Anotherbasic op- Jrationis the joining of apparatusunder an inert-gasflush. For example,the :ransferof a reactivesolid from a solidscontainer to a Schlenktube requiresthe :ube to be stopperedand carriedthrough severalpurge cycles. Then, with both :riccesopen to a nitrogen source,the cap is removedfrom the solidscontainer, :he stopperis removedfrom the Schlenktube, and the tu'o piecesare quickly ioinedwhile air is excludedby the flow of inert gasout of the two piecesof appa- mtus, as previouslyillustrated in Fig. 1.5. Theseoperations require that the l)ressurein the systenrbe only slightly aboveatnrospheric pressure so that the closedapparatus is not blown apart. A two stageregulator rvith good control in rhe low pressurerange is essential,and additional protectionagainst overpre- \surizationcan be achievedby the pressurerelease bubbler illustratedin Fig. 1.2.To maintainintegrity of the apparatus,springs, clips, or rubberbands are usedto secureeach joint, and stopcocksale heldin placewith sturdyretairrers.l A sinrilar sequenceof operationsis usedfor changingthe configurationof all tipes of Schlenkapparatus during the courseof a synthesisor purification. The apparatusfor severalother comnlon Schlenkoperations are sho*'n in Figure1.21. These operations include filtration (Fig. 1.21c),transferring solids from a filter to a solidscontainer (Fig. 1.21ä),and transferringsolids from a solidscontainer to an anrpulewhich will be sealedoff (FiB.l.2lc). Alternatives for adding solidsto an.rpulesare illustratedin Fig. 1,22.

D. Quonfilotive Addition of liquids ond Solids. The quantitativemea- surementof air-sensitivesolids and liquidscan be accomplishedin a numberof u ays.Chapter 2 will coverglove box operationswhich aresuited for the measurement of solids.The quantitativedelivery of solutionsis readilyaccomplished by the syringetechniques, which have been discussedearlier in this chapter(Sec- tion 1.3.G).In addition,liquids can be addedfronr graduated Schlenk-type ves- selsu'hich are fitted with a sidearmfor flushing.Microweighing tubes (Fig. 1.23) are usefulfor the deliveryof small known u'eightsof compoundsto Schlenkap- paratus.The solid is introducedinto the tube in an inert-atnrosphereglove box and the tube and contentsare then weighed.With a flush of inert-gasissuing from the Schlenkapparatus, the weighingtube is quickly uncapped.inserted into the Schlenkapparatus, and shakento deliverits contents.The tube is removedand quickly recappedand reweighedto givethe tare weight.Sodium- and 32 BENCH.IOPINERT.ATMOSPHERE TECHNIOUES

(c)

'fvpical Fig. l.2l, assembliesof Schlenku are. Conrnrercialapparatus is illustrated:sintilar apparatus s'ilh O-ring joints in placeof standardtaper joints is plefen'edbv the authors.(a) Filter and Schlenkflask rcceivcn(Ä) pouringsolid from a filter into a solidsstorage tube; (c)pouring solid from thc solidsstoragc lube into an anrpule.s'hich can be sealcdoff. All apparatusis purged bi puntp- and-fill operations.Whenoer the apparatusis openedor beingioine'd. a purgeof inert gasfrom the sidearmis usedto excludeair. ( Reproducedbl perniissionof the copyrightos ner KorltesGlass Co. ) potassium-filledtubes can be cut, measured.and droppedinto a reactionvessel rapidly to dispensea known rveightof thesemetals. Another methodfor dispensing weighedamounts of alkali metalsin thin breakablebulbs is describedin Section9.4A. Solidsalso can be dispensedfronr sealed anrpules, which are broken openunder an inert atmosphere.(Fig. 1.24)and quicklypoured into Sch- lenk apparatusunder an inert-gasflush. A full ampulecan be rveighedand the parts tared after the solid is added,or a methoddescribed in the next paragraph may be usedto determinethe weiqhtof sample. A kno*'n anrount of nraterialmay be sealedin an ampule by u'eighingthe ampule,adding solid, sealing. weighing the parts, and determining the weight of the contentsby difference.Filling an ampuleis accomplishedwith the apparatus illustratedin Fig. I .21or 1.22, or in a glovebox. In orderto achievea goodseal, the systemmust be under vacuunror at most at atmosphericpressure. When the ampule is attachedto a Schlenkapparatus, the systemcan be partially evacuated and the seal then rnade. or a remote sectionof the Schlenk line can be momentarilyopened up to vent the systemwhile the sealis being nrade.Simi- larll'. an anrpule*'hich has beenfilled in an inert-atmosphereglove box may be \

Rubber -*5'----l stopper 7*ffiSchtent

-_ Inertsas or vacuum

Fig. 1.22, Solidstransfer under an inert atmosphere.(c) Solidsare poureddown this solidsmani- fold into ampules,which are then sealedoff. (ä) An ampuleis purgedin the evacuablecylinder, and under an inert-gaspurge the stopperon the cylinderis removedand solidsare transferredfronr the Schlenktube adapter into the vial. The latter is quickly removedfrom the cylinderand sealedoff.

I TECHNIOUES 34 BENCH-TOPINERT-ATMOSPHERE

-..--<- - \-,4.5f-

^.-.--

Fig. 1.23. Weighing pigs with caps'

Fig'l.24.Openingasca|cdrnlpu|c'l.J)Thenecko|'theanrpulciscarefu||rscoredusingagIas\ neck is placedov;r tfe neck' lnert gas (b) metal tube ol largeräiuttttt than the ampule knife. A is of the ampulecontents to air oncethe neck flowingthrough the metattubl u.illminimize exposure tube' u'hichsnaps the neck off (t ) at the score' broken. A quick jerk is then appliedto the meial box. The scoreis administeredto the ampule This operationis easitymoäified for usein a glove The anrpuleis clanrpedto a standin the glove neck beforetransferring the anrpuleto the gloveüox. boxandthenecksnappedusingacorkborer.Thisnrininrizesthechancesofglassfragnrentscuttlng a glove.

stopperedwithaSleeveseptumcapwhichispiercedwitha'smallneedlejust beforetheanrpuleissealed'Asmallresidueofthecompoundremaininginthe neckoftheampulen1aycauSedefectsinthesealwhichallowtheentranceofair. in the usualsealing opera- To minimize this probiem. the glassis first collapsed portion, the parts are pulled tion, and then, asthe flanreis kept on the collapsed is generallyadequate apart with a twisting motion. Leis than onefull revolution develop.Details on this to closethe threadlike channelwhich would otherwise SCHLENKTECHNISUES 35

and otherglass blowing operations are given in Appendix Il. When an evacuated ampule is broken open, there is an inrush of air. To minimize exposureof the contentsto air, the ampule may be broken open as illustratedin Fig. 1.24 and the contentsquickly poured into Schlenkapparatus which is being flushedwith inertgas.

E. SeporofiOns. The basic filtration operation has been previouslyillustrated. Low-temperaturefiltrations for the collectionof thermallysensitive com- poundsor productswhich are solubleat highertenrperatures may be performed *'ith an H-type Schlenktube, Fig. 1.30, in a large low-temperaturebath. The jacketed,fritted funnel illustratedin Fig. 1.25also permits low-temperaturefiltration. Crystallizationis performedin Schlenkapparatus under an inert atnrosphere usingfamiliar techniques:partial removalof solventby evacuation,addition of a solventin which the solutehas reducedsolubility, and cooling.These methods are often combined; for example, a second,poorer solvent,chosen so that its vapor pressureis lessthan that of the more powerful.original solvent,may be added.Partial evacuationwill then concentratethe solutionand changethe sol- ient compositionto favor crystallization.The complicationwhich air-sensitive

t ig. I .25. Low-temperaturefilffation apparatus. Th is is ut ilizedthe sanreu ay asthe f ritte pictured ' Fig. I.20ü. The outerjacket is filled u ith a Dry lce/acetonesolution s'hen filtering heat-sensitive , ,nrpounds,liquid amnroniasolutions, etc. IReproducedby permissionof the copyrightowner. The \nrcricanChenricalSociety,fromJ,E.Ellis,K.L.Fjare,andT.G.Hayes."/. Ant.Chen..!oc. 103. . :rr0(1981).1

f,- 36 BENCH.TOPINERT.ATMOSPHERE TECHNIQUES materialspresent is that impuritiescreated by partial reactionwith adventitious air or moisture may make a product difficult to crystallize.If theseimpurities are insoluble,they can be filtered off before the crystallizationoperation; but solubleimpurities presenta more seriousproblem. The layeringof a poor solvent on a solutionof a compoundis often usedto grow crystalsfor crystalstruc- ture determinations.In this case,the crystalsgrow at the interfacebetween the two liquid phases.If the two liquid phaseshave significantly different densities, the more denseshould be placed in the bottom of the tube. It is best for the initial solution to be far from the saturation concentrationof the compound. Tubes fitted with sleeve-typeserum caps can be used for moderatelysensitive compounds,and a right-angleTeflon valvecan be usedto closethe crystalgrow- ing tube for more sensitivecompounds. When suitablecrystals have grown, the

Glasswool

0il bath

Fig. 1.26. Sublimationapparatus. Solids are introducedunder inert-gasflush, and a looseplug of 'fhe glassuool is introduced. oil bath should extend abovethe glassrvool. High vacuum mal'be appliedthrough thc standardtapcr joint. A louer vacuunrmal be appliedthrough the sidearnr. SCHLENKTECHNIOUES J/ liquidsmay be carefullyremoved by syringeand crystalsshaken from the tube in a glovebox. Sometimesit is necessaryto break the tube to gain accessto the crystals. Sublimationis readilyperformed in Schlenkapparatus of the type illustrated in Fig. 1.26.The sublimate,which collectson the upper walls, may be collected by positioningthe apparatushorizontally and scrapingthe product into a re- ceiverattached to the side joint while an inert-gasflush is maintained on the equipment. Column chromatographyunder an inert atmosphereis made possibleby the apparatusillustrated in Fig. 1.27.Most commonadsorbents contain large quantitiesof moistureand air, the eliminationof which is difficult. For example,it is generallyimpractical to eliminate all of the surfacehydroxyl groups from alu- nrina.Also, the absorbencyof inorganicsolids such as silicagel and aluminais \)ftena strong function of adsorbedmoisture. A convenientprocedure for de- gassingand partial moistureremoval of the adsorbentis to warm the solid in a Schlenktube while carryingout a seriesof pump-and-fill operations.(To avoid particlesof adsorbatef lyingthrought the Schlenkmanifold, a smallplug of glass sool is placedin the neckof the flask. and vacuumis appliedslowly while the r esselis swirled.) Under a blanket of inert gas,air-free solvent can then be added u ith a droppingfunnel and the slurrypoured into the column (generally.a transfer crossis necessaryso that the slurry can be washedinto the column by means of solventintroduced by syringe).Alternatively, the dry adsorbentin the column

- plug _/-Gloss wool

Adsorb ent

Gloss- woolplug

Stopcockwith Teflonplug

FIG. t.27. Colunrnfor adsorptionchromatography. Typical size: l;l/35 3 joints, 45-mm-diameter upper section,20-mm-diameter column, and a 500-mmcolumn length. O-joints and Teflon-in-glass valvesprovide greater solvent resistance than the greasedfittings illustratedhere. 38 BENCH-TOPINERT-ATMOSPHERE TECHNIOUES can be deaeratedby pump-and-fill operations.and solventadded later. Oc- cluded gas is then eliminated under an inert-gasflush by stirring the column with a long wire or rocking the slurry back and forth in the closedcolunrn. One sidearmon the column is usedto provide a nitrogen flush *'hen the systemis opento the air, and anothermay be addedfor the introductionof snlall samples by syringe.

F. Moleculor Weight Delerminofions. Molecularweights of slightlyair- sensitivecompounds can be determinedin standardcomntercial vapor pressure osmometersequipped rvith an inert-gaspurging line. Argon is preferredto nitrogen for purging this apparatus;the primary leakagepaths are around the top of the apparatusand thus a heavygas is desirable.Standard boiling point elevation apparatuscan be equippedwith an inert-gassupply to providevery good exclusionof air and thus permit the collectionof molecularrveight data on highly air- sensitivecompounds. rl The measurementof molecularweights by freezingpoint depressionis con' venientlyaccomplished on air-sensitivecompounds by meansof the apparatus illustratedin Fig. 1.28.In this design.the sampleis introducedto thecell from a weighingtube or syringeunder a nitrogenflush, or it may be introducedin an inert-atmosphereglove box. The microstirringbar in the sidearmof this apparatus is cooledwith liquid nitrogen and flicked by nreansof a magnet into the cell when the solutionsupercools. The temperatureis sensedrvitlr a thermistor. and a stripchart recordingof the coolingcurve may be extrapolatedby a linear approximationif the regionof supercoolingis short, or by more complexfunc- tionsdescribed in the literature.ll Cell designsto satisfya varietyof needsare describedin the literature.rsra

G. Voriolions in Schlenk Wore. A large number of modificationsof the basicSchlenk ware are in use.The double-endedfilter is a commonlyused variant of the standard Schlenkfilter. The particular unit illustratedin Fig. 1.29is equippedwith O-ring joints rather than standardtaper joints. (SeeChapter 8 for a discussionof joints and O-ring materials.)Either con.ventionalor modifiedO- ring joints, such as the Fischerand Porter Co. Solv-Seals,have several advan- tagesover standardtaper joints for Schlenkapparatus: these O-joints are nlore resistantto solventsthan the conventionalstandard taper ware,the O-jointsare more readilyclamped together, and, unlike standardtaper joints, the two halves

rrF.W. Waker and E. C. Ashby.J.Chem. Educ..45,654 (1968). I]W. J. Taylor and F. D. Rossini,J. Res.Nutl. Bur. Sttl.,32, 197(1914). r:Enclosedcell for cryoscop,vin sulfuricacid, usinga Pt resistancethermometer: R. J. Gillespie,J. B. Milne. and R. C. Thonrpson.Inorg. Chent.,5,468 (196b). rnEnclosedcryoscop-v cell uith thermistorsensor: T. L. Brou'n.C. L. Gerteis,D. A. Bafus,and J. A. Ladd,,/.Ant. Chent.Soc., 86, 2135(1964). j-Enclosed cell u'ith a conventionalthernromcter: S. U. Choi, W. C. Frith, and H. C. Brown,J. ,4nr. Chent.9oc..88. 4128 (1S66). >CHLENKTECHNIOUES 39

Needle- volve

Vent >o'|eno'o note L_:

Needle- volve

+To omplifier - Micro stlrnng bor

-z Refrtgeront

- Dewor

(o) fig. 1.28. Crvoscopl-cell. (a) TJpical dinrensionsof the lo$'crsection are 260-nrnrheight and 20- ' :r tlianreter.The thermistoru'ell is about 27 mnr. (b) Coolingapparatus fol the cr)oscopvce ll. Thc . -. ()scopeslips into the jacketedtube. The jacket is evacuatedor partiallyevacuated to control thc .,,lrngrate.Electricalreadoutisachievedrvithadigitalmultimeterolcomnrercialelectronicsfor ':crrristor thermonreters.

,f theseO-ring joints areidentical. When moderatequantities of solidsare being randled, a fairly completesetup for inert-atmospherepreparations and purifica- :ronsconsists of the double-endedfilter in conjunctionwith Schlenktubes. sol- ,cnt storageflasks. solids storage tubes. syringes, and additionfunnels. The H-type Schlenktube, sometimescalled a doubleSchlenk tube, is yet an- othertypeofgeneral-purposeinert-atmosphereapparatus,(Fig. 1.30).Thisap- paratusis basicallya combinationof two Schlenktubes and a filter. One advantageof the H-type Schlenktube is that it forms a very sturdy, leak-tightunit. In additionto the usual pouringof solutionsthrough the filter, it permitsthe distillation of volatilesolvents from one legto the other. This lastfeature can be used to washand dry a precipitate.The H-type Schlenktube alsois more satisfactory than conventionalSchlenk ware for low-temperaturefiltration. Weighedagainst theseadvantages, the H designis unnecessarilybulky for someoperations and it is somewhatmore difficult to usefor largequantities of solids.As with the con- Fig. 1.29. Double-cndedfilter. This tvpc 0f apparalusis a goodalternaliveto tlre r.norestandard Schlenkfilter. The versionillustrated is basedon greasclessjoints and valves.

Fig. 1.30. H-Schlenktube. ln addition to replacingthe standardSchlenk filter for routineopera- tions,this apparatuspermits lorv-tentperature filtration if a largccooling bath is used.See Chapter5 for the useof thc H-tube in the Wayda-Dyevacuunr apparatus.

40 OAPPABTEPRESSURE REACTORS 44

!entional designs,a completeset of common operationsfor synthesisand,/or purificationcan be designedaround the H-tube.

L6 cAPPABLEPREssURE REAcToRs

\ completemethodology for the manipulationand reactionof air-sensitivesolu- :ronshas evolvedaround cappableglass pressure bottles. Soft-drink bottlesare \()nletimesused (hence these procedures are sometimesreferred to as "pop bot- :le techniques");however, heavy-walled borosilicate glass pressure reaction ves- .r'ls are superior. In contrast to the modified standard taper ware discussed .'bove,this pressureapparatus offers advantageswhere modest pressuresare rccessaryand wherethe centrifugationof precipitatesis preferableto filtration. Ihesetechniques are especiallypopular in the preparative-scalestudy of cata- .r'ticreactions of small molecules,such as olefin polymerization.The pressure rottle is fitted with a capcontaining two 1/8 in. holesand a rubberliner, which :s securedby meansof a hand-operatedbottle capper (Fig. l.3l).'8 Dependingon their sensitivity,solids are loadedinto pressurereaction bottles :n the air or in an inert-atmosphereglove box. The bottle is cappedand may be carriedthrough severalpurge cyclesby meansof a hypodermicneedle attached

ryD-il:"':',

Fig, 1.31. Heavy-walledcentrifuge-tube, rubber cap liner, and cap. ("Pop bottle" reactor.)Tubes qith volumesranging from 20 to 250 mL are availablefrom Lab Glass. North West Boulevard. Vineland.NJ 08360.

I'Cappablereaction bottles, caps, and the rubber liner septaare availablefrom Lab Glass. Inc., Vineland, NJ and from Aldrich ChenricalCo., Milwaukee. Wl. Eottle cappersare availablefront large hardware stores. 42 BENCH-TOPINERT-ATMOSPHERE TECHNIOUES to a duaIinert-gas and vacuum manifold (Fig. 1.2).Ordinarily, the reactoris left under a small positivepressure (900-1000 torr, 3-5 psig), rvhichminimizes the entranceof air and facilitatesthe removalof liquidsby meansof a syringe.Reac- tionsu'hich evolve Iarge quantities of gasma1' require occasional venting through a hypodermic needle.Pressures in excessof 3,300 torr (50 lblin.2) should be avoided.The solution may be agitated by meansof a shaking machine or by means of a magnetic stirring bar which was included with the initial charge. Sincethe bottles are easilythermostated and samplesare readily removedby syringe,the cappablereactors have proven useful for kinetic investigationsof air-sensitivesolutions. These reactors are availablein shapeswhich fit largecen- trifuges, and are therefore quite useful for separatingsolutions from solids which do not filter well. Reactivesolids transfer operationsare readily performed in a glovebox becausethese sealed reaction vessels are easily transferred througha vacuumlock.

4 ,7 HoTTUBE AND SEALED TUBE rEcHNrouES

A. Hot Tube Reoctors. Many simplemetal halides, nitrides, and the like are convenientlysynthesized, and sometimespurified, at elevatedtemperatures in an apparatusdesigned to fit in a tube furnace.The generalstrategy is to contain one or nroreof the starting materialswithin the heatedtube. Often a reactive gasis passedthrough the tube. ln many instancesthe reactivegas is diluted with an inert gas, and the inert gas is usedrvhen purifying the product by sublimation. One example.given in Fig. 1.32,is the preparationof a nonvolatile product, magnesiumnitride, from magnesiummetal and nitrogen gas. When the reaction is complete.a back-flush of nitrogen is maintainedfrom the at- tachedSchlenk tube as the inlet joint is removed.A long, stiff wire is then used to push the boats containingthe magnesiumnitride into the attachedSchlenk tube. The secondexample in this same figure illustratesthe proceduresfor a volatileproduct, gallium chloride.reIn this casethe reactionis performedin an HCI stream and the product is subsequentlysublimed into a seriesof bulbs, which can then be sealedoff. The streamof inert gashas to be adjustedcarefully during the sublimation, so that the product is carried into the bulbs, but the inert-gasstream should not be so rapid that the sublimateis sweptout of the apparatus.In the courseof a typical hot tube reaction,large volumes of gas are exposedto highly reactivematerials in the reactor,thus exposingthe materials to the cumulativeamount of impurities in the gas. It is necessary,therefore, to use pure gasesor to purify all gasesby appropriatedessicants and/or oxygen scavengers.Chapter 3 may be consultedfor detailson inert-gaspurification.

f'W. C. Johnsonand C. A. Haskew,Inorg. Synth.. l, 2b ( 1939).present details of the galliunrchlo- ride synthesis. IOT TUBEAND SEALEDTUEE TECHNIQUES 43

To bubbler N2source ) -Tube furnoce

(o)

bubbler HCIor N2

tb)

Fig. 1.32. Reactionsin heatedtubcs. (a) Apparatusfor the prepatationand collcctionof nlagne- :rum nitride. Highly purified nitrogen is used. and only the product fronr the secondboal ts col- tected.Sample collection is perforned after the tube coolsb1'reversing the nitrogenflou throughthe rpparatus, insertinga long, stiff wire from the right end. and pushingthe boat into the Schlenk rube.(b) Preparationof a volatilehalide. Very dry gasis used.and its flou rate is carefull,vadjusted so that the halide neitherdiffuses back toivardthe gas sourcenor is suept pastthe first bulb. After rhereaction is complete.the halidenray be resublimedin a gasstream and then sealedoff in one or nroreof the bulbs.

B. SeOled TUbe PrepOrOliOnS. Sealedtube reactionsand purificationsaf- ford goodexclusion of the atmosphereand permit opel'ationsat nloderatepres- sures.The latter capability makes it possibleto work with highlv volatile solvents.such as liquid ammonia, at roonr temperature.Since the sealedtube is often loadedon a high-vacuumline, the detailson thesetechniques are givenin Chapter9. Another type of sealedtube processis employedfor chemicalvapor transport usedto synthesizeand purify many inorgatlics,such as metal disulfides.In the most comnton applicationsof thesetechniques a tube \\'ith one end sealedis chargedwith an impure or polycrystallinesample of the desiredconrpound plus a small quantity of a transportreagent. The tube is then evacuatedand sealedat the otherend. The sealedtube is placedin a furnacecapable of maintaininga temperaturegradient, with the hotter end correspondingto the chargedmateri- als and the coolerend empty. For example,the materialto be purified might be TaS2with a small amount of 12added as transportagent. Reaction of this trans- 44 BENCH.TOPINERT-ATMOSPHERE TECHNIQUES port agent*'ith the TaS2yields volatile products, u'hich are reconstitutedas purified singlecrystals of TaS2at the colderend of the tube.20'2r

GENERALREFERENCES

Angelici. R. J. l977,.Srrrtftesisund Techniquein Inorgunic Chentistry,2nded., W. B. Saunders. Philadelphia. Brauer,G.,Ed,.,Hundhuchdt,rPrepurativenAnorganis

roGrealerdetail and furtht'r cxamplesnrav be found in H. Schaefer.Chtnticul Vulxtr Trunsporl Resctiutrs,Ne* York. Acadenric.196,1. rlThe svnthesisof tungstcnox1'halides by this processis describedby J. Tillack, Inorg. Synth., 14. 109(1973) and detailsof the 1 aS1purification are given b1 J. F. Revclli.Irnrg. St,ttth.,19. 35 (1979). INERT.ATMOSPHERE GLOVEBOXES

his chapter describesthe principlesof inert-atnrosphereglove box operation, :redesign of gloveboxes, and glovebox procedures.The beginnerin a labora- ,rv*'ith an operatingglove box may wish to startby readingSection 2.1, and ':reconcluding section, "Equipment and Operations."Other sectionscan then -r consultedas the needarises. If the purchaseor designof a newsystent is being -,'nsidered,the wholeof this chaptershould be useful.The purificationof inert ..rses,discussed in Chapter3, is alsoreconlmended for individualswho wish to :.rin a thorough understandingof inert-atmosphereglove boxes.

2 I GENERALDEsTGN AND AppLrcATroNs i he inert-atmosphereglove box providesa straightforwardmeans of handling ,,ir-sensitivesolids and liquids.ln its simplestform. it consistsof a gastight box :itted with a window, a pair of gloves,and a gastight door or transferport. The -'ntirebox is flushedwith an inertgas, after which samples may be manipulated :n the inert atmosphere. Theglove bag is a simpleand inexpensivevariant of the dry box. It consistsof .i largepolyethylene bag fitted *'ith a nitrogeninlet and an openend, rvhichmay 'oe closedby rolling and clamping. The bag is purgedby severalcycles of filling '.rithinert gas and collapsing,or b1'a continuousflush. [n its prinritiveform, nranipulationsare accomplishedin an ordinary bag. but comn.rerciallyavailable

45 46 INERT.ATMOSPHEREGLOVE BOXES

glove bags with integral polyethylenegloves are much more convenient(Fig. 2.1).1 As u'ill be described.one of the prinrarl'sourcesof contaminationof the dry box atmosphereis diffusionof air through the gloves,In a few casesthis contam- inationhas prompted the useof manipulatorswhich, for simpletasks, need not be intricate. However, the use of manipulators has not met with u'ide favor, probablybecause other methodsare sinrplerand cheaper. The appealingsimplicity of glovebox manipulationsmust be weighedagainst the disadvantages,which are the slownessof operation and the difficulty in maintaining a water- and oxygen-freeatntosphere. Work in a dry box can be slowbecause of the needto passmaterials through an air lock and becausethe glovesand gloveports reducethe experimentalist'sdexterity. In addition, there is the problem of nraintainingan air-freeatmosphere, which is complicatedby impuritiesin the inert-gassupply, leaks in the glovebox. and diffusionof moisture and oxygenthrough the gloves.Solvent vapors or volatilereagents contanri- natethe atmosphere,and this sourceof cross-contaminationcan becomeserious if severalindividuals handling quite different materialsare using the samedry box. As describedlater in this chapter, a recirculatinggas purifier or a rapid

':.Nitrogen ,,4tnlel t\ _/

.) ,i,_a) ,-1"1^: ) 6 f]^ {,.-) (3\\ ,ra,Ä\ dri?"j '-7a .-),-'- /.-., '\z-'.

i i ; Entronce sleeve \ Rollup ond close withf he springclips \ :::=::::-=::

Fig. 2.1. Polvetltr'lcncglove bag. Severalsizcs are available.including glove bags u'ith t*o pairsof glovcs.(Adapted fronr Instrunrentsfor Researchand IndLrstlv.Cheltenhanr. PA. Glove Bag blo- chure.) rGlttvebags arc available lronr lnstrunreu(s for Rcsealcharrd Industrt. Cheltenhanr. PA I9012.and AldrichChenrical Co.. P.O. Bor 355.Mil*aukee. WI -S3201. REPLACEMENTOF AIRBY AN INERTATMOSPHERE 47

flushof inert gasthrough the box is oftenemployed to ntinimizeimpurities in the glovebox atmosphere.The most commonlyused inert gasis nitrogen;but rvhen the materialsbeing handled form nitrides, helium or argon is used. Somevery active research laboratories in the United Statesuse glove boxes for practicallyall of their chemicaloperations, including reactionsin solvents.In general,these situations involve one glovebox per investigatorand specialfea- tureswhich allow quick entry and exit from the glovebox. By contrast.in many Europeanlaboratories, very little, if any, use is made of gloveboxes. Instead, variousnleans are devisedfor handling solidswith Schlenk-typeequipment. In the authors'laboratories, glove boxes are usedfor intricatesolids transfer operations, but nrost reactionsand the handling of solutionsare perforned in Sch- lenk-typeapparatus or in a chemicalvacuum line. Operations such as weighing reactivesolids, making mulls for infrared spectroscopy,and loading capillary tubesfor X-ray diffraction are convenientlyperformed in a glovebox or glove bag. In addition to their use for handling air-sensitivecompounds, glove boxes havebeen used to good advantagein the transferof radioactive.poisonous, and hazardousbiological materials.The strong feature of the glove box for these applicationscomes from the easeof containment.Because of this characteristic, nruchof the developmentof inert-atmosphereglove box designhas occurredin conjunctionwith atomic energyprograms. General-purposeinert-atmosphere glove boxes are availablecommercially, so it rarely makes senseto constructa systemof this type locally.2Nevertheless, a knowledgeof the constructionfeatures is usefulfor the choiceof an appropriate glovebox and for the maintenanceand nrodificationof an existinginert-atmo- sphereenclosure. In addition, there are somespecial types of gloveboxes which n.rustbe constructedby the user becausethey are not generallyavailable commercially.

2,2 REpLAcEMENToF ArR By AN INERT ATMospHERE

There are two common methodsof replacingair by an inert gas in the main chamberof an inert-atmosphereglove box: evacuationfollowed by filling with the desiredinert gas, or a lengthypurge of the box by the inert gas. The second alternativeis generallyemployed for largeboxes, since extremely heavy and well- braced constructionis necessaryto prevent the collapseof a large evacuated chamber.On a small scale,the structural problemsare not so formidable,so a pump-down dry box is attractiveif a compact unit is satisfactory.Similarly, a

rManufacturersof inert-atmosphereglove boxes and accessoriesinclude Vacuum AtmospheresCo.. 4652W. RosecransAve., Hauthorne, CA 90250(aluminunr or stainlesssteel construction); Kewau- neeScientificEngineeringCo..Adrian,Ml 4922l(metal construction): LabconcoCorp.,SSll Pros- pect. KansasCity, MO 64132(fiberglass-reinforced polyester construction); Manostat Corp., 518 8th Ave., New York, NY 10018(polymethacrylate construction).

I 4B INERT.ATMOSPHEREGLOVE BOXES small punlpabletransfer lock is generallyattached to a largebox to facilitatethe introductionof apparatusu'ith minintum contaminationof the glovebox atnlo- sphere.

A. Pump-ond-Fill. Providingthe apparatusis leak-tight.it isnot necessary to attaina high vacuuntin a pump-and-fill operationfor eliminatingair from a transferlock or main chanrberof a glovebox. As discussedin Chapter1. the pump-and-fill processmav be repeateduntil the desireddegree of purity is attained. For the casein u'hich a vacuunlof.l'atmospheres is attainedon eachof rl cycfes of punrpingand filling.the fraction ol airA,remaining is given by Eq. (l ): A, :j\ (l)

Thus, a punrprvhich is capableof quickll achievingI torr (1.3 x 10-r atm) u'ill yielda residualair concentrationof 1.7parts of air per millionparts of gas after two cycles.lt must be stressed.however. that the limitation on the vacuunt must not be leakage.because in this casethe purity of the gas cannotbe im- provedby repeatedpump-and-fill cycles.Therefore, the standardsof construction of the apparatusshould be appropriatefor high vacuut'll,even though a high vacuum is neverachieved. To ensurethat the systenlis leak-tight,the chamber and plumbing to the punlp can be subjectedto a helium leak tester(Section 7.3D).Similarly, the pump canbe checkedon a high-vacuumtest bench or vacuum line. Sinceevacuation is usuallythe slou'eststep. sonle attention should be givento matchingthe pump to the system.For a chamberof volumeV and a pump of pumping speedS, the time requiredto reducethe pressurefrom P1to P2is given bv Eq. (2). PzV r:;sP'l' Q)

Sincethe pumping speedof a mechanicalpump doesnot vary greatlyat moderate pressures(e.g., Fig.6.3). it is reasonableto assumean averageconstant punrping speedif very low pressuresare not involved.Integration then yields Eq.(3). 2.3V P, t: toBP, (3) .,

As an example,consider the time requiredto pump a large air lock with a volume of 50 L from a pressureof 760 to 0.5 torr. The free-aircapacity of a widely availablepunrp is 140L/min, but three-fourthsof thisis a morereasonable aver- agepumping speedfor the abovepressure range. Insertion of thesenumbers into Eq. (3)gives a pump-downtinte of 3.5 min. This valuemay somewhat underesti- mate the pumping time. but the calculationillustrates a methodfor approximately matching the pump to the patienceof the experimentalist. REPLACEMENTOF AIRBY AN INERTATMOSPHERE 49

B. Pulging. Figure2.2 illustratesthree simple models for flushingair from a chamber by a stream of inert gas: perfect displacement,perfect mixing, and :hort circuit. The most desirablecondition for purging would be perfect displacement,since this involvesa gradually moving front of purge gas which pushesall of the unwanted air aheadof it (Figure 2.2a).Under this condition ,)nly one chamber volunte of inert gas would be required to obtain a perfect purge.In any practical case,perfect displacement cannot be attained,owing to interdiffusion,turbulence, and lack of an idea[geometry for the chamber.After due regardis taken to ensurethe proper positioningof the gasinlet and outlet, it rppearsthat interdiffusionis a nlajor limiting factor in the attainmentof perfect .lisplacement.Thus, rapid flushing has been found to be more efficient than 'lou'flushing.3If, on the other hand, the perfectmixing situationoccurred, the !'nteringpurge gas would inrmediatelymix with the gas in the chanrberand the nrixturewould exit the chamberat a rate equalto that of the enteringpurge gas , Figure2.2b). The differentialequation for the latter casemay be integratedto vield a simple exponentialdecay of the fraction of air remaining,/, in terms of the number of chambervolumes of gaspassed through the system,r, giving Eq. |{r:

Ai: g-' (4)

In contrastto perfectdisplacement, Eq. (4) demonstratesthat perfectmixing leadsto a reductionin the air contentby a factor of e-' (0.37)after one chamber volumeof purge gas is consumed.Similarly, it may be shownthat 8.8 chamber rolumes are required to reducethe air content to 150 ppm, and about l0 are necessaryto attain 45 ppm. Unlessa shortcircuit occursbecause of the inappro- priate placementof entranceand exit ports (Fig.2.2c), the actual situationcan be expectedto fall betweenperfect displacementand perfect mixing. Experi-

(b)

l---F* | \5ffi+

(c )

Fig.2.2. Schematicrepresentations of idealizedpurging conditions.(o) Perfectdisplacement; (b) perfectnrixing; (c) short circuit causedby the introductionof a light gasat the bottonrof the chamber.

'S. l. Cohenand J. M. Peele,USAEC ReportORNL-CF-SS-10-132 (1955). 50 INERT.ATMOSPHEREGLOVE BOXES mental resultswhich illustrate this situation are presentedin Fig. 2:3, and a recommendedarrangement for the inert-gasinlet and outlet is illustratedin Fig. 2.4a.

C. Recommended Conditions. Becauseof structuralconsiderations. it is generallymost satisfactoryto use the purging method for large chambers, suchas the main chamberof a largedry box. For smallerglove boxes and glove box antechanbers,air is convenientlyremoved by either pump-and-fill operations or purging. If purging is the method chosenfor replacingair in the antechamber, it is desirableto include a small manifold in the chanrberso that the interior of flasks or vials can be efficientlyflushed (Fig. 2.4b). In summary,the previousdiscussion indicates that threeprinciples should be followed:(1) to avoid short circuits,gases which are more densethan air (e.g., argon) should be introduced at the bottom of a chamber and conversely,less densegases (e.g., helium) shoutdbe introducedat the top; (2) interdiffusionof the incominggas with that in the chamberis a significantfactor, soa fast flush is more effectivethan a slowflush; (3) experimentalresults indicate that a chamber is purged at a rate slowerthan predictedby perfectdisplacement and faster than that indicatedby perfect mixing. Therefore,the perfect mixing equation

100 70 50 s30 -20 o X rn o7 -5C o c_ o CJ @ o o Pz o @ c o o o o .,1 = g ä o.z o l o5 9 o o o3 o 3 o o.? o J l o f o. 1 1?345678 No.ofbox volumechonoes

Fig. 2.3. Conrparisonof experimenlalresults with idealizedpurge conditiorrs.A, B, and C are experimental,with variousdesigns for the gas inlet and outlet. The bestof these,C, was obtained with the purging arrangementillustrated in Figure 2.4a. Point D was obtainedwith the heavygas (COz)entering at the top of the box, and point E was obtainedwith a light gas(He) enteringat the bottom. The latter conditionsresult in someshort-circuit flow. (Reproducedby permissionof the copyright owner. Butterworth from P. A. F. White and S. E. Smith, Iuert Atntosltheres,But- terworth, London, 1962,p. 148.) SOURCESOF AND REDUCTIONOF IMPURITIESIN ATMOSPHERE 5,1

(b)

(o)

Fig,2,4. Arrangenrentof purge lines.(a) Forthe main box the lou'ermarri{old should be the inlet * ith a densegas (for instance,Ar) and the outletwith a light gas(for instance.He). (ö) A purge-gas nranifoldin the transferport equippedwith outletjets to flush volumetricequipment

providesan ample margin of safetyin estimatingthe volume of purge gas required. Theserecommendations are basedon the assumptionthat the chan.rber can be flushedby smooth linesof gasflow betweenthe gas inlet and outlet. The placenlentof the gas inlet and outlet to achievesuch flow is illustratedin Fig. 2.4a.

2,3 souRcEsoF AND REDUcTToN oFrMpuRrTrEs rNGLovE Box AIMOSPHERES

A. Confominofion by Oulgossing. After the initial renoval of air from a glovebox chamber. the impurity levelswill gradually rise due to a variety of sources:(1) outgassingof hydrousor porousmaterials such as wood. paper, cloth. asbestos,and corrodedmetal; (2) leakagethrough seamsand joints; and (3) diffusion of atmosphericgases through permeablematerials, such as rubber gloves,rubber gaskets, and plasticwindows. Items 2 and 3 will be discussedin followingsection. Because of the first factor, wood or conposition board is not suitablefor the constructionof an inert-atmosphereglove box; and u'ood.paper, cloth, and asbestositems are not taken into the box when moistureis objectionable. A good substitutefor paper or cloth rvipesin cleaningup spilledsolids is the soft polyethylenesealing film sold by laboratorysupply houses(e.g., Para- film). When paperor cloth wipesmust be used,a considerablequantity of moisture may be removedprior to useby storageof theseitems in a desiccatorover a drying agent.

B. LeOks. Small leaksthrough seamsand gasketsare a significantproblem *'ith poorly constructedglove boxes. The maintenanceof a small positivepres- 52 INERT-ATMOSPHEREGLOVE BOXES

surein the box doeslittle to reducethe influx of air through smallleaks because countercurrentdiffusion of air is rapid. To reducethese problems, it hasbecome fairly standard practiceto adopt constructionpractices which approachthose usedin high-vacuumapparatus. Thus. permanentmetal seamsare bestwelded in a smooth and continuousfashion, and permanentseams in poly(methylmethacrylate)are best bonded with a solventcement (Appendix III). Perhapssome- what lessdesirable but still satisfactoryseams can be madewith rubber cements and rubberizedcaulking compoundson reasonablymatched mating surfaces. This practicesuffers from the potential deteriorationof the sealingcompound. Room temperaturevulcanizing silicone sealants are goodfor most dry box sealing applications.A pitfall to be avoidedis to purchasea poorly made glovebox or build one with sloppyconstruction techniques, with the thought that the as- sembledbox can be patchedby the applicationof paintsor sealants.In practice. sealantsapplied over a leak are likely to crack or channel,so one is foreverchas- ing leaks. Gross leaks may be detectedby slightly pressurizingthe box and painting suspectedareas with soap solution. NOTE: A normal nonevacuableglove box will tolerate only a small pressure or vacuum before the windows crack, the glovespop off, or the box is distorted. The most satisfactorymeans of finding small leaksis a halogenor helium leak tester(Chapter 7). In this casethe box is filled with Freon or helium and the "sniffer" of the leak testeris passedover the suspectedareas. Some glove box manufacturerswill guaranteea low leak rate as certifiedby halogenor helium leak testingat the factory.

C. Glove Box Dools ond Removoble Ponels. Temporaryseals cannot be avoidedon the entrancedoors and on panelswhich must be removedto recon- figure the glove box. Theseseals are best made with high-qualityfirm rubber gasketsor O-rings. It is important that the surfaceswhich are beingjoined are sufficientlyheavy so that they do not buckle when clamped together,and the panelor door shouldbe clampedevenly. The incorporationof thesefeatures in a suitableentrance port is accomplishedby the useof a floating hinge that does not constrainthe door, and the useof a latchingsystem that exertsits forcein an even fashion. Successfuldoor latchesinvolve an autoclave-typeclosure (Fig. 2.5a), a centrally located screw(Fig. 2.5ä), and evenlydistributed clamps or bolts(Fig. 2.5c).Large panelsare generally bolted together at closelyand evenly spacedintervals around the perimeter.

D. Diffusion of Ait inlo lhe Box. With good design and workmanship, leakagethrough seamscan be reducedto negligiblevalues. This leavesone remaining major sourceof atmosphericimpurities: diffusion of air through gloves and, to a lesserextent, through rubber gasketsand plasticwindows. Diffusion also is a significantsource of impurities in plasticglove boxes or glovebags. A few calculationswill illustratethe magnitudeof the problem. When the glovebox is constructedentirely from plastic,the diffusionof oxy- SOURCESOF AND REDUCTIONOF IMPURITIESIN ATMOSPHERE 53

Undercut lock bor /lo recetve ,,-Htnged clompingfingers -Flootrnq hinoe {

Clomping \ Hrnqedcotch for \lock- bo, Flootinghinges

(o) (b)

Flootrnghinge Yokeslo recetvebolts

K.oo"'.,, wtthwing nuts (c)

Fig. 2.5. Somedesigns for antichamberdoors. (a) Autoclavetype. When the hand wheelis turned, the wedge-shaped clamping fingersextend or retract.The door is clampedshut when thesefingers rre wedgedinto an undercut on the flange.(ä) A centralscrew lock design.(c) A hinged-boltdesign. Thereare many variants of this. A group of cam-actionclamps is sometimesused ii placeof bolts.

gen through the walls is significant.For an average-sizeglove box constructed from l/2-inch-thick poly(methylmethacrylate), a calculationof diffusion rates indicates that the influx of oxygenthrough the walls is about equal to oxygen diffusion through the gloves. Using the diffusion coefficientdata in Appendix III, and assuminga typical glove bag sizeof 8,600 cm2and a thicknessof 5.2 x l0 r cm, 12.-, of o"yg"n n'ill diffuseinto the bag at 25'C in one hour and, at a relativehumidity of 504, approximately 30 cm3 (gas at STp) of moisturewill diffuse into the bag in the same time period. For a neoprenegrove with an area of 1,900cm2 and with a thickness of 7.5 x l0-2 cm, an influx of 0.56cm3 of oxygenper hour is calculated' An experimentalvalue for the moisturediffusion rate oi 12.5cm3 (gas at STP) is availablein the literature for 25oc and 50% relativehumidity.a fuhen the glove box is in use,the worker generatesboth sweatand heat,and the rate of diffusionof moistureincreases by approximatelya factor of ten.l In otherwords.

'J. E. Ayers,R. M. Ma14ield,and D. R. Schmitt,Nuct. Sci. Ettg.,g,274(1960). trA INERT.ATMOSPHEREGLOVE BOXES when a dry box with two glovesis idle, the influx of impurities will be about a millimoleof atmosphericimpurities per hour. Assuminga typicalglove box volume of 212 L, this amountsto an increaseof atmosphericimpurities by 59 ppm/ h. When the box is in use,the influx may increaseto about500 ppm/h.

E. Moinfenonce of on Inert Atmosphele. From the previousdiscussion it is clearthat the dry box atmosphererequires continual purification to balance the influx of contaminants.A nunrberof methodsof widelyvarying complexity havebeen used. The simplestand mostcommon scheme is to maintain a continuous purge of the box. This also may be supplemented*'ith the useof an open dish of desiccantin the box. If the expenseof a continuouspurge of inert gasis too great, a recirculatingsystem is necessary.The n.rostcomnlon recirculators are basedon an oxygenscavenger, such as supportedCu or MnO, and a desiccant, such as molecularsieves. (The nature of and regenerationof oxygenscav- engersand desiccantsare discussedin Chapter3.) Systemsof this type may be constructed.as outlined in Fig. 2.6, or purchased.Commercial systemsare availablewhich regeneratethe columnsautomatically. Satisfactory operation is possiblewith manual regenerationbecause the unit can be arrangedso a setof columns can be switchedfrom purification to regenerationby attendinga ferv valvesand switches.One of the sinrplestcommercial units is nrountedon the side of the box, and large-diametercolumns with large-particlepacking are used.An air blowerin the box is sufficientto forcethe inert gasthrough the colunrn(Fig. 2.7).Mounting the blowerin the box simplifiesthe designbecause it avoidsthe leakagewhich is a problem with many pumps, and it avoidsany sourceof oil mist which can result from a pump. If an externalpump is used, a unit with a metal diaphragm is often preferred. Pumps with ordinary shaft sealsmay be nrountedin a metalbox which is purgedby inert gas.'in One earlytest of glovebox impuritiesindicated that a circulationrate of 5 box volumesper hour through the glovebox and MnO purificationtrain would lead to a steadystate concentration of 50 ppm of atmosphericgases in an argon-filled box. For a nroderncommercial purification unit the manufacturerclaims that the moisture and oxygenlevels are reducedbelow I ppm by purging in a large glovebox at a circulationrate of about50 box volumesper hour. A schemefor removalof nitrogenfrom a heliun-filled glovebox can be based on low-temperatureadsorption on charcoalor molecularsieves held at - 196oC. There appearsto be no easilyregenerated nitrogen scavengeru'hen the more condensableinert gas argon is employed.In this casea getterof hot calciunror hot zirconium-titaniumalloy is used.When the column of gettermaterial is consumed,it ntustbe replaced.The heat introducedfrom this or other sourcesis atr annoyancefor the glovebox user.This problem may be reducedby including a heatexchanger in the inert-gasstream. Both water-cooledand refrigeratedheat exchangershave been usedsuccessfully.

'8. C. Ashbyand Il. D. Schwartz.J. Chent.Erlrc.. Sl, 65 (1974). "P. A. F. White and S. E. Smith(General Refcrences, p.67). SOURCESOF AND REDUCTIONOF IMPURITIESIN ATMOSPHERE 55

13X

4A 13X

Fig. 2.6. Schematicrepresentation of a dry-boxpurification scheme. (A) Glovebox; (B) tank argon; (C) purgeline for punrp container:(D) gastightpunrp containeri (E). 2.7 ftr/min graphitering pump; (F) bubbler; (G) purificationtrain consistingof Liude l3X and 4,4 MolecularSieves, and Vernriculite-supportedMnO at roonl tenlperature(see Chapter 3). In sonreinstallations an additional drying column followsthe MnO column. Approxinratecolumn dimensionsare 3-in. dianteter by 4-ft length.(Unpublished design of T. L. Broun.)

Hydrocarbonsand polar solvents,which are sometimesinadvertently or in- tentionallyintroduced into a glove box, presenta contaminationproblem and may have a deleteriousinfluence on someoxygen scavengers. Volatile sulfides and halocarbonsare particularly strong poisonsfor copper-basedoxygen scavengers.Removal of thesetypes of materialscan be effectedby l3X molecular sieves;these in turn can be regeneratedat slightlyelevated temperatures as describedin Chapter3. Alternatively,the solventvapors and much of the moisture can be removedby rrreansof lou'-temperaturetraps held at -78oC.5 The pressurein a dry box must be closeto I atm for easymanipulation of the gloves.Significant deviations from 1 atm for a nonevacuableglove box can dam- agethe windou's,gloves, or box walls. If the dry box atmosphereis maintained by a continuouspurge, a large mineral oil bubbler on the exit will ensurethe proper pressure.With a closedrecirculating purifier, a pressurecontroller is desirablebecause large fluctuations in the dry box pressurecan resultfrom run- 56 INERT-ATMOSPHEREGLOVE BOXES

lbtlbl-

Fig.2.7. Recirculationunit installedon a dry box. (Reproducedby permissionfrom Vacuum At- mospheresCorp. )

ning the glovesin and out during routine manipulations.Commercial units are availableand a descriptionof the necessaryparts for the constructionof such a unit are given in the literature.s-r

F. Moniloting lmpurifies. Becauseof cost and complexity,the automatic monitoring of the glove box atmosphereis not comnlon in academiclaborato- ries, but someindustrial and many atomic energyinstallations employ continuous monitoring. Water is easierto nleasurethan oxygenand fairly simplemois-

'D. Eubanksand F. J. Abbott,Anul. Chent.,4l. 1709(1969). SOURCESOF AND REDUCTIONOF IMPURITIESIN ATMOSPHERE 57

rure metersare availablewhich operatein the parts per million range.8These nretersare basedon a varietyof principles,the most common beingthe conductivity of a hygroscopicmaterial. If the dry box atmospherewill be contaminated b-vvolatile solvents, a meter should be chosenwhich is insensitiveto thosesol- rents.In addition, a simpledewpoint meter may be built into the box in the form of a well which can be chargedwith a coolantsuch as Dry Ice.eThis well should extenddown far enoughinto the box so that its polishedsurface can be observed for signsof condensation.A dew point of -78"C correspondsto about 0.7 ppm of water vapor. Oxygen meters are commercially available,but their operation in conjunction *'ith gloveboxes presents some complications.r0 One method for the measurement of low oxygenconcentrations is basedon the potentialacross a solid oxide electrolytecomposed of CaO-dopedZrO2.Unfortunately, this systemworks at elevated temperatures where reducing vapors affect the reading. Another schemeinvolves an electrochemicalcell having an aqueouselectrolyte.rr Since this schemeintroduces moisture into the gas stream, it is best placed on the outletfrom the glovebox. Owing to the lack of simpleand inexpensivedetectors, a varietyof qualitativetests are employed.The most popular of theseis the light bulb test.In this test, the total oxygenand moistureis estimatedby the lengthof time it takes a light bulb filament to burn out while it is exposed to the glovebox atmosphere.The filament of a standard115-V, 25-W light bulb with a hole broken in the envelopewill burn for daysto weekswhen the oxygenplus moisture contamination is 5 ppm or lower. If the flow rate and nature of the filament are controlled in a reproduciblemanner, a calibration curve can be obtained;one such curve is presentedin Fig. 2.8.7 Often it is sufficient to determine oxygen and moisture by noting the changes which occur upon exposureof a highly sensitivecompound. Noüe:The common cobalt-impregnated desiccants, which turn from blue to nearly colorless when saturated with water, undergo this color change at far too high a moisture level to be useful for sensitivematerials. A qualitative test sometimesrecommended for moistureis the brief openingof a bottle of TiClr in the glovebox. If smoke doesnot appear,the moisturecontent is below 10 ppm. Triethyl aluminum or a hydrocarbon solution of diethylzinc will not fume when opened briefly in a box with oxygenin the low parts per million range. Theseparticular testshave the

nSourcesof moisture meters include Vacuum Atmospheres Co. (see footnote 2); Dupont Instru- ments, Wilmington, DE 19898;Panametrics, Inc.,22l CrescentSt., Waltham. MA 02254:Beck- man Instruments,Inc., 2500 Harbor Boulevard,Fullerton, CA 92634. qS. Y. Tyree, Ir., J. Chent.Educ., 31,603 (1954). r0Sourcesof oxygennreters include: Vacuum AtnrospheresCo. (seen.2); Anacon Divisionof High VoltageEngineering Corp., F.C. Box 416, South Belford St., Burlington, MA 01803;Mine Safety ApplianceCo., 600 PennCenter Boulevard,Pittsburgh, PA 15235(model 803 can be modifiedfor usein the ppm range). lrW.BahnretandP.A.Hersch,Ärcl.Chent.,43.803(1971): D.R.Kendall..4nal.Chent..43.944 (l971 ). 58 INERT-AIMOSPHEREGLOVE BOXES

c c, o) X

tr 102 o- o-

o246810121416 Frlamenttile min

Fig. 2.8. Oxygenconcentration versus filament lifetimefor an exposedlight bulb filamentburning in an inert atmosphere.By noting hou lorrgthe light bulb stayslit, a reasonableestinrate of the oxygenplus moistureimpurity levelcan be obtained.These data correspondto an A/C No. 63 buib filament run *'ith l0 V potentialand a gasflow rate of l.l L/min.

great disadvantagesof contaminatingthe glovebox atmosphereand contributing to undesirabledeposits on the glovebox walls.If ethersor hydrocarbonscan be tolerated in the glove box atmosphere, a solution of Cp2TiCl2ZnCl1solvent can be usedas a test for oxygen.r2A small amount of solutionis introducedby syringeinto an open aluminum pan in the dry box; if the compoundretains its original greencolor as the solventevaporates, the oxygencontent of the dry box atmosphereis lessthan 5 ppm. At higheroxygen levels the colorchanges to olive green or yellow; and if the oxygen contamination is very large, it will turn orange.The compoundmay be preparedby allowingCp2TiCl2 (Alpha Inorgan- ics)to reactwith a slight molar excessof zinc metal powderin dried and deoxy- genatedtetrahydrofuran, benzene, or toluene.The reactionma-y be run by stirring the mixture for approxim ately 12 hours in a 50-mL Erlenmeyerfitted with a serum cap. Manganousoxide supportedon silicagel has a very high affinity for oxygen, and the reactionis accompaniedby a vivid colorchange from Iight greento dark brown. A tube of this material in an inert-gasstream is used in the authors' r2D.G. Sekutou'skiand G. D. Stuckv.J. Chenr.Educ..53.ll0 (1976). GLOVEBOX HARDWAREAND PROCEDURES 59

laboratoryto measurethe oxygenimpurity level.and recentlya commercialde- tector of this type has come availablefor use in gas chromatographicsystems. Sincethe kineticsof this reactionare fast and the line of demarcationis distinct. a measurementof the lengthof progressof the brown regionalong the tube can be convertedto the amount of oxygenabsorbed. The levelof impuritiescan be measuredusing this schemeby knowing the quantityof manganeseon the silica gel, the volume of gas passedthrough the tube. and the stoichiometryof the reaction,Eq.(a). Although it has not yet beendone to the authors'knowledge, a small unit equippedwith a simple hand-operatedpump could be readily con- structedfor the periodiccheck of the atmosphereinside the glovebox. 2MnO + l/20z: Mn2O3 (4)

2,4 GLovEBox HARDwAREAND pRocEDUREs

A. Gloves ond Glove Porls. Judgingfrom the permeabilitydata in Ap- pendix III, butyl rubber glovesshould reducethe influx of water by one-halfto one-tenthand that of oxygenby one-thirdof that givenfor neoprenegloves. Ow- ing to this advantage,butyl rubber is routinely usedon most inert-atmosphere glove boxes. Natural-rubber glovesare sometimesused becausethey afford a better senseof touch and better dexteritythan the synthetics;however, natural rubber is much more permeable to atmosphericgases and less resistant to solvents.To improvedexterity without a largeincrease in the diffusionof atnrosphericgases, gloves are often constructedwith a thin crosssection in the region of the fingers and thicker rubber elsewherebecause the thicker materialshave reducedpermeability. When dexterityis not critical, someworkers use a pair of gauntletgloves inside the regulargloves. This practiceundoubtedly reduces diffusionof moistureinto the glovebox, and it providesan extra protectivebarrier when hazardousmaterials are handled. The accumulationof sweatin the glovesbecomes a great annoyance,which canbe alleviatedby a small tube carryingair tapedinto eachglove and terminat- ing at the back of the hand, or dividedand terminatedat the back of eachfinger opening. Electrician'stape may be usedto hold the tube in place.Ideally, the glove should ride in and out with the experimentalist'shands. To improve the adherenceof the glovesto the hands, glovesmay be mounted palm side up, which resultsin a slight twist of the glovearound the wrist whenthe handsare in an ordinary working position.Also, to avoid "losing" the gloves,they shouldbe no longerthan the worker'sreach. This is particularlyimportant whenthe box is operatedat slightly reducedpressures. Some manufacturersoffer gloveswith accordionsleeves which are supposedto providefree in-out travelof the gloves. In practicethe authorsfind theseto be cumbersome,and the complexconstruc- tion is likely to invite pinhole leaks. When a new glove box is being designedor an old one modified, the glove ports shouldbe positionedto provideaccess to the entirebottom of the box and 60 INERT.ATMOSPHEREGLOVE BOXES to any shelvesor mounting bars on the back wall. With a large box, this may require the useof more than two gloveports. One fairly common practiceis to provide a third glove port closeto the antechamberside of the box. A glovein this position provideseasy handling of the insideantechamber door and allows one to reach into the antechamber. The glove must be securelyfastened to the port so that it does not unexpect- edly pop off of the box. One common procedureis to usea large O-ring which holds the cuff of the glove to a groovein the glove port (Fig. 2.9a), and the glove must be further securedby electrician'stape and/or a steelclamping band. If the glovebox is of the evacuabletype, it is necessaryto pump on both the inside and outsideof the gloveto preventthe glovesfrom being suckedinto the box. Figure 2.9ä illustratesa designfor a vacuum-tightglove port coverwhich permits evacuationof the outer side of the glove.The box may be brought up to atmosphericpressure before the outsideof the gloveis vented,or the two opera-

Interiorof box (o)

\\.\ I

\,,'\.-\--!-- I \ ---f-- \-

ossoge for evocuotron

Inferiorof box (b)

Fig.2.9, Gloveports. (a) A conventionalglove port. (b) Glove port with cover to allouevacuation. (Adaptedfronr USAEC Report TID-16020. N. Garden,Ed.. 1962.) GLOVEBOX HARDWARE AND PROCEDURES 61 tionsmay be nearlysimultaneous. Once the systemis up to latm of pressure,the vacuum-tight cover is removed to provide unobstructed use of the gloves.

B. Confoinmenf of Hozoldous Moleriols. To reducethe chanceof loss of materialsfrom a containmentenclosure, the glovebox is operatedat slightly belowthe ambient atmosphericpressure. For gloveboxes in which major con- raminationof the atmospherecannot be toleratedduring the glovechanging operation,and for gloveboxes which serveas radioactiveor biologicalcontainment .'hambers,the gloveports shouldbe designedwith a doublerib (Fig. 2.9) sothat rhe new glovecan be installedbefore the old one is removed.In preparationfor rhisglove change (Fig. 2.10),the leakyglove is stuffedinside the box and the rib irn the cuff of this gloveis advancedto the outer groove.A newglove (which may be flushedout with inert gas)is slippedover the old one and its rib is securedon the inner groove.The old gloveis pulled off the gloveport and into the interiorof rhe box. If this glove is contaminated,it may be baggedout of the box as describedbelow. If radioactivematerial is involved,the whole operationmust be nronitored.As mentionedearlier, it is common practiceto wear an additional pair of gauntletgloves inside the dry box glovesto provideadditional protection of the experimentalistin the eventthat a leak developsin the gloveson the inert- atmosoherechamber.

(do (lnside) Glove Clompring Removesteel O-ring not box...-- (steel) clomp rrng disturb) - Glovebox Glove beod Glove 0 ring (neoprene) inside (fold os shown) ene) OU

Old O-rin9 Clompring (lnside) -Clomp ring glove(remove (steel ) Glove box (steel) osoc+ive woste) Glovebox Oldglove (inside)--

glove . New '(slip over Newring old cnd clomp (neoprene) os shown)

Fig. 2.10. Changinggloves. The procedureoutlined here prevents the lossof radioactivityfrom the box and minimizes the introduction of air. (Adapted from G. N. Walton Ed., Glove Boxesand Shielded Cel/s. Butteru'orth. London. 1958.) 62 INERT-ATMOSPHEREGLOVE BOXES

The bagging-outprocess, illustrated in Fig. 2.1l, providesa methodfor dis- carding wastematerials and used gloveswhich have been contanrinated.This processis widely used for radioactivewastes. A heavypolyethylene bag is attachedto a double-groovedport similar to a gloveport. When the time comesfor removalof the wastesdeposited into this bag, it is heat sealedand cut alongthe sealso that the disposableportion of the bag attachedto the box is neveropened to the atmosphere.A fresh bag is then attachedto the inner grooveand the remnant of the old bag is taken into the box by the procedureoutlined for the glovechanging operation, in Fig. 2.10.

2.5 TYPTcALGLovE Box sYsTEMs ln this sectionsome glove box systemswill be discussedwith commentswhich will put them into perspectivefor potentialapplications. When a laboratory is equipped with good Schlenk-typeapparatus and/or vacuumsystenls, the glovebox will be neededfor only occasionaltransfer operations. In this situationa commercialglove bag (Fig. 2.1), may be perfectlyadequate for transferringsolids. Bulk materialsor microcrystallinesolids are often much more resistantto oxidationor hydrolysisthan solutions.It must be borne in mind, however,that the volume of a glovebox or glovebag is largeand that prolongedexposure of a sampleto a contaminatedatmosphere runs the risk of decomposition.Thus it is best to work as rapidly as possible.particularly in a glovebag which is not providedfor efficientpurging. The mountingof air-sensitive crystalsinto small glasscapillaries for singlecrystal X-ray diffraction may sometimesbe convenientlyperformed in a glovebag fitted around a binocular microscope(Fig.2.12). This operationis tediousat best,and the lack of dexterity is particularly troublesomewhen handling the fragile capillaries.To aid in the manipulation of thesecapillaries. a capillary holder which is describedin Section2.6.E is a tremendousaid. The mounting of highly reactivecrystals may requirethe useof a glovebox.

Insidebox

Loborotory s ide

Fig. 2.11. Bagging radioactivewastes. (Adapted from G. N. Walton Ed., Glove Boxes and Shielded Cel/s. Butterworth. London. 1958.) TYPICALGLOVE BOX SYSTEMS 63

\-l N2 Inlet ___.._.-{-*-*--j_)-,- .'---.._ r l-\ ---.--.j- -

Fig.2.l2. Glovebag fitted around a binocularmicroscope. A holelarge enough to fit the eyepicce ,f the microscopeis cut in the top of the glovebag. The glovebag is then fastenedto the microscope irsingelectrical tape and purgedof atmosphericgases.

Unfortunately,the working distancefor commercialstereo microscopes is rather short, and the microscopealso doesnot accommodatereadily the usual large glovebox with a vertical or slightly inclined window. A single-chamberevacu- abledry box is availablecommercially which would appearto be satisfactoryfor crystalnlounting and other operationsin which the apparatusis not large.2 For generaluse with only moderatelyair-sensitive compounds, a plastic dry box may be more convenientthan a glove bag. Boxesconstructed from poly- (methylmethacrylate) or from fiberglass-reinforcedpolyester are availablecommercially.2As discussedearlier, the diffusion of atmosphericgases through the former material is significant.and it is likely to be lessbut still appreciablefor the fiberglassboxes. These boxes are light and relativelyeconomical and they are usefulfor all but the most air-sensitivematerials. A commercialwelded aluminum dry box, illustratedin Fig. 2.13,2has a helium-leak-testedevacuable transfer chamber and an overheadwindow to provide light. A stainless-steeltray inside of the box protectsthe aluminum from spills,and a sliding tray in the antechamberfacilitates the transferof materials into and out of this box. The two large doorson the transferlocks are mounted on a pivot arm through a central screw.These doors are equippedwith O-ring seals.The O-ring on thesedoors and similar gasket materialson other glove boxesshould be inspectedoften. This critical sealis subjectto the collectionof 64 INERT.ATMOSPHEREGLOVE BOXES

Fig' 2'13' Contmercialmetal glove box. An aluminum glovebox with a recirculatinggas-purifica- tionsystem(Reproducedbypermissionofthecopyrightou.nerVacuurnAtnrosphereiCorp.,North Hollp'ood. Calif.)

debris from the materiarsbeing handred, and it can be nicked if improperry treated' The supplier for this glove box offers efficient recirculatinginert-gas purif iers.

2,6 EoutpMENTAND opERATtoNs

A. Trqnsfer into o Glove Bog. It is cumbersometo transfer rargeitems into a glove bag once work is underway.Therefore all of the itenrsto be used should be placedinto the bag, which is then fully deflatedand sealedby rolling and clamping the inlet flap. Inert gas may then be introducedand the bag may be flushed through an exit tube and bubbrer,or openedstightty, coilapsed, and inflated severaltimes to expel air. : OUIPMENIAND OPERAIIONS 65

B. Exomple:Tronsfer of Moferiols through on Evocuoble Air tock. To introducea samplefrom the laboratorythe inner door of the port is -.,)sedand then the outer door is opened.Samples are placedin the lock and the 'rrerdoor is clamped shut. The lock is evacuatedand filled severaltimes with :.rertgas. After the lock is brought to atmosphericpressure the final time, the :ner door may be openedand samplestransferred into the box. Carehas to be :iken when filling the antechamberto avoid diverting too much gas from the :rain chamber if the box is not fitted with an automatic pressurecontrol. An- 'rher point requiring attention is the nature of the apparatuswhich is put into :ne evacuablelock. A closedvessel with standard taper fittings will fly apart .:ndervacuum unlessthe joints are securedwith heavysprings or heavyrubber rands.or unlessthe apparatushas been evacuated before it is placedin the port. O-ring ware has a big advantagebecause the clampsused to securethose joints ,rill hold securelyunder vacuum. Of course,closed containers going into the rlove box should havebeen previously purged or evacuatedto eliminateair. As mentionedin an earliersection, wood, paper,cloth, corrodedmetal, and asbes- :osare ordinarily not transferredinto the glovebox becausethey contain consid- .:rablemoisture.

C. Weighing Solids. There are severalmethods for weighingair-sensitive solids.(As mentionedin Chapterl, this processmay be carriedout without a dry box if the sample is containedin a sealedampule of known weight.)The most obviousmethod of weighing in an inert-atmosphereglove box is to employ a balancewhich is insidethe box. A sinrpletriple-beam balance is very usefulfor sometypes of weighing, and a torsion balanceor electronicbalance is useful *'henhigher sensitivity is required.Static build-up and flexingof the box aretwo problemsencountered in making preciseweighings. The antistaticdevices nren- tioned in the following sectionalleviate this problem to someextent. Another methodfor weighingan air-sensitivematerial is to introduceit into a cappableweighing container in the box and transferit out to performthe weighing. The weighingtube with cap (Fig. t.23) is usefulwhenthe sampleis to be shakeninto a reactionvessel on a vacuum line or other apparatusoutside the glovebox. It is filled and cappedinside the box, transferredout and weighed, and quickly opened and shaken into the receivingcontainer under a flush of inert gas.A tare weight is then obtainedon the emptyweighing tube. Vials filled in the box can be stopperedwith a septum cap, removedfrom the box, and sealedoff at the glassblowingbench. Beforethe seal is made a fine needleis insertedthrough the serumcap to relievethe buildup of pressureas the ampule is being sealed.To determinethe quantity of material in the vial, it is weighed beforegoing into the glovebox, the parts are weighedafter it is sealedoff, and the weight of the contentsdetermined by difference.

D. Sfofic Buildup. The very dry atmosphereof a glovebox or glovebag is conduciveto the buildup of static electricity,which can scattera finely divided INERT-ATMOSPHEREGLOVE BOXES

material,cause small crystallographic-sizecrystals to fly into oblivion,throw off balancereadings, and causesimilar vexing problems. There is no completesolu- tion to this problem, but two typesof antistaticdevices are availablewhich usually reducethe problem to manageableproportions. The headof an alpha-parti- cle static eliminator can be pointed toward the items being manipulated.13To providea sufficientflux of alpha particles,the radioactivesource should be replacedfrequently. The alpha particles have a rather short range in the glovebox atmosphereand they do not passthrough the gloves;so the radioactivesource has to be placedvery closeto the work. Another type of staticeliminator is the gunlike unit built for removingstatic from phonographrecords. This unit pro- ducesionized gas particleswhen a trigger is actuated,and thesecan be "shot" into vesselsand the like. Upon long standinginside the dry box thesedevices lose their effectiveness,so it is common practiceto take the staticeliminator into the box only when it is needed.It alsois worth notingthat flint glassis moreresistant to static buildup than borosilicateglass.

E. Ofhet llems ond Useful Operolions. A varietyof small items which are generallyuseful in a glove box are catalogedhere. The static eliminators, weighing tube, and Parafilm have already been mentioned. To preservethe cleanlinessof the dry box a sheetof aluminum foil is oftentaken in with eachjob to cover the working area. Cleanlinessis a seriousproblem, particularly in a communal glove box. If capillariesfor X-ray diffraction are kept in the glove box, they should be coveredso as to not collectsmall particleswhich fly about becauseof a staticcharge. A veryuseful holder for X-ray capillarytubes consists of a glasstube about 15 cm long, rvith an internal diameterof about 3 mm and a small flare at one end. This flared portion of the tube is lined with a small piece of Parafilm, which doesnot block the openingin the tube. When an X-ray capillary tube is pushedinto the film, it sticksin placeand the tube can be grasped firmly without danger to the capillary. Finely drawn glassrods or fine, hard stainless-steelwires are usefulfor transportinga singlecrystal into a capillaryor for tapping a collectionof fine crystalsin an X-ray capillary.Other potentially usefulitems include a collectionof spatulasand tweezers.lf the box is large, a pair of tongs may help to retrieveitems rvhich are out of reach. For infrared spectroscopyon air-sensitivesolids, samples may be mulled with mineraloil and sandwichedbetween infrared transmitting plates. A tissuegrinding apparatusis useful as a mulling tool and a supply of degassedmulling oil may be kept on hand in the box for this purpose.

GENERALREFERENCES

Barton, C. J.. 1979."Glove Bo.r Techniques."in E. S. Perry and A. WeissbergerTechniques o.l Chentistrv,Vol. 8, Wiley-Interscience,New York. p.221. A collectionof references.

riNuclearProducts Co.. El Monte. CA. :OUIPMENIAND OPERATIONS 67

::non, C. J., l963, "Glove Box Techniques,"in H. B. Jonassenand A. Weissberger.eds., fecft- nique of Ittorgunic Chentistry,,Vol. 3, Wilev-lnterscience,New York, p. 259. This chapter stressesthe containmentof toxic materialsand presentsa largecollection of referenceson the useof gloveboxes. .:crfey,J. M. Ind. Eng. Chent..46,435(1954); T. R. P. Gibb, Jr.,Anul. Chem.,29, (1957)l R. E. Johnson,J. Chent.Educ., 34, 80 ( I 957).Details on the constructionand operationof glovebox systems. ,\hite, P. A. F., and S. E. Smith, 1962,Inert Annosphercs,Butterworth, London. This book presentsan excellentdiscussion of the purificationof glovebox atnrospheres.and a good overviewof glovebox nrethodsas practicedin the United Kingdom atomic energyestablishnrents. Still the bestgeneral reference in the field. INERTGASES AND THEIRPURIFICATION

Nitrogen, argon, and helium are the most commonlyused inert gasesfor inert- atmospherework. There are, however,specific situations in which a more reactive gas such as carbon dioxide, hydrogen,or the like is usedto excludeair. Of the inert gases,nitrogen has the advantageof being quite cheap and readily available.On the other hand, nitrogen is reactivewith some metals, such as lithium, at room temperature.Nitrogen also reacts with many metalsat elevated temperaturesas well as with some metal complexes.Helium and argon are highly inert and similar in price, sothe choicebetween them generallyhinges on the differencesin their properties.Helium is the easiestto purify becausenitro- gen and othergases can be removedby low-temperatureadsorption. Argon n'rust be purified by chemicalmeans, since it has low-temperatureadsorption proper- tiessimilar to nitrogenand oxygen.The advantagesof argon arethat it doesnot diffuse out of systemsas rapidly as helium and it is heavierthan air, which makesit easierto maintain an inert atmospherein casesu'here a flask must be momentarilyopened. Inert gasesare generallyavailable in high-pressurecompressed gas cylinders and, in somecases, in medium-pressureDewars. Details on handlinghigh-pressurecompressed gas cylinders are givenin Chapter 10. The presentchapter will concentrateon the purification of inert gases.

3,'1 souRcEsAND puRtTy

A. Sourcgs. In the United States high-pressurecompressed nitrogen is availablein severalpurity grades. For example, the Matheson Company sells 68 9URIFICATIONOF GASES

\c'\'engrades ranging from "extra dry" (which is quoted to be 99.9% pure) to 'prepurified" grade (with 99.998% purity) at relatively economicalprices. Other grades,such as "oxygen free" (Oz < 5 ppm) and one called "Matheson Purity" (with the sum of 02, Ar, CO2,H2O, and hydrocarbonsequal to lessthan : ppm) are considerablyhigher in price. The moisture contentof the gas will rncreaseas the tank is emptied,because adsorbed moisture exerts a roughlycon- \rant partial pressurein the interior of the cylinder.Thus, as the total cylinder pressureis reduced,there will be an increasein the molar ratio of watervapor to :as. High-purity liquid nitrogenis availablein most metropolitanareas at prices lhat work out to be cheaperthan that for the compressedgas. For applications ',rhichrequire a large quantity of high-purity nitrogen, such as a continuous glovebox purge, large pressurizedDewars of high purity liquid nitrogenare of- ien the most economicalsource of inert gas.These Dewars are availablein gasor Iiquid take-off designs. High-purity gradesof nitrogen, helium, and argon are often satisfactoryfor applicationsin which impurity levelsof approximately50 ppm are tolerable.If relativelylarge volumesof gas are required and higher purity is needed,it is generallymost economicalto purify high purity or lowergrade gas, as described below.lt must be rememberedthat the purity levelis rapidly degradedby diffusionof air through rubber tubing or the rubber diaphragmsof ordinarypressure regulators.Special regulators, with metal diaphragms,greatly decrease contamination by atmosphericgases and are availablefor useon ultra-high purity gas c1'linders.

B. Pulity Requiremenfs. As an illustration of the purity neededin some specificapplications, consider a closedglass apparatus of 500-mLvolume. If the inert gas in this apparatus contains 50 ppm of water and oxygen, the total amount of impurity is about 0.001 mmol. This impurity levelwill be neglegible in a preparativesituation if much more than a millimole of compoundis being handled. If, on the other hand, the experimentrequires a continuousstream of gas,such as in a hot tube reactionor a catalyticflow reactor,50 ppm of impuri- tiesis likely to be unacceptable.It can be seenthat it is necessaryto estimatethe purity requirementson the basis of the amounts of material which are being handledand the total volumeof gasto which this materialwill be exposed.It is not difficult to purify inert gasesso that the total oxygenand moistureis below5 ppm, this being a safe standardfor most preparative-scalework. When ultra- pure gas is needed(parts per billion range),as in quantitativeresearch on sup- portedcatalysts, helium is the inert gasof choicebecause it is amenableto purification by a combination of low-temperatureadsorption as well as chemical methods.

3,2 PURrFrcATroNoFGAsEs

A. Principles. A majority of the inert-gaspurification schemesemployed in the laboratoryare basedon passingthe gas through a bed of solid reactantor 70 INERTGASES AND THEIRPURIFICATION adsorbent.In general,the purificationprocess is fasterfor finer particlesand for highly porousparticles. Often the adsorptionprocess is controlledby the rate of diffusionthrough the gasfilm within the microporousparticle, and in this caseit is advantageousto employa long and narrowbed ratherthan a shortbed of large diameter.These conditions of fine particlesize and largelength-to-diameter ratio increasethe pressuredrop acrossthe column, so it is necessaryto strike a compromisebetween efficiency and tolerablepressure drop. Data are availablein the literaturefor gas purification installationsranging from small laboratoryexperiments to plant-scaleoperations. To put this information on a common basis,gas velocities are often quotedin terms of the space velocity,rvhich is defined in Eq. (1). (volumeflou of gasat STP) sDacevelocttv : - (l) (volumeof the packing) The three primary methodsfor the removalof water from a gas streamare: ( 1) Iou'-temperaturecondensation, (2) compressionof the gasso that the partial pressureof water increasesand condensationresults, and (3) the useof drying agents.These methods are sometimescombined. For example,a molecularsieve desiccantwill take up more moistureper mole of inert gas at reducedtempera- turesand at high pressures.The primary methodfor the removalof oxygenfrom an inert-gasstream is reactionwith a solidor liquid reducingagent. In the case of helium, low-temperatureadsorption can be usedto removeboth oxygenand nitrogen. The following sectionspresent the detailsof thesepurification methods.

B. DesiCconls. There are significantdifferences between the water absorption isothermsfor substanceswhich form definitesolid phasesupon interaction with water and for adsorbentsand liquid desiccantswhich undergoa continuous increasein water content without the formation of new phases.For example, Mg(ClO,r)zforms definitehydrates. As is characteristicwith suchmaterials, the absorptionisotherm displaysplateaus corresponding to the coexistenceof two solidphases (Fig. 3.1). An analogoussituation is encounteredwith CaH2.where the reactionwith H2O producesCa(OH)2. This leadsto a broad regionin which the equilibrium vapor pressureof water is constant.and in this caseextremely low. By contrast,adsorbents (such as molecular sieves) or liquid desiccants(such as sulfuric acid) display a steadyincrease in vapor pressureas more water is taken up (Fig. 3.1). The adsorbent-typedesiccants also interact with many polar molecules,so competitivebinding resultswith a changein the equilibriumvapor pressureof water and with the total capacity for water. This factor is of little importancewhen thesedesiccants are usedto cleanup an inert-gasstream, but they may be veryimportant when the desiccantis incorporatedin a recirculating purifier of a glovebox. Roughequilibrium vapor pressuresfor H2Oabove a varietyof commondesic- cants are given in Table 3.1 along with commentson other propertiessuch as H2Ocapacity. Additional factorsthat are particularlyimportant in the dryingof PURIFICAIIONOF GASES 71

o T E E L-

Io-4

10-5 010?4304050 WerghlIncreose,7"

Fig. 3.1. Equilibrium vapor pressuresvs. capacitvfot'sonrc common desiccants.(A) Wide-pore silicagel; (B) narro*'-poresilica gel; (C) CaCl:, CaCl2 HzO, and CaCll 2H2O;(D) HzSOr;(E) MC- tClOr): and its hydrates;(F) PrOr0and HrPOr; (G) Molecularsieves 44.

a stream of gas are the flow rate and the physicalforn.r of the desiccant.For example,PaO16 is excellentfrom the standpointof equilibriunl vapor pressure and, as shownin Fig.3.l, the ultimatecapacity is not bad; however,PqOls is ordinarily supplied as a fine powder which virtually blocks the gas flow if this desiccantis packed into a drying tube. Furthermore,this material is quickly coveredwith a viscousfilm of phosphoricacid which drasticallyreduces the rate of further water uptake. (A supportedform of PrOro,available from the J. T. Baker Co., overconressome of theseproblems.) A similar complicationis encounteredwhen CaH2 is employedas a desiccant,because the product of the reactionwith water, Ca(OH)2.is producedas a fine powder which may clog a column. Somedesiccants introduce impurities into the gasstream which may be objectionable. This situation is obviouswith CaH2and other activemetal hydrides, where a mole of hydrogenis producedfor everymole of water adsorbed.Less obviousis the productionof tracesof phosphineby the tracesof phosphorus(III) impurity presentin PaOle. CAUTION: Magnesium perchlorate, which from many standpoints is an excellent desiccant, presents a serious explosion hazard.in the presenceof reducing agents,such as organic materials, CaH2,etc. This hazard is exacerbatedby mineral acids, such as H3POa,or substanceswhich can hydrolyze to acids, such as Ploro. Of all the desiccants,molecular sieves 44 or 5A are perhapsthe bestfor all- around use. Two obviousadvantages are their high affinity for H2O and good capacity.They are fairly inert and. becauseof their sizeexclusion of largemole- cules, are lesssusceptible than many adsorbentsto competitiveadsorption of other polar molecules.Molecular sieves are usually compacted with a claybinder into the form of small rods, which minimizes the restriction of gas flowing 72 INERTGASES AND IHEIR PURIFICATION

Ioble3.'l. Desicconls

Approximate Water Vapor Pressureat Agent 25oC(torr) Remarks

5 bastc CaH: < l0 Evolveshvdrogenl no regeneration; 5 Proro 2 x 10 Capacitylimited by formation of a surfacefilm; acidic;traces of PH3 evolved I in Mg(ClOr): 5 x 10 Good capacity;regenerate at 250'C vacuo;dangerous u'ith reducingagents { basic BaO 7 x 10 Small capacity;regeneration is unhandv; Linde Molecular in Sieves,4A or 5A I x 10-r Good capacity;regenerate at 400'C vacuoor in a "drY" gas streanl I Alumina (active) I X l0 Fair capacity;regenerate at 500"C in vacuoor in a "drY" gas stream,or 700oCin arr Silicagel (narrou I pore) 2 X l0 Fair capacity;regenerate at 300'C KOH 2 x l0-r Small capacitvou'ing to coatingof solid q'ithsolution: basic I CaO 3 x l0 Limited capacity;especially in the Presenceof C02; basic I HzSOr(concentrated) 3 x l0 Oxidizingagent; acidic H:POr (syrupy) 3 X 10-r Acidic CaSOr(Drierite) 5 X l0-r Regeneratedat 250'C CaCl2 0.2 Good caPacitY;slightlY acidic

per- through a drying tube. The regenerationof thesemoleculaf sieves can be folmed in vacuunror inert atmosphereat 400'C'

c.Low-TemperolureTroppingondAdsolptionofWolel.Alow- temperaturetrap is an effectivemeans of reducingthe moisturein a gasto a very lowlevel. Equilibrium vapor pressuresgiven in Table 3.2 demonstratethat at l0 3 Dry Ice temperature, -78oC, the water vapor pressureis approximately torr. There are. however,difficulties in achievingthe equilibriumvapor pressure when a streamof inert gas flows through a low-temperaturetrap, becausefine crystallitesof waterform in the gasphase and are readilyswept through the trap to by the streamof gas. Packingthe trap with glasshelices or glasswool is likely PURIFICATIONOF GASES 73

Toble3.2. Vopor Pressures(P) of lce ol VoriousTemperolures (t)o

toC P (torr)

-90 7.0 x 10 s -80 4.0 X 10-4 -70 1.94x I0-3 -60 8.08x 10 3 -50 2.96 x 10-2 -40 9.66x 10-2 -30 2.86x l0-, -20 7.76x l0 | -10 1.95 0 4.58

"8. W. Washburn,Internetional Critical Tables,Yol.3, p. 210.

improvethis situation. Also, two cold traps in seriesafford better trapping becausethe ice crystallitesvolatilize between the traps. Adsorbentsalso have lower equilibrium watervapor pressuresat low temperatures, but this advantagemay be offset by a lower rate of moisture uptake. Someisotherms for silicagel and molecularsieves are presentedin Fig. 3.1. A trap containing molecular sievesat liquid nitrogen temperature, - 196oC,is particularly effectivein removing moisture from a helium stream, and it also reducesoxygen and nitrogento low levels.The molecularsieve adsorbent can be readilyregenerated by heatingin vacuum or in a flowing streamof inert gas as describedpreviously.

D. Adsolplion from o Complessed Gos. The efficiencyof a desiccantis increasedat high pressures.The principle involvedis that when a gas is compressed,the partial pressureof moisturein the systemis held constantor nearly constantby the desiccant.Thus the molar ratio of moistureto inert gas is de- creased.For example,if a desiccantlowers the partial pressureof H2Oto I torr, a compressedgas storedover this desiccantat a pressureof 1,000psig will contain approximately19 ppm H2O; at 2,000psig the gaswill containabout 10ppm H2O.This techniqueis usedin many commercialair dryers.The processis generally basedon an automatedtwo-column system, with the moisturebeing adsorbedon one column at high pressurewhile a small amount of this dry gas is divertedto dry out a secondcolumn at atmosphericpressure. The gas streams are switchedautomatically so eachcolumn is periodicallyregenerated. Systems of this type can achievemoisture levels in the parts per million rangeand the air producedby thesedryers is usefulfor handling moisture-sensitivematerials in commercialoperations. These air dryersalso are commonlyused to providedry air for instrumentssuch as infrared spectrometersand NMR samplespinners. 74 INERTGASES AND THEIRPURIFICAIION

E. Oxygen Scovengels. A wide varietyof reducingagents has beenused to removeoxygen fronr gas streams.When vaporsof a solventcan be tolerated, the wet methodshave the advantageof being quick and easyto set up. Recipes for the preparationof somecommon oxygen-removing solutions are listedin Ta- ble 3.3. The gas is bubbled through thesesolutions using a simplegas scrubber or a more sophisticatedself-regenerating system (Fig. 3.2). Solutionscontaining

Toble 3.3. Recipes for Oxygen-Removing Solutions

Solution Preparation

Chromoussulfate (aqueous) A fresh solution0.4 M in chromealum and 0.05 M in sulfuric acid is contactedwith liehtly anralgantatedZn Alkaline pyrogallol(aqueous) 15 g pyrogallicacid in 100mL of 50% aqueous KOH Sodium hyposulfate(aqueous) 48 g Na2S2O1,40 g NaOH, and l2 g anthraquinonesulfonate in J00 mL H2O Sodium anthraquinonesulfonate 2% sodium anthraquinonesulfonate in 1.5M (aqueous) NaOH is contactedu'ith zinc metal Benzophenoneketyl (oil) I g Na dispersedin mineral oil plus 4 g benzophenonein 1L of mineral oil

A molgomoted

Fig. 3,2. A self-regeneratinggas scrubber.The incoming gas causesthe solution to percolate through the amalgamatedzinc. )URIFICATIONOF GASES 75

:he chromousion have a more favorablerate of oxygenabsorption than many ,rther solution scavengers.lSignificant concentrationsof foreign gases,other ihan the solvent,are introducedby someof thesesolutions. For example,the .'hromousion reactsslowly with waterto evolvehydrogen, and alkalinepyrogal- Iol is claimedto evolveCO. For many applications,the dry oxygenscavengers have the obviousadvantage rrfnot introducingsolvent vapors into the gasstream. Also, someof the dry scav- r.ngersare capableof achievingextremely low oxygenpartial pressures.Gener- ally, a column of dry oxygenscavenger is usedfor long-termapplications, such asthe purification of the inert gasfor permanentSchlenk or glove-boxinstalla- tions. In thesecases, the greaterinconvenience of settingthese up comparedto liquid systemsis more than offsetby the long-termstability and high capacityof the dry columns. Table 3.4 summarizessome of the most common dry oxygenscavengers. Al- though a heated tube containing bulk metal, such as copper turnings, is still occasionallyused, the bulk-metal oxygenscavengers have been largely displaced by high-surface-area-supportedmaterials. These highly dispersedmetal or nretaloxide materialsreact rapidly with residualoxygen and thereforecan be usedat or near room temperature,which is a tremendousconvenience. The procedurefor making highly activesupported copper metal is availablein the literature,2and materialsof this generaltype are availablecommercially.3 The commercial materials,Ridox and BTS Catalyst,are providedin pelletform, which reducesbackpressure in the flowing streamof inert gas.With a spacevelocity of - 6,000h ' Ridox shouldyield purified gaswith lessthan 1 ppm of oxygenat room temperaturewhen the feed stream containsas much as 5000 ppm of oxygen. Literatureon the BTS Catalystindicates a lower but acceptablerate of oxygen removalfor particleswhich are 2-3 mm in diameter.Ideally, the BTS Catalyst shouldbe crushedand screenedto the appropriatesize, although many research workersdo not take the trouble to do this. The Ridox particlesare smaller in size and appropriatefor useas supplied.One kilogram of BTS Catalystor Ridox will removeup to 4 L of oxygenat atmosphericpressure and room temperature.Al- though this capacitycan be increasedsignificantly by heating the material to 150'C, this is rarely done.A column at room temperature(which is packedwith a 700 X 50-mm bed of the scavenger)will sufficefor purifying a dozenor more large high-pressurecylinders of gas. Supported-copperoxygen scavengers are somewhatself-indicating. The color of the oxidized material is dull green,whereas the activereduced form is dark brown to black. Fig. 3.3 illustratesthat the rate of oxygenscavenging decreases as thesematerials take up oxygen.If oxygenlevels on the order of I ppm are required, the oxygen removal efficiencyshould not be allowedto drop below lH. W. Stone,J. Ant. Chetn..loc.. 58, 2591(1936). rF. R. Meyerand G. Ronge,Angeu.. Chern..52, 637 (1939). rRidox is availablefronr FisherScientific Co., 7l I ForbesAve., Pittsburgh,PA 15219;BTS Catalyst is marketedby Fluka ChenricalCorp.,255 Oser Ave., Haupage, NY. 11788. Ioble 3.4. MiscelloneousDry Oxygen Scovengers

Agent Description

Na-K (67-81% K by weight) Liquid aboveOoC and may be usedin a U-tube gas bubbler. RemovesOz, HzO, and Hg vapor." Na or K supportedon glasswool Similar to above.Supported Na is preparedby embeddingthe metal chunks in glasswool, evacuating.and heatingto 300oC.b CoO Removes02 at room temperature. Prepared by slowlyheating CoCOj to 340oCin vacuo.Not easilyregenerated.' MnO on silicagel Removes02 at room temperature.Easily regenerated.See text for preparation. Crr* in silicagel Preparedby adsorptionof a Cr+l solutionon silicagel followedby reductionat 500oCin H2. Efficient, low-capacity02 absorptionat room temperature.'1 Palladizedor platinized Removestraces of 02 from H2 at room asbestos(or "Deoxo" unit) temperature,removes 02 from inert gasesat room temperature. SupportedCu (BTS catalyst 70"C requiredfor catall'ticremoval of 02 from or Ridox) an H2 stream,30-.10"C required for catalltic removalof O2 frorn CO stream. Ba, Ca, Ca-10% Mg alloy, La Removalof 02 from Ar streamat 300, 650, 475. Mg, Th, or Zr 500, 600, 400. and 600oCrespectively." Also removalof 02 and N2 at 400, 650, 500, 800, 640, 800, and l,000oC respectively.' Brass,Cu, Ce, or U Removalof 02 from Ar or N2 streamat 500, 600, 300, 200"C respectively.'' Li Similar to Ca. RemovesN2 and 02 but reacts u ith quartzor glass./

"E. R. Harrison,J.Sti. Irtstr..29. 29-5(1952). /' H. H. Storch,J. Ant. Chent.Soc.. 56, 374 (1934);E. R. Harrison,J. Sci. Instr.,30, 38 (1953), supportedK. 'H. A. Pageland E. D. Frank,J. Ant. Cht'ttt.Soc.,63,1468(lq4l). JR. L. Buruell.Jr.. privatecomnrunicalion. 'D. S. Gibbs,H. J. Svec.and R. E. Harrington,Ind. Eng. Chern..48,289(1956)l note that hor Mg reacts* ith Vycor or fusedsilica tubing. /P. A. F. White and Smith (GeneralReferences) pp. 48,222.

76 PURIFICATIONOF GASES 77

c a o o E o c o o0 o

Standardcc of oxygenper gram of Ridox

Fig.3.3. OxygencapacityofRidoxattwodifferentflou'rates.A,spacevelocity3000hr;B.space velocity6000hr.(AdapteduithpermissionofthecopyrightownerfromFisherScientificCo.,Bul- letinl99B/8-021-01.)

95%. At this level of oxygen impurity in the exit stream, the capacityof the Ridox scavengerwould be L25 cmr of oxygenper gram of scavengerat a space velocityof 3,000h-'. Ridox and BTS Catalystare supplied in the oxidizedform and must be re- ducedat elevatedtemperatures with hydrogenbefore use. This processmust be done with some care to avoid the excessivelyhigh temperaturesthat causethe supportedcopper particlesto sinter, thus decreasingthe efficiencyof the catalvst.The regenerationstep for Ridox is carriedout by wrappingthe column with heatingtape and heatingto 200oCin a streamof nitrogen.The bed is then reducedby the introductionof hydrogengas diluted with the nitrogenstream. The hydrogencontent of this gas should be about 5% by volume. (The gas mixture 7B INERTGASES AND THEIRPURIFICATION can be formed by monitoringthe hydrogenand nitrogenflow rateswith paraffin oil bubblerson the inlet lines. The outletsof thesebubblers are joined by a T- tube and the combinedstream is conductedto the top of the column.)Sintering of the supportedcopper will occur if the temperaturewithin the column exceeds 250'C during this processor if the hydrogenconcentration exceeds 6 % . Alterna- tively,the regenerationmay be performedwith 5% hydrogenin nitrogenfrom a high-pressurecylinder of mixedgas. The temperatureconditions are the sameas thosealready mentioned. Temperatures around l50oC arerecommended for the regenerationof the BTS Catalyst.The effluent gasfrom the column shouldbe conductedthrough a paraffin oil bubbler, and from there to an efficienthood having no open flames. Large amountsof water are producedin the processof regeneratingthese materials. The bulk of the liquid water is convenientlydis- cardedby way of a valveat the bottom of the column, as illustratedin Fig. 3.4. When the reductionis complete,the lasttraces of moistureare removedby evacuating the heatedcolumn or by continuing to purge dry hydrogenor nitrogen through the heatedcolumn and gentlyheating the baseof the columnwith a hair dryer. Caremust be taken to avoidexposing the regeneratedcolumn to a sudden influx of air, sincethis rvitl causesevere overheating. These supported oxygen scavengerscannot be regeneratedif they are exposedto gas streamscontaining organicor metalloidhalides, halogens, mercury, sulfides. phosphine, or arsine. In addition, amnroniaand nrostamines are tenrporarypoisons in the sensethat they reduceor eliminatethe oxygentake-up, but the supportedoxygen scavenger can still be regeneratedand subsequentlyused in the absenceof thesematerials. Manganous oxide is another convenientoxygen scavengerrvhich has been used for the regenerationof inert atmospheresof dry boxesfor a long time.r s Recently,it has been shownthat a silicagel-supported form of MnO is capable of removingoxygen down to the parts per billion range, and that this material has little tendencyto polymerizeolefins.b These properties, as well as the easeof regeneration,make MnO very attractivefor the ultrapurificationof inert gases, the purification of olefinsto be usedin oxygen-sensitivecatalytic reactions, and more routine applications.There is evidencethat the MnO is poisonedby metal carbonylsat room temperature. A procedurefor the preparationof finely dividedMnO is to alternatelayers of vermiculiteand manganousoxalate in a column similarto that shorvnin Fig. 3.4. Initial activationis performedby heatingthe evacuatedcolumn to 330oCfor 6 h. The resultinggreen MnO is pyrophoricand must not be exposedto a sudden inrushof air. The predominantreaction with oxygen,Eq. (2), resultsin a brown- black product;so visual inspection of the columnreadily indicates its degreeof

rT. L. Bro*n, D. W. Dickerhoof,D. A. Balus.andG. L. Morgan.Ro,..!ci.lrsrr..33,191 (1962). 5P.A. F. White and S. E. Smith(general references), p. 199. nB.Horvath,R.Moseller,E.G.Horvath,andH.L.Krauss.Z.unorg.ullg.Chem.,lI8,l(1975)i R. Moeseller,B. Horvath,D. Lindenau,E. G. Horvath,and H. L. Krauss.Z. Nuturlirsch..3lb.892 ( I 976). PURIFICATIONOF GASES 79

Teflonin glassvalve

Fig.3.4. O-x-vgenscavenger coluntn. The colunrnis packedivith Ridox or BTS Catalvst.The heat. ing tape and therntocouple u ire are usedduring regeneration. Water u hich collectsdu ring regenera. tion can be bled out through the valveat the bottonr.

exhaustion.Since fine particlesof manganeseoxide slough off of this material,a large plug of glasswool is recommendedin the exit of the column. 6MnOfOr:2Mn3Oa ()r

Manganousoxide supportedon silica gel also is a very clean and efficient oxygen scavenger.6The following recipe was designedfor small quantitiesof fine-meshmaterial to be usedin the ultrapurificationof helium; it may be scaled up and larger-meshsilica gel may be usedfor packing large columns.A l0S-g quantity of 60-70 mesh silica gel is washedwith 1.5% nitric acid, followedby distilled water, and dried at 100oCovernight. A 32-g portion of Mn(NOr)z is INERTGASES AND THEIRPURIFICATION dissolvedin 85 mL of water. With constantstirring. 3-mL portionsof this solution are addedslowlv to the dry silicagel over a periodof approximatelyI h. At theend of this processthe silicagel should still appearto be dry. Water renroval and partial oxidation of this material are perfornledby heatingit overnightat 100"Cto producea blackmaterial, which is furtheroxidized at 300'C in oxygen for I h. CAUTION: Nitrogen oxides are evolvedduring both of thesesteps, and theseshould be vented in a good hood after absorption in base. If the oxidation wasnot donein a glasstube, the black solid is packedinto a Pyrextube and then reducedin a hydrogenstream at 370'C for I h, yieldinga pale-green,extrenrely air-sensitivesolid. The consumptionof the MnO b.ytraces of oxygenin an inert- gasstream is evidentby a sharp line of den.rarcationbetween the green.reduced form and brown-black,oxidized material. When regenerationis necessary,the last-mentionedreduction step is performed. As with the regenerationof supportedcopper. water is evolvedin the regenerationstep. This must be eliminated beforethe column is connectedin seriesrvith a desiccant.

F. Nifrogen Scovengels. The removalof nitrogen from an argon or helium streamis often donewith hot titanium sponge.Great careshould be taken to removeH2O from the gasstream before it contactsthe titanium. Noneof these ntaterialscan be regenerated,so the chargeof nitrogengetter has to be replaced periodically.Commercial nitrogen getter units are availablefrom Vacuunr At- mospheresCorp. With a helium stream it is possibleto adsorb nitrogen onto molecularsieves at liquid nitrogentemperature, - 196oC,and therebyachieve low levelsof nitrogen. The molecularsieves can be reactivatedperiodically by warming to room temperatureand, if water has been coabsorbed,heating to 400'C to removethis material.

3,3 INERT-GAspuRtFrcATroN sysTEMs

Desiccants,oxygen scavengers, low-temperature adsorption traps, and the like aregenerally combined to form purificationsystems. Systems of this type usedin conjunctionwith recirculatingpurifiers for glove boxeshave alreadybeen describedin Chapter2. This sectionwill provideadditional examples ranging from schemesfor the routine purificationof inert gasesto the ppm rangeto the ultrapurification of helium to the ppb range.

A. Purificolionof o LoborotoryIned-Gos Supply. A typicalarrange- ntentfor drying and deoxygenatingan inert gasfrom a high-pressurecylinder is shownin Fig. 3.5. The pressureregulator should ideally be of the two-stagetype, having an outlet control range of 0-15 or 0-30 psig to permit precisecontrol of the gasinthe2-4 psigrange. The valvesfollowing the needlevalve in Fig. 3.5 are usedto isolatethe columnsfrom the atmospherewhen a tank is being changed, and alsoto permit flushingair from the regulatorand gasline after a newtank is INERT-GASPURIFICATION SYSTEMS 84

Desiccant

I 1l' rli t,l 'l Pressure ' regulatot f';

Fig. 3.5. Inert-gassupply with generalpurpose purification train. Gascontamination is avoidedby conducting the gas through metal tubing. Where a flexible connection is desired, a short lenglh of heavy-walledpoly(vinyl chloride) tubing is used.Metal bellowsvalves are included in the inlet line to keepair out while changingcylinders, and to allow air to be purged from the valvesand regulator after installinga new cylinder. attached.This lastfeature greatly extends the lifetimeof the desiccantsand oxygen scavenger.Supported copper or MnO is the most convenientoxygen-scav- enging material, and molecular sieves4A or 5A are suitable desiccants.The amount of rubber or poly(vinyl chloride) tubing in the purified gas stream shouldbe kept to an absoluteminimum. Where it is needed,heavy-walled poly- (vinyl chloride)tubing or Teflon tubing is preferredbecause they displaylow gas permeabilityand do not degraderapidly. The columnsare generally arranged so that the oxygenscavenging column can be isolatedand regeneratedwithout exposingthe desiccantto the waterwhich is producedin regeneration.It is possible to regenerateboth the oxygenscavenger and molecularsieve columns simultane- ouslyby wrappingthem all with heatingtape. Alternatively,a singlelarge mixed bed of oxygen scavengerand molecularsieve desiccant can be used, with the regenerationstep being carriedout long enoughat 370oCto eliminateall water. As noted earlier, theseoxygen scavengers are self-indicating,so it is easyto determinewhen regenerationis necessary.However, there do not appearto be 82 INERTGASES AND IHEIRPURIFICAIION

convenientindicators for moisture. The commonry used cobalt-dopeddesic_ cants,which changefrom brueto nearrycolorress upon becomingsaturated. are insensitiveto lou' levels of moistureand thereforenot useful in"thesecolumns, exceptas a precaution againsta worst-casesituation. The qualitativetests discussedin chapter 2 are often usedfor checkinga laboratoryinert-gas system. For example,the experimentalist may exposea smau quantity of aruminum ar- kyl' titanium tetrachroride, or other sensitivemateriar to the jas as a prerudeto performingan experiment. In rargeinstalrations, continuous monitoring by oxygen and moisturemeters ntay be justified.

B. ulllopurificqtion of Herium. Arthough the parts per miilion rangefor impurities obtainabrein systems describedin the precedingsection meet or ex- ceedthe requirementsfor the vast majority of raboratoryJperations, there are situationsin which far higher purity is needed.For e*ample,a highly activehet- erogenouscatalyst may have a low concentrationof surface-actiue"rit.swhich are readilypoisoned by the steadyflow of a slightlycontaminated inert-gas stream in aflow reactor.In apprications requiringvery rowrevels of impuritiä a sequence of a low-temperatureadsorbent, suchai moiecurarsieves or silicager, ptus sirica gel-supportedMno will produce heriumwith reactiveimpurities ii th. purt, pe. billion range.one such purificationtrain is ilrustratedinFig. 3.6. The row-temperatureadsorption traps reduce water and hydrocarbonstJ veryrow reversand substantiallyreduce the rever of nitrogen, whereasthe Mno trap reducesthe oxygento the low ppb lever.The purification train and ail subsequentconnec-

l-1e ----->

Fig.3.6. Ultrapurificationtrain for helium. (A) Glass -196.C trap containingsilica gel which is main. tained at by imnrersionin liquid a Dewar; (B) glasstrap containingMnO,impreg. nated silicagel nraintainedat roonl temperaturei(C) Nupro be[ou,s'ar'es, n.,oun't"d ntetalplatel (D) on a sturdy Suagelockfittings with Teflon ferrules:(E) copperor stainless_steeltubing. A sec_ ond low-temperaturetrap (A) can follou,trap (B) to ensurecomplete HlO removal. DETECTIONOF IMPURITIES B3 tions must be very secureto preservethe purity of the gas stream.No rubber or plastictubing should be used.All valvesshould be of the metal bellowsor diaphragm type (seeChapter 10)and joints eithersoldered, welded, or of the swage rype.

3,4 DETEcToNoF TMPURITTEs

A seriesof qualitativeand quantitativetests for water and oxvgenimpurities is givenin Section2.3.F. Of the two, moistureis far easierto detectquantitatively than oxygen. One of the easiestand most versatileways to detectoxygen quantitatively in an inert-gassource is to use MnO-impregnatedsilica gel (describedin Section 3.2.E)in which the manganeseloading is known. A columnof the MnO/SiO2 nraterialis packedinto one arm of a U-tube of known inner diameterand activated. After activation, a known florv rate of inert gas is passedthrough the MnO/SiO2 column. The distancethe line of demarcationbetween the black, oxidizedmaterial and the pale-green,reduced n.raterial travels in a giventime is then measured.Using Eq. (3), the amount of oxygenin the inert-gasstream can be determined:

580d2lp(wt% Mn) O2(inppm):fr (3) whered is the inner diameterof the glasstubing (in mm), / is the distancethe lineof demarcationtraveled (in mm), p is the densityof the MnO/SiO2 (in g/cc). F is the inert-gasflow rate (ccltime), and t is the elapsedtime. As an example,if the MnO/SiO2 recipedescribed in Section3.2.E u'ereused (resulting in a nran- ganeseloading of approximately8%) in a 6-mm-i.d.tube with an inert-gasflow rateof 100cclmin, and assumingthe densityof the MnO/SiO2is 0.2g/cc. if the line of demarcationtravels 5 mnt in I h the inert gas containsabout 28 ppm oxygenby volume. Much lowerlevels of oxygen,such as in the ppb range,could be accuratelydetermined by loweringthe Mn loading, increasingthe inert-gas flow rate, and observingthe progressiveoxidation of the MnO/SiO2 for a longer period of time.

GENERALREFERENCES

Cook, G. 4., Ed., 1961Argon, Heliunt und RoreGuses,Interscience, Neu'York. The purification and handlingof rare gasesis describedhere. White, P. A. F., and S. E. Smith, l9b2 Inert AtntosTtheres,Buttersorth. London. This book presentsan excellentdiscussion of inert-gaspulification, $ilh emphasison the purificationof gloveboxatnrospheres for large plutonium-handlingfacilities. Since the appearanceof this book better methodsof supportingMnO havebeen developed and variousother advancesdis- cussedin the presentchapter have been made. Nevertheless,this book providesuseful general i nfornration. PURIFICATIONOF SOLVENTSAND REAGENTS

This chapter describesthe removalof water and atmosphericgases from some comnron solventsand the purification of some common laboratory reagents which are susceptibleto contaminationby moistureand oxygen.Equipment designsand proceduresare introducedhere as needed,but most of this materialis describedin othersections of this book: generalinert-gas techniques (1.1, 1.3- 1.5),conventional distillation (1.2), desiccants(3.2.B), freeze-pump-thaw degassing(5.3.A), and trap-to-trapdistillation (5.3.D,8).

4,4 soLVENTPURtFtcATtoN

A. Genelol Melhods of Purificofion. Becausethe solvent often is presentin largeexcess over most reagents,it is important to achievelow levelsof reactiveimpurities in the solvent.Distillation, purgingu,ith an inert gas,adsorption, washing,reaction with oxygenor water getters.and freeze-pump-thawde- gassingare the most common purification methods.

B. Distillofion ond Purging. The great efficiencyof fractional distillation for the removal of water from hydrocarbonand chlorocarbonsolvents is often not well appreciated.The physicalorigin of this good separationis in part the largepositive deviation of the watervapor pressurefrom Raoult'slaw becauseof the lack of affinity of water for theseliquids. Typically,the distillationof a simple hydrocarbonsolvent with a column of 100plates and discardingthe first two 84 SOLVENIPURIFICATION B5 fractionswill reducethe water contentto levelsacceptable for most work. Oxy- qenremoval from solventswhich do not reactwith oxygenis readilyachieved by r'vacuationor purging with an inert gas. The former method is most convenient for materialsbeing handledon a vacuum systemand is describedin Chapter5. 'fhe purging of solventswith an inert-gasline is readilyaccomplished using the rrrangementsillustrated in Fig.4.l. Thesemethods work well with saturated aliphatic,aromatic, and chlorinatedhydrocarbons. Purging methods are not effectivewith ethersand olefinswhere peroxide formation occursthrough chemical interaction.In thesecases, chen.rical nreans or adsorbentsare neededto purify the solventprior to distillation.

C. Adsotbenfs. Water can be removedfrom solventsby meansof adsorbents. Molecular sievesand alumina are the most common adsorbentsused to rttain very low moisture levels.These adsorbents should be activatedprior to use.as describedin Chapter 3. The purification can be carried out in a batch nrannerwith the molecular sievesor alumina introduced into a solventcon- tainer. After standing and allowing the adsorbentto settle,the solventmay be Jrawn off. Much lower levelsof impuritiescan be achievedby taking advantage ,rf the multiple-stagepurification with a column of adsorbent(see Fig. 1.27). fhe column is filled with activatedadsorbent, then purged with inert gas. The

Fig. 4.1. Apparatusfor purging solventswith inert gas.(a) A long needleattached to an inert-gas sourceis directedthrough the sidearmand into the solvent.A slorvinert-gas florv runs through the sidearnrto avoidback-diffusion of air into the flask. (ü) Solventpurge using a septumand a double- needlearrangement. 86 PURIFICATIONOF SOLVENTSAND REAGENTS

degassedand predriedsolvent is then admitted to the column, slowlyat first. It is bestto discardor recyclethe first few milliliters of material,and not to exceed the capacityof the column for impurities. A guide to the capacityof activealu- mina for water is givenin the literature,rAlumina effectivelyremoves peroxides from alkenesand ethers,but water is adsorbedmore stronglythan peroxides. Thereforepredrying of the solventin a batch manner rvith molecularsieves is advisable. One problem associatedwith usingsolid adsorbents to dry solventsis disposal of the usedadsorbent, especially if largequantities of solventare dried. Usually the adsorbentcan be reactivatedby careful heatingin a streamof inert gas or under vacuum. (If the adsorbentwas usedto dry olefinsor other peroxide-containing solvents,any peroxidesmust first be destroyed;see Section 4.1.D.) Reac- tivating Iargequantities ofadsorbent, however, can bejust as difficult as proper disposal.

D. Preputificotion of Solvenls. Somesolvent purification procedures call for sometype of wash. For example,saturated hydrocarbons are often washed with concentratedH2SOa to removealkenes. These washing procedures are generally done first, sincethey usuallyinvolve the useof an aqueoussolution or a substancethat containssignificant amounts of water. Unlike the followingpro- cedures,washes can be done in the presenceof air. sincefurther treatmentusu- ally involvesa step designedto eliminateoxygen. Bulk water is removedfrom organicsolvents by meansof a separatoryfunnel. Before distillation from a highly active desiccant,very wet solventsshould be dried with materialssuch as MgSOaor molecularsieve 4A. The solventis then degassedand chargedinto the still pot along u'ith the appropriatedrying agent. If ethersor olefinsare being purified, they shouldbe testedfor peroxidesbefore drying. CAUTIONT Peroxidesare strong oxidizing agentswhich may react ex- plosivelywith strong reducing agentssuch as LiAlH4 or alkali metals. Peroxides also can be extremely shock sensitive. The presenceof peroxidesin an organicliquid may be detectedby the devel- opnrentof an intensebrown color u'hen a feu' drops of aqueoussodium iodide solutionare mixed with a feu' millilitersof the liquid. A more quantitative method involvesadding 1 mL of the liquid to an equalvolume of a l0% sodium iodide in glacial acetic acid solution. A yellow color indicatesa low peroxide concentration,whereas a brown color indicatesa high peroxideconcentration. If the concentrationof peroxideis not too great,the materialcan be salvaged by shaking with aqueousferrous sulfate. In the caseof a u'ater-solubleether, solid CuCl may be usedto removetraces of peroxides.2Large amountsof perox- idesmay be renrovedby storingthe liquid over activatedalumina or by running the liquid through an activatedalumina column. CAUTION: Do not allow the

rM. L. Moskovitz,Ant. Lahorutory',12, 142(1980). )OrgutticSlrrtirreses. 45. 57 (1965). SOLVENTPURIFICATION B7 alumina to dry completely. The adsorbedperoxides may be removedby washing the alumina with an aqueousferrous sulfate solution.

E. Highly Aclive Desicconls ond Oxygen Scovengers. Alrhough the abovemethods are sufficientlyrigorous for many purposes,there are indications that theseprocedures still leavetrace quantitiesof oxidizing impurities in the solvent.For example,freeze-pump-thaw techniques do not removeall of the oxygenfrom benzeneas judged by NMR Z1determinations.r For greaterpurity it is common to employ distillation in conjunctionwith chemicalmeans for the removalof tracesof moisture,oxygen, and oxidizing impurities.A typical solvent distillationsetup is illustratedin Fig. 4.2. This particularstill is not designedfor high distillationefficiency, but rather as a meansof separatingthe solventfrom the purifying agents.In this designthe reservoirfor the distilledsolvent is situ- ated abovethe still pot. The vapor path alsopermits excess distillate to return to the pot. Thesefeatures minimize the amount of attentionrequired for the distillation. It is important to give the still pot an initial chargewhich substantiallyex- ceedsthe volume of the upper reservoirso that the still pot will not go dry. It is veryimportant to avoid letting the heatedstill pot go dry. The heatedflask may crack and the solid contentsin the pot may decomposeto contaminatethe system. In somecases an explosionmay occur(e.g. when LiAlH4 is used;see below). A metal catch pan shouldbe positionedunder eachdistillation apparatus to containany spillswhich may occur upon solventremoval. Each still should alsobe ventedto a fume hood. Someof the rigorousdrying and deoxygenatingagents which havebeen used includeLiAlH4, sodiumwire or shot, sodium-benzophenone,Na-K alloy,and CaH2. CAUTION: These strong reducing agentspresent an explosionhazard in the presenceof chlorocarbonsor reducible organic compounds. Of theseagents. solid Na and CaH2often haveunfavorable rates of reactionwith impuritiesand thereforeare not highly effectiveeven at the reflux temperatureof the solvent. Although the liquid Na-K alloyand solubleLiAlH.r are often usedfor the purification of solvents,the authorsdiscourage their usein their laboratoriesbecause thereis significantrisk of explosionif thesematerials are not handledcarefully. Lesstreacherous dehydrating agents are available.There are many examplesof explosionswhen LiAlHa hasbeen used to dry ethers,especially tetrahydrofuran.{ Both peroxidesand CO2 have been discussedas the possibleorigins of these explosions,and a dry or nearlydry still pot has alsobeen implicated. If LiAlH.r must be used to dry ethers,the peroxidesshould be removedfirst, the ether should be predried and degassed,and, in the distillationfrom LiAlH4, the still pot should nevergo dry. In addition, a sturdy shield should be usedto protect laboratory personnelfrom the still. Sodiunr-potassiunralloy likewiseis some-

rJ. Honrer,A. R. Dudley,and W. R. McWhinnie.J. Clten. Soc.,Chent. Contnt..839 (1973). alnorgunic St'rt&eses, 12, 317 (1970). BB PURIFICATIONOF SOLVENTSAND REAGENTS

,/.

Fig. 4.2 Inert atmospheresohent still. what treacherous.because superoxide buildup on the surfaceof this liquid metal can leadto spontaneousignition. Sodium-benzophenonerepresents a good conlpromisebetween ease of use and safety.As mentioned,the solventshould be prepurifiedto removemost of the water and oxygen,and the still pot should be purgedwith an inert gas. So- dium wire with a cleansurface is then introducedalong with a small amount(ca. DETECTINGIMPURITIES B9

5 g/L) of benzophenone.The pot is stirredvigorously with a stout stirring rod to break the residualsurface film on the wire. If the solventis relativelypure, a blue color may begin to form in the solution around the sodium. In the more usual case,it may be necessaryto stir for sometime to initiatethe formationof the blue color. With purging, the pot is then attachedto the still, and the solvent is brought to reflux temperature.The solventshould turn a deep blue or green, marking the formation of the sodium-benzophenoneand the exhaustionof water and oxidizing species.The distillation is then carriedout. If good gradesof startingsolvents are used,the pot can be replenishedwith prepurifiedsolvents, with perhaps the addition of some additional benzophenone.The principal drawbacksof sodium-benzophenoneketyl are the extra trouble of initiating its formation and the introduction of tracesof benzeneinto the dried solvent.

4,2 sorvENTsToRAGE

Freshly distilled solventsare readily contaminatedand, in the caseof ethers which are suppliedwith peroxideinhibitors, the purificationstep leaves the solvent susceptibleto rapid peroxideformation. Therefore,it is necessaryto providethe propermeans of solventstorage. It is possibleto minimizethe amountof fresh solventwhich must be storedby using the distillation setupillustrated in Fig.4.2, which has a reservoirthat may be tapped when needed.A simpleside- arm flask (seeFig. 1.3) is satisfactoryfor short-termuse when solventpurity is not highly critical. Solventmay be removedfrom sucha flask by syringethrough the openjoint while a flush is maintainedon the equipment,or a septumside- arm may be used. Much better exclusionof the atmospherecan be achievedby meansof a Teflon valveclosure, such as illustratedin Fig. 4.3. The advantages of this designare the excellentisolation of the solventby the Teflon-tippedvalve and the lack of contaminationof the solventby stopcockgreases. This type of solventstorage tube is idealfor usewith a vacuumsystem and is alsosatisfactory for removalof solventby syringewhile an inert-gasflush is maintainedfrom the sidearmof the valve.

4,3 DETEcTTNeTMPURTTTEs

Peroxidedetection in organicsolvents was previously discussed in Section4. 1 . D. It is imperative that solventssuspected of peroxide contaminationbe tested, sincean extremeexplosion hazard resultswhen peroxidesare concentratedin the still pot during distillation. The detectionof water in solvents,especially in tracequantities, can be troublesome.A method employing infrared spectrometryhas been developedby Barbetta and Edgell for the detectionof water in solventsat the submillimolar 90 PURIFICATIONOF SOLVENTSAND REAGENTS

Fig, 4.3. Solyentstorage tubes rvith Teflon valves.(a) The O-ring joint on the sidearmallo*s at- tachment to a vacuum line equipped with O-ring joints. (b) Sanrebasic designas in (r) rvith a straightsidearm. This designis easilyconnected to a Schlenkline via Tygon or otherflexible tubing that fits over the sidearm.

level.sIn this method, the intensewater fundamentalabsorption band at 3,590 cm-rwas usedto monitor the water contentof a varietyof solvents,including acetonitrile.THF. and Dvridine.

4,4 puRrFrcAnoNoFspEcrFrc sotvENTs

A. Wolel. Purging rvith inert gas or pumping on this solventwill rid it of dissolvedoxygen. Dissolved salts may be removedby distillationor by utilizing a commerciallyavailable deionizing system.

B. Soturoled Hydrocorbons. Purging and freeze-pump-thawmethods are effectivein degassingparaffins. Distillation u'ith the eliminationof the first fractionsproduces dry solvent.Molecular sieves nray also be usedto removewater. Distillation from sodium-benzophenoneketyl is highlyeffective in obtaining very low levelsof water and oxygen.Commercial grades of hydrocarbonsare often contaminatedwith olefins, which can be eliminatedby severalwashings

:A. Barbettaand W. Edgell.Appl. Spect.,32.93(1978). PURIFICATIONOF SPECIFICSOLVENTS 94 with concentratedsulfuric acid, separationfrom the acid, washingwith water, and, after preliminary drying with molecular sieves4A or 5A, subjectingthe solvent to fresh desiccantor one of the drying proceduresoutlined above.

C. Aromolic Hydtocorbons. The methodslisted for saturatedhydrocar- bonsmay be usedwith benzene.Thiophene and similar sulfur-containingimpu- ritiesare removed by sulfuricacid washes.Very-high-purity benzene may be prepared by fractional crystallizationfrom ethanolfollowed by distillation. Toluene and xylenesare purified in the samemanner as benzene;however, thesesolvents should be kept cool (at or belowroom temperature)during sulfuric acid treatment due to their greaterreactivity toward sulfonation.

D. Chlolocolbons. Molecularsieves provide a good meansof drying these materials. CAUTION: Strong reducing agents,such as metal hydrides, Na, and Na-K, react violently with halogenatedhydrocarbons and should never be used to dry thesematerials. Chloroform generallycontains 1% ethanol to suppress phosgeneformation. This may be removedby shakingwith concentratedH2SOa, separatingfrom the acid, washingwith water,predrying with molecularsieves or silicagel, drying with molecularsieve 44, and distilling,taking the centralfrac- tion. This materialmust be useddirectly or storedstrictly out of contactwith the atmosphere.Methylene chloride is lessreactive than chloroformand is not prone to phosgeneformation. It may be distilledfrom PaO16or dried with molecular sievesand distilled under an inert atmosphere.(Note that tracesof phosphine are introducedinto a material by the useof P4Oro.)

E. Elhels. Diethyl ether is availablein very dry grades,which for most pur- posescan be used directly from the freshly opened can. Similarly, purified gradesof tetrahydrofuranare availablewhich are often sufficientlydry to be useddirectly (Fisher).When extremelysensitive materials are handled, diethyl ether and tetrahydrofuranare often distilledfrom LiAl&. However,great care must be taken first to removeall peroxidesand neverto let the still pot go dry (seethe generaldiscussion in Section4.1). Sodium-benzophenoneketyl is also effectivewith etherswhich are peroxidefree, and it has the advantageof being safer than LiAlHl. A small amount of benzeneis introducedinto the solvent when sodium-benzophenoneketyl is used.

F. Nifliles. Acetonitrile is a convenientsolvent for many ionic compounds, but it is extremelydifficult to dry to much better than millimolar in water. In addition, degradationproducts of the solvent,ammonia and aceticacid, may be present.Strongly acidic or basicdrying agentsreact with this solventand strong reducingagents are ruled out. One recommendedprocedure is first to predrythe solventwith molecularsieves or silicagel if largequantities of waterare present,b

"J. F. Coetzee.Pure urrdAppl. Cherrr..13. 429-413(196b). 92 PURIFICATIONOF SOLVENTSAND REAGENTS

then to stir or shakethis material with calcium hydride,which will removeboth aceticacid and water. The predriedacetonitrile is then distilledat a high reflux ratio from PaOle(less than 5 g/L) under an inert atmosphere.A gel may form in the distillation flask. and care should be taken to leavebehind the bulk of the solventand residuesin the distillation flask. The solventis then refluxed over calcium hydride and distilled under an inert atmosphereusing a high reflux ratio and a good fractionatingcolumn. The middle fraction is collected.Acriloni- trile is an impurity which will contaminatethe product if this distillationis not efficient. As an alternativeto this procedure!some workers advocate stirring acetonitrile with calcium hydride, distilling it under a dry inert atmosphere,and passing it through a highly activatedalumina column under a dry inert atmosphere.

G. Alcohols. The removalof tracesof water from methanoland ethanolis difficult. Calcium turnings, magnesium turnings activatedwith iodine, and lump calciumhydride are sometimesused to removetraces of waterfrom methanol. However,these active metals may contain somenitride and giverise to contamination by ammonia. These same drying agentsmay be used with higher alcohols.A column of dry molecularsieve 4A is alsoeffective in removingwater from ethanol and higher alcohols.

H. Acefone. Acetoneis very difficult to dry, sincemany of the usualdrying agentscause reaction, including MgSOa.Storage over molecular sieve 4A yields relativelydry acetone.High-purity acetonemay be obtained by saturatingthe solventwith dry NaI at room temperature,decanting and cooling to -l0oC, isolatingthe crystalswhich form (Nal-acetonecomplex), warming the crystalsto room temperature,and distillingthe resultingliquid.

4,5 puRrFrcATroNoFsoME coMMoNLy usED GAsEs

A. Acelylene. This gasis soldin cylinderscontaining acetone, which maintains a low pressureof acetylene.Therefore, acetone is the principal contaminant and may be removedby passingthe gas through an aqueoussolution of NaHSO3.The gas stream is then dried with molecularsieves. When small amounts of acetone-freeacetylene are needed,it is convenientto generatethe gas from calcium carbide and water. Again, the resultingacetylene stream is dried rvithmolecular sieves. CAUTION: Acetyleneis thermodynamically unstable with respectto the ele- ments and it may explode spontaneouslyat high pressures.The gasshould never be handled above 15 psig pressure.If water addition to calcium carbide is used to generateacetylene, the generatormust be kept cool and the acetyleneallowed unrestricted flow from the generator. PURIFICATIONOF SOMECOMMONLY USED GASES YJ

B. Ammonio. This good low-temperatureor high-pressuresolvent may be purchasedin a fairly dry state. The last traces of water can be removed by condensingthe ammonia onto sodium on a vacuum line, allowingthe blue color of dissolvedsodium to develop,and trap-to-trap distilling of the resultingammo- nia into a metal cylinderor into a reactionvessel. The experimentalistshould be thoroughlyfamiliar with vacuum line operationsbefore attempting this procedure. The major pitfall is bumping the ammonia with a suddenpressure rise, which can propel stopcocksat great speedsor burst the glassapparatus. One other potentialproblem is contaminationof the vacuumline with sodiumresult- ing from a fine spraywhich forms as the ammoniaevaporates. A generousplug of glasswool abovethe drying tube reducesthis last problem, and a pressure releasebubbler (seeFig. 1.2)will reducethe chancesof pressurizingthe vacuum system.

C. Bolon Holides. Thesecompounds are best handled and purified on a vacuumsystem. Silicone stopcock grease reacts with the boron halides,and most hydrocarbongreases contain unsaturatedhydrocarbons which are polymerized by theseLewis acids. A halogenatedstopcock grease, Teflon-in-glass valves, and Viton O-rings all give satisfactoryperformance with the boron halides.Boron trifluoride is availablein cylindersand may be freed from residualatmospheric gasesby trap-to-trapdistillation in the vacuumsystem. For verycritical applications, further purification can be achievedby the formation of the benzonitrile adductat 0oC in a vacuumsystem; this adduct is then evacuatedto removevola- tiles such as the weaker acid SiFa.The BF3 is recoveredfrom its benzonitrile adductby thermal decomposition.TAdjacent to the trap containingthe adduct is a trap cooledto -78oC (Dry Ice), and this is followed by a trap cooledto - 196'C (liquid Nz). About 20 torr of dry nitrogenis introducedinto this train of three traps; the first trap containingthe adduct is warmed to about 60oC with hot water and the valve leading to the adjacent, -78o trap is cracked open slightly,while the valvebetween the -78'and -196o trap is opened.In this way benzonitrilecollects in the -78'trap and BF3,in the -196'trap. When the decompositionof the adduct is complete,the purified BF3 is trap-to-trap distilledto a storagebulb. The contaminants in commercial boron trichloride usually are HCI and COC|2,as well as oxychlorideswhich have somevolatility. The oxyhalidesare readily removedby one or two trap-to-trap distillationsin a cleanvacuum system. Most of the HCI can be removedby holding the BCl3at - 78oCand pumping awaythe volatilesfor a brief period (someBCI: is sacrificedin the process). Phosgene,which may be detectedby its gas-phaseinfrared absorptionat 850 cm r, is very difficult to remove.Liquid boron tribromide is generallysupplied in sealedampules. If it is straw colored,dibromine is a likely impurity, and this

-H. C. Brown and R. B. Johannsen.J. Ant. Chent.Soc. , 72,2934 ( 1950). PURIFICATIONOF SOLVENTSAND REAGENTS

can be removedby shaking the compound with mercury. Hydrogenbronride may be removedby trap-to-trap fractionationin which the BBr.ris collectedat -45oC and the HBr at - 196'C.

D. Colbon Dioxide. Water is generallythe main contaminantin carbon dioxide,especially if Dry lce is usedas the sourceof this gas.Trap-to-trap sublimation of the carbondioxide through an interveningactivated silica gel trap on a high-vacuumline effectivelyremoves water. Low-boilinggases such as nitrogen or oxygenare removedif the sublimationis done under dynanricvacuunt.

E. Colbon Monoxide. The most troublesomeimpurity in carbon monoxide generallyis oxygen,which may be removedby passingthe gasover supported copper(e.9., Ridox) or supportedMnO, both of rvhichare discussedin Chapter 3. It is reported in the literature that CO doesnot impair the performanceof MnO, but experiencein the authors' laboratoryindicates that MnO that has beenexposed to CO is not readily regenerated.

F. Efhylene. Oxygen is a very troublesomeimpurity for many studiesand can be removedby passingthe ethyleneover supportedMnO or supportedcopper.

G. Hydrogen. Oxygenmay be reducedto the low partsper million rangeby meansof a platinum-metal catalyst,which combinesthe residualoxygen with hydrogen.öThe ultrapurificationof hydrogencan be achievedby diffusionof the gas through a heated palladium thimble. Commercialunits are availablethat are basedon this principle.E

H. Hydlogen Holides. Water can be removedfrom HCI and HBr by trap- to-trap distillationin a vacuum systent.If thesegases are handledat 100torr or below,a trap held at -78oC may be usedto condensewater. An activated-carbon trap can be usedto rentoveany halogenimpurities in thesegases. Perform- ing the transfer under dynanricvacuum will also removeany lorv-boilinggases not condensableat liquid nitrogentemperatures. The purificationof HI is complicatedby the well-knownequilibrium between itselfand hydrogenand iodine,Eq. (t). 2HI(g)= Hz(g)* Iz(g) (l)

The attainment of equilibrium is very slow at room temperature.Residual iodine can be removedby passingthe gas over red phosphorousor shaking it with mercury.The gas may be then be passedthrough a trap at -78'C to con-

sAvailable from MathesonGas Products.P.O. Box 85. East Rutherford.NJ 07073. ANHYDROUSMETAL HALIDES 95 densemoisture, and condensedin a secondtrap at - 196"C.A high vacuumls maintainedon the exit of the secondtrap to removehydrogen. l. Sulfur Dioxide. This compoundis a usefulreactant and lou'-temperature solvent.The commercialcompressed gas rnay be condensedat liquid nitrogen temperatureand atnrosphericgases pumped away.Moisture is removedby passing it through a trap containingPaO16 dispersed in glasswool.

4.6 ANHYDRoUSMETAL HALIDEs

Thesevery useful starting materialsoften are reactiveu'ith atmosphericnrois- ture. Simple dehydrationby the applicationof heat is not effectivewhen the metal ion is small and,/or irr a high oxidation statebecause hydrogen halide is eliminatedand ntetaloxyhalides or hydroxyhalidesresult. Several general methods are available for the removal of oxygen-containingligands from metal halides;but elaborateschenres for the purificationof commercialhalides are not attractive,because the direct synthesisfrom pure starting materialsis generally lessdifficult. The cumulativeindices of Inorganic Syrtthesesmay be consulted for thesesynthetic procedules. Commercialgrades of aluminurn chlorideand aluminurnbromide are generally contaminated*'ith hydloxylicimpurities. Some purification can be achieved by sublimingthe rrraterialin a glassapparatus under vacuum. Better purification can be accomplishedby mixing good-qualityhalide (e.g. that soldby Fluka) with aluminum wire and l%-by-weightsodium chloride prior to the sublimation. The function of the NaCl is to fornr molten NaAlCll. which has an affinity for ionic impurities.eA secondsublimation is sometimesnecessary to remove fine particlesof alunrinum if the first sublimationwas performedtoo rapidly. The purestsamples of aluminum halidesare obtained by directsynthesis. A variety of transition metal chloridesand other chloridescan be dried by meansof thionylchloride. rvith the evolutionof SO3and HCl.r0Twenty granrs of the finely divided metal chloride is placed in 50 rnl- of freshlydistilled SOCI2. When the evolutionof gashas ceased, the mixture is refluxedfor l-2 hours.and then excessthionyl chloride is distilled from the reactionflask under reduced pressure.Residual thionyl chloride is renrovedfrom the product in a vacuum desiccatorcontaining KOH. The halide should be transferredand storedin a nroisture-freeatmosphere. Halides which have been successfullydried by this method include:LiCl, CuCl2.ZnCl2, CdCl2, Thcli, CrCl.r,FeCl.r. CoCl2. and NiCI,.

"J. Robinsonand R. A. Osteryoung../.Ant. Chent.Soc.. l0l, 323(1979): see also D. W. Seegmiller, G. W. Rhodes.and L. A. King. lrorg Nut'|. Chen. Zer.. 6, 8t'J5( 1970), for a rccrvstaiiizationtech- nique. r('4. R. Pray. lnorgunic Jl'nt,/rt'sc.r.5. r53 ( 1957). 96 PURIFICAIIONOF SOLVENTSAND REAGENTS

GENERALREFERENCES

Brakcr. W.. and A. L. Mossnran.1980, Mutht'sort Gus Dutu Book,6th ed.. MathesonDiv. Searle MedicalProducls, Lyndhurst, N.J..07071. Although this volume does not presentmethods of purification.it doesprovide information u'hich is usefulin the handlingof gases.such as tabu- lationsof physicalproperliL's. infrared spectra(sometinres shouing impuritiesrihich are not identifiedas such).safety information, and handlinginslructions. Dodd, R. E., and P. L. Robinson.l9-5,{. Ä.rTrerilrentul Inorgurtit'Chernistry', Elsevier, Amsterdam. Propertiesand methodsof preparationand purification for many inorganicconrpounds are givenhere. Gordon, A. G. and R. A. Ford. 1912.TheChentistsCornpunion,Wilev-lnterscicnce, Neu York, p. 429-439. The seriesentitle

VACUUM LINEDESIGN ANDOPERATION

When properlyhandled, a vacuum line is a true joy to usebecause it providesa closedreaction vessel with excellentexclusion of air, quantitativeretention of all reactionproducts, and a readymeans for the transferand quantitativemeasurement of gases. Vacuum linesare employedin problemsranging front the simpletransfer of volatilesubstances to the extendedseries of operationsinvolved in the synthesis, purification, and characterizationof new compounds.This chapterpresents an overviewof the designof glassvacuum systems.Following chapters give greater detail on individual componentssuch as pumps (Chapter 6), manometers (Chapter7), joints and valves(Chapter 8). and metal vacuum systems(Chapter l0). The presentalso describes the basicoperations for the transferand purification of condensableand noncondensablegases, the quantitativePVT (pressure- volunre-temperature)nleasurement of gases.and the characterizationof condensablegases by vapor pressure.More specializedoperations are describedin Chapter9.

5.4 GENERATDESTGN

A. TypicolSysfemS. A simplesystem for the transfer of samplesto anin- frared gas cell or to a NMR sample tube consistsof a fore pump, diffusion pump, trap, and manifold (Fig. 5.1). At the other extremeis a general-purpose chemical vacuum line, u'hich permits the separationof volatile compounds. transfer of noncondensablegases, and storageof reactivegases and solvents (Fig. 5.2). When attack of stopcockgrease is a seriousproblem, grease-free de- 100 VACUUMLINE DESIGN AND OPERATION

Therm ocou pl e vocuum gouge (or McLeodgouge)

Fig, 5.t. Simplevacuunt line. A line of this son might be usedto transfervolatile samples to infrared gascells, NMR tubes.etc. It might alsobe usedfor loadingtubes for sealed-tubereactions and for vacuum sublinrations.

signsbased on O-ring joints and glassvalves with Teflon stemsare frequently used(Fig. 5.3). Each stopcock,valve, or joint addsto the cost and to potential sitesfor leakage,so the vacuum line designshould be the simplestpossible to servcthe intended uses.

B. Moior Componenls. The extendedarray of glasstubing in a typical vacuum systemrequires proper supportto minimize breakage.A rigid latticeis essentialto reducethe differential movementof variousglass components. For large vacuum systemsthe lattice is generallyfirmly mounted on a sturdy low bench as illustratedin Fig. 5.4. Horizontal bars increasethe rigidity of the lattice, but they shouldnot be usedfor clampingapparatus. NOTE: It is important to clamp the vacuum line parts only to vertical bars, because a clamp may swivelaround a horizontal bar and thus not provide reliable support. Heavyper- manent items, such as mercury-filledToepler puntps or Mcleod gauges,are preferablymounted on the bench and supportedin a bed of plasterof Paris. When the vacuum line is first assembledand carefully but firmly clamped in place,it is good practiceto annealsegnlents of tubing betu'eenadjacent clamps to relievestress on the apparatus. The functionalunits in the general-purposevacuum line illustratedin Fig. 5.2 arefairly typical:(l) a sourceof high vacuum,(2) a high vacuummanifold, and (3) various working manifolds. These working manifolds may contain a train of U-traps for the separationof volatiles,or a seriesof containersfor the storageof either gasesor volatile liquids. In addition to U-traps, the working GENERALDESIGN ,10,1

Fig. 5.2, Multipurpose high-vacuumsystem. Bulbs for gas storageare at the top of the figure. Directlybelou theseis the high-vacuunrmanifold, rvhichis attachedto a trap and pumps at site I and connectedto a high-vacuumgauge at 2. The *orking manifold in the centerof the figure is attachedto a train of U-trapsand to variousinlets. It is alsoconnected to a Toeplerpump at 3. Gases and volatileliquids are introducedthrough the inletsattached to this manifold, and largereaction vesselsor specialapparatus are frequently attached to the largejoint. At the bottonlof the figure is a nranifoldu'ith solventstorage vessels attached; it is alsoconnected to a graduatedtrap which allows nreasurementof the volumeof solventbefore it is transferredto the nrain uorking manifold. Stan- dard high-vacuum stopcocksare employedexcept on the solventand gas storagebulbs, where greaselessneedle valves are used. manifold generallyhas sitesfor attaching reactionvessels, gas inlets, and the like. This working manifold usually includesone or more mercury-filledma- nometersfor the PVT (pressure-volume-temperature)measurement of gaseous reactantsor products,or for vapor pressuremeasurements. The main high-vacuum manifold is usuallyequipped with a high-vacuumgauge so the initial degree of evacuationcan be measured.This gauge is also valuablefor locating 102 VACUUMLINE DESIGN AND OPERATION

Fig, 5,3. Wavda-Dyegreaseless vacuum line. This apparatusnrakes extensive use of metalbellows tubing and O-ring seals.Thus thc reactionvessels, filters, and other itenrscan be tilted and manipu- latedlike Schlenku are, and high vacuunrconditions can be achievedfor the removalof atmospheric gasesand for baking out residualmoisture. Trap-to-trap distillation of volatilesolvents such as NH r or SOzis readil,vacconrplished with this apparatus.This versionis not designedfor the nreasurenrent of vofatilesor trap-to-trapseparation. (Reproduced from A.L. Wayda and J. L. Dye, J. Chenr. Educ. 62.356 ( 1985)by pernrissionof the copyrightowner the Divisionof ChemicalEducation of the AntericanChenrical Societv.)

leaksin the system.A Toeplerpump is generallyattached to the vacuum line if noncondensablegases are to be manipulated.The Toeplerpump is not an abso- lute necessityfor transferring noncondensablegases such as CO and CH4. As describedin Section5.6.8, low-temperatureadsorption provides a simple method for transferring these gases. The mechanicalfore pump is a heavyitem which setsup considerablevibra- tion. This vibration disrupts the menisciof mercury manometersand is other- wiseundesirable. To minimize the transferof vibrationsto the vacuumline. the fore pump generallyis mounted on the floor (rather than on the bench of the vacuumrack) and the connectionbetween the fore pump and the vacuumsystem is made with heavy-walledvacuum tubing or flexible corrugatedmetal tubing. Detailson pumps, manometers.vacuum gauges, special apparatus, and leak testing are given in Chapters6-10. It is the purposeof the remainder of this chapterto describethe transferof condensableand noncondensablegases, trap- to-trap fractional separationof volatiles,and the use of vapor pressurein the characterizationof volatilecompounds. These operations are basic to practically all chemicalvacuum line work. INITIALEVACUATION 103

Electncol outI el

Fig.5.4. Typicallattice. Glass apparatus is clanped to the verticalrods, uhich arespaced at 10-to l2-in. intervals.One or two horizontalrods aregenerally included to impart rigidity.When the rack th-in.-diameter is large, steelor slainless-steelrods are preferredto aluminunr lods becausethe latterdo not afford a rigid lattice.Frantes are constructedfrorn pipe (about 2-in. diameter).wclded angleiron, weldedH-beam, bolted Flexi-frame,or similar rigid members.The vacuum line lattice shouldbe groundedby running a copperwire fronr the latticeto a $ater pipe. It is advantageousto coverthe benchwith Transiteor a similar heat-resistantsurface, since this facilitatesglassblou'ing. The dimensionsgiven are typicalof a rather largerack- A hoodedvacuum rack is occasionall-tused to help containreactive or poisonoussubstances released in a mishap.To providethe requiredrigid- ity. it is sometimesnecessary to bracethe top of the vacuumrack to a wall.

5.2 tNrTrALEVAcuAloN

A good initial vacuum is necessarybecause noncondensable foreign molecules will impedethe movementof the condensablematerial. when largequantities of relativelyunreactive gases are being handled (for example, BF:). it is usually satisfactoryinitially to evacuatethe systemto 10 r torr. Small quantitiesof gas and highly reactivegases require a better initial vacuumfor their transfer( t0-'t- l0-s torr), and most preparativechemical vacuum systemsare designedwith this degreeof vacuum in mind. Mercury exertsa pressureof approximatetyl0 3 torr at room temperature,so mercury vapor is presentthroughout a vacuumline which is equippedwith mercurymanonteters and other mercury-containingap- paratus.Since mercury vapor is condensableand relativelyunreactive, its pres- enceoften can be ignored. To start a vacuum systemsuch as that illustratedin Fig. 5.1, the cleanmain trap is fitted in place with an evencoat of stopcockgrease on the joint. A Dewar partially filled with liquid nitrogen is raisedaround this trap, and the fore pump is immediatelyturned on. CAUTIoN: oxygen from the atmospherewill condensein a trap held at liquid nitrogen temperature; therefore, it is important never to leave a trap cooled to liquid nitrogen üemperatureexposed to the atmosphere for a significant length of time. when the line has pumped down to lessthan 1 torr, the 404 VACUUMLINE DESIGN AND OPERATION

stopcocksare turned to routethe gasthrough the diffusionpump, and the heater on the diffusionpump is then turned on. (If the diffusionpump is water cooled, the watershould also be turned on.) The progressof the evacuationis followedby meansof an electronicvacuum gaugeor a Mcleod gauge.If possible.the line shouldbe evacuatedfor severalhours beforeuse (overnight is preferablefor a large vacuumsystem) to permit the desorptionof moistureand a thoroughcheck on the performanceof the line. If the line doesnot pump down rapidly, the most likely sourceof leaks is poorly greasedstopcocks. Sometimes the offending stopcockor joint can be turned to work out the leakagepath in the grease.Details on the propergreasing of stopcocksand joints aregiven in Chapter8, and methodsfor hunting leaksare describedin Chapter7.

5,3 MANrpuLATroNoFvorATtrE uoutDs AND coNDENsABTE GASES

A. Fteeze-Pump-Thow Degossing. Liquids which havebeen exposed to the atnrosphereor to inert gasescontain appreciableamounts of dissolvedgases that shouldbe eliminatedbefore use. If smallquantities of liquid are involved, gasessuch as oxygenand nitrogenmay be eliminatedby meansof the transfer processdescribed in Section5.3.C. In the more common situationof needingto degasa largevolume of liquid, the freeze-pump-thau'technique is employed. This is accomplishedby coolingthe sampleto liquid nitrogentenrperature, pumping on the sampleat this temperature,closing the stopcockor valveso the sampleis isolatedfrom thevacuum, allowing the sampleto melt,then refreezing it and punrpingaway any noncondensablegases which boiledout of the material. This processis generallyrepeated several times. Note that ice and frozen methylenechloride, may break glassapparatus when they are thawed.The easi- est courseof plevention is to use a round-bottomedcontainer which is one- fourth full or less.Another effectivemeasure is to warnr the tube rapidly so that a film of liquid forms betweenthe containerand the massof the frozen solid. With experience,the latter techniquecan be effectivein very difficult situations suchas a water-filledthin-walled NMR tube.

B. Ihe llonsfer of Condensoble Goses. Condensablegases are conveniently separatedand transferredin a vacuumline by vaporizationand condensation. Prior evacuationof the systemand a suitablylow temperatureare necessary to quantitativelytransfer the material. The vapor pressurecorresponding to "quantitative" condensationof a compound will dependon the volume of the systemand the quantity of materialbeing transferred; as a generalrule, a maximum vapor pressureof 10-3 torr is satisfactory.For simpletransfer operations, liquid nitrogen (bp - 196"C) is the most commonlyused refrigerant.

C. Exomple:Tronsfer of o CondensobleGos. Supposewe wish to transferthe HCI from a 1-L glassbutb into a trap on the vacuum system(Fig. MANIPULATIONOF VOLATILELIOUIDS AND CONDENSABLEGASES 105

Fig. 5.5. The transferof HCi fronr a bulb into a trap bi condensation.See Section 5.3.C for a dcscriptionof the transferprocedure.

5.5). The bulb is attachedto the vacuum line by meansof a carefullybut lightly greasedtaper joint, and is held in placeby springs,clamps, or rubber bands. The system,exclusive of the bulb, is evacuatedto at leastl0 3 torr pressure (stopcockV closedand II, III, and IV open).The U-trap is cooledwith a Dewar of liquid nitrogen,and then HCI is admittedby slowlyopening stopcock V. Stop- cock lV is generallyleft open at this point becausethe HCI is quantitatively trapped at the boiling point of liquid nitrogen, - l96oC, and the open stopcock allowsany contaminating"noncondensable" gases such as oxygenand nitrogen to be renroved. CAUTION: Avoid pressurizing a vacuum line. Failure to keep the pressure below one atmosphere may result in stopcocks popping out with high velocityor explosionof the glassapparatus. In the examplejust given,the bulb may have been of lL capacityand filled with 1 atm of HCl. If this were condensedinto a smaller U-trap, followedby closingstopcocks III and IV, the liquid nitrogen would have to be maintained around the trap to prevent the buildup of excessivepressure.

D. Trop-fo-Trop Froctionotion. Compoundsof significantlydifferent volatility can be separatedby passingthe vaporsthrough a seriesof traps, eachof which is cooledto a temperaturewhich will condenseone of the components. Judgedby the standardsof ordinary distillation,trap-to-trap distillation is very inefficient.Therefore the processis usefulonly whenthere is a largedifference in the vapor pressuresof the componentsbeing separated.A rough estimateof the separationefficiency may be gained from vapor pressuredata (assumingthe compoundsdo not stronglyinteract in the condensedstate). If. at a particular temperature,the ratio of vapor pressuresof tu'o compoundsis l0{ or greater,an 106 VACUUMLINE DESIGN AND OPERATION excellentseparation should be possible;a ratio of 103will usuallylead to a good separation;and a ratio of 102will permit fair separation.The separationis influencedby the rate of the trap-to-trap distillation:(l) the finite vapor pressureof the lessvolatile componentwill lead to its accumulationalong with the more volatilecomponent; and (2) if flow ratesbecome too high and the more volatile componentis in substantialexcess, the more volatile gas will entrain the less volatilecomponent and sweepsome of it through the low-temperaturetrap. In order to achieveefficient separation,the first factor leadsone to favor a quick distillation, while the secondleads to the choiceof a slow distillation. Each separationproblem presentsits own peculiarities,so there is no single best procedurefor trap-to-trapfractionation. For example,if the componentof primary interestis a minor constituentmixed with a more volatilecompound, the entrainmentproblem may be serious.To reduceentrainment, the mixture may be passedthrough severalcold traps, and each trap should be deeplyim- mersedin the cold bath to afford maximum contactwith the cold surface.Some- times entrainmentis minimized by the inclusionof glasshelices or indentations (Vigreaux)in the trap. However,a principal origin of entrainmentappears to be the formation of microcrystallitesin the gas phaseand theseare sweptthrough the trap by the secondcomponent. Low flow ratesand large-diametertubing in the traps minimize this mechanicalentrainment. To achievea low flow rate, the volatilizationof the mixture is often moderatedby placing a chilled but empty Dewar around the sampletube as illustratedin the followingexample. The use of two or more traps cooledto the sametemperature allows the crystallitesto volatilizebetween traps and increasesthe chancethat the componentwill con- denseon the walls of the next trap. As alreadypointed out, it is possibleto monitor the purity of the fractionsby methodssuch as vapor pressure(see below) or gas phaseinfrared spectroscopy (Chapter9). In planning an experiment,solvents and reactantsare often chosen such that their vapor pressuresfacilitate the separationof reactants,products, and solvent. For compounds of similar volatility, more advancedseparation techniquesare required, such as fractional codistillation,low temperature column distillation,or gaschromatography, all of which are describedin Chap- ter 9.

E. Exomple: Seporolion of BFg ond CH2C|2. Boron trifluoride (bp -110.7'C) is readilyseparated from methylenechloride (bp 40.7"C)as illustrated in Fig. 5.6. Inspectionof the vapor pressuredata in Appendix V reveals that BF3exerts 75 torr at - 126"C,whereas extrapolation of the vapor pressure data for CH2Cl2to this temperature(log P vs. l/T plot) indicatesa vapor pressureof lessthan l0-3 torr for this component.Therefore, the reactionmixture is slowlypassed through a trap cooledto - 126'C (methylcyclohexaneslush bath, see below), which retains the methylene chloride, and into another trap at - 196"C(liquid nitrogen),which retainsthe boron trifluoride. The rate of trans- MANIPULATIONOF VOLATILELIQUIDS AND CONDENSABLEGASES 107

\Liquio 126" slush nrtrogen rt (-196" C) ll t Reoction CH2Clz 8Fs mtxture conoenses condenses BF3ond CH2Cl2

Fig. 5.6. Schematic representation of trap-to-trap fractionation for a BFr-CH:CI2 mixture. See Section5.3.E for a descriptionof the separationprocedure.

fer of the gasesthrough the traps is moderatedby placing a chilled Dewar around the tube containingthe reactionmixture. (This is accomplishedby initially condensingthe mixture in the left containerat liquid nitrogen temperature, pouring the liquid nitrogen out of this Dewar, and replacingthe chilled Dewararound the sampletube.) After the distillationis complete,the individual traps can be isolatedto retain the components.The recoveryof BF3 should be quantitative.This may be verifiedby expandingthe gasinto a calibratedvolume attachedto a manometer,followed by pressuremeasurement and calculationof the molespresent by the idealgas law. Finally, purity checksmay be performed by vapor pressuremeasurement, gas-phase infrared spectroscopy,andlor mass spectrometry. This sequenceof separation, quantitative measurementof volatiles, and physical identification of components affords a powerful method of studyingreactions involving at leastone volatilesubstance.

F. PVT Meosuremenl of Goses. One of the primary advantagesof the vacuumline manipulationof gasesis the easewith which quantitativemeasure- mentsare made. If the problem simply requiresdispensing measured amounts of gas, a proceduresuch as the following may be employed.The idealgas law is sufficientlyaccurate for most chemicalwork if the compoundsare well removed from their condensationtemperatures and pressures.For example,the van der Waalsequation of statefor CO2indicates that 1 mmol of this gas in 25 mL will exert749.7torr pressureversus the idealgas value of 748.4torr. This disparityin pressuresamounts to a 0.2Voerror, which is lessthat the other errorsinvolved in routine PVT measurements,and is perfectlyadequate for most chemicalprob- lems. 108 VACUUMLINE DESIGN AND OPERATION

G. Exomple:Colibrotion of o Bulb ond PVTMeosuremenl of o GOS. In this examplewe are interestedin obtaining a known quantity of gas, using as our gassource a storagebulb attachedto the vacuumsystem. First it is necessaryto haveat hand a calibratedvolume. If a bulb of known volumeis not available,an evacuatedgas bulb of the type shownin Fig. 5.5 is weighed,filled with water (if it is large) or mercury (if it is very small), and reweighed.The volume is then determinedusing the weight differenceand the densityof the liquid at the ambient temperature. The clean,dry, calibratedbulb is attachedto a vacuumsystem, such as siteA on the line illustratedin Fig. 5.2, and evacuatedto 10 3 torr or lower.Gas may be admitted to the calibratedbulb by isolatingthe working manifold from vacuum and openingthe stopcocksand valvesleading to one of the upper gas storage bulbs, C, while the pressureis monitored by manometerD. When the desired pressureis reached,the valveon the storagebulb is turned off, pressure and temperaturemeasurements are made, and then the stopcockon the calibrated bulb is turned off . At this stagewe know the pressure,temperature, and volume of the gas in the calibratedbulb, which permits the calculationof the number of molesvia the ideal gas equation. Beforethe gasin the calibratedbulb can be dispensedit is necessaryto eliminate the gaswhich fills most of the working manifold and the manometer.This may be accomplishedby condensingthe excessgas back into the storagebulb and closingoff that bulb. The gas which is containedin the calibratedbulb attachedat siteA can now be condensedinto any of the evacuatedtraps on the line or into an evacuatedreaction vessel, which might be attachedat site B.

H. Exomple:Colibrofion of o Tropond Meosuremenlof o GosSom- ple. In contrastto the previousexample, the objectivehere is to measurethe anlount of an entire gas sample,such as the BF-jrecovered in the trap-to-trap distillationdiscussed in Section5.3.E. In thistype of measurementa manometer is includedin the calibratedvolume. and it is necessaryto accountfor the change of volumeas the mercurylevel changes u'ith changesin pressure.As describedin Chapter7 a constant-volumegas buret can be used,but this is somewhatcum- bersonre.So the sin.rplerprocedure described here is more frequentlyused. Supposethat we wish to calibratethe volumeof trap E connectedto manometer D on the vacuum line in Fig. 5.2. A known quantity of a gas,such as CO2,is condensedinto trap E usingthe calibratedbulb and the techniquesjustoutlined in Example 5.3.G. The stopcocksare then turned so that trap E communicates with the centralmanometer D but is isolatedfrom the restof the vacuumsystem. At this point, the cold trap is removedfrom E, the trap is allowedto come to room temperature,and the pressureand room temperatureare measured.The volume of the manometer-trap combination is determined from the known molesof gas, the pressure,and the temperature,using the ideal gas law. The processis repeatedwith successivelylarger samples of CO2,and a plot of volume versuspressure is constructedfrom the data. Sincethe bore of the manometeris of constantdiameter, this plot should be a straight line. It also is possibleto LOW.IEMPERATUREBATHS 409

determinethe variation of volume with pressureby previouslymeasuring the inside diameter of the nlanometertubing. The volume-versus-pressureplot is enteredinto the laboratorynotebook for future use. we can now determinethe total molesof gas in a sampleby condensingthis gas into trap E, measuringthe pressureon manometerD, measuringthe room temperature.and using the volume-versus-pressureplot to determinethe volume of the gas so that the ideal gas equationcan be applied.

5.4 row-TEMPERATUREBATHS

A. Liquid Nilrogen ond Liquid Air. Liquid nitrogenis the mostcommonly usedrefrigerant for the manipulationof condensablematerials on a vacuumsystem becauseit is easyto use.inexpensive, and will not supportcombustion. Fur- thermore,its boilingpoint is low enough,-196oC (77"K), to lowerthe vapor pressureof most materialsbelow l0 I torr, which is necessaryfor the quantitative transferof corrdensiblentaterials on the vacuulllsystent. CAUTION: Skin contact with liquid nitrogen may lead to a frostbite burn. An occasionaldroplet of nitrogen, such as is encounteredwhen filling a Dewar, often does not freeze the skin becauseof an insulating film of gaseousnitrogen which forms immediately. However, the skin is readily frozen if the liquid nitrogen is held on a spot by clothing which is saturatedwith the refrigerant, or by any other means which leads to extended eontact. CAUTION: The releaseof large quantities of liquid nitrogen in a confined spacedisplaces air and can lead to asphyxiation. The areaswhere liquid nitrogen is dispensedor handled in significant quantities should be well ventilated. In most largemetropolitan areas liquid nitrogenis readilyavailable commercially.It may be deliveredas the liquid from the Dewaron a truck trailerto a large storageDewar on site. More commonly, it is deliveredin medium-size pressurizedor atmospheric-pressureDewars which can be movedinto the laboratory (Fig. 5.7). As illustratedin that figure, liquid nitrogenis u'ithdrarvnfronr the pressurizedDewar by meansof a valveand spigot.much asone drawsu'ater from a tap. The differencebetween filling a vesselu'ith water or a small Dewar with liquid nitrogen is that the deliverytube and small Dewar must cool to - 196"c beforeliquid canbe collected.Initially only cold gas will issuefrom the deliverytube. After the liquid starts to flou' it will be rapidly volatilizedin the small receivingDewar until that Dewar is cooledto the boiling point of nitrogen. Similarly.Iiquid is generally drarvn fronr medium-size atnrospheric pressure De- warsby applicationof a small positivepressure of nitrogengas (about l-3 psig). which forcesthe liquid out of a dip-tube.Again there is an initial cool-dow'n period as the dip-tube is initially insertedinto the Deu'arand the deliverytube and receivingDewar are cooled. The Dewarsused on a vacuumsystem are generally of the r.r'ide-mouthedvari- ety, with capacitiesranging from r,/rto I L, although larger Dewarsare some- 1,10 VACUUMLINE DESIGN AND OPERATION

Lrqurd-level indicator Dewarvacuum Rupturedrsk Rupturedisk

N2gas+

LiquidN2

(a) (b)

Fig.5.7. Liquid nitrogen storageDeu'ars. (a) Atmospheric-pressureDeuar. Liquid nitrogen is drawn front the Deuar bv applyinga small pctsitivepressure of nitrogengas to the inlet on the sleeve of the metal dip-tube,forcing liquid nitrogenout the dip-tube.(D) Schematicdrawing of a pressur- ized storageDewar. Spigotsare generallyprovided for both liquid and gaswithdrawal.

times usedon the main traps of a vacuum system.Because of the coolingtime and the lossesof nitrogen involvedin drawing liquid nitrogen front a storage Dewar, it is common to employ a 3-5 L dispensingDewar when the vacuunl systemis in operation(Fig. 5.8). This dispensingDewar then requiresonly occa- sionalfilling, and it can be of a narrow-mouthdesign, which reducesevapora- tion losses.To further reduce losses,a looselyfitting cap or cork is generally placed over the mouth of a Dewar containing liquid nitrogen, and a Dewar which has a U-trap or storagetube protruding from its mouth is generallycovered rvith glassu'ool. This loosecap also greatly reducesthe condensationof oxygen(bp - l8J'C) in the Dewar.CAUTION: It is veryimportant neverto seal a Dewar of liquid nitrogen, becausethe insulation on a Dewar is never perfect; so the liquid is constantly boiling and a sealedDewar will eventually explode. Liquid air is a potential substitutefor liquid nitrogen but is not commonly usedbecause the vaporsr.r'ill support combustion and there is ordinarily little or no price advantagein its use.

B. Slush Bofhs. Liquid nitrogenand Dry Ice are convenientand inexpensive refrigerants.But, as shou'nin the examplesin this chapter,a wider rangeof lo$'- temperaturebaths is necessaryfor trap-to-trapfractionation of gasesand for the characterizationof a substanceby vapor pressuremeasurements. A convenient constant-temperatureslush bath consistsof a nrixtureof a frozencompound in equilibriumwith its liquid. The bath is made in a cleanDewar no morethan LOW-TEMPERATUREBATHS 444

Fig.5,8. Laboratory-sizeliquid nitrogenDewars. (o) Crosssection of a wide-mouthedglass Dewar. These range in capacity from l,/r to I L or larger, and are generally used to cool traps on vacuunl systems.(b) Crosssection of a metalDewar. To minimizeliquid nitrogenlosses, a loose-fittingcap is usuallyplaced over the mouth of the Dewar.

three-quartersfull with the pure liquid and placed in a good hood. Freshly drawn liquid nitrogen is slowlyadded while the liquid is rapidly stirred rvith a stout stirring rod. There is a tendencyfor a hard frozenring to form around the sidesof the Dewar at the surfaceof the liquid. The addition of liquid nitrogen should be slow enough and the stirring adequateto minimize the sizeof this frozen ring, which in an extremecase will preventthe slush bath from fitting around a trap. Liquid air or liquid nitrogenwhich has condensedoxygen fronl the air shouldnot be usedto nlake slushbaths of combustiblecompounds. The consistencyof the final product shouldbe similar to a thick malt. If the slushis too thick it cannot be penetratedby a trap, and if it is too thin it will not hold a constanttemperature for long. A list of convenientmaterials for slushbaths is givenin Table5.1. Many slushbaths havepoor lastingproperties, which makesit advantageous to precoolthe trap. This is accomplishedby coolingthe trap with liquid nitrogen, removingthe Dewar of liquid nitrogen, and placing the slushbalh below the trap. The stirring rod is then usedto swaba spot on the trap with the slush. At first the bits of slushwill freezeon the trap, but as the trap warmsthe frozen slushwill melt. At this point the slushbath is raisedaround the trap. The liquids from a slushmay be reused. 412 VACUUMLINE DESIGN AND OPERATION

Ioble 5.4. Compoundsfor CryostoficBolhs

Tenrp."C" Conrpound Temp, oC" Compound

+ 6.55 Cyclohexane - 95.0 Toluene +5.53 Benzene - 96.7 Methylenechloride -1ll 0.00 Water/' Trichlorofluoro methane (Freon-lI.bp 23.8"C)' - 8.6 Methyl salicl'late - 1il.95 Carbon disulfide - r5.2 Benzylalcohol - l 18.9 Ethyl bronride -22.95 Carbon tetrachloride - 126.59 Methylcyclolrexane - - 30.82 Bromobenzene IJJ DichlolofI uoromethane (Genetron-21.bp 8.9'C)' -37.4 Anisole - r38.3 Ethyl chlotide -15.2 Chlorobenzene -5r.5 Ethyl nralonate - r39 CHClr. 19.7%by u'eight C2H

"Most of thescvalues are taken fronr J. Tinrlernrans. Piln'srco-chcnticalConstuttts ol'Pure Orpurtit Cotnpoutttls,Vols. I and 2, Elsevier,Antsterdanr. 1950 and 196-5. i'Purecrushcd icc in contactu ith distillcdu ater. 'Thesefluorocarbons have lou toxicityand are nonflanrmable.The liqLridnray be storedfor reusein a stopperedDeuar in a freezer. 'iReagent-gradechloroform contains a significantquantity of alcohol, u'hich lowersthe nrelting pornt.

C. Dry lCe BOlhS. In contrastto the fixed temperatureof slushbaths, a Dry Ice bath is sonrewhatless reliable becausethe equilibriunl temperatureis a strongfunction of the partial pressureof CO2above the bath. For example,one test in which Dry Ice was freshlypowdered in air had a temperature8oC below the normal sublimationtemperature of - 78.5"C. In anothertest, l0-h standing was requiredfor a Dewar of Dry Ice to attain - 78.5oC.1However, a small electric heaterburied in the Dry Ice producedenough CO2 to expelthe air and attain the normal sublimationtemperature in a matter of minutes.The temperatureof an equilibratedDry Ice bath at any barometricpressure may be found usingthe expressionfor sublimationpressure: - rogP:e.81137 itk

'R. B. Scott,inTemperuture, Its Measurenentund Control, Vol. l, Reinhold,New York; 1941,p. 212. MANIPULATIONOF NONCONDENSABLEGASES 413

whereP is in torr and t in degreesCelsius. Generally Dry Ice is usedin a bath containingacetone or anotherlow-melting liquid to aid thermal conductionand promoteequilibration.

5,5 vApoRpREssuRE AsA cHARAcTERrsncpRopERTy

Vapor pressures,which are readilydetermined on a vacuumline, providea convenientand sensitivemeans of identifyinga volatilecompound and/ or checking its purity. The sampleis condensedat liquid nitrogentemperature and all of the residualgases are pumped out of the system.If the compoundhas been exposed to the atmosphereimmediately prior to the measurement,it shouldbe degassed by severalfreeze-pump-thaw cycles. The trap or tube attachedto the vacuum systemcontaining this sample is maintained at the desiredlow temperatureby meansof a slushbath, and the pressureis read on a mercurymanometer. The samplemust be largeenough so that liquid is presentwhile the measurementis being performed.The presence of an impurity of differentvolatility can be detectedby the disparitybetween the known vaporpressure and the observedvalue. Another effective means of checking the purity is to removeby condensationa significantportion of the sample into a trap for temporarystorage and then redeterminethe vapor pressure.If the secondvapor pressureis different from the first, impurities are presentin the sample.Vapor pressuredata for somecommon compoundsat convenientslush bath temperaturesare given in Appendix V.

5.6 MANrpuLATroNoF NoNcoNDENsABLE GAsEs

Liquid nitrogen is the coldestinexpensive refrigerant available. The two lower- temperaturerefrigerants, liquid hydrogenand liquid helium, areexpensive, difficult to handle,and the former is dangerousbecause of the productionof explo- sivevapor. Thus gasessuch as Hz, Nz, 02, CO, and CHa,which havehigh vapor pressuresat liquid nitrogentemperature, - 196'C, require specialmethods for their transfer.The two most commonlyused techniques for these"permanent" gasesare a reciprocatingmercury pump (Toeplerpump) and low-temperature adsorptionon high-surface-areasolids. The Toepler pump is very predictable and, when it is operatingproperly, quite trustworthy. However,it is expensive and complicated,and if mishandledit can fail spectacularly.Low-temperature adsorptionis cheap, versatile,and easyto implement,but requirescareful checkingto avoid erroneousresults.

A. Ioepler Pump. The principlesof operationof a Toeplerpump are outlined in Fig. 5.9, where it will be noted that a systemof internal check valves permits gas from the vacuum systemto enter the upper chamber, and subse- quentlyto be compressedand expelledinto a gasburet. The systemmay be man- 414 VACUUM LINEDESIGN AND OPERATION

To vocuum lrne

Fig. 5.9. Toeplerpump and gasburet. In this installationa "constant-volume"manometer is used for measuringthe pressure.Stopcock B allowsthe attachmentof a samplingbulb or a largeexpan- sionbulb for usewith largevolunres of gas.Stopcock A is usedfor initial evacuationof the calibrated volunreand samplebulbs. lt is closedduring the operationof the pump. When a gas is to be measured,the nrercurylevels in the right arm of the Toeplerpump and in the left arm of the manometer are adjustedto levels(C) for which the gasvolume has beencalibrated. An excellentversion of this pump is manufacturedby the Rodder InstrumentCo., Los Altos, Calif. ual, but mostoften it is controlledby meansof contactswhich sensethe mercury level. Theseare connectedto a relay and solenoidvalve which control the air pressurein the bottom chamber. On the inlet cycle,the gas being pumped is distributed betweenthe vacuum systemand the upper chamber of the pump. Thus the fraction of gas removedper cycleis equal to the volume of the upper Toeplerpump chamber V, divided by the volumeof the vacuum systemV, plus the volumeof the upper chamber.The fraction of gasremaining in the vacuum line after /r cyclesis - v, ), -lr: [r V,,+ V,] from which it is easyto estimatethe number of cyclesnecessary to collectthe gas "quantitatively." The completenessof gascollection also can be judged by failure of gasto bubble through the outlet valveon the compressioncycle, or by the lack of pressurechange for the collectedgas over severalcollection cycles. The primary modesof failure of this type of pump are leakagepast the internal check valvesor sonle mishap which leadsto a suddenrush of air into the upper or lower chamber. The first problem impairs the pumping action and is MANIPULATIONOF NONCONDENSABLEGASES 445 most commonly causedby poor check valve design or dirt on the check valves. The inrush of air from operator error or a malfunction results in a surgeof mercury which may break the apparatus and create a shower of mercury.

B. Low-Iempetofule Adsorplion. This method providesa convenient methodof transferringand separatingsome permanent gases. The utility of low- temperaturegas adsorptionwas recognizedby Dewar in 1875,but the applications describedhere are in part basedon the selectivityof certain solidswhich were not recognizeduntil fairly recently.2Since the adsorption of one gas can affect that of others, materialswhich are condensableat - 196'C are first removed by the conventionalcondensation procedures discussed earlier in this chapter.The noncondensablegases are then adsorbedon a suitablesolid surface at low temperature.Molecular sieve4A, at - l96oC will stronglyadsorb Hu, Oz, N2, CO, CHa, and similar "permanent gases."Silica gel at this sametemperature adsorbshydrogen only lightly and the othersstrongly. Thus it is possibleto separatehydrogen quantitatively from the other permanent gasesby an adsorption trap of silicagel followedby anotherof molecularsieves; or. in placeof the molecularsieves, one may usea Toeplerpump to collectthe hydrogen.It is important to cool the adsorbentsbefore they are exposedto the gas mixture, because cooling silica gel in contact with hydrogen from room temperature to -196oC leadsto the retentionof a small amount of the hydrogenin the silica gel. Heat flow is not efficient between the particles, so it is necessaryto wait patientlyfor the trap to cometo the desiredtemperature. In this connection,it is desirableto avoid traps with very large crosssections, which are especiallyslow to come to temperature. This simpletechnique can be appliedto a varietyof transferoperations, and it often servesto replacethe more cumbersomeand expensiveToepler pump. The solid adsorbentshould be sievedto eliminatefines or largeparticles. Parti- clesof about50 mesh(0.3-mm diameter) are ideal, and theseshould be contained in a suitableU-trap or other trap designwith a small plug of glasswool on the inlet and outlet to preventthe adsorbentparticles from being sweptinto the vacuum line (Fig. 5.10). Before use, the freshly packed trap is heated to about 300oCwhile beingevacuated to a high vacuum.The initial evacuationand heating must be done slowlyto avoid sweepingthe adsorbentout of the trap by the copious quantities of adsorbedgases and water vapor which are evolved. Low-temperatureadsorption is also useful for the quantitativetransfer of gasesinto specialapparatus. For example,a small quantityof activatedmolecu- lar sievein a freeze-outtip on an infrared cell may be usedfor the identification of methane;or, when placedin a freeze-outtip on a manometerand calibrated volume,the molecularsieves permit the measurementof the quantityof noncon- densablegas.

2The principfes of selectiveadsorption by zeolitesare discussedin D. W. Breck, Zeolite lgloleculur Sreves,Wiley, New York; 1974. 11ö VACUUMLINE DESIGN AND OPERATION

Fig. 5.10. 1'rap designfor gas manipulationby lou'-temperatureadsorption. (o) Solid adsorbentl (b) Teflon-glassvalve (4 mm): (c) glasswool plugs;(d) O-ring connectors(9 nrm); (e) ground-glass stopcockor 1'eflon-glassvalve on high-vacuumline; (D to high vacuummanifold. The trap mav be movedfronr one attachnrentpoint on a high-vacuumline to anotherattachment point withoutexpos- ing the adsorbent(and any gas samplecollected in the trap) to atnrosphericgases.

5,7 sAFETY

As with most scientificapparatus, improper handlingof the vacuumline can be hazardous.Appendix I presentsa detailed listing of laboratoryhazards, and Section7.1.E describesthe correcthandling of mercury.This brief sectionu'ill serveas a reminderof potentialsafety problems which areencountered in the use of a vacuum system.Since there alwaysis the possibilityof explosionor implosion of pressurizedor evacuatedglassware, eye protection should be worn at all times around a vacuum line. Other hazards include; explosionof glassware which is inadvertentlypressurized by the uncontrolled\\'arming of condensed gasesin a small volume;implosion of evacuatedstorage bulbs and Dewars(these items shouldbe surroundedwith tape or a specialplastic coating to containfly- ing glass);exposure to mercury, which is a cumulativepoison (spills shouldbe promptly and thoroughlycleaned up); asphyxiationby nitrogengas (liquid ni- SAFEIY 4 Ä-7 trogen should not be handled in a small, poorly ventilatedroom); and frostbite from the contactof skin with low-temperaturerefrigerants. CAUTION: Since electricity is used to run equipment such as vacuum pumps, gauges,and Tesla coils, proper care must be exercisedwhen using and maintaining this equipment. Individual items should be grounded through a three-prong plug, and vacuum racks must be properly grounded, for example, by means of a copper wire betweenthe vacuum rack and a water pipe.

GENERAIREFERENCES

Angelici,R.J.,1977,SynthesisundTechniqueinlnorgunicChentistn-,2nded.,Saunders,Philadel- phia. This book providesa usefulexercise in vacuumline practicefor the neu'conrc.rto the field. Brauer.G.. Ed., 1981.Huttdhuth tler PrepurutivenAnorgctrtischen Cherttie,3rd ed.. Enke Verlag, Stuttgart.The first chaptel includessome infornration on vacuunrline technique.and various s\'nthesesthrougbr)ut this lhrcr'-volunreset illustrate the applicationof racuur)1sYstenrs to inor' ganic preparations.The Englishedition of the secondcdition of this book is of someuse, but it is not up-to-date. Jolly, W. L., 1970, The Synthesisund Churucterizutionttf Inorgatic Cotnpounds.Prentice-Hall, Engle*ood Cliffs, N. J. An excellent,concise introduction to chemicalvacuum line technique. uith someexperiments which rvill providegood exercisesto the newconrerto chemicalvacuunl Iines. Melviffe.H.. and B. G. Gouenlock, 1964.Experinreutul lvlethods in Gus Reactiotrs,Macnrillan, London. Primarilydevoted to experimentalmethods for gas-phasekinetic studies, but the prin- ciplesand apparatusare of interestin generalchemical vacuunl line technologv. Moore, J. H.. C. C. Davis,and M. A. Coplan, 1983,Building ScientilicApparutus, Addison-Wes- ley, Reading,Mass., A good, physicallyoriented reference on laboratorytechnique. Chapters 3 and 4 coverglassblowing and vacuumapparatus, respectivel). O'Hanfon. J. 4., 1980,A User'sGuide to VatutrtrrTechnologl'. Wiley. Neu York. A practicalguide to the generalarea of vacuurntechnology and relatedprimarily to semiconductorand optics technology. Sanderson,R. T., 1948,Vucuurrt lglunipulati

This chapter is primarily devotedto pumps for high vacuum-operation(10-3- 10-s torr), which is the vacuum range of greatestinterest in chemicalvacuum lines.In addition, rough-vacuumsystems (760-0.1 torr) are discussedin connection with their use in manipulating mercury-filledapparatus, such as Toepler pumps and Mcleod gauges.

6,4 RoueH-vAcuuMsYsTEMs

A. Applicofions for Rough Vocuum. In the descriptionof the operation of a Toepler pump given in Chapter 5, mercury was transferredfrom a lower reservoirto an upper pumping chamberby the useof pressuredifferentials. The upper chambercommunicates with the high-vacuumline and the lowerreservoir with a rough-vacuumsystem or the atmosphere.Mercury is pulled from the upper chamberinto the lowerreservoir by meansof a rough vacuumapplied to the lowerreservoir, and on the other stroke,mercury is forcedinto the upper chamber by admitting air to the lower reservoir.There are other typesof equipment where mercury is added to or withdrawn from the vacuum systemby similar means,including the constant-volumegas buret (Chapter7) and varioustensim- eters(Chapter 9).

B. Design of Equipmenl. Sincethe rough-vacuumsystem may have a practical vacuum limit of I torr to severaltens of torr, equipnlentmust be de- signedand filled with mercury to take into accountthe disparity in pressures betweenthe high-vacuumside and the mercuryreservoir. The reservoirmust be ,t.lI HIGH-VACUUMPUMPING SYSIEMS 119 placed low enough so that the apparatus can function properly with a differential in the mercury heights on the high-vacuumand reservoirsides. It is also important to bear this differentialin mind whenfilling apparatuswith mercury.

C. Rough-Vocuum Sysfem. A relativelyinexpensive single-stage pump (seeSection 6.2) will servewell for most rough-vacuumapplications. It is important to protect this pump, by meansof an uncooledtrap of appropriatesize, from the possibleinrush of liquid mercurywhich may occur during an accident. To avoid the buildup of toxic mercuryfumes in the work area,the exhaustfront the pump is conductedto a hood. The rough-vacuummanifold may be constructedfrom glass,copper, or polyethylenetubing. The latter, morerobust materials are often preferredbecause the rough-vacuummanifold often is placed belowthe main vacuum systemand is thus vulnerableto itemsthat are dropped. A typical rough-vacuumsystem is illustratedin Fig. 6.1.

6,2 HGH-vAcuuMPUMPTNG sYsTEMs

A. Rofory Oil-Seoled Pump Designs. All of the commercialoil-sealed mechanicalpumps are based on a rotorinside a cylindricalstator. These individ-

Rubbervacuum tubing

Solenoid valve

To Toepler pump Exhaustto hood

Fig. 6.1. Rough-vacuumsystem. Frequently used itenrs such as the Toeplerpump and constant- volume manometerare often connectedpermanently into the rough-vacuunrsystem. Also, one or two outlets,with vacuum tubing attached,are includedfor generaluse, The manifold generallyis constructedfrom rigid plasticor metal tubing. 120 PUMPSFOR ROUGH AND HIGHVACUUM

ual stageswill be discussedbelow. Of greatestimportance is not the designof thesestages, but rather whetherthe pump has a singlestage or two stagescon- nectedin series.A well-constructedsingle-stage pump is capableof attaining about 0.01 torr, but a more practicallimit is on the order of I torr, This type of pump is useful in rough-vacuum systems.Two-stage pumps generally are quotedto attain between10 3 and 10-a torr, althoughpumping speedsare slow nearthese pressure limits. Two-stagepumps aregenerally preferred for backing diffusion pumps in high-vacuumsystems. There arethree common designsfor the internalworkings of rotaryoil pumps and theseare illustratedin Fig. 6.2. All employ a rotor which revolvesinside a cylindricalstator; a sealbetween the fixed and moving parts is maintainedby a thin film of oil. Of the three designs,the internal-vanepump is by far the most common in the laboratory;it is generallyused to back a diffusionpump in highvacuum systems.Internal-vane pumps generally make relatively little noise when operatingat high vacuum. The rugged and easilyrepaired external-vane pump is mainly availablein small pump sizesand finds its greatestuse in rough pumps. Thesepumps appear to stand up to a hostileenvironment better than the internal-vanepumps, but they have the disadvantageof producing a loud clanking sound when operating at their vacuum limit. The rotary-plunger pumps are used in high-vacuumapplications and are fairly common in large vacuum systems.Very good pumps are availablein all three designs. For many yearsthe connectionbetween the pump and motor wasmade with a V-belt, but "direct-drive" pumps are becomingcommon. The latter are more compact, smootherrunning, and perhapsa bit quieter and more reliable. On the other hand, the semiflexiblecoupler between the motor and pump shaftcan

Fig. 6.2. Internal-vane,external-vane, and plunger-typerotary vacuum pumps. It will be noted that the internal-vanepump involvesa rotor concentricwith the driveshaft, but which is off-center with respect to the stator. By contrast, the external-vane and rotary-plunger pumps have a rotor which is asymmetric with respectto the shaft: however,the shaft is centeredin the stator. All three involveclose tolerances, so the high-vacuum performance is impaired by particlesof dirt or corrosive gases.Some pumps are partially constructed from soft die-castmetal, which is eroded by mercury. Specialcorrosion-resistant pumps and inert flourinated pumps are usedin the semiconductorindus- trv. HIGH.VACUUMPUMPING SYSTEMS 124 wear out, and when this doeshappen, the coupler is more difficult to replace than a belt. Many vacuum pumps are suppliedwith a gasballast valve which is designed to preventthe condensationof moistureand similarcondensable materials. This valvebleeds a small amount of air into the pump and as a result the ultimate vacuumand pumping speedof the pump suffer.There is no occasionto usethis featureon a pump on a typical chemicalhigh-vacuum line, and it rarely,if ever, is usedin typical laboratoryrough-pumping systems.

B. Troubleshoolingond Mounfingo MechonicolPump. It willbe notedin Fig. 6.2 that gasfrom a rotary pump is exhaustedthrough an immersed flapper valve.For this valveto make a good sealit must be coveredwith oil. One common causeof the loss of ultimate vacuum performancein thesetypes of pumps is a low oil level,and this should be the first item to be checkedwhen a pump is not performingwell. A telltalesign of low oil is a changein the soundof the pump. With a little experiencethe experimentalistbecomes used to the soundof a properly operatingpump, and any deviationin this sound is a sign of trouble. The distinctivesound when there is a small leak in the system,or a low oil level (the soundsare often similar), or the slappingsound characteristicof a worn belt, is a tip-off that remedialaction is necessarybefore the problemgets worse. A vacuum pump shouldbe scrupulouslyprotected from corrosivevapors and materialswhich will be absorbedin the pump oil or condensein the pump. For most laboratoryoperations a low-temperaturetrap is employedfor this purpose, and in the caseof fluorine handling systemsa soda-limetrap is usedto neutralize the corrosivegases. Despite these precautions,the pump oil does eventually break down and becomecontaminated. Regular oil changesshould be sched- uled for a pump at about yearly intervalsfor a well-protectedpump and more often for pumps which are not well protected. Specialcorrosion-resistant pumps are now widely usedin the semiconductor industry. Often theseare equippedwith pump oil purifiersand are neverturned off when contaminantsare present.These pumps areexpensive and under harsh conditionsthey break down much more oftenthan a well-protectedconventional pump. As mentionedin Section5.1.B, the transmissionof vibration from the mechanicalpump to a vacuumrack decreasesthe accuracyof manometerreadings. To minimize this problem, it is generallybest to mount the pump on the floor below a vacuum rack and to connect the pump to the systemwith a short length of heavy-walledrubber tubing, Tygon tubing, or flexible metal tubing.

C. Diffusion Pump Design ond Operolion. The pumping speedof a two-stagemechanical pump generallydrops very rapidly below 10 I torr. By contrast, Fig. 6.3 showsthat a typical diffusion pump hasgood pumping speedbe- low this pressure.Therefore, a tandem arrangementof a diffusionpump with a 422 PUMPSFOR ROUGH AND HIGHVACUUM

100

1 o -i ) Mechonrcol 0.1

1O-7 10-6 to-s 1O-4 1O-3 i)-z 1O-r O B torr

Fig. 6.3. Comparisonof the pumping speedof a typicaltwo-stage mechanical pump with a single- stagediffusion pump.

rotary fore pump is commonlyemployed for the evacuationof high-vacuumsystems. The designof a diffusionpump is illustratedin Fig. 6.4. Thesepumps operate by boiling mercuryor a low-vapor-pressureoil and conductingthe vaporsout of a nozzle.This nearly unidirectionalstream of vapor moleculescollides with gas moleculeswhich havediffused into the pump from the systembeing evacuated. As a resultof thesecollisions, momentum is impartedto the gasmolecules in the directionof pumping. The vapor is then condensedand returnedto the boiler, and unwantedeffluent gas is removedby the mechanicalfore pump. Frequently the diffusion pump is designedwith two or more nozzlesin seriesto allowopera- tion of the pump at a high fore pressurewithout sacrificingultimate vacuum. An oil pump is fasterthan a mercurypump of comparablesize because of the higher collisionalcross section of the large oil moleculesand the higher velocitiesof thesehigher boiling materials.An oil diffusion pump requiresperiodic reprace- ment of the fluid, whereasa mercury pump can operatemany yearswithout attention. Among the commonly usedfluids for diffusion pumps presentedin Table 6.1, the siliconeoils are the most popular in chemicalsystems. Because of increasedawareness of the health hazardsof mercury,oil diffusionpumps have becomethe standard in most laboratories.when a mercury diffusion pump is employed,it is highly advisableto include a cold trap (-78'c is satisfactory) betweenthe diffusion pump and the fore pump to reducethe amount of mercury vapor reachingthe atmosphere. The rate of boiling of the pumping fluid is determinedby trial and error. The useof too low a rate of boiling will reduceboth the pumping speedand the limiting fore pressure.In general,the heaterinput shouldbe high enoughso that the HIGH.VACUUMPUMPING SYSTEMS 123

+tl C

Fig. 6.4. Cross-sectionof a metaldiffusion pump. The upperstage in this punrphas a wideannular opening(A) which providesa good ultimate vacuunl.The louer stagehas a snlallannular opening (A') so the puntp uill operateagainst a high fore ptessure.(B) High-vacuunrconnection to the lou- temperaturetrap and vacuunrline. (C) Connectionto rotaryoil-sealed pump. This pump is cooled by meansof water tubes (D). Air-cooledversions have fins in placeof thesetubes and a fan is in- stalledto blow air over thesefins. (E) Electricallvheated oil reservoir.

vapor is condensingbelow the nozzleat a brisk rate. Ifthe boilingrate is too fast, the pumping efficiencygoes down becauseof backstreamingof the pumping vapors.Bumping, or eruptiveboiling of the fluid, has an adverseeffect on the pumping action and is to be avoided.The sourceof bumping is an inversionin the vapor pressureof the fluid, owing to cooling of the surfaceof the fluid by evaporationwhile heat is appliedfrom below.Because of its low thermalconductivity and high heat of vaporization,oil is much more susceptibleto bumping than is mercury. Heaterswhich protrude into the pumping fluid are generally most effectivein reducingbumping. 124 PUMPSFOR ROUGH AND HIGHVACUUM

Toble6.'l. Comporisonof Fluidsfor DiffusionPumps

Vaporpressure Resistanceto Type at 25"C(mm) Air Oxidation

Mercury Metal 2x103 Best Apiezon A Hydrocarbon 2 x 10-s Poor Apiezon B Hydrocarbon 4 x 10-? Poor ApiezonC Hydrocarbon l0E Poor Silicone702 Silicone Better Silicone704 Silicone l0 6 - l0-lr Better Silicone705 Silicone l0-e - l0 r0 Better Octoil Ester 2xl0r Fair Octoil S Ester 2 x lO-s Fair

D. Motching lhe Fote Pump ond Diffusion Pump. A diffusionpump hasa critical pressureabove which it doesnot operate.Therefore, the fore pump must be capableof achievingthis limiting pressurein a reasonabletime period. Furthermore, the fore pump should be capableof removingat least as many molesof gasper unit time asthe diffusionpump delivers.The throughput(speed in volume per unit time X pressure)is proportionalto the speedon a molar basis;so a match of the pumps is obtainedwhen S1P1 : SzPz.In this equation, 52is the speedof the diffusionpump at the appropriatehigh vacuumP2, P1 is the limiting fore pressurefor the diffusionpump, and Sqis the pumping speedof the mechanicalpump at this pressure.Generally, the pump manufacturersprovide the information necessaryfor approximatethroughput calculations.

E. COld Trops. In additionto the fore pump and the diffusionpunlp, a third activepumping elementin most chemicalvacuum systemsis a liquid nitrogen- cooledtrap situatedbetween the main high-vacuummanifold and the diffusion pump.This trap pumpsthe systemby removingcondensables. and it servesto protectthe diffusionand mechanicalpumps from corrosivevapors. It is undesir- able to accumulatelarge quantitiesof condensablesin this trap and it is poor practiceto usethe trap to discardunwanted condensables in the vacuumsystem. (Theseunwanted materials should be condensedinto a tube attached to the working manifold and renoved to a hood.) Even a slight buildup of condens- ableseventually causes some lossof vacuum. As the liquid nitrogen levelfalls. the ntaterialcondensed near the top of the trap will volatilize;while most of it is immediatelyrecondensed in the lou'erportion of the trap, a small amount dif- fusesback into the vacuumline. Thus. whenthe vacuumis critical.the Dewar shouldbe kept full of liquid nitrogen.Special trap designsprevent this problem by condensingthe vaporsat the bottom of the liquid nitrogen reservoirrather HIGH.VACUUMPUMPING SYSTEMS 125 than the top.' However,these traps are cumbersomeand difficult to clean. so they are not commonly usedon chemicalvacuum lines. A trap designwhich allowsperiodic cleaning is highly desirablefor chemical vacuumsystems. Two suchdesigns are illustratedin Fig. 6.5, wheresome of the desirablefeatures are described.

F. Alrongemenf of the Pumping Componenls. To avoid oxidationof the pumping fluid, the hot diffusion pump shouldnot be exposedto largequantities of air. Therefore,an arrangementof stopcocksis usedto bypassthe diffusion pump when large arnountsof air are being pumped. This bypassfeature alsomakes it unnecessaryto wait for the diffusionpump to cool down when the main trap must be removedfor cleaningor whenthe vacuumsystem is turned off

(o) (Dl

Fig.6.5, Main traps. (a) This trap is long enough to extend to the bottonr of a l-L De*ar and sufficientlysmall in diameterto avoid excessivedisplacement of liquid nitrogen.These features allow the trap to remain partiallv immersedin liquid nilrogenafter standingovernight. The arrangement of inlet and outlet shou'nhere minimizes clogging of the trap becauscmost of the condensateis depositedon (he largeouter tube rather than the snrallerinner tube. (ä) A U-trap is advantageousif there is a likelihoodof condensingsignificant quantities of pyrophoricor highly toxic compounds, becausea finite amount of materialis alwayscondensed on the centertube of trap (a). To removea trap suchas (b) from the line, one shouldfill it with nitrogenand quickly take it to a hood, wherea slo$'streanrof nitrogennray be passedthrough it to nroderatethe reactionu'hich will occurwhen the contentsof the trap warm up and volatilize.Ball joints facilitatethe removalof a U-trap.

rA.Jordan,,/.Sci.lnstr.,39.447(1962);H.W.Jones,Rev..lci./rsrr..35,1240(1964).Trapsofthis type. having internal liquid nitrogenreservoirs. are availablefrom Eck & Krebs ScientificLabora- tory GlassApparatus lnc.. 27-0940th Ave..Long IslandCity, NY ll10l. 126 PUMPSFOR ROUGH AND HIGHVACUUM and the fore pump is vented to the atmosphere.This bypassmay be accomplished with one two-way stopcockin conjunctionwith a conventionaloff-on stopcock.as illustrated in Fig.6.6. Also, a specialthree-way stopcock is available which combinesthese two functions.2To maintain good pumping speedin the system,large-diameter tubing and large stopcocksshould be usedon items leadinginto th; diffusionpump. Itemsconnecting the diffusionpump outlet and the mechanicalfore pump can be of smaller diameterbecause the pressureis higher in this section.

G. Exomple: Initiol Pump'Down ond Venling the Pumping SySfem. Initial evacuationof the systemis accomplishedby attaching all

Fig.6.6. Pumps, traps, and bypass.(A) Mechanicalfore pumpl (B) short lengthof vacuumtub- (E) trap in!; (C) stopcockfor ventingsystenr when fore punrp is turned off; (D) diffusionpump; cold (G) at -lg6oC; (F). (H) stopcockwhich allou,the diffusion pump to be isolatedand bypassed; stopcockwhich allowsisolation of the nlain nranifoldfrom the trap and pumps'

2ltem8555 from Eck & Krebs (seefootnote l). HIEH-VACUUMPUMPING SYSTEMS 127 traps, starting the fore pump, and evacuatingthe vacuum line. At this point a Dewarcontaining liquid nitrogenis slowlyraised around the main trap (E in Fig. 6.6), the stopcocksare turned to route the gasesfrom the main trap (E) through the diffusion pump (D), and on to the fore pump. The diffusionpump is turned on and the systemallowed to pump down. To shut the systemoff, stopcocks(F) and (H) are turned to isolatethe diffusion pump and to establishstraight communication between the main trap (E), and the fore pump; also,the main valveto the vacuumsystem (G) is closed.The foltowing set of operationsis then carried out in sequenceand without delays betweeneach step: the fore pump is switchedoff , stopcock(C) is openedto bring the systemto atmosphericpressure, the liquid nitrogen-filledDewar on trap (E) is lowered,and trap (E) is removedand placedin a hood. The diffusion pump heatercan then be switchedoff. The reasonfor carryingthese steps out in fairly rapid sequenceis that oncethe fore pump is turned off , oil may back up into the evacuatedsystem if the flapper valvein the pump fails. In addition. if trap (E) is left at liquid nitrogentemperature for verylong, it will condenseoxygen from the atmosphere;so it is important to removethe liquid nitrogen and discard the contentsof the trap soon after the systemis vented. CAUTION: It is important never to leavea trap which is cooled by liquid nitrogen open to the atmosphere. The condensedliquid oxygen presentsan explosion hazard in contact with oxi- dizable materials and sudden warming or bumping of an oxygen-filledtrap will pressurizethe system,with potential breakageor explosion. If pyrophoricmaterials are presentin trap (E), it may be safestto isolatethis trap from either pump by stopcock(F), and carry out a trap-to-trapdistillation of the material into a tube attached to the vacuum system. If this tube is equippedwith a stopcock,it can laterbe ventedinto a nitrogenstream in a hood. Alternatively,a U-trap of the type shownin Fig. 6.5 may be usedand the proceduresdescribed in that figure caption may be followed.

H. Limitolion of Pumping Speed by the Apporolus. The time required to reducethe vacuum in a line below l0 I torr is often limited by the stopcocks and tubing in the line and not by the pumps. In this situation,little advantageis gained by the use of a large fore pump-diffusion pump combination, and, as describedpreviously, the increasedvibration of a larger mechanicalpump may lead to inaccurate manometer readings. The major limitations on pumping speedoccur at pressureswhere the mean free path of a moleculeexceeds the small dimensionsof the system.Under theseconditions collisions with the walls becomemore frequent than intermolecularcollisions. For example,the mean free path of oxygenat l0-r torr and 25oC is about 5 cm, which is much larger than the usual tubing diameter. It is instructiveto considerthe formula for the number of moleculesper second. g, streamingfrom one end of a cylindricaltube of diameterd and lengthI to the other, Eq. (l). 428 PUMPSFOR ROUGH AND HIGHVACUUM

Nd3r P,\ ._ (P, _ (1) " 3L \ 'lr= "2"un JT,l P1and Z' are the pressureand temperatureat oneend and P2 andT2referto the other end, M is the molecularrveight of the gas,R is the gasconstant, and N is Avogardo'snumber. This equationapplies in the above-mentioned(molecular flow) region, which commencesat about 10-2 torr. of particular importanceis the direct proportionalitvof the flo*' to the cube of the tube diameter. Thus, large-diametertubing and large-borestopcocks improve the pumping speedat low pressures.As with a serieselectrical circuit, the total impedance(proportionalto 1/q)is equalto the sunrof the individualimpedances, Eq. (2). lll Q\ q-u: ^* * Therefore,one small-borestopcock or a length of small-boretubing will pre- dominatein the determinationof the impedanceof the system.The analogylvith electricalcircuitry alsoholds for the parallelarrangement of impedances.Thus, if there are two or more connectionsbetween a manifold and the sourceof vacuum, the impedanceq is givenby Eq. (3).

4:Qrlqz (3) To take advantageof this effect,and alsoto be able to pump severalsections of the line at once, it is advantageousto designthe main high-vacuummanifold (e.g.,Fig.5.2) and the main trap u'ith larger-diametertubingand largerstop- cocksthan are found in the working manifolds.

GENERATREFERENCES

l-hereare ntanygood books on (hescientific and technicalaspects of vacuunrand onlv a few arecited here.

Duschnran.S., 1962,Scientilic Foundutiorts ol VucuutttTechnique.2nd ed.. rev. by J. M. Lafferty et al., wiley. New York. Pumpsfor high vacuumand ultrahighvacuunl are discussedin some detail, and equationsfor the kinetic behaviorof gasesare presented. Holland, L. . w. steckelmacher,and J. Yarwood. 1974.vttcuurtt Msnuul, E. and F. N. Spon.Lon- don (in the U.S.: HalstedPress div. ofJohn Wiley & SonsInc.). A veryuseful general reference, coveringprinciples of gasflou, materialsof construction,sealants, and commercialequipment. Roth, A.. 1982,Vucuum Technologv,2nded., North-Holland,Amsterdam. This excellent,compre- hensivebook coverssintilar material lo the abovevolunres ancl it doesnot neglectrougn-vacuunr and high-vacuumregions. Wissfer,G L. and R. W. Carlson.Eds.. 1979,Vucuunt Science ond Technologv,Yol.l4 of Methods ol'ExperintentulPhvsics, L. Marton and c. Marton, Eds. Academic.Neu york. An excellent multiauthorvolume covering all ntajoraspects of vacuumtechnology. The emphasisis on physical applicationand ultrahigh vacuum, but there is plenty of useful informationfor chenrical applications.

O'Hanlon, J. F.. 1980,A lJsersGuide to VucuutttTechnologl,. Wiley, New York. This book is ori- entedsomewhat to semiconductorand opticsapplications. It hasvery useful sections on residual gas analysis. PRESSUREAND FLOW MEASUREMENTAND LEAKDETECTION

The measurenrentof pressuresis quite important in vacuum line rvork, where determinationsare performedroutinely in the medium- or high-vacuumrange to estimatethe initial vacuunrin a system,and in the l-760-torr rangeto mea- suregases which are being n-ranipulated.Flow measurementand control is commonly employedin catali.ticflow reactors,in reactorsfor the growth of electrical and opticalmaterials from gas-phasereagents, and in gaschromatographic analytical systems.Leak detectionis relatedto thesetopics and is of major inrpor- tance in troubleshootingvacuum and gas-handlingsystems. The implententa- tion of thesepressure and flow measurementsand techniquesfor leak testing will be coveredin this chapter.

7 ,4 MANoMETRY(.r-760 ToRR)

A. Melcuty Monomefels for Routine Work. The pressure-volume-temperaturemeasurement of gasesis the backboneof quantitativechemical vacuum line work. For thesemeasurements an error of a few percentis frequentlysuffi- cient and may be attained by a simple U-manometerattached to a calibrated volume and read with an "inexpensive"cathetometer. The manometersillustrated in Figs. 7.l and 7.2 are convenientfor use in conjunctionwith a chemicalvacuum system.The simple U-manometerin Fig. 7.1 minimizesthe amount of mercuryused and thereforeminimizes the massof the manometer.The bubbler manometerillustrated in Fie. 7.2 usesmore mer-

129 430 PRESSUREAND FLOWMEASUREMENT AND LEAKDETECTION

T I I

Co 420 mm

Copillory (o) (b)

Fig. 7.1. The dimensionsfor a U-manometer.(a) U-manometerbefore it is filled with mercury. The dimensionsshoun give a rangeof pressuresup to 1 atm. Usingcapillary tubing in the lowerpart of the manometerreduces the volumeof mercuryrequired. (ä) Mercury-filledU-manometer. The procedurefor filling the manometeris as follou's.First, triple-distilledmercury is filtered directly into the manometeruntil the mercurycolumn is about 425 mm high in both legs(i.e., about 5-10 mm abovethe union with the capillarytubing in the referenceleg). Both sidesof the manometerare then evacuatedand gently flame-dried.The evacuatedreference side is sealedoff at point A, and mercuryis forcedinto the smallupper U by pressurizingthe measuringarm. This traps anyresidual gasin the small upper chamber.To retainthis residualgas permanently, a vacuumis establishedin the referencearm by gentletapping or heatingat point B whileevacuating the measuringarm. This final processmay be repeatedon occasionto ensure a good referencevacuum. cury but providespressure release, and is thereforedesirable for applications whereexcess pressure might build up inadvertently,as, for example,in the introduction of gasesfrom a compressed-gascylinder or in chemicaloperations with low-boilingsolvents, such as liquid ammonia. Filling instructionsfor both manometersare given in their respectivefigure captions.Accurate manometry requires a clean mercury surface,so either manometershould be filled with freshly filtered triple-distilled mercury, and the interior of the manometer MANOMETRY(,|-760 TORR) ,134

Tovacuum line

- 850mm

spraytrap ano /'" atmosphere (orvacuum)

Fig.7.2. A versatilebubbler manometer.The bubbler manometeris securelymounted by the reservoirand attachedto the vacuunrsystem. It is then easilyfilled by the followingprocess. The levelof the bottom end of the verticaltube dipping into the reservoiris marked on the outsideof the reservoir. Next, a calculatedamount of mercuryis filtered into the reservoir.With the valvebetween the two arms open, a vacuum is s/ox'{t'drawn on the manometer. The mercury levelmust not drop belos' the mark on the reservoir,or elsebubbles u'ill enterthe verticaltube and shootnrercury through the vacuum system.If the mercury level in the reservoircomes close to the nrark, the manometeris brought up to atnlosphericpressure and more mercuryis added.When the properamount of mercury is presentin the fully evacuatedmanometer, the mercurylevel should be about 10mm abovethe mark on the reservoir,and the upper meniscusshould be in a regionof the manometersuitable for measurenlent.as illustrated. Once the manonleteris properly filled and evacuated.the valve is closedto isolatethe referencearm at hish vacuum.

should be clean and dust-free.The proportionsof thesemanometers and the amount of mercury should be arrangedsuch that pressuresfrom zero to somewhat over 760 torr can be spannedby the manometerwithout gas being forced around the bottom of the U-manometeror out of the bubbler on the bubbler manometer.To minimize errorsarising from capillarydepression, the two arms of the manometershould be of the samediameter in the regionof the menisci(a minimum internal diameterof 8 mm is preferable). 132 PRESSUREAND FLOWMEASUREMENT AND LEAKDETECTION

B. Monomeflic Meosulemenls. The ideal gas law is generally sufficiently accurateto measurethe amount of gas at the subatmosphericpressures encounteredin vacuum line work. When the gas is being measuredin a U-trap with an attachedmanometer, the volumeof the systemwill changewith pressure becauseof the varying heights of the mercury level. One way of avoidingthis complicationis to employ a manometerin which the mercury levelcan be adjusted to a fixed height in the measuringarm by introductionof mercuryfrom a reservoir.However, this is cumbersome,so the usual practiceis to calibrateone leg of a simple manometer(Fig. 7.1 or 7.2). This processhas beendescribed in Section5.3.H. To achieveacceptable errors arising from capillarydepression of the mercury, the manometerarms should be constructedfrom glasstubing having the same internal diameter, preferablynot lessthan 8 mm. When the interior surfaceof the manometeradsorbs vapors or becomesdirty, the meniscuson the exposed legof the manometeroften will not havethe sameheight as that on the reference side.lf this conditionarises and if smallpressures are being measured, it may be necessaryto make a capillarydepression correction as indicatedin the next section. Suchcorrections are unnecessaryin routine work (i.e., in the 100-700torr pressureregion) using a cleanmanometer. Ordinarily, the largesterror in manometerycomes in measuringthe differential mercurycolumn height. A cathetometer(Fig. 7.3), is routinelyused for this process,but a meter stick attachedto the manometerprovides sufficient accuracy for rough measurements.The cathetometerconsists of a telescopewith a crosshairwhich is alignedwith the top of the mercurymeniscus. This telescopeis mounted on a calibratedvertical scaleequipped with a supplementaryvernier scalefor accurateinterpolation of the readings.Before use, the cathetometer must be leveledso the travel of the telescopeis indeedvertical. Similarly, if a manometeris read by meansof an attachedmeter stick, the manometermust be strictlyvertical. This can be accomplishedat the time of constructionby usinga bubble levelor a plumb line. It is good practiceto mount all manometerson a true vertical. Whether the meniscusheight is measuredwith a cathetometeror a meter stick, it is important to have good illumination of the meniscusand to do the illumination in a consistentmanner throughout a setof measurements.A sheet of white paper behind the manometeroften providesgood definitionof the meniscus.Under many lighting conditions,illumination of this paper from behind may further improvethe visibility of the meniscus.

C. Monomelers fot High Acculocy Work. For a mercury manometer with one arm evacuated,the pressureis givenby P : hdg, whereä is the differencein the height of the mercury columns,d is the densityof mercury,and g is the accelerationdue to gravity. In the old setof pressureunits the pressurewas reportedin mm of Hg. This pressureunit wasdefined for mercuryat 0oC, where its densityis 13.5951g/cmr, and the accelerationdue to gravityirgo : 980.665 MANOMETRY(,r.760 TORR) 133

Focus odJUstment Level

Talcsaonp- -:--'- /'.reveilnq screw

vernlel

\_'rrne-oolusTmenT elevotionscrew

Colibrotrons

Levelrngscrews

Fig. 7.3. Cathetometer.This type of cathetometeris used in routine manometry. It is light in weightand may be movedeasily from one siteto the next. A sturdythree-legged platform *hich is the sanreheight as the vacuunrline bench nray be usedto bring th(}cathetometer to the properheight for the observationof manometerson the vacuum line.

cnl/sec2.More recently,the torr pressureunit has conle into wide use, and to within 7 x l0-l percentthe torr is equal to the mm of Hg. (Further definitions of the various pressureunits may be found in Appendix VI.) Precisework requires the correctionof the mercury height by a factor of g/gs (whereg is the local value for the accelerationdue to gravity), and a secondfactor oI dt/dy, which is the density of mercury at the measuringtemperature divided by the densityat 0oC. Valuesfor the ratio d,/ds aregiven in AppendixVI, and the local 434 PRESSUREAND FLOW MEASURFMENTAND LEAKDETECTION value of g/90 may be determined from the data given in the CRC Handbook oJ Chemistry and Physics. If the manometer arms are not of equal diameter or if their interior surfaces are coveredby different adsorbedmolecules, the menisciin the two arms will be different and a capillary depressionerror is introduced. The accuracyof this correctionis low. so it is best minimizedby employinglarge-bore tubing and the purest availablemercury. Despite these precautionsthe menisciare rarely of identicalheight. A table of capillarydepression corrections is givenin Appendix VI. Further discussionsof precisionmanometry are availablein the literature.r'2

D. Generol Propedies of Melcury. No other liquid rivals mercury as a general-purposemanometric liquid. However,mercury is not without its draw- backs: it is toxic, and it is attacked by strong oxidizing agentssuch as NO2, halogens,and oxidizing fluorides. In addition, it reactswith tin tetrachloride and with a few organometalliccompounds, such as dimethylcadmium.Mercury amalgamatesand appreciablydissolves many metals,such as the alkali and alkaline earth metals,Zn, Cd, Sn, Pb, Bi, Ga, Au, and Tl. Tracesof thesemetals influencethe surfacetension and glass-wettingtendency of mercury. Copper, Ag, Pt, and AI are somewhatless soluble, but they are solubleenough (about 10-3% by weight) so as to affect the surfacetension. Finally, there is a group composedmostly of transition metalsthat are quite insoluble(5 X 10-s% or less):Cr, Co, Fe, Mo, Ni, Sb, Ti, W, and V.r

E. Reducing Exposule lo Metcury. Elementalmercury vapor and dust of mercurycompounds are absorbedthrough the respiratorytract, skin, and diges- tive tract. The current acceptablethreshold level in the United Statesfor contin- uousexposure to mercuryin the air is 0.05 mg,/m3,which correspondsto a partial pressureof 4 X 10-6 torr. Sincethe vapor pressureof mercury is on the order of 2 X l0-3 torr at room temperature,it is clearthat an enclosed,poorly ventilatedroom containing exposedmercury would vastlyexceed the accepted limits. The hazardsof working with mercury are minimized by adopting good housekeepingpractices. The laboratoryshould be well ventilated,mercury ves- selsshould be closed,and spillsshould be thoroughlyand promptly cleanedup. After all traces of visible mercury have been picked up, the area of the spill shouldbe treatedwith zinc dust or charcoalwhich hasbeen treated with a solution of iodine. lt is particularlyundesirable to heat mercuryin the open, so care must be taken to clean it from glassapparatus before glassblowing and to keep mercury off warm surfaces,such as mechanicalpumps. Mercury dropletshave a greattendency to roll, making it difficult to cleanup

rG. W. Thonrpson.TechtiquesolOrganicChenristry,3rded.. Vol. I,I't. l, A. Weissberger,Ed.. Interscience(New York: 1959),p. 410. rA. F. Germann, J. Ph1,s.Chem., 19,437(1915). rP. Pascal,Ed... Nouveuu Truite de ChenrieMineraie. Vol. 5, (Paris:Mason et Cie, 1962),p. 5lOff. MANOMETRY(1.760 TORR) 135 spills. A vacuum pickup devicefor mercurycan be constructedfrom a vacuum filtration flask with its sidearmconnected to an aspirator,as illustratedin Fig. 7.4a. Another meansof picking up small globulesof mercuryis a spiral of copper wire, as shownin Fig. 7.4b. A varietyof mercurypickup devicesis available from laboratorysupply houses.

F. Cleoning Melcury. When it is received,mercury is generallycovered with a scum which can foul manometers,Toepler pumps, and similar apparatus. This scum can be removedby a simplefiltration procedure.A standard filter paper is folded to fit an appropriatefunnel and a pinhole is piercedin the tip. The hole must be large enoughso that mercury dropletswill run through, but smallenough so that the last drop and its associatedscum are retained by its surfacetension. This type of filtration processis routinelyperformed before filling an apparatus. Mercury that has been contaminatedby metallic impurities is cleanedby a nitric acid washto removemost electropositivemetals, and it is then distilledto

Sprrolof omolgomotedwire

Tovacuum source

(a)

Fig. 7.4. Mercury pickup devices.(a) Vacuum pickup device.Collected mercury is trapped in the flask for recyclingor disposal.(ä) Amalgamated copper wire pickup device.The wire is first cleaned in nitric acid, then dipped into a solutionof mercuric nitrate to give a thin coatingof mercury. Droplets of mercury readily cling to the spiral and may be shakenoff into a mercury wastecontainer. 136 PRESSUREAND FLOWMEASUREMENI ANO LEAK DETECTION

remove nonvolatileimpurities. These servicesare availablecommercially and thereforewill not be describedfurther.

G. Bourdon Gouges. As an alternativeto mercurymanometers there is a variety of gaugesbased on mechanicalor electricalpressure transducers. This sectionpresents a descriptionof purelymechanical gauges which still find usein this electronicage.a The metal Bourdon gauge(Fig. 7.5) is fashionedaround a semicircularthin-walled metal tube with mechanicallinkage to a pointer. Fused-quartzspiral gaugesare alsoavailable. In this case,a thin spiral is sensitive to a pressuredifferential, and the deflectionis balancedwith air pressurein the surroundingenvelope. The air pressureis then measuredwith a manometer.

H. Electronic Pressure Tlonsducers. Electronicpressure transducers equippedwith digital pressurereadout provide a convienientand fairly compact

Bourdontube

Closedend

Mechanicallink

AppliedIpressure

Fig. 7.5' A nretal Bourdon gauge.The thin Bourdon tube is sensitiveto the pressuredifferential betweenthe surroundingatmosphere and the gas containedwithin the tube. The tube deflectsan indicatingneedle u'hich allowsa direct pressuredetermination from the calibratedscale. rBourdon and spiral gaugeswith dial readoutare availablefrom Wallace& Tiernan, 25 Main St.. Belleville.NJ 07109.Warden quartz spiralgauges are availablefrom RuskaInstrument Corp., Box 36010, Houston, TX 77036;Texas InstrumentsInc., Display systems,Box 1444, Houston, TX 7700t. MEDTUM-AND H|GH-VACUUMMEASUREMENTS (10'1-,10-6 TORR) 137

methodfor pressuremeasurement in a varietyof environments.Although a wide variety of designsare available,the most common units are basedon capaci- tance or inductancedetection of the displacementof a diaphragm (Fig. 7.6).s The specificationson the gaugeshould be carefullymatched to the range and accuracywhich are required. Someattention must be paid to long-termdrift in the gauge,especially when the gaugeis exposedto changesin temperatureand mechanicalvibration. The portion of the gaugewhich is exposedto the gas can be made from a varietyof materials,includine fluorine-resistantmetals.

7 .2 MEDTuM-AND HtcH-vAcuuM MEAsuREMENTS (,to-''-.t0-6 ToRR)

Gaugeswhich are sensitivein this range are primarily usedto determineulti- mate vacuum on a systemand to hunt leaks.This pressurerange is measurable by a varietyof gaugetypes ranging from the manually operatedmercury-filred Mcleod gaugeto variouselectronic gauges.

A. Mcleod Gouges. This gauge providesa simple and reliable way of measuringpressures greater than l0 " torr. It works on the principle of conr- pressinga largevolume of low-pressuregas into a small volumewhere the pressure is great enoughto be measuredwith a mercurycolumn. Gas which is containedin the upperbulb of the gaugeillustrated in Fig. 7.7 is compressedinto the upperclosed-end capillary. and the heightdifferential between the mercury in this closedcapillary and an adjacentopen-end capillary is relatedto the origi-

Fig. 7.6. Electronicpressure transducer. This sensingunit is basedon the nreasurementof the capacitancebetueen the diaphragnrD and sensorsS. P, is the pressurebeing nreasuredand P" is a referencepressure which may be a high vacuum. iDiaphragnr gaugeswith digital readoutare availablefrom MKS lnstrunrentslnc.,22 Third Ave.. Burlington,MA 01803;Validyne Engineering Corp.,8626 wilbur Ave., Nonhridge,CA 9l32gl DatanretricsDressler Industries Inc.,340 Fordham Rd., Wilmington, MA 01887;Fluid precision. lnc., I l0 MiddlesexSt., Chelnrsford,MA 01863. 138 PRESSUREAND FLOW MEASUREMENTAND LEAKDETECTION

To vocuum 3ystam Ralcrence c0prllofy

6 Coprllory (r'lh ctoscd cnd) 8o

Arr ond YocuumInltl lor odiusfmGnt of mercury Hg rcservoir htrCht

Fig' 7'7' The Mcleod gauge.The principlesof operationfollou,. Let the unknou,npressure rn a svstenlbe P whenthe Hg levelis belou'point l. Let the volunreof the bulb and closedcapillary above I be V' uhich is knoun. When the mercury is allo*ed to rise past point l. the gas rs trapped and finally conlpressedinto the capillary. Supposethat u'henthe mercuryin the referencecapillary is at 0, the nrercur-yin the dead-ended capillarvis B mm belou 0 (i.e., the pressureof the conrpressedgas isB nlm)' Since the initial pressure-volumeproduct equals the final pressure-volumeproduct, pV = thevolumein the capirrary ,trr', r sill be the heightB timesthe areaof the L-apilaryborel. Thusp : 1tr/ v = B2(A/ w. Since,4 and v are knoun arrdB is nreasured,the originarpressure (p) ma1,be calculated'Most conrnrercial gaugesare provideduith a calibratedscale u.hich presents pressures directly' Alternatively,it is possible to dcvisea linear scalefor the Mcleod gauge. In one such nrethodthe nrercuryheight in the closedcapitary is aruaysadjusted to the sanlepoint (8,,),and (hen the differencein nreniscusheights betu.eenthe ts,o capillariesis nreasured(ÄB). For this casethe pressurebeing nreasured|e p : pt,niv : (BtiA/v)aB. As in the previousexampre. the quantity in parenthesesrepresents the gaugecalibration constant.

nal pressure in the vacuumsystem. Further detailson the operationof this gauge are explainedin the caption to Fig. 7.7. A cleangauge _ and pure mercury are essentiarfor reliableoperation because the presence of impurities causesmercury to cling to the capilrarywalls. This ntay lead to unreliablereadings and a tendencyfor the mercurycolumn to break up in the capillary' If the mercurycorumn in the capiilaryis bioken by gasbub- bles,the pressure readingsare highly inaccurate.In any case,the capilrarytub- ing is tapped to settlethe mercurybefore a pressuremeasurement is obtained.It is very important to run the mercury rntoothryinto the upper chamber. If the mercury surges into this chamber, it may break the apparatusand showerthe surrounding areawith mercury.The Mcleod gaugesintended for the high-vac- MEDIUM-AND HIGH-VACUUMMEASUREMENTS (,IO-1-,IO{ TORR) ,139 uum rangeare generally bulky and containa largequantity of mercury.Because of its mass,the gaugeis generallymounted on the benchof the vacuumline. The reservoiris well supportedby a cork ring and/ or plasterbase inside a pan which is deep enough to catch the mercury in the event of a mishap. The Mcleod gauge is not suitable for the determination of pressuresof easily condensedgases, such as water vapor, and it hasthe additionaldisadvantage of being slowand sometimesclumsy to operate.Because of this naturally slowre- sponse,the electronicvacuum gaugesare superiorfor tracing leaks. The tilting Mcleod gauge(Fig. 7.8) is a simple, inexpensive,and portable gaugewhich may be usedto measurepressures down to about 10-l torr. These gaugesare very useful for checking rough vacuum systems,Schlenk systems, and for the calibration of thermal conductivityvacuum gauges.

B. Thelmol Conduclivity Gouges. Includedin this categoryis a seriesof similar gaugeswhich go under a variety of names:Pirani, thermocouple,and thermistor gauges.These simple and relativelyinexpensive gauges contain a heatedelement, and the temperatureof that elementis detectedby meansof a thermocoupleor thermistor(Fig. 7.9). Direct readoutin pressureis providedby meansof a calibrateddial. It is commonfor theseunits to be calibratedover the 1-10-3-torr range;however, at either end of the scalethe readingsare approximate. A gaugeof this type is usefulfor measuringthe pressurein the antechamber of a glovebox, for monitoring the fore pump pressurein largevacuum sys-

Reference coprllory Reservoir

Copillory (wrthclosed end )

Fig. 7.8. Tilting McLeod gauge.The gaugerotates around the centersection. This centersection alsocontains a nipple (extendingout from the back of the drawing)which may be attachedto the vacuumsystem through a hose.For a morepermanent arrangement, the centersection is attachedto a vacuum line by meansof a standardtaper joint and the baseis discarded.Initially, the gaugeis rotated so that the mercuryruns into the reservoir.When pressureequilibrium is establishedwith the systembeing measured, the gauge is rotated back so that gas is compressedinto the dead-end capillary and the top of the mercury in the referencecapillary coincideswith the top end of the dead- end capillary.Generally, the gaugeis providedwith a scalewhich may be read directlyin terms of pressure.These gauges cover the medium-vacuumrange, but generallydo not extendinto the highvacuum region. 140 PRESSUREAND FLOWMEASUREMENT AND LEAKDETECTION

To vocuumsys'fem

Therm ocoupl e

To power mrcroomme.rer supply Filo me nl

Fig. 7.9. Sensingelement for the thermocouplevacuum gauge.The thermocoupleis in contact with a heatedfilament and measuresits temperature.A variant involvesa thermistorwhich serves both as a heatingand a sensingelement.

tems, and for chemicalvacuum systemsin which high vacuum is not required. The thermal conductivityof a gasis dependentnot only on the pressure,but also on the heat capacity, molecular weight, and accommodationcoefficient (efficiency of energy transfer with a surface) of the gas being measured. Further- more, the accommodationcoefficient will vary if the surfaceis coatedwith foreign matter. Therefore, these gaugesare generallynot suitable for accurate pressuremeasuren.rent, but this is of little consequencein their most frequent applicationas sensorsof the generaldegree of vacuum in a system. One of the most troublesomeaspects of the thermal conductivitygauges is the alteredresponse caused by the pyrolysisof thermally unstablemolecules on the hot sensingelement. To minimize this problem, the gaugeshould be turned off, or the sensingtube isolated,when thermally sensitivecompounds are handled. The calibrationof the gaugecan be checkedperiodically with a tilting Mcleod gaugeand the sensingtube replacedwhen the unit getsbadly out of calibration. The sensinghead is generallyconstructed from metal with a tube inlet. This sensormay be attachedto a glassvacuum systemby the useof vacuum wax to securethe inlet tube insidea glasstube on the vacuumsystem. To facilitatemak- ing a goodseal, the latter tube shouldhave an insidediameter just slightlylarger than the outsidediameter of the tube on the sensor.Often the tube on the sensor has pipe threadsand this may be attachedto a pipe thread-to-swageunion. As describedin Chapter8, a swagejoint fitted with a Teflon ferrulecan be attached to glasstubing of appropriatediameter.

C. lonizolion Gouges. This rather broad classof gaugesincludes cold- cathodeionization gauges (sometimes called Penning gauges) and thermionicor hot-cathodevacuunl gauges(one highly efficient versionis called the Bayard- Alpert gauge).These gauges are ntainly usedin the pressurerange below l0-l torr, and the thermionic gaugesextend into the ultrahigh vacuum range(10 r2 torr). The operationof thesegauges is basedon a common principle:the measurementof the positiveion current from gasmolecules which havebeen ionized by electronimpact. MEDIUM.AND HIGH.VACUUMMEASUREMENTS (.10.1-,I0-6 TORR) 441

In the cold-cathodegauge, a glow dischargeis initiatedby a very-high-voltage starting pulseand is maintainedby an appliedhigh voltage.A schematicof the sensinghead is shownin Fig. 7.10.A magneticfield is employedin this sensorto confinethe electronsto a spiral path and thus increasethe probability of colli- sionwith gasmolecules. The sensitivityto variousgases varies with the natureof the gas,with the sensitivityfor helium and hydrogenbeing low and that for mercury and polyatomicmolecules such as acetonebeing high. In its most common application,judging the initial degreeof evacuationof a system,the factor of 30 or so in sensitivityto variouscommon gasesis of little importance. The cold-cathodegauge is a good choicefor measuringthe initial vacuum in chemicalhigh-vacuum systems because the pressurerange is appropriateand the gauge is robust. Standard commercial units are availablefor measuring pressuresin the approximaterange of l0 2 to 10 7 torr, and the rangeof most interestfor syntheticchemical systemsextends from this upper limit to about 10-6 torr. The sensingelement collects debris from the fragmentaionof poly- atomic molecules,and thereforeit is necessaryto turn off the instrumentor isolate the sensingelement when significantpressures of polyatomicmolecules are present.Fortunately, the gaugeis tolerant to a fair amount of depositand the sensinghead can be cleanedby scrapingout or dissolvingthe deposits.The re-

Fig. 7.10. Cutawayof a cold cathode(Penning) gauge. The u ire anode(A) is connectedthrough a ceramicinsulator (l) to the high-voltagelead (H). Under the influenceof the magneticfield created b1'M, the elect(rnstravel a long spiral path bet$eenthe bodl'and the anode.The current, uhich arisesfrom clectronsand positivcions of the ionizedgas nroleculcs,is relatedto the pressure.The open end (C) is attachedto the vacuum system. 142 PRESSUREAND FLOWMEASUREMENT AND LEAKDETECTION sponseof the ionizationgauge is fast, which makesit an excellenttool for tracing leaks. The sensingelement for a cold-cathodegauge is generallycontained in either a glassor metal envelope.If a unit with a glassenvelope is used,it may be sealeddirectly to the vacuum systemand cut off from the systemwhen the time comesfor cleaning.Metal headsmay be waxedto a largetubular openingon the vacuum system,or attached by an O-ring joint, such as a Cajon Ultra-Torr union (seeSection 8.1.B). In the cold-cathode gauge a steady-stateconcentration of electronsis maintained by electronimpact on the moleculesbeing measured.By contrast,the primary source of electrons in hot-cathode gauges, such as the Bayard-Alpert gauge,is a hot filament. Theseelectrons are accelefatedtoward a positivegrid, and in this region moleculesare ionizedby electronimpact. The positivegrid collectsthe electronsand permits positiveions to passthrough to an electrode which is biasednegative with respectto the filament. This positiveion current is then relatedto pressure.These types of gaugeshave excellent high-vacuum sensitivity and are routinely used in high-vacuumand ultrahigh-vacuumsystems. For chemical systemswhere there may be a moderatelyhigh background of large molecules,the hot-filamentgauges are fairly readilyfouled, and if exposedto air the hot filament is burned out. For thesereasons, the hot-cathodegauge is preferred for clean,very-high-vacuum systems and is rarely usedfor vacuum lines primarily devotedto syntheses. Both the thermionic and cold-cathodegauges exert a significant pumping action on a vacuum systemdue to the breakdownand depositionof molecular ions createdby electronimpact. Thesegauges are pfone to degasdeposited material when turned off, or soon after they are turned on.

D. ReSidUol GOS AnOlyzerS. A residualgas analyzeris basicallya small mass spectrometerwhich provides a method of identifying the foreign gas in a vacuum chamber as well as judging its pressure.These devices are widely used on ultrahigh-vacuumapparatus to judge the nature of the backgroundgas and to detectthe sourceof contamination. They also are usedto diagnosethe performance of a variety of apparatus employedin modern thin-film researchand technology,such as vacuum evaporators,plasma etching devices, and the like. The residualgas analyzeris indespensablein the ultrahigh-vacuumapparatus employedfor the study of chemistryon singlecrystal surfaces, where the nature of contaminant gasesis important. This type of apparatusis also useful for studyingthe temperature-dependentdesorption of moleculesfrom surfaces,and to identify gaseousproducts in chemicaland catalyticsystems. Typical residualgas analyzersemploy electron impact to generateions and a quadrupole "mass filter" to obtain the mass-to-chargeratio of thesespecies. Massranges for theseanalyzers vary: 2-80 atomic massunits for small units; l- 500 on larger, more expensivegas analyzers.Electron impact ionizationof the gas is achieved using a hot filament as the source. Many instruments are equippedwith a secondfilament which can be switchedinto usein the eventof a failure of the first. When a robust detectorof moderatesensitivity is needed,a LEAKDETECTION 143

Faradaycup is usedto collections and thus providea direct measureof the ion current. For higher sensitivityand rapid response,an electronmultiplier detector is employed.In this devicethe acceleratedions impingeon a surfacewith the emissionof secondaryelectrons. These are multiplied by a cascadealong either a channelor set of plateshaving a large potentialgradient. The residualgas analyzer sensing head is generallysupplied on an ultrahigh- vacuumflange which can be readily accommodatedon most metal vacuum apparatus.

7 .3 LEAKDETEcnoN

A. Sflofegies. Leaks are a ubiquitousproblem with vacuum systems.They come in two varieties:real and virtual. A real leak involvesan opening in the vacuum chamber. Examplesare a pinhole or hairline crack in the glass,or a stopcockin which the greasehas channeled.Virtual leaks,on the other hand, are containedwithin the vacuum systemand might include such things as the outgassingof stopcockgrease or O-rings which have absorbedsolvent vapors. The walls of a glassapparatus present a large virtual leak as the moisture is desorbedfrom the freshly evacuatedapparatus. A knowledgeof the prior useof the apparatuswill often permit oneto spot a virtual leak. Alternatively,the outgassingof condensablematerials can be verifiedby coolinga sectionof the vacuum systemwith liquid nitrogen while the pressureis checkedwith a vacuum gauge.Another method of differentiatingreal and virtual leaksis to pump out the sectionto be tested,isolate the section,and measureand recordthe pressure asa function of time. The rateof pressurerise for a real leak is constant,whereas the virtual leak will tend to leveloff asthe effectivevapor pressure of the outgassing material is reached.The following sectionswill be devotedprimarily to the ddtectionof real leaks. It is important to conductthe searchfor leaksin a thorough and methodical fashion,as outlined in Table 7.1. The examplesgiven here are for a glasssystem with greasedstopcocks and joints, but the readershould have little difficulty in applyingthe samestrategy to other typesof apparatus.In many instancesthere may be a suspectsite which a quick checkwill revealto be the sourceof the leak. If, however,there is no obvioussource, a methodicalcheck should be inititated. For any system.the vacuumpump shouldbe checkedfirst to ensureit is deliver- ing the appropriatevacuum. In a typical preparativevacuunl system, stopcocks, valves,and joints are the most common sourcesof leaks.Freshly greased joints, particularly those which have been greasedtoo heavily, are likely to develop leakagepaths which generallytake the form of dendriticchannels. Old greased joints or those which have been subjectedto solventvapors may developleaks when turned, becausethe greasefilm is too thin. Theseleakage paths are generally evident in the form of fine striationswhich extendaround the diameterof the stopcockbut interconnectat variouspoints. Thus a visual inspectionof the greasedjoints and stopcocksmay turn up the sourceof the leak. Once a suspect 144 PRESSUREAND FLOWMEASUREMENT AND LEAKDETECTION

Toble7.'1. Summory of fhe Sfrofegyfor Locofingond ConfrollingLeoks

Prelintinun, Survevo.f \ra1t.t

Preliminaryvisual check of any greasedstopcocks and valves.(Look for striationsor channelsin the grease.)

Methodicul SeurchJor Leuk

I Checkpumping systemto be sureit is achievinga goodvacuum. If necessary,correct problem with fore pump, diffusion pump, or cold trap. z- Pump out entire systemand turn off stopcocksor valvesto isolateevery systent possible.

J. After a shortwait, opensection to the vacuumgauge and notewhether or not thereis a largepressure rise. A When a suspectsection is located,punrp it out, isolateit from the pump and measure the pressurerise at regular time increnrents.A steadypressure rise indicatesa real leak. A levelingoff of pressurerise with time indicatesa virtual leak. 5. Inspectgreased stopcocks and joints in the vicinityof the leak, and turn the stopcock or joint while noting the pressure.Run a Tesla coil over glass-blownjoints to locate pinholes. Inspect O-ring contact on glassware.Squirt CH,OH on suspectedparts while noting pressureon an ionizationgauge. Use a halogenor helium leak tester(a necessityon metal systenrs). 6. Cleansystem andlor bake it out if virtual leaksare indicated.

Fixittga Leuk l. Regreasefaulty stopcocksor joints. 2. CleanO-rings and/or replaceO-rings on leaky O-joints or valves. 3. Tighten Swagelokjoints or remakethe joint with new tubing and ferrules. 4. Troubleshootthe seat,packing, or bellowson metal valves. 5. Repair pinholesin glassor poorly weldedor brazed metal parts.

joint or stopcockis found, its potentialrole as a leakagesite can be checkedby rotating it slightlywhile checkingan electronicvacuum gauge for fluctuationsin the vacuum. Often O-ring joints or glassvalves containing O-ring sealsare potential sitesof leakage,but here the problem is more difficult to spot visually. If visual inspectionof the most suspectjoints or stopcocksfails to revealthe leak, a systematicisolation of parts of the vacuumsystem is in order. For a vacuum line of conventionaldesign (e.9., a line approximatingthat in Fig. 5.2), it is generallybest to turn off all stopcockswhich interconnectthe variousparts of the vacuum system.As a result, the high-vacuummanifold is isolatedfrom the pumps and the rest of the line, and it is checkedby determiningif there is a steadypressure rise in that section.If this sectionappears to be intact, but it LEAKDETECTION A AE.

doesnot pump down well when reopenedto the pumps, the vacuum sourcers suspect.In the eventthat the vacuumsource and main manifold are not at fault, eachsection of the vacuum systemis then openedto the high-vacuummanifold, with an eyeon the pressuregauge to indicatethe leaking section.Once the general region of the leak is identified, this part of the apparatusis thoroughly checkedto pinpoint the leak. A visual checkofjoints and stopcocksmay again be in order, or the searchmay be conductedwith one of the devicesmentioned below.

B. Leok Defecfion Using o Teslo Coil. Pinholesare a major sourceof leaks, particularly in newly constructedglassware. One of the common devices for locating theseleaks is the Tesla coil, which providesa high-voltage,high- frequencyspark dischargein air. The probe of the Tesla coil is touchedto the glass apparatus at various spots until a glow dischargeis initiated inside the vacuum chamber. The probe is then passedover the suspectparts of the glassware, and the presenceof a pinhole is revealedby an intenseblue spark which jumps through the hole. The Teslacoil shouldnever be usedaround thin glass, such as bread-seals,since it will puncture holesin the apparatus.Similarly. it may punctureO-ring materialsand generallyis not usefularound greased joints. The Tesla coil is also ineffectivearound metal parts, which simply serveas a ground. The color of the glow dischargeinside the apparatusis characteristicof the gasespresent and of somehelp in locatingthe leak. For example,if the atmospherein the vacuum systemis primarily ntercury,a light blue glow is seen;but if there is an air leak, the dischargetakes on a more purple color. When the pressurein the systemdrops below approximately10 3 torr, the glow discharge cannot be sustained,and this is sometimesuseful as a crude indicationof the degreeof vacuum.

C. [eok Defeclion Using Vocuum Gouges. Referencehas already been made to the use of an electronicvacuum gaugein hunting leaks. A cold- cathodegauge is particularly usefulbecause it has rapid responseand operates well in the presenceof small leaks. Becauseof this rapid response,acetone or methanolcan be squirtedon the suspectedarea. If a hole is present,a momen- tary pressuredrop will be observedbecause the acetoneor methanolmolecules are slowerthan air to diffuse through the hole. Sometimesa helium stream is directed on the suspectedleak; in this casea pressurerise is noted when the helium passesover the site of the leak, becausehelium diffusesmore rapidly than air. It also is sometimespossible to use a puttylike material, such as Apiezon Q, to covertemporarily a suspectedleak. If the leak path is tortuous, thesetechniques do not work rvell and a leak detectormay be more suitable.For example,leaks in swage-typefittings (Sec- tion 10.3.C)and valvesof varioustypes may be difficult to detectusing these methods. 146 PRESSUREAND FLOW MEASUREMENTAND LEAKDETECTION

D. Leok DelectionUsing Helium or HologenLeok Deteclors. Com- mercial leak testershave high sensitivityand are very useful with metal vacuum systems.Only two common types, one basedon halogenatedcompounds and one basedon helium, will be coveredhere. The halogenleak testeris widely usedin refrigerationapplications, but it is sufficiently sensitivefor many typesof chemical vacuum systems.The apparatus is filled with a halogenated hydrocarbon and the probe of the tester is passed over the suspectedarea. The gas that is collectedby the probe is passedover a hot platinum wire with the resultingformation of positiveions which are collectedand measuredwith a microammeter. Helium leak testershave far higher sensitivitythan thosebased on halogens. In this case,helium is detectedby a small massspectrometer set on mass4. In the leastsensitive mode the apparatusis filled with helium and the suspectsites are "sniffed" with a probe connectedto the vacuumchamber of the massdetector. In a more sensitivemode the leak detectoris connectedto the vacuum system often asthe solepump on the system.A streamof helium is then passedover the suspectsites for the leak. An audible and/or meter signalis usedto indicate the amount of helium reachingthe massdetector. Since the natural background at mass4 is very low, thesetesters can be highly sensitiveand very specificin pinpointing leaks.The helium leak testeris, however,fairly complexand expensive,since it includes,in addition to the mass spectrometer,a vacuum system completewith liquid nitrogen trap, diffusion pump, fore pump, and often a large roughing pump.

E. LeokDelecfion Using ResiduolGos Anolyzers. Theresidual gas analyzer,which has been describedin Section7 .2.D, is an excellentdevice for locating both virtual and real leaks. Most of theseinstruments can be scanned through the low molecularweight mass range. This massspectrum allows ready discrimination betweenvirtual leaks from solventsand the like, versusreal leaks,which show up with high peakscorresponding to the atmosphericgases. The locationof the specificsite of leakagemay be accomplishedby settingthe instrumenton mass4 and passinga smalljet of helium overthe suspectedareas.

7 .4 FLowMEAsUREMENT

When working with apparatussuch as catalyticflow reactors,the measurement and control of gas flow becomesas important as the measurementof pressure just describedfor vacuum line work. Some of the more common methodsfor measuringand controlling gas flow in gas-handlingsystems will now be discussed. Gas flow is usually quoted in terms of velocity(cmls) or "mass flow" (standard cm3/s).Velocity may be measuredby a venturi tube pointing into the flowing stream with a pressuretransducer or manometerconnected to the venturi tube. The two schemeswhich are more attractivefor small-scaleapparatus are FLOWMEASUREMENT 147 the rotameter, which is basedon a "float" which is bouyed by the stream of gas, and a variety of thermal methods based on thermal conductivity or heat capacity. The thermal methods are readily adapted to digital output and automatic flow control. Although the temperature of the operating sensorelement is not high (generallyunder 100"C), thermally sensitivecompounds can be pyrolyzed in this type of flow meter.

A. Flow Meosutemenl by Displocemenf. A variety of flow meter designsare basedon the positivedisplacement of a small amount of easilyvisual- ized materialwhich doesnot alter the flow rate. A simpleand easilyconstructed massflow meter of this type, the soap-film meter, is basedon timing the displacementof a soapfilm up a buret tube (Fig. 7.11). This type of flow meter is often placed at the exit of a gas chromatograph or small flow reactor. It is very

Buret

Rubberbulb

Fig. 7.11. Soap-filmflow meter. Soapsolution is pouredinto the rubber bulb so that the solution levelis just below the levelof the sidearm. After attachingthe flexible tubing to the flowing gas source,the rubber bulb is gentlysqueezed. This allowsthe flowinggas to percolatethrough the soap solution,picking up a thin film of soapwhich will travelup the buret. By notinghow longit takesfor the film to travel betweentwo points on the buret, the flow may be determined. 448 PRESSUREAND FLOWMEASUREMENT AND LEAKDETECTION usefulfor occasionalmeasurements. but cumbersomeif the flow must be monitored frequently.

B. Flow Meosutemenl by Orifice Areo. The simplestand most popular laboratorymass flow gaugeis the rotameter,which consistsof a float in a vertical taperedtube with the larger diameterat the top and the gas inlet at the bottom (Fig. 7.12).The float maintainsa constantpressure differential on the gasflow- ing past it, and asthe float rideshigher a largerannular opening is availablefor the gas. Graduationson the side of the glassor clear plastic taperedtube are thus relatedto the flow rate. Thesegraduations are calibratedfor a specificgas (often dry air); a calibration chart is neededfor other gases.The calibration of a rotameteris dependenton the pressurein the system.If true "massflow" (molar flow) is required, a pressurecorrection is necessary.

C. FlowMeosurement by PressureDrop ocross on Orifice. Another common schemefor the measurementof flow is basedon the determinationof the pressuredrop on either sideof a constriction,such as an orifice or venturi. Either a liquid-filled differentialmanometer or a pressuretransducer with asso- ciateddigital readoutmay be usedfor this pressuremeasurement. The flow rates determinedby these meters are in units such as cmr/s, and it is necessaryto make a correctionfor total pressureto convertthese to standardcm3/s or mol/s. A popular seriesof massflow metersis availablewhich is basedon the useof a thermal sensorin a side stream (Fig. 7.13). Generally,these flow metersare

Fig. 7.12. Rotameterflow meter.The ball is bouyedby gasflou up the conicaltube. A graduated scale is provided for visual measurementof the flow rate. FLOWCONTROL 149

Fig.7.l3. Schenraticof a massflow nleter.The flos'is proportionalto (2, - I,) I. This t1'peof nreteris often employedin an electricallycontrolled flou'regulator. Z, and T, are tenrperatur!'sen- sors:Hisxheater.

suppliedwith a digital readoutcalibrated for the massflow of one specificgas. Thermally sensitivecompounds may be pyrolyzedon the therrnalelement, and the small sensorchannel can be blocked by the decompositionproducts. The calibration on thesemeters is dependenton the heat capacityof the gas being handled and, to a somewhatlesser extent, on the viscosityof the gas. The calibration factor can be electronicallvaltered for conveniencein handlinedifferent gases.6

7 ,5 FLowcoNrRoL

A. Flow Confrolwifhoul Feedbock. Flowcan be controlledby meansof a needlevalve ifthe pressuredrop acrossthe valveis constant.The pressureon the upstreamside often can be held constantwith a single-or two-stagemechanical diaphragm regulator(Section 10. l.B). If the streamof gasdoes not experi- encea variableconstriction after the needlevalve, the abovecombination provides a simple and convenientmeans of providing a steadyflow. Often an arrangementsuch as this is usedin conjunctionwith a rotameteror electronic massflow meter(Fig. 7.14). i'Flo*'nretersbased on thernralsensors and electronicflos'controllers arc availablefrom the following companies:MKS and Datanletrics,listed in footnote5: BrooksInstruments Div., EmersonElec- tric Co.,407 W. Vine St., Hatfield, PA 19440;Teledyne Hastings-Raydist. Hampton, VA 23661: Tylan lnc.. 23301S. Wilmington Ave., Carson,CA 90745;Unit InstrumenlsInc., 1140E. Valencia Dr.. Fullerton.CA 92631. 4(n PRESSUREAND FLOWMEASUREMENT AND LEAKDETECTION

Fig. 7.14. Combination of t\r'o-stagepressure regulator (P), shutoff valve(S), flow control valve (F), and rotameter(R). O is the qasoutlet.

D. Flow Confrol wifh Feedbock. More positivefeedback control of the flow rate is neededfor applicationssuch as flow reactorsfor the epitaxialdeposi- tion of semiconductorfilms, and catalltic flow reactors.Several electronic flow controllersare available.One of the most commonly usedversions is basedon the massflow meterwith a thermal sensingelement, mentioned above, and feed- back control to a valve,which typicallyis either actuatedthermally or magneti- cally.bSome of thesevalves have rather small orificeswhich can be cloggedby the decompositionof reactivemolecules, for exampleSiHa and Ga(CH:):, which may react with traces of oxygen. As with the flow metersbased on the same principle, thesecontrollers regulate the molar flow, independentof total pressure. A calibration factor is necessaryfor differentgases. but this can be determined from the ratio of heat capacitiesfor gasesof similar nature. A large changein the characterof the the gas-say, hydrogenin place of nitrogen- requiresexperimenta.l recalibration.

GENERALREFERENCES

Benedict,R. P., 1984,Funduntentals ol Tentperaturt',Pressttre, and Flou'Meusuremt'nts.3rded., Wile1. Neu'York. Part Il of this book. entitled"Pressure and Its Measurement,"presents an excellentovervieu of the conceptand standardsof Dressure,and the use of mechanicaland GENERALREFERENCES 45.1

electronic transducers to measure pressure. "Flow and Its Measurement" is reviewedin Part III, includingchapters on the conceptof flow rateand theoreticalrates for constant-densityand compressiblefluids in closed-channelfiow. Introduction to Helfun Mass SpectrometerLeqk Detection,l980, Varian Associates,Palo Alto. This referencepresents a good overviewof the fundamentals and methods of leak detection, followed by a detailed discussionof the helium leak detector. Leak DetectorManual, 1981,General Electric Co., Lynn, Mass. The manual focuseson halogen leak detector methods developedby this company. O'Hanfon, J. F., 1980, A Users Guide to Vacuum Technologt,,Wiley, New York. This book is a good sourceof information on vacuum gaugesand residual gas analyzers. Thompson,G. W., 1959.Techniqueso.f OrgunicChemistry. Vol. l. Part l,3rded., A. Weissberger, Ed.. lnterscience.New York. JOINTS,STOPCOCKS, AND VALVES

This chapter describesthe various stopcocks,valves, and joints used in glass vacuum and inert-atmospheresystems. Although greasedstopcocks and joints are familiar and straightforwardin design,their use on high-vacuumsystems requiresmore than the usual amount of attentionto detail. The newerO-ring- sealedjoints and valves,which are taking the place of greasedstopcocks and joints in many applications,are also discussedhere. Metal bellowsvalves are more leak-tightthan glassvalves or stopcocks,but their useon glassapparatus requiresspecial designs which are outlined at the end of this chapter.

8.'l JorNrs

A. Slondold Toper ond Boll Joints. Thesejoints (Fig. 8.1) have been usedfor many yearson vacuumand inert-atmospheresystems, and the availability of a varietyof syntheticgreases and waxeshas extendedtheir utility. Of the two, the ball-and-socketjoint permits more flexibility in the orientationof the two halves.When this flexibility is important, this type of joint is obviouslyto be preferred, even though the ball joint is somewhat more prone to leak than a standardtaper joint. Both metal ball joints and metal standardtaper joints are available,rand theseitems provideone meansof joining metal and glassapparatus,

rMetal ball joints, metal standard taper joints, and O-ring joints with a step tooled into the groove are availablefrom Kontes Glass Co., P.O. Box 729, Vineland, NJ 08360.The first two items are also availablefrom Ace GlassCo., P.O. Box 688. Vineland, NJ 08360.

,52 JOINTS 153

R rdn ik PT mma V,,lBmm=\ l.+ Ffl '+ommfr9mm-l-r-'i I )r (l- tl 1l r\l 6 ß 5 24/40 J 1Bl9

Fig. 8.1. Standardtaper (3) and sphericaljoint ($ ). When the joints are lubricatedwith grease, theymust generallybe held together.Springs or rubber bandsare frequently entployed on standard taperjoints, while a spring-loadedclamp (illustratedhere) or a screwclamp (illustrated in Fig. 8.3) is usedwith ball joints. The method usedfor specifyingjoint sizesin the United Statesis illustrated. and it is describedin detail in National Bureauof Standards,Commercial Standard CS 2l-39.

Teflon sleevesare availablewhich may be usedto replacegrease as a sealing agentin standardtaperjoints. Thesesleeves are usefulon still pots and in other harsh but not highly demanding situations;however, it has been the authors' experiencethat they are not suitablefor high-vacuumapplications or in situations requiring very good exclusionof the atmosphere.To achievegood vacuum- tight performance with standard taper joints, the greasemay be applied in several thin stripeswhich run parallel to the directionof the male joint (Fig. 8.2). The joint is then worked togetherwith an oscillatingmotion which squeezesout the pocketsof air and leads to a thin, uniform film. Good-quality stopcock greasecontaining a minimum of volatilesand uncontaminatedby dirt or dust is essential,because volatiles outgas badly and particlesinterrupt the film and produce leaks. The film of greasemust be thin becausethe pressuredifferential acrossthe joint will pull channelsin a thick film. Siliconeand hydrocarbon greasesare the most popular; the chemicaland physicalcharacteristics of these and other common greasesare given in Table 8.1. In general,stopcocks which havebeen disassembled should be cleanedthor- oughly before they are regreasedand reassembled.Hydrocarbon solventswill removemost greases.When the glasswareis being cleanedrigorously, hydrocarbon residuescan be removed in an acid-dichromatecleaning bath. Residues from silicone stopcock greaseare much more tenacious.Thin films of such residues can be removedby meansof alcoholic KOH (methanol nearly saturated with KOH). Ground-glassitems, and particularlyfritted items, should not be left in the alcoholic KOH bath for extendedperiods, sincethis cleaning solution slowlyetches glass. When a joint is only occasionallyopened and flexibility at the joint is not ^qA JOINTS,STOPCOCKS, AND VALVES

Fig. 8.2. Applicationof greaseto joints and stopcocks.(a) Greaseis appliedin severalthin stripes tr'hichrun parallelto the directionof the malejoint. A woodensplint mav be usedto applythe grease to avoid contamination by moisture or dust on fingers. (ä) The joint is worked together with an oscillatingmotion and slight steadypressure. needed,it is generallypreferable to use wax insteadof grease.Wax makes a much more permanentjoint than greasebecause it doesnot flow out of the joint and is somewhat less sensitiveto solvent vapors. Two excellent waxes are Apiezon W, a black hydrocarbonwax, and Kel-F 200, a colorlesschlorofluoro- carbon of low vapor pressureand good resistanceto chemicalattack. The characteristicsof thesewaxes are given in Table 8.2. Both halvesof the joint are heatedto somewhatabove the melting point of the wax usinga small gasburner flame or heat gun. A stick of the wax may then be rubbed on the male joint, preferably in stripes as describedabove. The two warm parts are joined and the wax is worked into a uniform film by oscillatingthe joints and pushingthe two parts together.usually with additionalheating of the outerjoint. Temperatures well abovethe melting point causebreakdown of the wax; this is particularlytrue of DeKhotinsky-typewaxes, which polymerizewhen heated too strongly. To open a waxedjoint, it is heateduniformly and gentlyto just abovethe melting point and disassembled.It is most satisfactoryto cleanoff old wax with the appropriate solventand apply fresh material beforethe joint is reassembled.

B. O-Ring Joinfs. The major difficulty with greasedand waxedjoints is their failure to hold vacuumwhen exposed to solvents,heat, and somechemicals. For many applicationsO-joints overcomethese limitations. A successfulglass O- ring joint which is in wide useis illustratedin Fig. 8.3, whereit may be seenthat both halvesof the joint are identical. They mate with an O-ring fitted into a groove,and the two parts are held in placewith a clamp. The two halvesof these Toble8.'1 . SomeCommon Greosesfor Vocuum Apporolus

Approximate Vapor Resistance Pressure Approximate to Organic (nrm,at Usable Solvent Brand and Type room temp.) Application Range("C) Vapors ChemicallyAttacked by

Hydrocarbons Apiezon L l0-r0 Ground joints Max. 30 Poor Reactivehalides such as Apiezon M l0 7 Ground joints Max. 30 Poor BCl.1,and very strong ApiezonN l0 6 Stopcocksand joints Max. 30 Poor oxidizingagents such as Ol ApiezonT l0 ö Stopcocksand joints Max. I l0 Poor

Halocarbon 25-55 < l0 '" Stopcocksand joints Max. ca. 30 Poor Strongreducing agents such as alkali metals,and strong nucleophilessuch as alkyl phosphines

Silicone 6 -20to Dow Corning Hy Vac < l0 Stopcocksand joints Ca. > Fair Tends to cake after long 100 exposureto NH.1gas Reactivemetalloid fluorides like BF.

"Man-ysamples of this greasecontains some low-nlrlccular-weight volatrtes and silicagel. HalocarbonProducts, 82 BurlewsCourt, Hackensack,NJ 07601.

(rr atr ,156 JOINTS.STOPCOCKS. AND VALVES

Toble8.2. SomeCommon flord Woxeslor Vocuum Apporolus

Approximate Maximum Temperature UsableTemp. for Application Resistanceto Organic Brand and Type ("c) ('c) Solvents

Apiezon W' 80 100 Hydrocarbons and nonpolar (hydrocarbon) solvents-poor Lower alcohols-good

Sealstixä 100 140 Hydrocarbons-good (improved Alcohols,acetone, ethyl DeKhotinsky) acetate,and dioxane-poor Kel-F20tr 40 90 Hydrocarbons and nonpolar solvents-poor Lower alcohols-good

'Available from most scientific suppliers. 6CentralScientific Co., Chicago,IL, and many other scientificsuppliers. 'Minnesota Mining and Manufacturing Co., St. Paul, MN.

'---.\- O E+ffi tol #

ta,<---:r I (öne) tlll qv il (c) il( )

Fig. 8.3. Cross-sectionof a Urry-type glassO- ring joint and two types of screwclamps. (c ) An O- ring. (ä) Crosssection of a Urry-type O-joint. Note the ridge which is tooled into the groove.(c) Two typesof joint clamps. The upper one is manufacturedby A. H. Thomas Co.. Philadelphia,PA 19r05.

O-ring joints are identical, which givesflexibility in apparatusdesign and use. Although thesejoints are nominally standardizedso thosemade by the various manufacturerswill take the samesize O-rings and clamps,there are important differencesin the way the O-ring grooveis tooled. Somecommercially available O-ring joints have a groovefor the O-ring which has a simple rounded cross section.This type of joint is much more prone to leak than joints made with a JOINTS 4F'7

ridgeor steptooled into the the O-ring groove.rThe stepor ridgeprovides higher pressureon the O-ring and thus givesa better sealthan the designsin which the pressureis distributed more uniformly over the groove. SinceO-rings are manufactured from elastomericmaterials, they are subjectto the absorptionof solventswith attendantswelling. In addition to the undesirablechanges in dimen- sionsthis causes,swelling also leadsto a lossin strengthand, in extremecases, disintegrationof the O-ring may result.The problemis considerablyless serious than for greasesand waxes,and it is often possibleto choosean O-ring material which is only slightlyaffected by the solventsor chemicalsbeing handled. To aid in this selectiona summary of elastomerproperties is given in Table 8.3, and a moreextensive discussion of elastomersis givenin Appendix III. The bulk of the laboratoryapplications is servedby two typesof O-ring materials:hydrocarbon rubbers, such as ethylene-propylenerubber or butyl rubber, and halocarbon rubber, such as Viton. The former withstandspolar solventsand strongreducing agents,whereas the latter holds up to nonpolar solvents,oxidizing agents, and Lewis acids. Teflon O-rings and Teflon-coatedO-rings are available,but most of theseare not sufficientlycompliant to providereliable leak-tight seals. The Solv-Sealis a variant on the aboveO-joint designwhich reducescontact of the O-ring with solvents.2As illustratedin Fig. 8.4, thisjoint consistsof a pair of O-rings fitted to the outside of a Teflon cylinder and a pair of glassjoints which mate with this seal.The cylinderfits insidethe glassparts and the parts are clampedtogether with a standardcompression clamp of the type illustrated in Fig. 8.3. The vacuum sealis made at the concentricO-rings, but the support- ing Teflon cylinder also mates with the glass parts sufficiently well to reduce contactbetween the O-rings and solvents.As with the standardO-ring joint describedabove, the symmetryof the two halvesof the Solv-Sealjoint and the ability to positivelyclanrp the two halvestogether make thesejoints especiallyversa- tile. Both types of O-ring joint are very useful in the Schlenk-type inert-atmosphereglassware (see Chapter 1), and on high-vacuumsystems in which organic solventsare handled extensively. There is a varietyof O-ring fittings which attach to straightglass tubes (Fig. 8.5). The outer body of thesefittings is constructedfrom metal or plastic and containsa threadednut which either directlyor indirectlycompresses an O-ring betweenthe outer wall of a tube and the inner wall of the fitting.r Thesefittings providegood vacuum-tightperformance and are especiallyuseful for attaching NMR tubes and storagetubes to a vacuum systemso they may be sealedoff. They are alsoconvenient for joining metal and glasstubing and find application in situationswhere the two parts of an apparatusmust rotate while a leak-tight sealis maintained(for example.the vacuum line filtration apparatusdescribed

2Solv-seals areavailable from Fischerand PorterCo. , Lab-CrestDiv.. CountyLine Road,Warminsi- ter. PA 18974. yfhe concentric O-ring fittings are available from Crawford Fitting Co., 29500 Solon Rd., Solon, OH 44139(under the trade name of Cajon Ultra-Torr fittings);and Kontes GlassCo. (addressin footnote l: items K-179900and K-179910). (rl @

Ioble 8.3. Properfiesof some Eloslomerso'D

SolventSensitivity ChemicalReactivity Approximate" Usable Polar Chlorinated Strong Strong Covalent Conc. Temp. Elastomers Hydrocarbons Organics Alcohols Hydrocarbons Oxidants Reductants Halides Sulfuric Range("C)

Butyl Rubber P,P F,G,P,F.F G,F P P,F G,P F -54, 150" Buna N G,P P,P,P.P,P G,G FtoP P,P G,P P -54, 120' EPR P,P F,G,P,F,F G,F P P,F G G,P F -54, t50' Chloroprene F-,P P,P,F,P,P G,F P P,P P,P P -54, 150' Silicone P,P P,P,P,F,P F,F P P,F F,- P -80,230' Vitono G,G P,P,P,P,P G,G G G,G ; G,G G -50, 300' Solvent code/ 1.2 3,4,5,6,7 8,9 l0,ll t2 r3,14

"G : Good, F : Fair, P : Poor. All ratings are for room temperature. 'Adapted in part from data supplied by E. L duPont and by Parker Seal Co. 'For the dry O-ring in air. The low-temperaturelimits are only attainablewith specialformulations. rl, rr-hexanel2. bcnzene;3, pyridine;4. acctone;5, diethylether; 6, ethyl acetatc;7, nitromethane;8, nrethylalcohol; 9, r-hexyl alcohol;10, bromine; I l, 509o chromic acid; 12. Na in liq. NH,; 13, stannicchloride: 14, sulfur chloride. Fig' E.4. Solv-sealjoint' A pair of o-rings form the seal between the Teflon cylinder and glass joints. The cylinderfits inside the glassparts. A compressionclamp (seefig. g.Jc) holds the joint tpgether.

t)loss or met0t ?uDlng

(b)

Fig. 8.5. A cutaway illustration of O-ring coupling devices.(a.) The body and knurled nuts are made of metal (cajon union). (b). Body and compressionnuts made of plastic (Kontes).

{59 160 JOINTS,STOPCOCKS, AND VALVES in Chapter 9). Fittings such as the Cajon Ultra-Torr require tubing of closely matching diameter. Still another O-ring joint design is based on a glassfitting with an inner threada(Fig 8.6).

C. Swoge-Type Fitlings. Thesefittings are widely usedfor joining metal tubing, but they can alsobe usedwith glasstubing. Swagejoints are describedin detail in Section10.3.C, which should be consultedfor details. Although thesefittings are used successfullyfor glass-to-glassseals, the aforementioned O-ring joints are generallymore satisfactorybecause they are easierto tighten and lesslikely to lead to stresson the glasswhen they are installed.The major applicationof swage-typefittings is in joining metal and glassparts: for example, to attach a metal gas deliveryline to a glassapparatus, or to attach metal valvesto a glasssystem. A taperedTeflon ferrule is usedto form the sealbetween the fitting and the glasstube. Sincethe complianceof this ferrule is not great, it is essentialto usea ferrule of the correctdimensions to match the glasstubing. This may require the use of medium-walledtubing, which is sized in English units, to mate the standard swagejoints, which are generallysupplied with di- mensionsin Englishunits. It is alsopossible to obtain fittings and ferrulesmade to metric dimensionsswhich will mate directly with the appropriate-sizestan-

Bushing

Threadedglass

O-ring

Fig. E.6. Ace threaded connector. This connectorprovides an O-ring sealbetween a threadedglass tube and an inner tube which may be glass,plastic, or metal. aThreaded O-ring connectorsare available from Ace Glass Co. (addressin footnote l). sSwage-type fittings to metric and English dimensionsare availablefrom Crawford Fitting Co. under the trade name Swagelok(address in footnote 3). sToPcocKs 461 dard walled glasstubing, which is also made to metric dimensions.To avoid cutting the ferrule or crackingthe glasstube insidethe swagefitting, it is bestto finish the glasstube with a cleancut perpendicularto the tube axis, and to remove the sharp edge with very light sanding or a very light fire polish. Because Teflon tends to cold flow, it is sometimesnecessary to retightenthese joints.

8,2 sToPcocKs

A. Vocuum Sfopcocks. The proper selectionand maintainanceof stopcocks is important becausethey are a primary sourceof leaks in vacuum or inertatmosphere systems.Close tolerances are necessary,and therefore most highvacuum stopcockshave the plug and shell individually lapped together and numberedto avoid mismatch. Hollow-plugvacuum stopcocksseem to give the best performance. The common patterns for such stopcocksare shown in Fig. 8.7. For thoseshown in Fig. 8.7a through 8.7d, the plug is held in the stopcock by the vacuum on the back side of the stopcock,thus reducingleakage. These types of stopcocks are only useful on vacuum systems.It is important to avoid

Fig. 8.7. Hollow-plug vacuum stopcocks.The hollow plug is firmly seatedin types (a), (ä), and (c) as long as the lower section is at reduced pressure.Stopcock (d) has a hollow plug with an oblique tube in the center; when the plug is turned by 180", the lower section may be evacuated. Subse- quently, only occasionalevacuation of the vacuum cup is necessary.Type (e) doesnot have provision for evacuationof the plug and is therefore more liable to leak. Prolonged exposureof any of these stopcocksto solvent vapors erodesthe greaseand introduces leaks. (Adapted from Catalog C-64, Eck and Krebs Co., Long Island City, NY lll0l.) 162 JOINTS,STOPCOCKS, AND VALVES pressurizingthese stopcocks, because the plug is then loosenedand in an extreme casecan becomea projectile.It shouldbe noted that the vacuumcup on the stopcockillustrated in Fig. 8.7d can only be evacuatedthrough the lower sidearm.This factor requiresthat the stopcockbe orientedwith that arm pointing toward the sourceof vacuum. Proper application of greaseis evenmore important with stopcocksthan with joints, becausestopcocks generally have shorter leakage paths than dojoints and the frequent actuationof the stopcockresults in a more demandingsituation. The barrel and plug shouldbe cleanand lint free. Four even,longitudinal stripes of greaseare appliedto the plug and it is insertedin the openposition (Fig. 8.2). By applicationof pressureand small oscillationsto the plug, the greaseshould form a continuousthin film. Large stopcocksmay requireevacuation to achieve a continuousfilm of grease.Permanent striations running around the stopcock and barrel may be due to minute particles of dirt or uneven or insufficient grease.For a reliable, vacuum-tight seal these striationsmust be eliminated; however,one must avoid the temptation to solvethis problem by the useof ex- cessgrease. NOTE: If a stopcock is greased too heavily, the greaseextrudes into the orifice and clogs the opening. Furthermore, the thick film of grease will break down under vacuum by the formation of channels.A guide to the choiceof the optimum stopcockgrease is given in Table 8.1. It is bestto evacuatea freshlygreased system at leastseveral hours before it is to be used and to work in the stopcocksby occasionallyturning them. When high vacuum is required, it is usuallyadvantageous to evacuatethe systemover- night and to flame the glass,exclusive of stopcocksand joints, to desorbmois- ture. It is important to minimize the exposureof stopcocksand valvesto volatile organicsolvents at room temperaturebecause the vaporsdissolve in the stopcock grease.The presenceof solventvapors acceleratesthe tendencyfor stopcock greaseto be squeezedout of the stopcock;and on long standingin the presence of solventvapors, the stopcockgrease will literally washout of the joint or stopcock. Once the greasehas absorbedsolvent vapors, high vacuum may be unat- tainablebecause the solventvapors outgas for a long time. When the greasefilm has becomeextremely thin, either by the influenceof long standingor of solvents,the leak-freeoperation of the stopcockwill be impaired. This is generallyevident by the appearanceof striationsin the stopcock greaseor by the suddencloudy appearance of the greasefilm when the stopcock is turned. In this event,thorough cleaning and regreasingare in order. When the greasebecomes too thin, it is possiblefor the stopcockto stick in the shell. A seizedstopcock can be freed by heatingthe shellwith an air-gasflame and pulling the plug out with a twistingmotion. This operationshould be carriedout in a smooth, rapid sequence.A bushy medium- hot flame is usedand the stopcock shell is heatedevenly for perhaps 15 seconds.The shell is graspedwith a cloth towel or glovedhand to stabilizeit and the plug is simultaneouslyturned and pulled out with the other hand. As describedfor joints in Section8.1.A, stopcocksshould be thoroughlycleaned before they are regreasedand reassembled. SIOPCOCKS 163

B. Lopping Slopcocks. Even though commercialvacuum stopcocksmay be lappedby the manufacturer,it is occasionallynecessary to repeatthe process in the laboratory. A stopcock for which a striation-free film of greasecannot be attained, or one in which the greaseconsistently fails prematurely,are candi- datesfor relapping.In the extremecase, a poorlymatching plug and shellwill be evidentfrom a tendencyfor the plug to bind when it is turned. Sometimesstop- cocksdistort when they go through an annealingoven, and this is veryoften the casewhen a repair is madevery close to the stopcock.Finally, if onemember of a lappedpair is broken, the substitutepart will haveto be lappedwith the remaining part. Before the operation is started, greasemust be thoroughly removed from both parts, not only on the mating surfacesbut also in the orifices. To provide an indication of the progressof the grinding operation,the plug and barrel are both marked with four or more pencil lines running the length of the ground glass. If the stopcockis badly warped, it is necessaryto start with coarsegrit, such as 1SO-meshcorundum. A small portion of grit is madeinto a pastewith glycerin or a 50-50 mixture of waterand glycerin.This thin pasteis appliedto the plug in a smooth,even layer. The glycerinis not essential,but it is highly recommended becauseit reducesthe tendencyfor the parts to seize.The two parts are ground togetherby an oscillatingmotion; the plug is then removed,turned by about one-fourthof a revolution,and replaced.The grinding is continuedwith careto replenishthe grit and lubricant before the plug becomesdry. If the parts become dry or areforced, the plug may seizein the shelland ruin thejob. Progressof the rough lapping should be followed by noting the disappearanceof the pencil marks. Excessivegrinding with the coarsegrit must be avoidedbecause this causesa mismatch of the orificesin the plug with thosein the shell. When the rough grinding is complete,the parts are washedthoroughly to removethe last tracesof grit, and the roughnessof the surfacesis reducedby repeatingthe pro- cessusing a fine grit and the water-glycerinlubricant. Either 600-meshcorundum or abrasivepolishing alumina is satisfactoryfor the finishing operation. The latter has the advantagethat it can be removedeasily and thoroughlyfrom the apparatusby a quick sodium hydroxiderinse followed by water and acid rinses.

C. Slopcocks fol Plessure ond Vocuum. In a typical Schlenksystem, the apparatusis repeatedlyexposed to a small positivepressure and to vacuum. This causesstopcocks to become dislodged; therefore, satisfactoryperformance requiresgood stopcockretainers. An excellentretainer designis illustratedin Fig. 8.8. This particular retainer requiresthe useof the stopcockproduced by the samemanufacturer.b

6An excellent stopcock and retainer design for use with Schlenk systemsis available front Kontes GlassCo. (addressin footnote1). 464 JOINTS.STOPCOCKS. AND VALVES

tI r--=+/___ tl tl /\ e-F E*\ ffiffi \o.,.ing ffi g 4 I

(b)

Fig. 8.8. Retainer stopcocksfor vacuum and pressure.This style of stopcock(Kontes Inc.) is especially useful on a Schlenk manifold where both vacuum and small positivepressures of inert gas are used.(a) The retaineris beingsnapped onto the baseof the stopcockplug. (ä) The knurled nut has beentightened to hold the plug in place.

D. Metering wilh Sfopcocks. Stopcocksare not very satisfactoryfor regu- lating the flow of gases,but improved flow control can be achievedby notching the orificeson the plug, as illustratedin Fig. 8.9. This is accomplishedby drawing the corner of a three-corneredfile acrossthe orifice in the direction which is at right anglesto the plug.

8.3 vALVES

A. Gloss Volves. A few of the manydifferent styles of glassvalves on the marketare illustrated in Fig. 8.10.The generaldesign consists of a glassbody housingeither a glassor plastic(Teflon or Kel-F)stem. When the stemis con-

Fig. E.9. Notched stopcock plug. A triangular file drawn acrossthe orifice at right anglesto the length of the plug will notch the orifice. This may then be used to better control gas flow, such as an inert-gasflow while working on a Schlenkmanifold. VALVES 165

Teflonstem O-ring

Glossbody ond seol

(o)

(b)

Fig. E.10. Teflon-glassvalves. A number of variantsof this basicdesign are on the market. A "straight through" flow pattern shownhere for valve(a); (b) is a "right-angled" design.Type (a) usesa threadedTeflon stemu'orking in a threadedglass body. ln type( b) the stemdoes not rotate, so when the cap and Teflon nut are turned, the stem is forcedup or down. Both stylesare available with an O-ring on the tip of the stem. Also, somemanufactures offer extendedtips, shownin (o), which permit gas flow control. (lllustration ( b) reproducedby permissionof the copyrightowner, Kontes Inc.)

structedfrom Teflon, a directTeflon-to-glass seal provides good gas cutoff at the seat.The sealbetween the glasshousing and the stemis generallyachieved with O-rings, although there are at leasttwo designson the market (Quick-Fit and Young) in which the sealis Teflon-to-glass.Although they are generallynot as leak-tight as conventionalstopcocks, these grease-free valves have the tremendous advantagethat they may be usedin the presenceof liquid solventsor with solventvapors close to their condensationtemperature. The Stockmercury float valve,which formerly providedthe most satisfactoryglass vacuum valve for use in the presenceof solvents,has beenalmost completely replaced by thesenewer glassvalves. In severalvalve designs,the sealat the seat is made by meansof an elasto- meric O-ring on the tip of the valve stem. Leak testsindicate that this design offersno improvementin sealingover the valvesin which thereis a directTeflon- to-glassseal at the seat. Furthermore, an O-ring at this point is vulnerableto solvents;so it is the opinion of the authorsthat a directTeflon-to-glass seal at the seatis preferablefor generaluse. When a valveis subjectto temperaturefluctua- tions, an O-ring on the tip of the stemis an advantage.Teflon hasa much higher expansioncoefficient than glass,so a valvewith a Teflon stemordinarily should not be cooled.If cooling is necessary,the sealat the seatcan be maintainedby tightening the valveas it cools.If the valvehas an O-ring on the seat,it should not be cooledbelow the brittlenesstemperature of the elastomer. The major leakagepath in thesevalves is past the sealbetween the glassbody and the valvestem, and the variousproducts on the market vary widelyin their 466 JOINTS,STOPCOCKS, AND VALVES leak rate at this point. A visual indication of a potential leaky valveis poor O- ring contact with the shell or, in those designsusing a Teflon contact, uneven contact betweenthe Teflon and the glassbody. In general, it is desirablefor the O-ring to be under high compressionagainst the glassbody. If there is only a thin line of contact, the chancesare great that the valvewill leak badly. Some improvement in performance is achievedwith a light coat of stopcockgrease on the O-ring, but this measureis defeatedin the presenceof solvents.Most valve designsprovide protection of the O-ring seal on the stem by means of a Teflon wiper machined into the stem, or a Teflon O-ring adjacentto the elastomericO- ring. Sincethe Teflon-to-glassseal at the seatof the valveis much more dependable than the O-ring-to-glassseal at the stem,the valveshould be attachedto a piece of apparatusin the orientationwhich best utilizesthe seatseal. For example,if the valveshown in Fig. 8.10ais usedon a portablegas bulb, the seatseal on the valveshould be closestto the bulb. Any leakageinto the bulb would then haveto occur past the seatseal. If the bulb wereattached to the other arm on the valve, the bulb would be exposedto the relativelypoor stemseal. Any leakagepast the stem sealwould then contaminatethe contentsof the gasbulb.

B. Mefol Volves in Gloss Apporofus. The excellent performance of metal diaphragmsand metal bellowsvalves has promptedtheir usein glasssystems. The various types of metal valvesare discussedin detail in Chapter 10; therefore,this sectionwill addressthe problemsof compatibilityof metal valves and glass apparatus. The union of metal valvesto glass apparatus can be achievedeasily by means of the swage-typeconnectors described in sections 8.1.C and 10.3.C. Becausemetal valvesare generallyheavy and more robust than the glasstubing they are connectedto, the metal valvesmay imbalancea

Gloss Angle- rron TuOrng brocket 'l boltedto volve

lo--l f,Fq Rl glosstubing

(b)

Fig. 8,1l Mounts for metalvalves used in conjunctionwith glasssystems. (a) The valvesare rigidly mounted on a metal framework. (b) A semiflexibleloop of glassis includedto reducemechanical strain with bulky parts. '(tt'g'3lg) 3urqn1sse13 ralauerp -ll€rus Jo dooyu .ro 3urqn1 s.r\olleqIeleru Jo qlEuayuoqs e Jo suueru Äq uapds sse13aql o] uorlJeuuoJ elqrxelJrrües€ esn o1 sr sped sse13aql 01 sseJlsJo uors -srrusueJlar.{l eJnpeJ ol eJnseeuJeq}ouv '{JeJ tunnJe^aql ol ,{1pl1ospelunou '}aIcBJq sr uJnl ur qJlr.{^\ l€laru € o} a^le^ or{i lloq o} sr sr.ualqoJdeseql azrlulurru 'pelenlr? o1 qceordde lereua8lseq eql ro pellelsursr e^le^ eql ueq^\ Eurqnl sse;8aql uo ssoJlsqJnru ool 1ndo1.{cuapual e eq Äeu araql pue snleruddessu;3

L9' S]AIVA SPECIALIZEDVACUUM LINEEQUIPMENT AND OPERATIONS

In Chapter5 the basicdesign and operationsof a vacuumline werepresented to providea conciseintroduction to chemicalvacuum line techniques.This chapter describesa varietyof more specializedoperations which may be consultedas the reader'sneeds dictate. Familiarity with the basic vacuum line operationsde- scribedin Chapter5 is assumed.Some of the topicspresented here are usedfor the quantitative characterizationof chemical reactions:tensimeters (Section 9.1.A) and tensimetric titrations (9.1.C); or propertiesof compounds:vapor pressuresabove room temperature(9.1.E), molecular weight determinations (9.1.F),melting points (9.1.H), and spectroscopicdeterminations (9.1.I.) An- other group of techniquesis employedfor separations,either for isolationof products or for analytical purposes: low-temperaturefractional distillation (9.2.8), vacuum line filtration (9.2.A), and gas chromatography(9.2.C). The long-termstorage of gasesand solventsis describedin Section9.3. Sealedtube reactionsare describedin Section9.4. Finally, a pair of miscellaneoustopics are givenin Section9.5: samplingalkali metals(9.5.A) and generationof dry gases (9.5.8).

9,4 cHARAcTERtzATtoN

A. Tensimeters. A tensimeteris an apparatusused to isolatea volatilesam- ple on a high-vacuumsystem, and to characterizethe sampleby measuringthe equilibrium vapor pressure.The tensimeteris usedin a varietyof important de-

,r68 CHARACTERIZATION 169

terminations, such as vapor pressuremeasurements on pure substances,gas- solutionequilibrium measurements,gas-solution kinetic measurements,and related purposes such as molecular weight determinations and tensimetric titrations. Becauseof the wide variety of applications,scores of designshave appearedin the literature. This sectionprovides three examplesof tensimeter designsand discussesthe main parameterswhich must be consideredin the design of new systems. The apparatusillustrated in Fig. 9.I providesa simple,portable, and grease- free systemfor the wide varietyof applicationsmentioned in the introductionto this section.To achieveportability, this apparatusis built with approximately 10-mm-tubing,which enablesthe determinationof pressureswith acceptable accuracy for most purposes and yet limits the volume of mercury so that the

+ Somple

Fig, 9.1. Multipurposetensimeter. Since the standardtaper joint is positionedclose to the manonl- eter, the joint is closeto the balancepoint of the apparatus.The tensimeteris best supportedby clantpingat the taperjoint and by restingthe bottom of the tensimeteron a pieceof foam in a snrall dish uhich in turn is supportedby a ring clamp. The bracebetween the left arm of the manometer and thejoint is held in placewith epoxycement and addsstability to the apparatus.The tensimeteris filled with mercuryin the samemanner as a U-manometer(see Fig. 7. I caption).To minimizethe volunteof mercury,capillary tubing is usedfor the bottom and part of the left leg. \70 SPECIALIZEDVACUUM LINE EOUIPMENT AND OPERATIONS apparatusis easilyportable. The demountablesample tube permits the introduction of nonvolatilesolids. This sampletube is attachedto the apparatuswith an O-ring joint (rather than a greasedjoint), therebypermitting long-termmea- surementsin the presenceof solventvapors. The apparatusis equippedwith a Teflon-glassneedle valve with the seattoward the interior of the tensimeter.As explainedin Section8.3.A this orientationof the valvereduces leakage into the interior of the tensimeter.Also note that the main standardtaper joint is positionedclose to the manometer,and thus closeto a point of balancefor the apparatus. This feature, as well as the crossbrace, make the apparatusreasonably sturdy and easyto handle. The volunreinside this tensimetervaries with pressure.Therefore. in situations which requirea knowledgeof the number of molesof gas,it is necessaryto constructa calibrationcurve relating the internalvolume of the tensimeterto the nlercurylevel. The procedurefor calibratinga manometerand attachedvolume hasbeen described in Section5.3.H. Another type of tensimeterpermits the mercury levelto be manipulated so that a constantgas volumeis achieved.One suchconstant-volume tensimeter is illustrated in Fig. 9.2. This apparatus is sufficientlyunwieldy that it is best treatedas a permanentitem of equipment,with the mercuryreservoir well supportedby a fixed plasterbase and the inlet tube fusedto the vacuum system.In the versionshown here, the sample tube is also fused to the apparatus,thus reducingleakage which is inevitablewhen joints are used.Owing to the lack of leakagepaths, this apparatusis usefuIin situationswhere very long equilibration times are necessary.Since the apparatusis fixed, it is possibleto uselarge- diametertubing in the manometerand thus obtain great accuracyin the pressure measurements,if this is necessary. Vapors can be transferredinto or out of the apparatusby applying a rough vacuumto the reservoirwhich drawsmercury out of the U and into the reservoir. After the volatile materialsare condensedinto the apparatus,they are isolated from the vacuum systemby bringing the mercuryreservoir to atmosphericpressure and slowlybleeding mercury into the U. If it is important to know the gas volume in the apparatus,the mercury levelis adjustedto somereference point. suchas A in Fig 9.2. for which the volumeof the apparatushas previouslybeen determined. Electronic manometersprovide a convenientmethod of pressuremeasurement in a tensimeter,and the generalarrangement may be very simple (Fig. 9.3). The one problenr which must be anticipated is long-term zero pressure drift, which can be encounteredwith an electronicpressure gauge. Drift is minimizedby maintaininga constanttemperature on the pressuretransducer and by avoidingmechanical vibration at the transducer.

B. Thermol Tronspirotion. In most tensimetry,it is correctlyassumed that the pressureat the manometeris equalto the pressurein the samplecontainer to CHARACTERIZATION 171

To hrghvacuum lrne * tr Sealofl -$(

tlI H Sample l tube

- 850I mm Ballbearing

Sampletube' tensrmeterseal

Breakseal

Sample

Grou nd'gla ss

To atmosphere Teflon needle valve --.>

Mercury reservoir To roughvacuum line

Fig. 9.2. Constant-volumetensimeter. The sampletube (enlargedview. upper left) is loaded*ith solid in a dry box or by sublimationfrom the vacuum line. The tube is evacuated,sealed, *eighed. then glassblownto the tensimeter. After evacuating and flame-drying the tensinreter,the mercury levelis raisedand the break-sealcracked. Sincethe mercury servesas the cutoff to the vacuum manifold, the sampleis not exposedto grease,stopcocks, or joints. This designis desirableuhen very long equilibrationtimes are necessary.The mercurylevel is adjustedat the volume-calibrated referencepoint, suchas A on the diagram,if it is importantto know the gasvolume in the apparatus. which it is connected.However, at low pressures,where the diameterof the con- nectingtubing is small relativeto the mean free path of the gas molecules,the pressuresin the two chambersare relatedby P"/P6 : (To/Tr)t'2.1

rThermal transpiration is discussedin many books on vacuum technology. See, for example: S. Dushman,ScientiJic Foundatiotrs of VacuuntTechnique,2nd ed., rev.byJ. M. Laffertyet al. (Ne* York: Wiley, 1962). 172 SPECIALIZEDVACUUM LINE EOUIPMENT AND OPERATIONS

To vacuumsvstem

Fig. 9.3. Tensimeter based on an electronic pressuretransducer. The sample with a microstirring bar is immersed in a constant-temperaturebath. The pressuretransducer (P), is connectedto the glassapparatus by a glass-to-metalseal or a Swagelokfitting. S is a magneticstirrer.

C. Exomple: Stoichiomefry of Inleroction by Tensimefric TifloliOn. This techniqueprovides a convenientmethod for followingthe stoichiometryof a reactionbetween a gasand a solutionor pure liquid. Also, similar techniquescan be applied to the study of gas-liquid equilibria and gas-solid equilibria. In a tensimetrictitration, measuredamounts of a gaseousreactant are addedto a solution.After eachaddition a pressuremeasurement is made. A plot of thesepressures versus the molesof added gas is then inspectedfor the break-point,which representsthe stoichiometryof interaction(Fig. 9.4). A typical arrangementof componentsin a tensimetrictitration is presentedin Fig. 9.5, which showsthe previouslydiscussed tensimeter and a calibratedbulb attachedto a vacuumline.2 The samplecontainer on the tensimeteris fitted with a small reciprocatingstirrer which consistsof a thin glassrod connectedto a glass-encasedheadless nail or glass-encasedbundle of soft iron wire. This stirrer is driven by an externalsolenoid, the field of which is switchedon and off by a current-interruptingdevice, the detailsof which are laid out in Fig 9.6. The size of the calibratedbulb is chosenso that it will containthe desiredamount of gas for each addition at a pressurewhich is convenientand accuratelymeasured (e.g., 100-500torr). The calibration procedureand stepsused dispensinggas from such a bulb are describedin Section5.3.G. rExamples of tensimetrictitrations may be found in J. J. Rupp and D. F. Shriver,Inorg. Chent.,6., 755 (1967). CHARACTERIZATION 473

150 I

100 E E

10 20 Moleratio BF:/ FezCpz(C0)q

Fig.9.4. Typical tensimetrictitration curve.Total pressurein the tensimeteris plottedagainst the mole ratio of BFr added to reactant.In this casethe solventwas toluenewhich was maintainedat - 78'C for eachpressure measurement. The horizontalportion of the pressurecun,e originates from the low toluenevapor pressureat this temperature.Above the l:1 ratio of reactants,excess BFl is present and the pressureincreases steadily with each addition of BF-r.

The sequenceof operations(assuming the initial solid is not air sensitive) would be to load the sampletube with a weighedamount of reactivecompound and the stirrer, to attachthis tube to the tensimeter,and to pump out the air in the tensimeter.The sampletube is cooledto liquid nitrogen temperatureand solventis then condensedinto the sampletube from a storagecontainer on the vacuum line. The main valveon the tensimeteris then closedand the sample containerallowed to warnl so the solid may dissolve,perhaps rvith the aid of the stirrer. A constanttemperature slush bath is next placedaround the sampletube as illustrated in Fig. 9.5 and an initial pressuremeasurement is taken on the manometer.Next, the first alloquotof the reactivegas is transferredfrom a storagebulb elsewhereon the vacuumsystem into the calibratedbulb usingthe tech- niquesoutlined in Section5.3.G (the bubblermanometer shown in Fig. 9.5 is usedfor the pressuredetermination required for this process).This gas is con- ,"."W m0nometer

Deworwith consr0nl- rempero lure slush

SOlutrOnof somple

Fig. 9.5. Apparatus for a tensimetrictitration. The bubbler manometeris usedto measureali- quots of the reactive gas.

- Com Motor - | n/' _ \l lHl -- ro sorenoid ll, "o,r, ä4+Microswirch

Fig.9.6, Detailsofthesolenoidstirrer. If thesolenoidiswoundwith2lbof 22-gaugemagnetwire, it will withstand115 V in intermittentbursts. The current interrupter.shown above. involves a cam which opensand closesa microswitch.

174 CHARACTERIZATION 175 densedinto the sample tube, which has again been cooledto liquid nitrogen temperature,the contentsof the tensimeterare isolated by meansof the tensimeter valve, and the sample is again warmed to the slushbath temperaturewith stirring. When the pressurein the tensimeterhas become steady, the pressureis recorded.Additions of gas and pressuremeasurements are continued in this fashion, and eventually a plot of pressureversus moles of added gas can be con- structedas illustratedin Fig. 9.4. Often the equilibrationtimes stretch out in the vicinity of the break-point if the reactantsandlor products are only partially soluble.Slow equilibration times also result from slow gas diffusion when the vapor pressureof the solventis great. In general,it is bestto choosethe solvent and the temperaturefor the measurementso that the solventvapor pressureis low.

D. Exomple:Stoichiometry of Inferoctionby DifferentiolGos Ab- sotplionMeoSuremenl. Thegreatest utility of the tensimetric titration is in observingreactions which are favored at low temperatures.If, however,the product has a negligibledissociation pressure at room temperature,it is simpler and often quite satisfactoryto add an excessof reactivegas to the solutionin the tensimeter,to stir the solution,and to monitor the pressureuntil no nroregas is absorbed.The solventand excessreactive gas can then be condensedinto the vacuum system,separated by trap-to-trap distillation as describedin Section 5.3.D, and excessreactive gas measuredby its pressure,volume. and temperature in a trap on the vacuum line (see Section5.3.H). Another check on the stoichiometryof the interactionis providedby the weightgain of the sampletube and its contents.Assuming that the product is air sensitive,the weight after reactionis determinedby filling the tube with nitrogen,quickly removingit from the tensimeter,capping it with a small tared plug, and weighingthe tube and plug.

E. Vopor Pressules obove Room Tempelofute. Sincea volatileliquid will distill to the coldestpoint in an apparatus,it is necessaryto thermostatthe entire tensimeter systemwhen vapor pressuresare determined aboveroom temperature.Two different designsare presentedin Fig.9.7 which n.reetthis re- quirement;alternatively an immersibleglass Bourdon pressuretransducer may be used. The apparatusin Fig. 9.7.b \s suitablefor the measurementof gas- phaseequilibria as well as vapor pressures.The first and simplestdesign of the two (Fig. 9.7.a),called an isoteniscope,ris operatedin the followingmanner: On a vacuumsystem, liquid is condensedinto the terminal bulb. A few hundredtorr of an inert gas is introduced, the valve is turned off, the apparatusremoved from the vacuum system,and the frozen liquid is allowedto melt. The part of the liquid in the terminal bulb is now tipped into the lower U, and inert gas in the regionbetween the bulb and the U is removedby gentlepumping on the system,

rA. Smithand A. W. C. Menzies.J. Am. Chenr.Soc..32r 897,907,1412 (1910). 176 SPECIALIZEDVACUUM LINE EOUIPMENT AND OPERATIONS

Fig. 9.7. Tensimeters for vapor pressuresabove room temperature. (c) Isoteniscope.(ä) An im mersible tensimeter.

with perhaps some warming of the bulb with one's fingers to promote gentle boiling rather than bumping. The apparatusis next attachedto a manometer and surgebulb equippedwith a stopcockthrough which inert gasor vacuumcan be applied.The isoteniscopeis immersedin a constant-temperaturebath, and at eachgiven temperature the liquid levelon the two sidesof the lower U is evened up by adjusting the inert-gaspressure in the external manometer-surgebulb combination.When a null point is reachedfor the liquid levelsin the lower U, the vapor pressureof the liquid is indicatedby the pressureon the externalmanometer. The presenceof the inert gas in this manometer systemprevents the rapid distillation of liquid out of the isoteniscope. The apparatusin Fig. 9.7.b is the simplestto operatebecause the entire ma- nometersystem, the sample,and its vaporare immersedin the constant-temperature bath. The mercury reservoir permits the removal of mercury from the U- manometerportion of the apparatus,and the material to be measuredis then condensedinto the terminal bulb. While this material is still condensedand thereis a high vacuum in the system,the mercuryis reintroducedto the U, thus isolatingthe sample.The apparatusis immersedin a constant-temperaturebath to the levelof the wavy lines. With a vacuum on the upper portion of the apparatus the vapor pressurescan be measured directly. If vapor pressuresbeyond the range of the immersiblemanometer must be measured,the mercury in the CHARACTERIZATION 477 thermostatedapparatus can be usedas a null indicator as describedabove, with an externalmanometer and supplyof gas connectedat the upper joint. Many other methodsfor vapor pressuremeasurements may be found in the literature and in generalthese may be adaptedfor air-sensitivecompounds.a-7

F. Moleculol Weight Delerminolions. In principle, any standard method of molecular weight determinationmay be adaptedfor use under air- free conditions,and thosewhich involveinert-atmosphere techniques have been coveredin Section1.5.F. This sectionwill cover molecularweight determinations which require the useof a vacuum system. Vapor densityprovides a usefulmeans of molecularweight determination for substanceswhich exert a high vapor pressureat or near room temperature.In the simplestcase, an evacuatedbulb of known volume is tared, filled with a measuredpressure of the gas at a known temperature,and is reweighed.These pressure,temperature, and volume data yield the molesof gas (if the ideal gas law is assumed)and the additional weight data permit the calculationof the number of grams per mole. The high surfacearea of the bulb and smallweight of the gasreduce the accuracy of this determination becausethe large surface can pick up significant weightby adsorptionof moisturefrom the atmosphereand from fingerprints.To minimize thesesources of errors, the bulb may be wiped with a lint-free cloth moistenedwith water or alcohol before each weighing. The inaccuracyintro- ducedby the adsorptionof atmosphericmoisture on the surfaceof the bulb can be minimized by using another bulb of the same size as a counterweightand treatingboth bulbs in an identicalmanner. The two bulbs are allowedto equilibrate with the atmospherein the double-panbalance enclosure for about one- half hour beforeweighing. Liquid samplescan be weighedin a small,grease-free bulb and then transferred completelyto an apparatussuch as the one shownin Fi1.9.7.b, wherethe sample is completelyvolatilized and the pressure,volume, and temperature measuredat an elevatedtemperature. Other methodsfor volatilesubstances include the gas densitybalance8 and effusionmeasurementso. The molecularweights of nonvolatilesubstances which havea high solubility in a solventwith a high vapor pressureare convenientlymeasured on the vacuum

{D. E. Mclaughlin and M. Tameres,J. Ant. Chenr.Soc., 82; 5618(1960)l D. E. Mclaughlin, M. Tameres.and S. Searles,Ir.,J. Ant. Chent.Soc.,82;5621 (1960). sG. W. Thompson and D. R. Douslin, in A. Weissbergerand B. W. Rossiter,Eds.,Techniques oJ Chemistry,Wiley-Interscience. 1971, Vol. l, No.5, p.23. 6W. Swietowlawski,Ebulliometric Measuremenls. (New York: Reinhold. 1945). 'G. W. Thompson and D. R. Douslin, in TechniquesoJ Chentisr4,,A. Weissbergerand B. W. RossiterEds., Wiley Interscience,1972,Yol. I, pt.4, p.23. nH. L. Simons,C. L. Scheirer.and H. L. Ritter. Rcy. Sci.Instr.,24:36 (1953). 'gL.K. Nash,Anal. Chem., 20; 258 (1948);D. P. Schoemakerand C. W. Garland,Experiments itt Physical Chemistry, (New York: McGraw-Hill, 1962). p. 102. 478 spEctALtzEDvAcuuM LINEEeutpMENT AND opERATIoNS line by the vapor pressuredepression of the solvent.Assuming the solutionbe- havesideally, Raoult's law can be usedto calculatethe mole fraction of solutein the solution:

P : PoXro1""n, Xsotute:1-Xrolu.nt

In principle, only the weightsof the soluteand solventused to preparethe solution, and the vapor pressureof the solutionP, would haveto be determinedat a known temperature.To reduceerrors, the vapor pressureof the pure solventPo is simultaneouslydetermined, with both solutionand pure solventtubes thermo- statedin the sameconstant-temperature bath. Very good data can be obtained by usingtwo of the tensimetersillustrated in Fig. 9.1. A more specializedappa- ratus, which utilizesa differential manometer,is shownin Fig. 9.8. To obtain the best resultsusing either apparatus,it is important to make carefulmeasure- mentswith a cathetometer,and to employas high a temperatureas practicalso

Solenoid

Slush-, both \

Fig. 9.8. Apparatusfor the deternrinationof molecularweights b-t'vapor-pressure depression. The bottom of the differential manometer (D) may be frozen with Dry Ice to keep the mercury from sloshingwhen solventis addedor removed,or when the sampletube is attached.The solenoidused to stir the sampletube is describedin Fig. 9.6. V and V' are grease-freevalves. CHARACTERIZATION 179

that Po is large and the difference betweenP and Po is magnified. Under these conditions, it is quite important to recognizethat a correction may be necessary for the quantity of the solventin the gasphase, since for high temperaturesand largevolumes the amount of solventin the solutionmay be significantlyreduced. For molecularsubstances, a wide varietyof solventsare useful-for example, methylenechloride, pentane,dimethyl ether, and trimethylamine.Liquid ammonia is alsofrequently used. With l:1 electrolytes,ammonia has the advantage that the primary speciesare ion pairs, whereassolvents of lower dielectriccon- stant generallylead to higher and lessdefinite degreesof aggregation.Correc- tion for nonidealitycan be made by determiningthe apparentmolecular weight as a function of concentrationand extrapolatingto infinite dilution. The isopiestic(isothermal distillation) method for the determinationof molecular weightsis closelyrelated to the vapor pressuredepression method.l0 A weighedamount of standard is introducedinto one leg of an apparatusand a weighedportion of the unknown is placedin the other leg. Solventis introduced into the apparatus,which is then evacuatedand thermostated.The solventwill distill from one solution to the other until the vapor pressures(and therefore mole fractions)of the two have equalized.If the solutionsare ideal, or if the deviationsfrom ideality are similar, equilibrium will occur when the mole fraction of the known equalsthat of the unknown. A simpleisothermal distillation apparatus is illustratedin Fig. 9.9. While not specificallydesigned for air-sensitivecompounds, the apparatusmay be loaded in a dry box. After introduction of samplesand solvent,it is sealedoff under vacuumand allowedto equilibrate,with the apparatusarranged so the liquid is in the large bulbs in order to afford a maximum area of exposedsolvent. The apparatusis periodicallytipped sothe two solutionsflow into the calibratedlegs. When no changein volume is observedfrom one time to the next, the relative volumesof the solutionsare, to a goodapproximation, proportional to the moles of solutein the two legs. Sinceequilibration sometimestakes daysor weeks.the isopiesticmethod is not suitablefor unstablecompounds or compoundswith appreciablevolatilities. Also, long equilibrationtimes require leak-freeand grease-freeapparatus. An- other designfor an isothermaldistillation apparatusis givenin Fig. 9.10.

G. Iempelofule Defelminotions. In vacuum line work it is frequently necessaryto measurelow temperatures.While the mercury-in-glassthermometer is convenient, it does not extend below the freezing point of mercury, -38.9". Pentane-in-glassthermometers have a similar convenienceand may be useddown to about - 150"C,but they areonly usefulfor roughwork (an error of 5"C is common).For more precisedeterminations, a calibratedthermocouple or thermistor, or a vapor pressurethermometer, is useful. The vapor pressurethermometer consists of a manometerwith one arm ex-

roG. L. Beyer, in TechniquesoJ Chenistry, A. Weissbergerand B. W. RossiterEds.. Wiley Inters- cience,1972, Vol. 1. pt.4, p. 183. 480 SPECIALIZEDVACUUM LINEESUIPMENT AND OPERAIIONS

Fig. 9.9. Signer-typeisopiestic molecular weight apparatus. The sample, standard, and solventare introduced through the upper tubes, which are then sealedoff after freezingthe solutionsand evacuating the apparatus.The apparatusis allowedto stand in the positionshown to allow maximum exposureof the solution to the vapor. Volumes of the standard and unknown solutionsare found by tipping the apparatus so the calibrated legs are filled.

posedto the vapor of a pure substancewhich is condensedin the probe (Fig. 9. I 1). Providingthat somecondensate is present,the temperatureof the probe is found by comparisonof the observedvapor pressurewith tabulateddata for the thermometricmaterial. The vapor pressurethermometer illustrated in Fig. 9.11 is similar to Stock'sdesign.tr.tz More compactdesigns have appeared in the liter- äture,l3'tlbut somesacrifice in accuracyseems inevitable with these. Any substancewhich may be obtained pure and for which accuratevapor pressuredata are availablemay be usedfor vapor pressurethermometry. Stock recommendeda convenientseries of compoundsand, in collaborationwith Hen- nig and others,he obtainedaccurate vapor pressuredata for thesecompounds.ls Thesedata wereobtained on a temperaturescale for which 0'C : 273.1K; however,more recentdata on severalof the compoundsshow it would be difficult to improve on Stock'svapor pressuretables. When high accuracyis desired,the usualprecautions involved in precisemanometry (Chapter 7) must be observed. Thermistors, or "thermally sensitiveresistors," are semiconductorswhich havehigh negativetemperature coefficients of resistance.There is no simplere-

IrA. Stock,Z. Elektrochemie,29:354(1923). rrA. Stock.Hydrides oJ Boron ard Silicon,(lthaca, N.Y.: Cornell UniversityPress, 1933), p. 190. rrA. Farkas and L. Farkas, Ind. Eng. Chent. (Anal. Ed.), 12:296 (t940). I'S. C. Liang, Rev. ^Sci.Instr.,23',378 (1952). lsF. Hennig and A. Stock,Z. Ph.,-sik.,\ 227 (1921). CHARACTERIZATION 484

Fig.9.l0. Apparatusfor the determinationof molecularweights of air-sensitivecompounds by the isothermaldistillation technique. Temperature fluctuations of the two solventsare minimized in this illustration by a Dewar filled with water. This apparatus is used in the following manner. In a dry box the sample is placed in a tared tube through sidearm A, the sidearm is then sealedoff, the tube and remnant of the sidearmare weighed,and the tube is attachedto the apparatusby glassblowing at B. A weighedportion of a standardis introducedinto the other bulb, and the filling tube is sealed off. After evacuation, opening of the break-seal,and reevacuation,a measuredportion of solvent is distilled into both arms of the apparatus. The processof equilibration is followed by periodic re- nrovaland measurementof the solventfrom one atm. The solventmay be measuredvolumetricly in the liquid or gas states,or by weight.

lationshipbetween the resistanceR and the temperature7. However,the following empirical resistance/temperaturerelationship is quite useful:rö Rr:R.',.0f-r(i-*)]

whereRo is the resistanceat a temperatureTo, Rr is the resistanceat a temperature T, and .B is a constant. Low-ten.rperaturethermistors are usuallymade from nonstoichiometriciron oxides and have a resistancesensitivity of around 15% per Kelvin at 20 K.17 Thermistorsact as ohmic conductorsat any fixed temperature.Therefore, one advantageof using a thermistor is that ordinary copper wiring may be usedto build the circuit; referencejunctions and special extension wires are not needed.r8Thermistors are generallyquite stableto long-termfluctuations after an initial agingperiod.

rbS.D. Wood, B. W. Mangum,J. J. Filliben,and S. B. Tillelt.J. Res.NBS,83; 247(1978), rrT. J. Quinn (generalreferences), p. 223. r6R.P. Benedict(general references). 482 SPECIALIZEDVACUUM LINE EOUIPMENT AND OPERATIONS

is filled as describedin the caption to Fig. 9.11. The vapor-pressurethermometer. The manometer a joint attachedat point A' A Fig. 7.1. The manometerrs then evacuatedand outgassedthrough off undervacuum at point pure compound is condensedinto the pfobe, and the apparatus is sealed care must be taken not to A. For thermometric compounds which boil below room temperature, overfill the apparatus.

which are Thermocouples consist of two dissimilar electrical conductors wires constituting joined to form a measuringjunction, with the free ends of the betweenthe mea- ihe referencejunction. When a temperature difference exists the free ends of the ,uring and reiere.tcejunctions, an emf is produced between can be used device.This emf, which is a function of the temperaturedifference, junction referencejunction to determine the temperature at the measuring if the circuit is shown in temperature is known. A schematicof a typical thermocouple Fig.9.12. situation is the The most common thermocouple type used in a laboratory and a use- Type J iron/constantan thermocouple' Low cost' high thermopower' CHARACIERIZATION 183

Measunng Cu \ / MaterralB lunctron

lce bath referencejunction

Fig,9.12. Typical thermocouplecircuit. The ice water bath may be preparedin a Dewar for ex- tendeduse of the circuit.

ful temperaturerange of -200-760oC contributeto the popularityof the TypeJ thermocouple.Below 0oC, rust and embrittlement may becomea problen.re Therefore, it is a good practice to remove the referencejunction from the ice water bath and dry it thoroughlywhen the thermocoupleis not being used. When using a measuringjunction at a remote site relativeto the reference junction, it is important to usethe proper extensionwire betweenthe junctions. Usually, a wire with the samecomposition as the thermocouplewire itself, but not made to such a high specification,is used.

H. Melling Point Determinolions. The melting point, or more correctly the triple point, of a volatilesolid may be determinedin a standardmelting point block or bath after the solid is sublimedfrom the vacuum line into a capillary and sealedoff under vacuum. To avoid sublimationof the sampleduring the determination,the capillarymust not protrude fron'rthe melting point block or bath. Stock devisedthe apparatusillustrated in Fig. 9.13 to obtain melting points of volatileand reactivesubstances below room temperature.This particular ap- paratusovercomes the problem of poor visibility of the sample,which is being maintainedat a low temperature.The apparatuscontains a glassplunger which has an iron core on the top and a glasscross at the bottom. The plunger is slippedinto a tube which allowsmoderate clearance. In operation,the tube with plunger is evacuated,the plunger is lifted by a hand magnet, and a ring of the sampleis distilledinto the apparatusbelow the cross.The plungeris loweredso that the crossrests on the frozenring, and a bath of cold liquid is placedaround the tube and allowedto warm slowly.The temperatureof the bath may be measured with a vapor pressurethermometer and the top of the plunger observed

''T. J. Quinn (generalreferences), p. 264. 184 SPECIALIZEDVACUUM LINE EQUIPMENT AND OPERATIONS ,ll

Fig. 9.13. Stock-typemelting-point apparatus. A, tube; B, magneticcorel C. glasscross resting on the bottom (left drawing), poisedabove the ring of frozen solid (right drawing); D, tip of plunger which is observediE, hand magnet usedto raiseplunger.

through a cathetometer.The nlelting point correspondsto the temperatureat which the plunger beginsto move. Visual observationof melting pointsmay be madein the apparatusillustrated in Fig. 9.14. The sample(s)and a mercury-in-glassthermometer are held by sup- ports constructedfrom thin-walled brass tubes. The bath is cooledbelow the freezingpoint of the samplesand stirred by a motor-drivenstirrer. The apparatus may be placed in a warm water bath, and the rate of warming may be controlledby the extentof evacuationof the jacket. If the substancefreezes as a solidphase which is difficult to distinguishfrom the liquid, it is illuminatedfrom behind by light which is passedthrough a Polaroidfilm and then viewedthrough a crossedPolaroid. l. Specfloscopic Delerminofions. Gas-phaseinfrared spectraprovide a useful adjunct to vapor pressuremeasurements in the identificationof volatile materials.The cell illustratedin Fig. 9.15 allowsthe sampleto be quantitatively returnedto the vacuum line afterthe spectrumhas been obtained, so the process is completelynondestructive. The primary problemwith a gascell is to obtain a vacuum-tightseal between the window material and the cell body; this may be accomplishedwith Glyptal paint or with wax. If the latter is used,it is necessary to warm and coolthe alkali halidewindows slowly to avoidcracking them due to thermal stress.For this purposean infrared lamp is handy. The most satisfactory method of attaching windows is O-rings becausethis allowsthe easyre- moval of the windowsfor cleaningand polishing. Arr- d/lven stirrer\

Fig.9.l4. Apparatusfor the risual observationof melting points

reeze- oul rrp

Alkoliholide windows Sideview End view

is includedbetween the nletalretarn- Fig. 9.15. A gas-phaseinfrared cell. Note that a thin gasket orving to unever'ltightening o{ the irr! ptut. and Äe windou.. This helps to reduce windov breakage nuts.

,t85 18ö SPECIALIZEDVACUUM LINE EOUIPMENT AND OPERAIIONS

A versatilelow-temperature infrared cell is presentedin Fig. 9.16.20It is suitablefor mull or pressed-diskinfrared spectraof solids,solid stateinfrared spectra of condensedvapors, and spectra of products from solid-gasreactions. Mulled or powderedsamples are supportedbetween alkali halidewindows in the copperblock B, which is cooledby refrigerantin the cold finger A. Beforethis refrigerantis added,the cell must be evacuatedthrough the needlevalve. When the cell is usedfor low-temperaturespectra of condensables,the vaporsare bled through the needlevalve and squirteddirectly onto one surfaceof a cold alkali halideplate held in block B, The cell illustratedin Fig. 9.17 has provenvery useful in the determinationof visible and ultraviolet spectrafor air-sensitivesolutions. Despite its simplicity, this cell is quite versatile.To introducean air sensitivesolution, the cell is evacuated and filled with dry nitrogen through the O-joint, the stem of the needle valveis removedwhile a streamof nitrogen is maintainedthrough the cell, the solution is injectedby meansof a syringeequipped with a long needle,and the stem is replaced.When the needlevalve is closed,the solution may be tipped

18/9 O-r ng lo nt

Needle VOIVE

40/54 - KBr drsk

Nletol / end plote

B Copperblocf KBrdrsk

Fig. 9.16. Low-tcnrperatureinfrared cell (cross-section).An indiunr gasketbetseen the *'indorv and copperblock greatlyincreases the efficiencyof heattransfer. If the temperatureof the u'indou is to be nreasured*ith a thernrocouple.the leadsma1'be passed though pinholesin the upper O-ring. Under contpressionof the ioint, this typeof electricallead-through is vacuunr-tight.Threaded rods usedto clanrpthe end plateshave been omitted for clarity. A springholds the KBr disk in place.

:oThis cell is similar to one describedby E. L. Wagner and D. F. Hornig.J. Chent.Phvs., l8; 296 ( 1950). CHARACTERIZATION 187

l-cm e- prece cuvet te Reservoir

Fig, 9.17. Evacuable cell for visible spectroscopy.

into the cuvetteand the spectrummay then be run. If a measuredportion of reactivegas is to be addedto the solution,the contentsare frozen in the reservoir, the cell is evacuated,and the gasis distilledinto it. When this cell is usedin conjunctionwith most visible-ultravioletspectrometers, it is necessaryto replace the usual cell compartmentcover with a speciallyconstructed, light-tight cover which providesspace to accommodatethe needlevalve. The cylindricalreservoir is an important featureof the cell becausethe cuvette,which has a squarecross section,is easilybroken by frozen solutions. Commercial cylindrical quartz cells can be adaptedfor gas-phasework as illustratedin Fig. 9.18. Sucha cellfinds usein the nearinfrared for the determination of overtonevibrational frequencies,and also in visible and ultraviolet spectroscopy.A much lessexpensive cell which is adequatefor most gasesmay be constructedfrom Pyrexalong the linesof the cell shownin Fig. 9.18. Quartz windowsmay then be attachedby epoxyresin. A cell which is filled from a con- ventionalvacuum line will generallycontain nercury vapor which absorbsat 2$7 ^. Oncethe origin of this absorptionis recognized,it causeslittle difficulty becauseof its narrow bandwidth. Many specializedspectral cells designed for reactivesubstances are described in the literature, and referencesto someof theseare given in Table 9.1. Laser Raman spectroscopyis well suitedfor the study of air-sensitiveliquids becausethe samplemay be containedin an all-glasscell.2r Such a cell is much easierto load on a vacuumline and to maintain leak-freethan is an infraredcell. Also, such a tube is easierto heat or cool than the typical IR cell.

2rD. P. Strommen,and K. Nakamoto,Luborato1, Runtun Spectroscop.y,Wiley Interscience.New York. 1984.Chapter 2. 488 SPECIALIZEDVACUUM !INE EOUIPMENT AND OPERATIONS

Fig. 9.1E. A quartz gas cell. The adapterwith joint, stopcock.and freeze-outsidearm is u'axed onto the taper joint of a commercialcell.

Severalmethods may be used to attach an NMR tube to a vacuum system. The O-ring union, illustratedin Fig. 8.5, permitsattachment of standardNMR tubesto a vacuum outlet. Once the NMR tube has beenfilled with an air-sensitive sampleon the vacuum system.it is necessaryto bring the tube up to atmospheric pressurewith inert gas, removethe tube, and quickly stopperit. Re- cently. a small in-line valve has been introducedrvhich has a provisionfor an O-ring sealwith a speciallyconstructed NMR tube.22This valveallows the NMR tube to be sealedbefore it is disconnectedfrom the vacuumline. and the valveis left on the tube during data collection.Owing to its symmetricdesign, the valve doesnot interferewith the spinner. The best exclusionof air is achievedby glassblorvingan NMR tube onto a joint so that the joint may be attachedto the vacuum line when volatile compoundsare to be sampled.The sample,solvent, and referenceare distilledinto the tube, which is then sealedoff under vacuum.A symmetricseal helps to avoid erratic spinning. A highly volatilereference, such as tetramethylsilane,may be storedin a small"solvent container" (Fig. 9.19)and measuredin the gasphase. The large expansioncoefficient of many solventscan crack the sanrpletube whenthe sampleis warmedfrom the liquid nitrogentemperature. To reducethe chanceof breakage,the tube is withdrawn slowlyfrom liquid nitrogenand. as it is removed,the sampleis thawedwith the fingers;it is particularlyimportant to usethis processwith the thin-walledvariety of NMR tube. The expansioncoefficient also has to be taken into accountso that there is sufficientdead spaceto accommodatethe sample when it has warmed to room temperature.If high pressuresare anticipated,a checkis madeof the strengthof the tube by immers- ing it in a warm water bath beforeit is insertedinto the NMR probe.

2zThe in-line valveand associatedNMR tube is manufacturedby J. Young Ltd., ll ClovilleRoad, Acton. London W38BS, U.K. In the United Statesone supplieris R. J. Brunfeldt Co.. P. O. Box 2066. Bartlesville.OK 74005. Toble9.'1. Relerences lo lnfroredond Visible-UltroviolefCells for Air- sensiliveCompounds

Description Reference I nJrured Vacuum-tight infrared cell for liquids A. B. Burg and R. Kratzer, Inorg. Chem., 1, 725 (1962). Infrared cell for carbon suboxidepolymer R. N. Smith,D. A. Young,E. N. Smith, and C. C. Carter,Inorg. Chem.,2,829 ( 1963) Pressure-tightcell for infrared spectra of D. C. Smith and E. C. Miller,./. Opt. Soc. liquids Am., 34, 130(1944). Method of attachingdissimilar window E. Schwarz,J. Sci.Instr., 32, 445(t955); materialsto a vacuum-tightlow- V. Roberts.J. Sci.Instr.,31, 251(1954) temperaturecell lnfrared spectra of adsorbed species R. P. Eischens,S. A. Francis,and W. A. Pliskin,J. Phys.Chenr.,60, 194 (1956); M. Courtoisand S. J. Teichner,"/. Caralysis,I, l2l (1965). C. Tessier-Youngset al., Organometallics,2, 898 (1983).

All-glasscell for the infrared1<4.7p) F. L. T. A. Cotton and Reynolds,"/. .4nr. spectra of gases. Chent.Soc., 80, 269 (1958).

Low-temperaturenear-infrared and W. J. Peerand J. J. Lagowski,J. Phvs. visiblecells for liquid anrrnonia Chent.,84,lll0 (1980),E. C. Fohn, solutions. R. E. Cuthrell,and J. J. Lagou'ski, Inorg. Chent..4, 1002(1965).

Heatedinfrared cell for solidsin a T. Wydevenand M. Leban,Anal. Chenr.. controlledatmosphere 39, 1673(1967).

Lo\4'-temperatureliquid infrared cells R. G. Steinhardt.P. A. Staats.and H. W. Morgan, Rer,..lci. hstr., 38, 975 (1967)

Silverchloride window-to-body seals J. F. Harrod and H. A. Poran,Rcv. .lci. lrrsrr., 38. l105 (1967);A. Guestand C. J. L. Lock.Rer'. Sci. Instr., 39. 780 ( r968). Optical matefialsand variousinfrared R. G. J. Miller, 1965,Luboratory Methods celldesigns. in Irt/rured Spectroscopv,Heyden and SonsLtd.. London. Protectiveholder for KBr presseddisks P. A. Saatsand H. W. Morgan, Äp,oi. Spectry., 22, 576 ( 1968). Visible-Ultruviolet Lou'-temperaturevacuunr-tight visible- R. Nakane.T. Watanabe.O. Kurihara, ultravioletcell for solutions. and T. Oyama, Bull. Chem. Soc.Juputt, 36,r376 (r963). Low- and high-tenrperaturegastight Y. Hirshbergand E. Fischer,Rey. Sci. visible-ultravioletcell. lrrslr..30, 197(1959).

489 190 SPECIALIZEDVACUUM LINE EQUIPMENT AND OPERATIONS

r8/9 J

Fig. 9,19, Solventstorage container. Solvent is distilled in through the sidearm,which is then sealedoff under vacuunr.The containeris attachedto the vacuumline throush a l8/9 ball ioint or O-ring joint.

Sampling for ESR work is often more complex than for NMR becausethe high sensitivityof the ESR spectrometerrequires careful exclusion of paramagnetic impuritiesor their progenitors.Also, the radical is generallyextremely re- activeand presentin low concentrations,so that exclusionof tracesof moisture and air is important. Frequently,paramagnetic low-valent metal complexesand anion radicalsare producedby alkali metal reduction;a typical cellfor the generationand samplingof suchspecies is illustratedin Fig. 9.20. Avarietyof other samplingmethods have been described.23

9,2 sEPARAToNs

A. Vocuum Line Filltotion. For their work on the diammoniateof diborane, Parry, Schultz, and Girardot2adevised a versatilevacuum line filtration apparatuswhich is usefulwhen small quantitiesof solid are handledand when the solventis sufficientlyvolatile to be distilledon the vacuumline. The filter is attachedto the vacuum systemthrough a standardtaper joint which allowsit to be rocked or inverted (Fig. 9.21). Prior to filtration, any volatile contentsare frozen down and the apparatusis thoroughlyevacuated (Fig. 9.2la). By inver- sion of the apparatus,the solutionis then poured onto the frit, and the solvent vapor pressureis employedto effect a "suction" filtration by closingthe stopcock in the equalizingarm and coolingthe lowertube (Fig. 9.21b).The precipitate is washedby distillationof the solventfrom the lowerreceiver into the upper portion of the apparatus(with the stopcockin the sidearmopen) and repetition

rrC. P. Poole,Jr., Electron Spin Resononce,(New York: Interscience.1967), Chapter l5; J. L. Dye, J. Phys.Chent.81,1084 (1980). 2{R.W. Parry,D. R. Schultz,and P. R. Girardot,J. Ant. Chent..Soc.,80;I (1958). SEPARATIONS 494

10/30 24/40 |

Alko li metol

Sompleoddition tube Sr 2-mm S2 copillory ESR tube Solventdistilled into this orm

Re oction

Front view Sideview

Fig. 9.20. Apparatusfor the generationand samplingof anionradicals. The sampleis addedto the purged apparatus,Sr is sealedoff, and the appartusis evacuated.Chunks of sodiunrare melted through the capillaryand then sublimedinto the reactiontube. Solventis distilledinto the sidearm from the vacuunlline, and the apparatusis tipped so that the resultingsolution is pouredonto the sodium mirror in the reaction zone. The resulting solution of radical is poured into the 5-mm ESR tube, frozendown, and sealedoff at S2.The radicalgeneration and collectioncan be carriedout at reducedtemperature by immersingthe tube in an appropriateslush bath.

of the suctionfiltration (Fig.9.2lb). The condensationof solventin the upper portion of the filter can be accomplishedby wrappingpart of the upper tube with glasswool and pouring small quantitiesof liquid nitrogen into the glasswool. When the filtering and washing operationsare complete,the solventmay be removed under vacuum. The apparatus is filled with nitrogen, capped, and taken into a dry box for the transfer of solids.This set of operationsis easily carried out when using solventswhich exert lessthan 1 atm pressureat room temperature;in this casethe major precautionis slowremoval of the solventto avoidsplattering of solidin the filtrate. However,solvents which boit belowroom temperaturerequire much more skill in handling becausethey are liable to bump and blow the apparatusapart. The chanceof bumping may be reducedby a rocking motion impartedto the apparatuswhen the solventis volatilized.Also, pressurizationof the apparatusis minimizedby alwaysleaving it opento a bubbler manometer. Even though the designpresented in Fig. 9.21 avoidsdirect contact of the liquid with stopcockgrease, the presenceof solventvapors may lead to the eventualerosion of the grease.This can be minimized by working 192 SPECIALIZEDVACUUM LINE EQUIPMENT AND OPERATIONS

Fig.9.2l Vacuum line filtration apparatus.(c) A solutionready to be filtered;(b) apparatusin- vertedand bottom receivercooled to bring about suctionfiltration. The precipitateis washedby openingthe stopcock,allo*'ing the bottom tube to warm, and coolingthe top $'ith glassu'ool dipped in liquid nitrogen. The conrponentsare he'ldtogether by springsor rubber bands. A grease-free versionof similar dimensionsma,v be constructedb,v nraking the follouing substitions3 24r,10stop- cock - valve;S l4lJS - r/t_in.Caion O-ioint.

fairly rapidly and maintaining the solventbelow room temperature,or by using the O-ring versionof this apparatus.which is describedin the caption to Fig. 9.2t. When a largequantity of solid is handled,a scaled-upversion of the vacuum line filter may be used;but if the quantity is too large,it becomesunwieldy. The vacuum line filter designby Wayda and Dye, Fig. 5.3 is the best choicewhen largequantities are handled. Many specializedvacuum line filters are described in the literature.2s2b

zsG.D. Barbaras,C. Dillard, A. E. Finholt,T. Wartik, K. E. Wilzbach,and H. l. Schlesineer.J. Ant. Chenr..loc.,73; 4585(1951). roA. B. Burg and R. Kratzer, Inorg. Chenr., l:725 (1962). SEPARATIONS 493

B. Low-Tempeloture Floclionol Distillotion. A versatilelorv-temperature distillationcolumn has been designed by Dobsonand Schaeffer.2'Itis suitable for the separationof small anounts of compoundswhich haveappreciable volatilitiesin the - 160-0'C range.The column(Fig.9.22) is evacuated.and the sampleto be distilledis condensedin the lowerU-trap. A streamof cold nitrogen gasis maintainedthrough the centertube, and the U-tube is warmedso that the sampleis introducedto the column. The temperatureof the column is controlled by varyingthe boil-off rate of liquid nitrogenfrom a Dewar (Fig. 9.23). When a sufficientlyhigh temperatureis reached,the first componentwill slowlymove up the column and may be collectedover a periodof time at liquid nitrogentemperature in the upper U-trap. Ordinarily. a good separationis obtainedfor conrpo- nentsu'hich boil 15' apart. A number of other designsare presentedin the literature for low-temperaturedistillation columns.282q A closelyrelated technique is the "fractional codistillation" methodof Cady and Siegrvar1fi.l0'rrThe amount and boiling rangeof the componentswhich may be handled by this techniqueare comparableto those describedabove for the low-temperaturedistillation column. Essentially,a gas chromatographyapparatus is employedwith the column replacedby a t/+ or r/rl-in.copper U-tube packed with approximatelyS0-mesh metal powder. The mixture to be separated,which may be as much as2 mL of liquid for the largecolumn, is distilled onto the inlet sideof the U-tubeat liquid nitrogentemperature, and a suitable helium flou' rate is then established.The liquid nitrogenis pouredfrom the De- war and the Dewaris replacedaround the U-tube.As the chilledDervar and U- tube u'arm up, the componentsprogress through the colunrnand then thlough a thermal conductivitydetector, which is followedby cold traps for the collection of fractions.A simpleversion of this apparatusis illustratedand explainednrore fully in Fig.9.24.

C. Gos Chromofoglophy. Gas chromatographyhas been employedfor the separationof reactivecompounds ranging from boron hydridesto interhalo- gens. For manv reactiveliquids, conventionalinstrumentation (Fig. 9.25) has beenemployed. However, gases generally require an inlet systemwhich is rrrore involvedthan the familiar syringeinjection port routinelyused for organiccont- pounds. There is no lack of books and articlesdealing with the major facetsof gas chronratography;for examples,see the generalreferences list at the end of this chapter.Furthermore, most chemistsare familiar with the technique,and many r-A. Nornrarrand R. Schaeffer,private comnrunication. rrJ.R. Spielnranand A. B. Bwg, Inorg. Chetn.,7: 1139(1963). :uD.J. LeRoy,Cun. J. Chent.,28,492 ( 1950);A. A. Conrstockand G. K. Rollefson,J. Chen. Pltl's.. l9: 4,1I( l95l ). r('G.H. Cadyand D. P. Siegrvarth.Atrul. CIrcm.. Jl;bl8 (1C59). lH. w. Myersand R. F. Putnam.Anul. Chem..34;6tr'l (1962). 194 SPECIALIZEDVACUUM LINEEQUIPMENT AND OPERAilONS

Coldgos /- Pe^lone in I 'E gloss thermometer

Cold N2 To vocuum lrne

Som ple collected here Coolontgos, 15mmOD

Sompletube VOCUUM 8mm OD

C0.172mm gop throughwhich the moterioldistills

Dewor jo cket 25mm OD

Exponsionbellows

Coolont veni

L Somple 10mm ID' N2out

to J (b)

Fig. 9.22. Low-temperaturefractional-distillation colunrn. (c) Norman's modification of a design by Dobsonand Schaeffer.(ü) An alternatecolumn design (J. Dobson. Ph.D. thesis. Indiana Univer- sirv.I 967). commercialinstruments are available.Therefore. this sectionwill focuson inlet systems,particularly inlets which serveas an interfacebetween a gaschromato- graph and a vacuumsystem. Also, a brief accountwill be givenof the conditions and equipmentwhich havebeen used successfully in the separationof somere- activeinorganic substances. An inlet systemfor quantitativervork must presenta represeiltatilesample to the carriergas stream in the chromatograph,This can be a problemwith highly To Vorioc

Cold N2+ Soleiy plug

Glosswool or expondedplostrc Insul0lron

Heoter

Fig.9.23, Attainment of low temperaturesby boiling nitrogen.In many applicationssuch as the stifl in Fig. 9.22, the Variac is set to provide a convenientsteady-state boil-off temperature. When closetemperature control is desired, a commercial control with a thermocoupleor thermistor sensor may be usedto control the heat input.

To bridge

Tovocuum I ne He suppy

2-mm copillory iubrng

Som ple Insuloiron

- /4Ot"/A UU Coppel ruDe f lled wrih powdered metol

Fig. 9.24. Fractionalcodistillation apparatus. In this design(due to S. M. Williamson),the sample is distilled into U-tube A and then carried by a helium stream into the upper left leg of the metal tube, which is cooledwith liquid nitrogen.When the liquid nitrogenis pouredout and replacedby a chilled Dewar, the fractions are carried through the column by the helium stream and collectedin trap B when they appear in the detector. (Only one trap for fraction collecting is illustrated.)

.t95 196 SPECIALIZEDVACUUM LINE EOUIPMENT AND OPERATIONS

Deteclor

o O

lrne

Fig. 9.25. Schematic of a gas chromatograph. The flow control generally consistsof a standard pressureregulator plus a needlevalve. Gas purificationis sometimesnecessary, particularly u'ith air- and moisture-sensitivecompounds. A short column of molecularsieves held at -78'C is frequently adequate.The traps (for the collectionof fractions)and flou nreterare optional.The dashedlines indicatepoints at which communicationwith the vacuum line is possible.

volatile substances,because partial condensationof a multiconlponentsysten will lead to a differentrelative concentration of the componentsin the gasphase than in the liquid phase.The followingprocedure is recommendedfor obtaining a representativesample of a liquid containinghighly volatilecomponents:32

'l . The liquid phaseis made homogeneous, 2. A portion of the tiquid phaseis isolatedfrom the bulk of the liquid without changein composition(i.e., without boiling). 3. The isolatedportion is completetyevaporated into a suitablecontainer again without changein composition. 4. The vapor is made homogeneous.

Similarly, it is advantageousto obtain a gas samplefrom a homogeneouspoly- componentmixture by isolating a segmentof the homogeneousgas phaseby meansof a valve(s)and then removingall of this samplefor analysis. Volatile reactiveliquids presentfew problemssince they generallycan be distilled from the vacuum line into a tube equippedwith a serum bottle cap (Fig. 9.26). Nitrogen is then admitted to the tube, and the sample is taken with a syringe. Another scheme involves an inlet with a capillary tube or ampule breaker.33-3sThis method is potentiallyuseful for vacuum line work, sinceit is relativelysimple to fill and sealoff a sampletube attachedto the vacuum line. When slightcontamination of a gassample by air is not objectionable,syringe techniquesmay be used. In order to minimize contaminationby air. a syringe

IV. Diebler and F. L. Mohler. J. Res. NB.i. 391149 (1947). rrM. Dimbat, P. E. Porter, and F. H. Stross,Arro1. Chem., 28:290 ( 1956). uS. W. S. McCreadieand A. F. Willianrs,J. Appl. Chent.,7:17(1q57). rsJ.Wendenburg and K. Jurischka,J. Chronntog., l5l 538 (1964). SEPARAIIONS 197

>. Serumbottle - cop

Fig. 9.26. Liquid samplingtube. The gasvolume of this apparatusis kept smallto minimizedeple- tion of the more volatilecomponent in the liquid phase.

with a Teflon- or rubber-tippedplunger is employed,36the syringeis flushedwith carriergas, and the pressureof the gassample is adjustedto slightlymore than 1 atm beforethe aliquot is rvithdrawn.While veryconvenient, this approachis not appropriatefor highly reactivegases or situationsin which rapid, accuratesam- pling is desired. The common methodof gassampling is to employa loop of tubing which may be cut in or out of the carriergas stream. The loop is filled with a gassample and then switchedin serieswith the carriergas source and column. The loop may be filled by evacuatingit and then either admitting the sampleat a measuredpressure from the vacuum line or distilling the entire samplefrom the vacuum line into the loop (Fig. 9.27). Obviously,this processrequires the useof valveswhich will hold a high vacuum. The valve requirementsare lessstringent when the sampling operation is performed by flushing the samplegas through the loop (Fi9.9.27). This approach is well adapted to the analysisof commercialgas streamsand is usefulin the laboratoryfor samplingthe output of flow reactors. However.it is not convenientfor most vacuunl Iine work. A wide varietyof valvesmay be usedto achievethe aforementionedgas injection. Specialvalves are availablewhich provide synchronousswitching of the sampleinto the gas stream.One type involvesa body attachedto the carriergas 'Ihe line and sampleloop(s). passagesin this body open on a flat, polishedsurface. A rotor with passagewayswhich will interconnectthose on the body is pressedfirmly againstit. By turning the rotor, the gas streammay be switched betweendifferent ports. One of the most satisfactorydesigns from the stand- point of leak-tight performanceis basedon a spring-loadedcone of graphite- impregnatedTeflon which rotatesin a metal body.37The porting is schemati- cally illustrated in Fig. 9.28. Another type of valve involvesa shaft bearing a rbS.H. Langer and P. Panlages,Anal. Chent..30; 1889(1958). Teflon-tipped gastight syringes are manulacluredby the Hamilton Conrpany,Whittier. CA. "Disposable"svringes with rubber'-tipped plungersare nranufacturedbv Becton,Dickinson, Co., Rutherford,Nl. r-Thesevalves are manufacturedby Valco and are alailablefrom supplyhouses of chromatographic equipment.such as Supelco,Inc., SupelcoPark, Bellefonte,PA 16823. 198 SPECIALIZEDVACUUM LINE ESUIPMENT AND OPERATIONS

Injectrng

rter Cor +Column

Somple > tn

Corrrer +Column gosxx-- +Colu mn .tl s".i,{l-l nU\ I \, lVonometer

Corrre/ + Column

Fig.9.27. Some configurations for gas sampling. .""ffi,.ffi,.Lo00 Loop

LooP LooP

Fig. 9.28. Gas inlet valve. Schematic of cone-typeor disk-type valve'

seriesof O-rings in grooves.This fits inside a cylinder from which passageways extend. Communicationbetween the passagewaysis alteredby sliding the O- ring bearing shaft in or out. before discussingsome individual systems,it is worth pointing out that an ordinary analytical chromatograph will handle sampleswhich are very closeto t/a-\n.' the scaleencountered in vacuum line work (up to 1 to 3 mmol with a diametercolumn). Therefore,the usual analyticalchromatograph is potentially useful for the purification of products or reactantsfor small-scalevacuum line preparative wärk. For preparative work or for subsequentcharacterization of iheiractions, the gas from the chromatograph is led through a small collection manifold where individual components are trapped.3s'3qEfficiency is improved by including looseglass wool or similar material in the trap'

rsJ.Haslam. A. R. Jeffs,and H. A. Willis,,Analysr,86' 45 (1961)' (London: iqC.M. Drew and J. R. McNesby,in Desty,Ed., Gas Chromatogroph.y1958, Butterworth, 1958),p. 216; G. Guiochon and C. Pommier, Gus chromatographv in Inorganics and organometal- ircs. Ann Arbor Sci. Pub., 1973. SEPARATIONS 499

Permanentgases may be separatedby gas-solidchromatography. For example, oxygen,nitrogen, and hydrogenmay be separatedby a column packedwith Linde 5A or 13X Molecular Sievesand detectedby thermal conductivity.40'1r Permanentgases such as H2, 02, N2, CO, and CHa. as well as carbon dioxide, terminal alkenesand straight-chainalkanes up to pentaneare well separatedby a temperature-programmedcolumn consistingof a carbon molecular sieve calledSpherocarb.42 The separationof H2, N2,CO, CO2,NO, and N2Ois possible on speciallyactivated silica gel at reducedtemperatures.a3 A more thorough review of the separation of light gasesis given by Littlewood,aaand by Thomp- son.asThe fairly strongoxidizing agent NO2 can be separatedfrom CO2,air, and other nitrogenoxides by using ordinary materialsof constructionfor the chromatograph.a6However, very strong oxidizing and fluorinating agentsrequire the useof nickel, Monel, Teflon, and Kel-F as constructionmaterials, and Kel-F oil on a powderedTeflon supportfor the column packing.aT'48For example,a chro- matographof this sort was usedfor the separationof Cl2, ClF, ClF3, HF, and UFu.otA thermal conductivitydetector employing nickelaT or Teflon-protected elementsa8has been used.The gas-densitydetector, where the heat filamentsdo not come into contact with the samples,ae'soand flame ionization have also been used for strong fluorinating agents. A number of metal and metalloid halideshave been separatedwith rather conventionalarrangements. For example,Keller and Freiserseparated SnCla, TiCl4, Nbcls, and TaC15at 200'C using a coppercolumn packedwith squalane on Chromsorb P (a modified diatomaceousearth).sr A varietyof chlorosilanes and methylchlorosilaneshave been separatedusing siliconeoil plus diethyl ph- thalate as the stationary-phaseand thermal conductivitydetectors.s2 In his study of methyl-ethyllead alkyls, Dawsonfound that pretreatmentof the ChemsorbW supportwith sodium hydroxidereduced the interchangeof alkyl groups betweenthe lead species.SE-30 silicone rubber was used as the sta-

aOS.A. Green,Anal. Chent.,3l; 480 (1959). alG. Gnauck, Z. Anal. Chem., 189: 124(1962). a2Availablefrom Analabs,The FoxboroCompany. 80 RepublicDrive, North Haven.CT 60473. arl. Marviflet and J. Tranchant, in R. P. W. Scott, Ed., Gas Chrontatography, /960 (London: But- terworth, 1960),p. 321. {aA. B. Littlewood, Gas Chromatogruphv (New York: Academic, 1962), pp. 372ff.. {sB. Thompson (general references). aoJ.M. Trowell,Anal. Chem.,37; ll52 (1965). a]A. G. Hamlin, G. lveson,and T. R. Phillips,Anal. Chent.,351 2037 (1963). aER. A. Lanthealume,Anal. Chem., 36;486 (1964). 4qJ.F. Ellis, C. W. Forrest,and P. L. Allen,Anal. Chim. Acta,22t27 (1960). soT.R. Phillips and D. R. Owens in R. P. W. Scott, Ed., Gas Chrontatographl.-.1960 (London: Butterworth,1960), p. 308. slR. A. Kefferand H. Freiser,in R. P. W. Scott, Ed., Gas Chromatography,/960(London: But- terworth, 1960),p. 308. s2G. Fritz and G. Ksinsik, Z. Anorg. Chem., 304;241(1960). 200 SPECIALIZEDVACUUM LINE ESUIPMENT AND OPERATIONS tionary phaseand, in line with previouswork, electroncapture detectionwas found to give high sensitivityfor the lead alkyls.ss The gaschromatographic separation of many hydridesmay be accomplished with relative ease. For example, Borer and Phillips resolved2l silanes up through Si6H16and 5 germanesthrough Ge.rHroon a column of siliconeoil on Celite.slThis sametype of column hasbeen used to separatethe boron hydrides through pentaborane,sswhile paraffin oil was used as the stationaryphase in anotherstudy.sb The boranesamples of Borer, Littlewood,and Phillipsincluded the unstablecompounds BaHl6 and BsH". In order to checkfor decomposition, they perfotmed severalrepeated passes of their samplesthrough the chromatograph and this revealedslight decompositionof BsH11.A check of this sort ap- pearsadvisable whenever unstable compounds are handled.Thermal conductivity detectorshave been used with all of thesehydride compounds;however, less thermallystable hydrides create deposits in the detector,which impairs its function. An interestingtechnique which circumventsthis problemand increasesthe sensitivityof detectioninvolves the use of a furnace on a quartz capillarytube which is placedbetween the exit of the column and the detector.Complete pyrolysisof the hydride occursin this tube to yield hydrogen,which is then detected by thermal conductivity.Highly purified nitrogen u'asused as the carrier gas, and the best separationof SiHa,GeHa, AsH3, and PH3was obtained with a siliconeoil stationaryphase.s-

9,3 sToRAGEoF GAsEs AND soLVENTs

Small quantitiesof gasesare most convenientlystored in glassbulbs, which are selectedto be free from thin spotsand are well annealed.Despite these precautions, there is the chanceof implosionwhen the bulb is evacuated;the resulting hazardof flying glassmay be avoidedby wrappingthe bulb with tape.enclosing it in a wire mesh cage, or coating it with a tough plastic paint.ssThe requirementsfor a stopcockor valveon a storagebulb are much more stringentthan for ordinary use becausecontinual exposureto the gas may break down stopcock grease.A Teflon-glassvalve does not sufferfrom this disadvantage,but when it is usedon a storagebulb, the seatside of the valveshould retain the gassince the stem side is more subjectto leakage(Fig. 9.29). Large quantitiesof gas and solventswith high vapor pressuresmay be stored srH.J. Dawson,Ir., Anal. Chent., 3\ 542(1963). saK.Borer and C. S. G. Phillips,Proc. Chem..9oc., 189. (1959). ssK.Borer, A. B. Littleu'ood,and C. S. G. Phillips,J. Inorg. Nucl.Chem., 15;316 (1960). :nJ.J. Kaufnran,J. E. Todd. and W. S. Koski,,4ral.Chent.,29t 1032(1957). srG.G. Devyatykh,A. D. Zorin, A. M. Amelchenko,S. B. Lyakhmanov.and A. E. Ezheleva.Akad. Norl<.,SSSR (English trans.), 156; S91 (1961). :sAvailablefrom Ace GlassCompany, Vineland, NJ. SIORAGEOF GASESAND SOLVENTS 201

Cooted

\Freeze-out Tomorn monrf old tip

Fig. 9.29. Typical arrangenrentof gas storagebulbs.

in 200-mL stainless-steelcylinders fitted with packlessvalves and mounted firmly on an angle iron frame. The tank may be attachedto a small manifold (equippedwith a mercurybubbler manometer)through a glassbellows or a loop of 6-mm glasstubing to take up any slight differentialmovement (Fig. 9.30). It is convenientto store frequently used solventsin containersdirectly attachedto the vacuum line. The valverequirenrents are even more stringentthan for gas storage,because the attack of stopcockgrease by organicsolvent vapors is a certainty.Therefore, Teflon-stemmed valves are generally called for. A good solventstorage container may be constructedfrom a distillationflask. As shown in Fig. 9.19, the solventmay be fractionallydistilled directly into the sidearmof

,,Glossloop :_pockless

Fig. 9.30. Storageof gasesin metal tanks. The valveis bolted directlyto the steelframe. which is rigidly mounted. 202 SPECIALIZEDVACUUM LINE EQUIPMENT AND OPERATIONS this flask. The solventis then frozen down, the flask is evacuated,and the sidearm is sealedoff. Inclusion of a drying agent, such as calcium hydride, in the flask ensuresthat the solventwill remain anhydrous. The long-termstorage of liquids and gasesis bestaccomplished in an ampule or bulb fitted with a break-seal.Once the sample is sealedoff in such a container, leakageis no problenr as it would be if a stopcockor valvewere used. Furthermore,this practiceis economicallysound, since a break-sealis much less expensivethan a stopcockor valve.

9,4 sEALEDTUBE REAcnoNs

The difficultiescreated by stopcocksand valvescan usuallybe minimized.How- ever,it is occasionallynecessary to completelyeliminate these sources of leakage and contaminationby the useof break-sealsand vacuumseal-offs. Typical situationsin which sealedtube techniquesare widelyused are quantitativehydrolysis and oxidation reactionswhich require elevatedpressures and temperatures, precisephysical measurements on highly reactiveorganometallic compounds, long-term storage of reactive samples, and nonaqueous reactions under high pressure(for example,SOz or NH: at room temperature).Each pieceof apparatus must be constructedto meeta specificneed, so it is not possibleto outline an apparatuswhich is of generaluse. Nevertheless, several examples will be pre- sentedhere which serveto indicatethe approach. Break-seals(Fig.9.3l) are commonlyused on sealedreaction and storage tubes becausethis type of seal allows recoveryof volatile materials.The type illustratedin Fig. 9.31c may be openedin an apparatuswhich containsan off- centerarm which may be rotated to break the small tube (Fig. 9.32a).Among the many variantsof this designof tube opener,one by Mahler and Velmeyis constructedfrom al,/4-in.stainless-steel needle valve which is drilled out to re- ceivethe break-sealso that the valve stem may be screweddown on the small tube (Fig. 9.32b).seThe break-sealand vacuum systemare connectedto this

tl Seol- lhrougn II { lornt [-! I rl

Fig,9,3t. Break-seals. sqW.Mahler and H. V Fefmey,Rey. Sci. Instr.,33,'t127 (1962). SEALEDTUBE REACTIONS 203

To vocuumltne

To seoledtube v

(b)

Fig.9.32. Tubeopeners.

modified valveby Swagelokfittings in which a Teflon front ferrule is used(see Chapter4). The break-sealsillustrated in Fig. 9.31b andc are openedby means of a magnetichammer which consistsof a glass-encasediron rod actuatedby meansof a hand magnet. The reactiontube illustrated in Fig. 9.33c is usefulfor hydrolysisreactions and other situationsin which considerablepressure may build up in the tube becausethe break-sealused here withstandshigh pressures.The procedurein- volvesdistillation of the compoundand outgassedwater (or HCI-watermixture) into the tube on the vacuum line. It is then sealedoff under high vacuum (Ap-

Fig. 9.33. Typical sealedtube designs 204 SPECIALIZEDVACUUM LINE EQUIPMENT AND OPERATIONS

pendix II) and allowed to warm to the appropriatetemperature. When high pressuresare anticipated.every precaution must be taken to avoidendangering laboratorypersonnel. In general,a safety-glassexplosion shield or a small metal containmentshield around the tube shouldbe used,and the experimentshould be arranged so that the tube can be cooledto a low temperaturebefore it is handled. The break-sealis easilybroken by clumsyhandling, so it is protected by an openjoint. Glassapparatus under pressuremust alwaysbe treatedas dangerous;however. some rough guidesare given in Appendix II for the minimiza- tion of breakage.It is quite important for a glassbomb tube to be smoothly blown and well annealed. After hydrolysisor similar reaction,the tube is cooledin liquid nitrogento reducethe pressureof the gasesand openedwith a specialdevice (Fig. 9.32). If noncondensablegases result, they are collectedwith the Toepler pump or low temperatureadsorption for measurementand identification. If the weight gain of the contentsof the tube is of interest.the break-seal describedabove (Fig. 9.31a) is inconvenientbecause the broken parts are not easyto collectand weigh. In this casethe break-sealsillustrated in Fig. 9.316 and c are more useful. The former is availablecommercially at low cost, and eithertype is easilyconstructed. These break-seals are broken openby meansof a glass-encasediron rod or, if it will not reactwith the gasesunder study.a clean ball bearing.The breakeris raisedwith a hand magnetand allowedto fall on the thin break-seal.The tube shown in Fig. 9.33c is usefulfor studyinggas-solid reactionswhere the reactionhas to be allowedto standfor a long time or whereit requiresheating. A typical procedureinvolves weighing the tube and a small stopper,introducing the solid, outgassingunder high vacuum, reweighing. reevacuating,distilling a measuredquantity of reactivegas back into the tube, and sealingthe tube off under vacuum(Appendix II). When the reactionis complete,the tube is attachedto the vacuum line, the spaceabove the break-sealis evacuated,and, after the gasin the tube hasbeen condensed, the tube is opened by meansof the magnetichammer. The tube is allowedto warm very slowlyby means of a chilled Dewar to preventthe solid and glassparticles front being carried into the vacuum systemby a suddensurge of gas. After the gas is collected,dry nitrogenmay be admittedto the tube, and the tube removedfrom the vacuum line while the magnetichammer is quickly removedand a small rubber stopperis usedto sealthe open end. Both parts of the tube are then weighedin order to calculatethe weightgain of the solid.In addition,the recoveredgas may be measuredand identified. The trap-to-trap condensationof compoundswith low volatility is ahvays troublesome,and the situation is aggravatedif the compound evolvessmall quantities of lesscondensable decomposition products. When thesecases are encountered,the sample is best collectedin a U-tube (Fig. 9.33b) becauseit allowsthe distillation of the compoundthrough one leg while a high vacuum is maintainedon the other. Both arms of this tube must then be sealedto isolate the sample. Sealed-tubemanipulations have been employed in physical studieson SEALEDTUBE REACTIONS 205

Grignard reagentswhere tracesof oxygen and stopcockgrease may lead to erroneousresults.60'br As illustrated in Fig. 9.34, the apparatusis designedwith a specificsequence of operationsin mind. Reactionsof liquefied gases,such as NH-rand SO2,may be carried out in sealedtubes at room temperature.Liquid ammonia exerts approximately10 atm pressureat room temperature,so a tube diameterlarger than l5 mm should be avoidedand the previouslymentioned safety precautions must be observed. Franklin and his studentscarried out many acid-baseand metathesisreactions in multileggedtubes such as those illustrated in Fig. 9.35.62The reagentsmay be chargedinto the legs,the solventintroduced on the vacuum line, and the tube sealedoff. The reactionbetween two or more solutionsis accomplishedby tipping the tube. If a solid is formed, the supernatantliquid may be decantedand the leg containingthe solid may then be cooledin an ice water bath to accumu- late ammonia for washing the solid. Some workers prefer to use multilegged vesselsof this sort with a small pressurestopcock fitted to the inlet tube, in which

Fig. 9.34. Apparatusused for the preparationand samplingof Grignard reaqentsfor NMR spectroscopy.The apparatuswas evacuated through J1and the Mg baked. Excessether and alkyl halide were distilledonto the metal, and the apparatuswas sealedoff at Sr. Upon warming to 0'C and shaking,a rapid reactionoccurred. The apparatuswas evacuated at J,. the break-sealB wasbroken, and etherand excessalkyl halidewere removed. Fresh dry etherand the tetramethylsilane standard weredistilled in, the apparatuswas sealedoff at S,, and a small portion of the solutionwas filtered through the frit F into the NMR tube, which uas sealedoff at 52.(Adapted from D. F. Evansand J. P. Mahler, J. Chenr."loc., 1962,5125.) noA.D. Vreugdenhilland C. Blomberg,Rec. Truv. Chin.,82:453 (1963). nlD. F. Evansand J. P. Mahler.J. Chent..ioc..1962: 5125. nrE.C. Franklin. The Nitrogen SystentoJ'Contporiads (Neu York: Reinhold,1935). 206 SPECIALIZEDVACUUM LINE EQUIPMENT AND OPERATIONS

^ #

//l\ /\ U\JUUU/t[\ UU (o) (b) (c)

Fig. 9.35. Sealedtubes for the observation of reactions in liquefied gases.Liquid phasesmay be decanted from one leg to the next. casethe tube is easilyopened to samplegases or removethe solvent.63Of course, the tube may alsobe fitted with a break-sealthrough which gaseousand volatile productsmay be removed.This wasthe approachtaken by Stock,who included a slightly constrictedportion in the middle of the tube with a wad of glasswool to serveas a filter.

9.5 MrscELLANEousTEcHNteuEs

A. Sompling Alkoli Mefols. Of the alkali metals, lithium is in some re- spectsthe most difficult to handle.It reactsslowly with nitrogen;so when purity is important, it should be handled in an argon atmosphereor in a vacuum. In addition, the molten metal reactswith Pyrex,causing it to crack. For rough applicationsit is satisfactoryto cut and weighsodium or potassium chunks under a hydrocarbon. CAUTION: Halogenated hydrocarbons should not be used because they present a serious explosion hazard in the presence of alkali metals. In the case of potassium, the oxidized layer should be carefully scraped from the surface before the metal is cut, becausean explosion may result if this crust is embeddedin the metal. For many, purposesweighed quantities of pure sodium may be introducedin sealed,thin-walled glass bulbs which may be broken with a glass-encasedmagnetic hammer to releasethe metal. Thesebulbs are preparedas follows. A thin glassbulb is blown onto a joint so that there is a constricted region between the bulb and the joint (Fig. 9.36). The bulb is weighedand its volume is measuredfor a subsequentbuoyancy correction. A chunk of metal of the approximatedesired weight is placedin the apparatusso it restson the constriction,and the bulb is attachedto a vacuum line and evacuated. When a high vacuum is attained,the constrictionand regionabove it are flamed gently so that the metal melts and runs down into the bulb. The crust of oxide is left behind in this process.The bulb is sealedoff under vacuum at the constriction.After the top part is cleaned,it is weighedalong with the bulb, and brW.C.JohnsonandW.C.Fernelius,./. Chent.Educ.,6:441(lg2il.lnthisreferenceandfootnote 63, the procedureswhich are describeddo not involvethe useof a vacuum line. MISCELLANEOUSTECHNIQUES 207

--i; \a .i'7 ll ll I lt tel ll l'l td OV

Fig.9.36. Preparationof weighedsamples of pure alkali metal. On the left the sodiuntis being melted under vacuum by meansof a cool flame. On the rieht the bulb has been sealedoff under

a buoyancycorrection is then appliedto givean accurateweight for the metal in the bulb. Sodium, which is sealedoff in this manner, is usefulfor quantitative work on the vacuum line sinceno extraneousgases or solid impuritiesare intro- ducedwith the sample. The sodium-potassiumalloy (45-90 weight %K) is molten at room temperature and cesiummelts at 28.5o, so both of theseare easilyhandled as liquids. For example,a hypodermicsyringe is convenientfor their transfer.The sodium- potassium alloy is made by heating the two metals together while they are protectedby a high-molecular-weighthydrocarbon. With the exceptionof lithium, the alkali metals may be distilled in an all- glass, high-vacuum apparatus to yield a very pure sample. Finally, a novel methodfor the quantitativeintroduction of smallamounts of sodiuminto a glass apparatusis the electrolysisof the metal through glass.oa

B. Genelofion of Dry Goses. Directionsare given below for the preparation andlor purificationof severaluseful gases.

Oxygen.oo A tenfold excessof potassiumpermanganate (calculated on the basis of 2KMnOa : MnO2 * K2MnOa * Or) is placedin a glassbulb which is sufficientlylarge to allow doubling of the volume of solid as the reactionpro- ceeds.A plug of glasswool is placed abovethe sampleto avoid contamination of the vacuum systemby solid particles.The sampleis heatedto 100oCwhile it is evacuatedovernight under high vacuum. After this initial bake-out,the sample is left open to the vacuum pump while the temperatureis raisedto approximately 200oC, where oxygen production commences.The vacuum pump is closedoff briefly so that oxygenevolution can be roughly estimated. Evacuation is continued until 5-10% of the theoreticalquantity of oxygen has been dis-

HW. L. Jofly. J. Phys.Chent., 62',629 (1958). 208 SPECIALIZEDVACUUM tINE EQUIPMENT AND OPERATIONS carded. The oxygen sample is then collectedwhile the solid is heated above 200'C (but not in excessof 230'C).

Methane. ResearchGrade (about 99.65 mote % pure) and CP (about 99.0 mole 7o pure) methaneare availablein cylinders.The removalof CO2,Oz, Nr. and higher hydrocarbonsfrom methaneby adsorptionon charcoalhas been describedin the literature.6s

Ethylene. This gas is availablefrom the Matheson Company in CP (99.0% pure) and ResearchGrade (99.9 To pure). Oxygenmay be removedby passing the gas through a tube containingMnO. sulfur Dioxide. High-purity sulfur dioxide is availablein cylinders.It may be further purified by passingit over Pao,6to removewater and degassing.In their precisework on the vapor pressureof SO2,Giauque and Stephensonprepared this gasby the reaction of concentratedsulfuric acid with sodium sulfite.66It was then passedthrough water to removeSO3, through PaO16to removethe water, and finally subjectedto severaltrap-to-trap distillations. following by degassing.

Ammonia. The major contaminantsin the "anhydrous ammonia" available from the Matheson Company in cylindersare water, oil, and noncondensable gases.Most of these impurities are removed by passingthe NH3 through a trap -22"C held at and condensingit at -196'C undervacuunt.The wateris removed by distilling the ammonia into a tube which containsa small lump of sodium.The tube is warmed slightlyto n.reltthe an'rmoniaand form a blue solution, and the resultingdry ammoniais punrpedaway. A fairly largeplug of glass wool must be included betweenthis tube and the vacuum systemto avoid contaminating the line with a fine sprayof sodium metal. The gas is condensedat -196'C under high vacuum to removehydrogen and other noncondensables.

GENERALREFERENCES

Temperolureond TempeloluteMeosuremenf

Benedict, R. P., 1984,Fundantentals o;f Temperuture, Pressure,and Flov' Measurements,3rd ed., Wiley. New York. Quinn, T. J. , 1983, Tenrperuture, Academic, London. A comprehensivereview of thermometry over the temperaturerange 0.5-3000 K. The book includeschapters on resistancethermometrv and thermocouples, and is extensivelyreferenced.

o:J. H. Eisemanand E. A. Potter."/. Res. Nar. Bur. Std., 58; 213(1957); H. H. Storchand P. L. Golden,J. Am. Chent.,.loc.,54, 46620932\. 66W.F. Giauque and C. C. Stephensen,"/. .4nr Chent.Soc., 60; l3B9 (1938). GENERALREFERENCES 209

Schooley,J. F., Ed., 1982, Tentperuture-lts Meusurentent und Control in Scienceund Industry, Vol. 5, American Instituteof Physics,Neu York. An excellentsource of state-of-the-artther- mometry comprisedof papersfrom the Sixth InternationalTenrperature Symposium. Topics which are coveredinclude temperature scales and fixed points, radiation,resistance, thermocouple,and electronicthermometry, temperature control, and calibrationtechniques. Preced- ing volumesin the seriesdate back to 1939.

Gos Chromotogrophy

Keszthelyi,C. P., 1981,in P. T. Kissingerand W. R. Heineman,Eds., LaboratoryTechniques in Electrounulyticul Chentistry, Marcel Dekker, New York. Vacuum line designand experimental methodsfor electrochemicalexperimentation. McNair, H. M.. and E. J. Bonelli, l969,.BasicGas Chrontutogruph,-,Sthed., Varian Associates, lnc. Thompson, 8.,1977, Fund.antentalsqf Gus Anulysisby Gus Chronntogruphy,Varian Associates. Inc., PaloAlto, CA. 40 MetolSysfems

Glassapparatus often is widelyused for the constructionof laboratoryapparatus becauseit is relativelyinert, light. transparent, and easyto clean. However, metal apparatus has decided advantagesin some applications.For example, metals are mechanicallymore robust than glass,many metals are resistantto reactivefluorides, and metal valvesand joints can be much more leak-tightthan their glasscounterparts. Because of thesequalities, metal is usedfor the constructionof high-pressureapparatus, fluorine-handling vacuum lines, and very- high-vacuumsystems. In addition, metal is a popular materialfor gas-handling manifolds and flow reactorsfor catalysisresearch. The first part of this chapteris devotedto the properhandling of gascylinders and compressedgases. This sectionshould be requiredreading for anyonework- ing with compressedgases for the first time. The constructionof apparatusfrom seamlesstubing is describednext, and the designand characteristicsof common metal components,such as valvesand joints, are presented.The chapterends with detailsof somegeneral-purpose metal apparatusfor catalltic reactorsand fluorine chemistry.Attention alsois directedto Appendix IV for detailson the propertiesof metals.

'10.'l coMPREssEDGAsEs

A. Sofe Hondling of Cylindels. Severalpopular cylinders for the containment of compressedgases range from the sizeoften usedfor nitrogen or oxygen (about 9 in. in diameter by 52 in. high, exclusiveof the valve and cap) to the lecturebottle (2 in. in diameterby l5 in. long) which is usedto dispensesmall amountsof reactivegases. In the United States,the cylindersizes vary from one 2tio COMPRESSEDGASES 241

supplier to the next; however, there is fairly uniform adoption of valve outlet fittings as perscribedby the CompressedGas Association.A typicalcompressed gas valveand fitting for large cylinders consistsof an emergencypressure release fixture, an on-off valve, and the outlet fitting. CAUTION: Never tamper with the emergency pressure release fixture. Unfortunately, the emergency pressure release fitting sometimes has a hexagonal outer contour and therefore can be loosenedby means of a wrench. The valve assemblyis the most vulnerable part of the cylinderand it can be broken off if a cylinderis accidentallydropped. A pressurizedcylinder which has broken open is very dangerousbecause it is pro- pelled like a rocket. CAUTION: To minimize the chance of a cylinder being ruptured by falling, the cylinders should always be strapped in place when the protective cap is removed, and the cap should be replaced before the cylinder is moved to another location. Of course, a cylinder should never be deliberately dropped, evenwhen the protectivecap is in place. Some of the common high-pressurecylinder fittings are illustrated in Fig. 10.1.Many of thesehave as their sealingsurfaces a conein the outlet and a cone- shapedor rounded nipple on the connectingpiece. Those fittings, which do not havegaskets, require firm tighteningto achievea gastightseal. For a few gases which are deliveredat lower pressure,the connectionis made by meansof flat surfaces,one of which containsa washerof lead or other soft metal. NOTE: Left-handed threads are used on flammable gas cylinder fittings, for example, H2e propane, and CO. The connector for these flammable gasescan be identified by means of V-shaped indentations on the edges of the hexagonal nut (Fig. f0.f .b). It may seemto the user that the wide varietyof outlets is a nuisance; however,they servethe beneficialpurpose of avoidingaccidental connection of the wronggas to an apparatus,and they avoidthe possibilityof usinga regulator for a flammablegas on a cylindercontaining oxygen or anotheroxidizing agent. Trapped gas or oil residuesfrom a flammable gas are likely to explodeif sud- denly compressedwith high-pressureoxygen. The CompressedGas Associationspecifies two typesof outletson lecturebot- ttes(Fig. 10.2),depending on whetheror not the gasis corrosive.A lead washer is insertedbetween the tank outlet and the connectorfitting. Thesegaskets generally last for only a few cyclesof assemblyand disassembly,so a good stock shouldbe kept on hand. Theseare readily made usingtwo hole punchesof appropriatediameter and a sheetof r/ro-in.-thicklead. As with the largertanks, the outlet valveon the standardlecture bottle is of the on-off type and is not suitable for the control of gas. Both pressureregulators and needlevalves are available which will mate with the lecturebottle fitting. A needlevalve is the most generally usefulmeans of gasregulation because lecture bottles are mostoften usedto dispensesmall quantitiesof gas for chemicalreactions. In placeof the lecture bottle, somechemical supply houses provide gases and highly volatileliquids in small welded steelcontainers (about 3 in. in diameterand 5 in. high) that are light and easyto handle. In general,these cylinders are usedfor low pressure and relatively noncorrosivegases, and are fitted with a needle valve outlet equippedwith a swageor pipe thread fitting. The valvethat is suppliedon the 212 METALSYSTEMS

8?5 t3 l6

(a)

CONNECTION -T T- J .825' 830" 13/1 6', |3/r6" 1_r l-

(b)

OUTL E1 CONN€CTION ----r-- f -..J 845" ffi" 1t8 7ta ll:l

(c)

I OUTLET L,..,r-_T_

-.^^^.I.UJV -.'l | 1" "ll-__r WASHE

(d)

Fig. 10.1. Somecommon high-pressuretank fittings.The sealin the top threefittings is made by contactbetween the nipplein the connectionand the seatin the outlet.Note the cone-shaped,round, and bullet-shapednipples for (,r),(ä), and (c) respectively.The bottom connection(d) is sealedby meansof a flat soft-metalgasket. Never atlenrpt to mix outlet and connectionsbetueen the various designs.Note the grooveson the connectionnuts for connections(6), (c), and (d). This grooveindi- catesa fitting with left-handedthreads. (Reproduced by pernrissionof the copyrightholder, Mathe- son Gas Products.lnc.) tank often is satisfactoryfor controllingthe gasoutlet, but if thereis any doubt, an additional needlevalve (see Section10.5) or pressureregulator should be added.

B. Sofe Delivery of Goses. The vast majority of compressedgas cylinders are supplied with efficient on-off valveswhich provide no significantflow or pressurecontrol. CAUTION: It is necessaryto equip a compressedgas cylinder with some means of controlling the pressureand/or flow of the gas being deliv- COMPRESSEDGASES 243

OUILET

I .561l 5625 .5524 9/ 16 9/16', +l

OUTLET LEAOWASHER --T-

(b) 5/16" 32 I ffiEtt

Fig, 10,2. Fittings for lecture bottles. Both fittings are designedto seal by means of a soft lead washer, which must be replacedfrequently. Fitting (c) is for noncorrosivegases and (b) is for corrosive gasses.(Reproduced by permission of the copyright holder, Matheson Gas Products, Inc.)

ered. The choiceof pressureversus flow control is basedon the nature of the experimentbeing performed.The deliveryof gas to a closed,low-pressure system requiresthe useof pressurecontrol by meansof a diaphragmregulator (Fig. 7.14). For example, the deliveryof nitrogen or argon to an inert atmosphere Schlenk-typeapparatus (Chapter 1) dictatesthe useof a goodpressure regulator which will deliverabout 3 psig of gas. Similarly, the oxygenfor a glassblowing torch is suppliedvia a diaphragmregulator. The leastexpensive pressure regulators are fitted with only one stageof regulation.This resultsin a slowchange in the outlet pressureas the tank pressuredecreases. Much better regulationis obtained with two-stageregulators. Another point which requiresattention in the choiceof a regulatoris the output regulationrange. A differentregulator is chosenfor high-pressureoutlets (to fill high-pressurereactors) than for general use.The general-usemodels listed by many distributorshave output regulation in the 0-75 or 0-50 lb/in.2 range, which is not optimum for someof the most common laboratoryapplications. The best choicefor inert-gaslines and glassblowing torchesis a regulatordesigned for a 0-15 lb/in.2 output. As described below, corrosiveand high purity gasesrequire specialregulators. If gasis to be deliveredto a reactionflask which hasan unobstructedoutlet, a simple flow control valve on the high-pressurecylinder will provide adequate regulationof the gas delivery.In this casea needlevalve is attachedto the cylinder, or to a pressureregulator which in turn is attachedto the cylinder.It alsois possibleto delivergas to a closedsystem, such as a vacuum line, with a flow control valve. In this casethe pressurewithin the apparatusmust be carefully monitored by meansof a manometerand the systemshould also be equipped with a meansof pressurerelief, such as a mercurybubbler manometer(Fig.7 .2). When reactivegases such as HCI or BF3 are handled,the regulatoror valve shouldbe constructedof a metal which is corrosionresistant. The sas distribu- 214 METALSYSTEMS tor's cataloggenerally Iists the appropriatevalve material.r For example.a needle valve controller for the deliveryof hydrogenhalides or metalloid halidesfrom a lecture bottle should be constructedfrom Monel. whereasbrass valveswill suffice for unreactivegases such as Freons,sulfur hexafluoride,and the like. The combination of mechanical action of the valve. the corrosiveaction of the gas, and moisturefrom the air can readilylead to corrosionand seizureof valves or regulators. Therefore, it is good practice to purge out the valveafter eachuse. In the caseof a lecture bottle needlevalve. this entailsremoval of the needle valveand flushing it with a streamof inert gas. Someof the commerciallyavailable regulators and fittings for corrosivegases are equipped with a purging inlet so the system can be purged with inert gas before and after the reactive gas is dispensed. When very-high-puritygases are handled, specialpressure regulators with metal diaphragmsare desirableto avoid contaminationby atmosphericgas diffusion through elastomericmaterials on conventionalregulators. Similarly, metal or glass delivery lines are preferred over rubber for the delivery of high- purity gas.

10,2 cuTnNeAND BENDTNG TUBtNc

Seamlesscopper and stainless-steeltubing are usedfor a varietyof gasdelivery and reactor systemsin the laboratory, and it is a tremendous convenienceand time saver if the researchworker is able to perform simple fabrication and re- pairs. Seamlesstubing of r/.r-in.O.D. or larger is fairly rigid; therefore,when high flexibility is needed,a loop of r/s-in.seamless stainless-steel tubing may be used.An evenbetter choicefor low-pressureapplications which requireflexible metal tubing is thin-walled corrugatedstainless-steel tubing. The methodsof joining corrugatedtubing to apparatuswill be describedin this section. Seamlesscopper or stainless-steeltubing may be cut with a hacksawor, more conveniently,with a tubing cutter by the processillustrated in Fig. 10.3. In either case,the cut shouldbe squareand cleaniffittings areto be usedon the tube ends. Any burr on the tube can be removedwith a file or the specialrouting blade attachedto most tubing cutters. When bent on a sharp radius, tubing tends to collapse. To reduce this problem, a hand-operated tubing bender is very helpful (Fig. 10.3). Sturdy, tightly coiled spring setsmay be pur- chasedfor bendingtubing. The springis slippedover the outsideof the tube and removedafter the bend is completed.It is alsopossible to minimize kinking by packing the tube with sand and corking the ends.The advantageof theselatter two methodsare that the bend can be made with any radius around the circum- ferenceof a pipe or bar of suitablesize. If the exact radius is not critical, the tAirco Rare and Specialty Gas Catalog, Airco,575 Mountain Ave., Murray Hill, NJ 07974',Linde Specialty Gasesand Related Products, Union Carbide Corp., Linde Div., Box 444, Somerset,NJ 08873; Matheson Gas Products, Matheson Gas Products, P.O. Box 1587, Secaucus,NJ 07094. TUBING.JOINTS. AND FITTINGS 215

Cutlrng wheel Stotroncry bendrngform

0t0cx

Compressron f ype

Roto

\Siotronory pressuredie

Drow type

(c)

Fig. 10.3. Cutting and bendingtubing. (c) Sideview of a tubing cutter. (ä) The tubing cutter in use:The handleis turned until the cutting wheelslightly penetrates the metaltubing. (b) The cutter is then rotated around the tubing. The handle is retightened and the processis repeateduntil the tubing is conrpletelysevered. (c) Two designsfor tubing benders. (Reproducedbv permissionof the copyright holder, Crau'ford Fitting Co., Cleveland, Ohio.)

tubing bender is generallypreferred. Large-diameter tubing is not easilybent, and sharp turns are impractical in any diameter tubing, so in thesecases an elbow fitting is used. Thin-walledcorrugated tubing can be crushedby swage-typefittings. Some- times this type of tubing is fitted by the supplier with heary-walledend tubes which can be connectedby conventionaltechniques (Section 10.3) to an apparatus. If the tubing is not soequipped, it is necessaryto havethick-walled tubing brazedor weldedto the ends.One manufactureralso provides heavy-walled in- sertswhich can be slippedinside the thin-walledtubing to provideadded rigidity.2

',l0,3 TUBTNG,JorNTs, AND FTTTTNGs

A. Soldel ond Weld Fittings. Copperelbows, T's, andoosses are manufacturedto be solderedor brazedto coppertubing (Fig. 10.4). When soft solder

2CrawfordFitting Co., 29500Solon Rd., Solon,OH 44139. 216 METALSYSTEMS uuNH :) lt

(o) (b)

Fig. 10.4. Two solderfittings. (a) Cross-sectionof an elbow.(ü) A T-fitting. (Reproducedby permissionof the copyrightholder. Crawford Fitting Co.. Cleveland,Ohio.)

is used,the insideof the fitting and outsideof the tubing are tinned with solder and the hot parts are slippedtogether. An acid-typeflux, for example,l0% HCI plus l0% ZnCl2 in water, aids in the tinning process.Similarly, hard solder (brazingor silversolder) joints can be used.Soldered joints are compactand can be very leak-tight,but they are permanentand the solderingprocess introduces impurities andlor oxidation of the tubing; therefore.the apparatusshould be thoroughlycleaned before it is used.Weld fittings, similar in generaldesign to the solderfittings, are availablein a varietyof materials.2

B. Flote Fittings. This type of fitting (Fig. 10.5)is one of the oldestmeans of making a removabletubing joint. As shownin the figure, annealedtubing with a smoothlycut end is flared by clampingit into a flaring tool and tappingthe inner die on this tool with a mallet. If the metal is not annealedor if the flaring process is roughly performed, a crack may developon the flared edge,rendering that surfaceuseless. The flared tubing forms a joint betweena nut and a coneof the flared tubing. Considerabletorque is neededto obtain a leak-tight seal. The flare fitting is cheapand works well with copper.but it is more trouble to make than swage-typefittings and is not practical with many hard metals.To over- come thesedisadvantages, a varietyof swage-typefittings havebeen developed under trade namessuch as Swagelok.Gyrolok. and Tylok.

Fig, t0.5. Cross-sectionof a flared tubing fitting. Annealedtubing is flared by meansof a simple flaringtool, and this flaredtubing is compressedagainst a nipplefitting by meansof a threadednut. TUBING.JOINTS, AND FITTINGS 247

C. Swoge-Iype Fitlings. These popular connectorsare availablein various metalsand plastics,and they are usefulfor joining similar or dissimilarma- terials, such as metal to plasticor metal to glass.2'3The common swagetubing couplerhas four parts: the body, into which the tube is placed,two ferrules,and a packingnut (FiB. 10.6).In general,the tubing shouldbe softerthan the fitting so that during the tighteningprocess the ferrulessink into the tubing and at the sametime the end of the tubing is butted tightly into the body. In the caseof stainlesssteel, hardened tubing should be avoidedbecause it is not sufficiently ductile to conform to the ferrulesand body. In general,brass fittings are used with copper tubing, stainless-steelfittings with stainless-steeltubing, Monel with Monel, and so on. The joint is assembledas illustratedin Fig. 10.6and the nut turned down finger tight. By meansof a wrenchon the body and anotheron the nut, further tightening by lt/e revolutionscompletes the assembly.These typesof fittings can be openedand closed;however, the ferrulesare not remov- able. When a fitting is reassembled,a fraction of a revolutionis sufficientto completethe seal. The swage-typefittings begin to leak if openednumerous times, and the flare joint describedabove or the modified flange-typejoints describedbelow are preferredwhen frequent openingis necessary. Swage-typejoints alsoare convenientfor joining metal apparatusto glassapparatus. In this case,the body of the joint may be made of any metal and a Teflon or graphite front ferrule is employed.The ferrule deformson compres- sionto make the seal.Because Teflon will cold-flow,it is sometimesnecessary to retightenthese joints. A graphite front ferrule is preferredwhen elevatedtem- peraturesare employed,as in the caseof heatedgas chromatographycolumns. In either case,the backing ferrule is generallychosen as a harder materialthan the front ferrule, for example, nylon or metal in the caseof a Teflon front fer-

io) (b)

Fig. 10.6. Swage-typefittings. (d) T-fitting (ä) Cross-sectionshowing the front ferrule A and the back ferrule B. (Reproducedby permissionof the copyrightholder, F. J. Calahan,"Swagelok Man- ual," Crawford Fitting Co., Cleveland,Ohio.)

rHoke Inc., I Teanakill Park, Creskill,NJ 07626. 218 METALSYSTEMS rule, or metal in the caseof a graphitefront ferrule. It is criticalto employtubing which makes a precise fit with the Swagefitting and ferrules. Unfortunately, most swage-typejoints availablein the United Statesare made to English standards,whereas the standard-walledborosilicate glass tubing is manufacturedto metric specifications.Because the toleranceson ordinary glasstubing are not highly precise,it is possibleto find the occasionalpiece of standard-walledtubing which will match a swagefitting with English dimensions.The better solution is to employ medium-walledtubing, which is manufacturedto English dimensions.It is important to havea squarecut and no sharp edgeson the end of the glasstube, becausesharp or jaggededges will cut or scratchthe soft ferrule materialsand irregularedges are likely to break. It is possibleto achievea satisfactory edgeby meansof a cleanbreak and a very light fire polish, but the preferred method is to cut the tube end on a diamond sawand removethe edgeby very light grinding on a water-cooledsanding belt or similar grinding surface. Most gas chromatographysupply housesalso stock one-pieceferrules made of Teflon, graphite, or Vespel(a polyimide).The upper working temperature quotedfor eachof theseis 250, 450, and 350'C, respectively,and all of theseare quite usefulfor connectingglass tubing to metal fittings. The Vespeland graphite ferruleshave the advantageover Teflon that they do not cold-flowand they givegenerally better performanceon joints that are heatedand cooled.Vespel is more mechanicallyrobust than graphite. New ferrules made from a Vespel- graphitecomposite can be usedup to around400o and haveeven better mechanical propertiesthan Vespel.

D. Flonge lubing Conneclols. Recently,metal tubing connectorshave becomeavailable in which inner and outer packing nuts are employedto hold two flangestogether.2 In somedesigns an O-ring sealis made betweenthese two flanges,and in others a metal gasketis employed(Fig. 10.7).These flange fittings are attachedto tubing by solderingor welding,so they are lessconvenient to install initially than the swage-typefittings, but they areeasily assembled and disassembledand are preferablewhen the systemis openedoften. Sincethe ends of the fitting are flat, thesetypes of fittings can be usedwhere a component must be removedthat is in line with the entranceand exit tubes.This is not possible with standardswage or flared connectors.The CajonVCR fitting, which is availablein stainlesssteel or Monel, givesgood service in fluorine vacuumsystems. In this application,flat gasketsof copperor nickel can be used.

E. Miscelloneous lubing Connecfols. The varietyof tubing couplersis enormousand a comprehensivelist would be out of placein this book, but several additional typeswill be mentionedhere which are usefulin the laboratory. Metal standard taper and metal ball joints are available,and thesewill mate with correspondingground-glass joints to provideone means of connectingparts made of dissimilar materials.aAs with glassstandard taper joints, the seal is

{KontesGlass Co.. P.O. Box 729. Vineland. NJ 08360. HEAVY.WALLEDTUBING AND PIPEJOINTS 249

(b)

Fig. 10.7. Flangetubing connectors.(a) Cajon VCO O-ring sealedfittingl (b) Cajon VCR metal gasketedflange fitting. (Reproduced by permission of the copyright holder, Markad ServicesCo.) made with greaseor wax. Another useful type of joint is basedon an O-ring which is compressedbetween the insideof the joint and the outer dianleterof a tube. Plastic annular O-ring fittings of this type, designedprimarily for glass apparatus,are described in Section8.1.B. Fig. 8.5. Similarly, an annularO-ring joint, which was originally designedfor a metal apparatus.is illustratedin Fig. 8.5. This joint is equally serviceablewith plastic or glasstubing. As with the swage-typeconnectors, glass tubing must be chosenwith an outside diameter which conformsto the dimensionsof the fitting. This generallydictates the use of medium-walledtubing with fittings made to English dimensions.Also, the ends of the glasstubing must be preparedas describedfor the swagejoint, so that the O-ring is not damaged.These annular O-ring sealsare generallynot satisfactoryfor pressuresabove 1 atm. One usefulfeature of this type of joint is that the tube insidethe fitting may be rotatedwithout breaking the seal.

40.4 HEAVv-wALIEDTUBTNG AND ptpE JotNTs

Many of the fittings describedabove may be employedwith heavy-walledtubing or metal pipe. Somefittings which are more specializedfor this purposeare describedhere. zzv METALSYSTEMS

A. Cone Joinls. The cone-typefitting, illustrated in Fig. 10.8, was designedfor usedwith heavy-walledtubing for high-pressureapparatus.s A special tool or lathe is employedto shapethe tube end into a cone.In one modification the outsideof the tube is threadedto receivea small collar. When the gland nut is tightenedagainst this collar, the coneis forced againstthe conicalinner surface of the body. Since the two parts have a slightly different cone angle, the contact area is small and good leak-tight performance is achieved.At one time thesecone joints were often usedon vacuum systenrsfor fluorine handling becausethe joint can be made and broken repeatedly.Horvever, flange joints have generallysuperseded the conejoints in this applicaton.

B. Pipe Joints. Goodjoints suitablefor vacuumor pressureapplications can be made by meansof taperedpipe threadjoints in heavy-walledtubing. Unlike all of the joints discussedso far, the sealis made in the threadsof this joint. The threadedportions of both the male and female pipe joint are tapered,and as a result the inner and outer threads are wedgedinto each other when they are screwedtogether (Fig. 10.9). To achievea good sealthe male pipe threadsare wrapped with two layersof Teflon pipe tape, which servesthe role of sealantand

Body, Collor Glond Cold-worked ruornq

Fig. 10.E. Conehigh-pressure joint. ln this particulardesign the heavy-walledtubing is beveledon the end and threadedto receivea collar.The gland nut thrustsaeainst the collarand forcesthe cone- endedtube into the bodv.

Fig. 10.9. Normal pipe threadedjoint. Note the tapered threadson both the ntale and female components.Unlike most other joints. the sealis formed in the threadedportion of the joint.

sAutoclaveEngineers, Inc.. Erie, PA. HEAVY.WALLEDTUBING AND PIPEJOINTS 224 a lubricant for the threads. NOTE: The use of Teflon tape should be confined to pipe threads. It makes no $ense to use Teflon tape on the threads of flared, flange, or swage-type fittings because the seal is not made at the threaded portion of those fittings. The commonlyused tapered pipe thread in the United Statesis designatedas Normal Pipe Thread (NPT), whereasthe designspecified by the International StandardsOrganization is designatedas an ISO taperedpipe thread. Tapered pipe-threadedjoints can be openedoccasionally. If frequent opening is necessary, other joints, such as the ISO parallel-threadedpipe joint, are preferred. When pipe-threadedjoints are specifiedwithout any further qualifier in the United States,it is generallyunderstood that the fitting is NPT. The ISO parallel pipe thread is basedon parallelthreads and an O-ring or other gasketbutt-type seal. NOTE: Neither ISO fittings nor standard threaded fittings should be screwed into tapered pipe threads.

C. Bolled Flonge Closures. The flangejoint is widely usedto link large- diametertubing and to provideaccess to the interior of reactionor vacuumves- sels (Fig. 10.10). Typically, the flanges are bolted together and are sturdy enoughto withstandthis pressurewithout appreciabledistortion. The bolts are spacedevenly around the flangeto distributethe load evenlyon the gasketmaterial. Very often one of the flanges is cut with a grooveto take an O-ring or sometimes a metal V-ring. The joint is designedso that thereis significantbut limited compressionon the O-ring. The limit is achievedby metal-to-metalcontact of the flanges.The grooveis larger than the width of the O-ring, to permit radial expansionof the O-ring when it is under compression.The generalstrategy in O-

Fig. 10.10. O-Ring sealedbolted flange closure. This typeofjoint is usedfor largediameter open- ings.The grooveto receivean O-ring sealis machinedso that the depth E is 80% of the O-ring width and F is I 35% of the O-ring width. The extra clearanceis on the insideof the groovefor applications in which the apparatusis to be pressurizedand on the outsideof the groovewhen the apparatusis to be evacuated. 222 METALSYSTEMS ring groove design is to specifythe depth of grooveto be 80% of the width of the O-ring and the width of the grooveto be 135% of the O-ring width. As illustrated in Fig. 10.10,the designof the groovediffers for vacuum and pressure applications. For ultrahigh-vacuumand many high-pressureapplications, O-rings do not providethe required degreeof seal,so metal gasketsare employed(Fig 10.11). Annealed copper or soft aluminum gaskets are the most common, and the flanges are machined with opposing circular ridges or steps which provide a small area of contact with the gasket and thereby a high force per unit area. Flangesof this type are commerciallyavailable.6 To maintain alignmentof the two halves.guide pins are sometimesincorporated into one flangewith holesin the opposingpart.

40,5 vALVEs

Becausethey involve moving parts, valvesare generally more troublesome in a vacuumor pressuresystem than arejoints. Furthermore,valves are readily damaged if improperly handled and they are often designedfor a specific purpose. Becauseof thesefactors, the intelligent use of valvesrequires a knowledgeof their constructionand mode of operation.For example,a meteringvalve and a cutoff valve have different internal design, although they may look identical from the outside.Similarly, the natureof the seatmaterial and the way in which the seal is made around the valve stem are often essentialinformation in the choice of the proper valve and the maintenance of a metal system.

A. Volve Seols ond Sfems. Valves which are intended for fine gas flow control are designedwith a long needlelikestem and a gentlytapered seat (Fig. 10.12a).Although these"metering valves"give good flow control, they do not in general give a positive shutoff . When the valve is designedfor positive shutoff a

V/ 7) | 600 f9 @

Fig. l0.ll. Metal gasket sealedbolted flange closures.A soft metal gasket,generally made of aluminunror copper,is clampedbetween knife edges(a) or steppedflanges (ä).

bVarianVacuum Accessories,Varian Associates,Palo Alto, CA. VALVES 223

blunt stenrtip and simpleseat is employed(Fig. 10.12b).Cutoff valvesare available for which some degree of flow control is achieved by means of a fairly sharplytapered conical tip. However,if good flow control and positiveshutoff are required, a metering valve and a cutoff valvein seriesare generallycalled for. This type of configurationhas alreadybeen discussedin connectionwith high pressurecylinders. One of the most commonetrors in the useof smallvalves is to shut them too tightly. A good shutoff valveis designedso that there is fairly large force per unit area between the stem and seat; therefore, if the valve is overtightened,the seatand/ or stemis distortedand the valvewill not seatproperly in subsequentuse. Similarly, metering valves are often delicateand not designedto be overtightened.In somevalve designs, wear on the seatand stemtip is minimized by meansof a "floating tip" which permitsthe valvestem to rotate inde- pendentlyof the tip. Thus, asthe valveis tightened,the tip is not ground into the seat.

B. Pocked Volves. Someof the leastexpensive and most common valves have a sealingmaterial (packing) compressedbetween the valve stem and the valvebody. For valvesused in laboratoryapparatus this sealis generallyaccom- plishedby meansof an O-ring (Fig. 10.12a),or a Teflon washer.Compression on the O-ring is determinedby the groovedimensions on the stem and inside diameterof the valvebody. If a leak developsalong the stem,the valvemust be disassembled,cleaned, and the O-ring replaced.The situationis differentwith a Teflon packing washer.In this casethe packing is causedto pressagainst the stem and the valvebody by meansof the packing nut (Fig 10.13).This packing nut may require occasionaltightening to maintain proper contact with the valve stemand body. Clearly,it is important to identifythe valvetype in order to rem- edy a leak past the stem. In dealingwith O-ring packedvalves, it alsois important to recognizethe chemical sensitivityof the O-ring and, if necessary,to changethe O-ring to match the compoundsbeing handled.(See Chapter 5 and Appendix III for information on the solventsensitivity of variouselastomers.) Another variation in the design of packed valvesis the relative position of the threadswhich actuatethe valvestem and the packingmaterial. With the O-ring valvesit is common to positionthe threadsso they are protectedfrom liquids or gasesinside the valveby the O-ring seal(Fig l0.l2a). However,with Teflon and similar packing materials, which must be maintained under pressureby the packing nut, it is more common for manufacturersto thread the valvestem insideof the packing material. This arrangementis undesirablewhen highly corrosiveliquids are being handled, becauseexposure of the threadedsurfaces to the corrosivematerial is likely to seizeup the valve.Some Teflon-packed valves are availablein which the threadsare protectedby the packing (Fig. 10.13).

C. Diophlogm ond Bellows Volves. For high-vacuumapptications, rhe leakageof a packedvalve is sometimesunacceptable. so diaphragmor bello*s valvesare employed.In thesevalves the packingis eliminatedby usinga flexible metal diaphragm or bellows sealed to the valve stem and the body (Fig. 224 METALSYSTEMS

(o)

Fig. 10.12. Two valvedesigns. (a) An O-ring sealsthe valvestem to the body.

10.12b).The diaphragm or bellowsflex as the stem is actuatedand thus permit the transmissionof the throttling actionof the valvewithout the useof packing. A varietyof designsare possible;in somevalves the diaphragmsand valvestems may be replacedbecause the diaphragmor bellowsis attachedto the valvebody by meansof a demountableseal involving a gasketor O-ring. In valvesdesigned for very-high-vacuumperformance, the diaphragm or bellowsis sealedto the body by brazing or welding.

D. Boll, Plug, ond Gote Volves. The valvesdiscussed above often intro- duceconsiderable restriction into the systembecause of small orificesand tortu- ousflow patterns.Such restrictions are not seriousfor mostapplications at 1 atm pressureor above,but they may be unacceptablefor vacuumapplications, where small-diameteropenings are a seriousimpediment (seeChapter 6). Ball and VALVES 225

(b)

Fig. 10.12(ä). A metal bellowsattached at one end to the body and at the other end to the stem forms a highly leak-tightbut bulkier and more expensiveseal. (Reproduced by permissionof the copyright holder, Markad ServicesCo.)

plug valves,which provide large orificesand straight linesof flow (Fig. 10.14), bear a strongsimilarity to glassstopcocks.2 In the ball valve,a smoothball, with a large hole along one axis and a handle attachedalong an orthogonalaxis, is surrounded by a spherical cavity and an elastomer seal. A 90o rotation of the valvebody will closeor openthe valve.The plug valveis similar,but in this casea cylindricalplug is usedand the plug is equippedwith O-ring seals.Both typesof valvescan be manufacturedwith closetolerances and are suitablefor medium- and sometimeshigh-vacuum applications.The more expensivegate valve is TeJlon pockrng

Needle

Fig. 10.13. A high pressurevalve with Teflon packing.The threadson the valvestem (not shown) are above the Teflon packing and are thus protected from corrosive materials. The packing nut tightensthe Teflon packing washeragainst the needlevalve stem and the valvebody. Occasional tighteningof the packing nut is requiredto maintain a good seal.

Fig. 10.14. A metat ball valve. This type of valve shown here in a 3-way version, provides a large unobstructed aperature. (Reproduced by permissionof the copyright holder, Markad ServicesCo.)

226 TYPICALMETAL SYSIEMS 227 availablewith a bellowsclosure along the stem. This type of valveis often used betweena diffusion pump and an associatedmetal high-vacuumsystem.

E. Mounfing Volves. It is often desirableto mount a valvesecurely, so that when it is actuatedthere is no mechanicalstress on the connectionbetween the valveand the tubing. For example,if a valveis attachedto small-diametertubes by meansof swage-typejoints, repeatedflexing of thesejoints can openup leaks. Occasionally,mounting holeson the valvebody are providedby the manufacturer for bolting the valveto apparatus.The secondcommon fixture is a bulk- headconnector, which consistsof threadson the outsideof the valvebody and a pair of nuts on this threaded section.To use this mount, the valve handle is generallytemporarily removed and the valveis mountedby meansof thesenuts through a hole in a sturdy sectionof sheetmetal, as illustratedin Fig. 10.12b. Gate valvesare generallyequipped with boltedflange conectors so that they can be connectedto large-orificetubing.

'10.6 PREssUREeAueEs

The measurementof pressurefrom a few torr to l0a torr in an all-metalsystem can be accomplishedby meansof a metal Bourdon or diaphragmgauge with a dial readout.Although a bronzechamber is the most common,these gauges are availablewith more corrosion-resistantmetals. and someare available which are accurateto 0.5 torr.7 Various typesof pressuretransducers with digital readoutare availablewith metal interior construction.These have become quite popular for fluorine-handling systemsand the like. A descriptionof someof the commontypes is givenin Chapter 7.

40,7 ilPrcALMETAL sYsTEMs

A. Fluotine Hondling Syslems. Fluorineis thermodynamicallycapable o{ reactingwith most materialsof construction,but the reactionrate may be extremely slow below certain critical temperatures.The slow rate of corrosionof many metals occursbecause of the formation of a passivefluoride film. Some generalizationson the resistanceof various materialsto fluorine are given by Peacock.sFluorine which is free from hydrogenfluoride may be handledin borosilicateglass for periodsof up to a few hours and temperaturesup to 200oC without extensiveattack; fused silica is suitablefor longer periodsand slightly highertemperatures. However, surface moisture on the glass,which is extremely

TAmericanChain and CableCo., HelicoidGauge Div.,230 Park Ave., New York. NY. öR. D. Peacock,inAdyancesin Fluorine Chenistry',M. Stacey,J. C. Tatlow, and A. G. Sharpe, Eds., Vol 4, (WashingtonDC: Butteru,orth.1965), p. 31. 228 METALSYSTEMS

hard to eliminate,catalyzes the reactionof fluorine with theseglasses, and therefore, glassis rarelyused for fluorine handling.Copper may be usedup to 500'C, while nickel and Monel are usefulto about 800"C. Fluoriteand ceramicalumina are resistantto 1,000oC,but the latter becomesporous eventhough it is not erodedby fluorine. Stainlesssteel and brasshave been used occasionally to contain fluorine at room temperature, but they are less desirablethan Monel, nickel, or copperfor laboratoryapparatus. Passivated aluminum is satisfactory for fluorine handling even at temperatures somewhatabove room temperature, but it has the practical disadvantageof not being readily soldered.Mixtures of fluorine and hydrogen fluoride are more reactivethan either component, and a fair number of fluorine derivatives,such as ClF3,are more reactivethan F2.For thesehighly reactivefluorides, nickel or Monel are the preferred metals of construction. The strongestand leastporous joints are made by inert-gaswelding (see Ap- pendix IV), but serviceablesilver solderjoints are possible.Lead gaskets,soft solderjoints, and brazedjoints may be usedwith fluorine and most all gaseous fluorinating agents,but are unsatisfactorywith liquid BrF3.Soft solder(lead-tin solder)is very sensitiveto HF. Junctionsbetween dissimilar metals, such as copper and nickel, are subjectto electrolyticcorrosion when exposedto liquid fluorinating agentswhich also are electrolJtes,such as BrF3 and F2-HF. Most metal systemsare passivatedby conditioningwith fluorine andlor volatile fluorides prior to use. It is often desirableto precedethe conditioningstep with a hydrogenreduction of the interior of the apparatusbecause the mixed oxyfluorideof an element,which might be producedfrom oxide coatingsin the apparatus,are frequently similar in volatility to the simplebinary fluorides.A typical reductionand conditioningcycle involves filling the previouslyevacuated systemwith closeto 1 atm of hydrogen, after which the traps, tubing, and other heat-resistantitems are heatedwith a gas-airflame. The systemis then evacuated and heatedagain to expelmoisture. To passivatethe apparatus,a mixture of 5-10% fluorine in an inert gas is first introduced,and nickel or Monel parts are heated.The gas is replacedby fluorine somewhatbelow I atm of pressure, and nickel and Monel parts are heated to a dull red until the pressuredrop ceases.Sometimes this passivationis followed by another treatment with a highly reactivefluorine compound, such as ClF3,which is introducedfor a few hoursto conditionparts which cannotbe heated,such as Teflon packedvalves or fluorocarbonreaction vessels. The disadvantageof this last passivationstep is that ClF3 is strongly adsorbedon the walls of the apparatus, and extensive pumping is neededto removeit from the system.As a generalrule, the condi- tioning shouldinclude a fluorinating agentwhich is at leastas strongas any that subsequentlywill be handled. Somematerials, such as stainlesssteel, platinum, and gold, do not form a protective fluoride film and therefore cannot be condi- tioned. Two typical metal vacuum systemsfor fluorine compoundsare illustratedin Fig. 10.15.In either systemthe vacuum pumps are protectedfrom the vacuum I Topump (o)

Fig, 10.15. Metal vacuum systemsfor handlingfluorine and reactivefluorides. (a) A designused extensivelyat Argonne National Laboratory constructedof nickel tubing and Monel valves(A) u'ith conejoints(illustratedinFig.10. l3);(D)nickel U-trap;(E)Monel Bourdengauge(0-l000torr); (F) 130-mLnickel reactorcan (Fig. 10.17);(G) 1,500-mLnickel storageor nreasuringcan, (H) 85-mL nickel can, (J) brassvalve: (K) soda-limetrap to protectvacuum pumps; (L) Monel valve.(Repro- duced by permissionof the copyright holder, The University of Chicago Press,Irom Nobel Gus Com- pounds,H. H. Hyman(Ed.), Chicago, 1963.) (ö) A lessmassive vacuum system: (A) Kel-F or Teflon reactiontubes (illustrated in Fig. 10.16); (B) Flarefitting for the reactiontubel (C) nickelexpansion can; (D) calibratednickel canl (E) Monel Bourdongauge; (G) to soda-limetraps and pumpsl (H) to samplingcells. Monel bellowsvalves (V), Monel Swagelokjoints, and nickel tubing are used for the main componentsin the vacuum line. (ReproducedfromT.A.O'DonnelandD.F.Steu'artlrorg. Chent.5,l134(1966),bypermissionof the copyrightholder, The American ChenricalSociety.)

229 230 METALSYSTEMS line by meansof a sodalime trap. Kel-F or Teflon reactiontubes are convenient becausetheir translucencepermits the observationof the contents.Details of the reactiontube are givenin Fig. 10.16.The tube can be machinedfrom Kel-F bar stock or it can be fashioned from heat-formable and -sealableTeflon FEP. The metal reactioncan illustrated in Fig. 10.17is preferredwhen the reactantsdo not have to be observedand when modest pressuresof reactantsare desired. For the manipulation of HF solutions,apparatus made from Kel-F or Teflon is desirable.A reactionvessel is illustratedin Fig. 10.18and a cellfor spectroscopyis shownin Fig. 10.19.

lry'onel Conehigh-

fitting 1t/16 -14 thre o d

Reoc'tion tube (b)

I sue'ff

*-5/C >

lVetol nut 3/e" 4f or 45' florefiiting

Trop (o) (c)

Fig. 10.16. Perfluorocarbonreaction tube and flange-fittings.)(a) Detailed cross-sectionof the components;(b) and (c) two adaptationsof the basicdesign. The fluorocarbontube may be machined from Kel-F; alternatively, Teflon FEP tubing may be heat molded to form a flange and heat crimp sealedat the base. Swogelok fitting

Bellows

Welded nackeI

1/q" NPT Monel plug (o)

HokeM-327 It 7a" OD tube I %" OD,3/6"ID MonelfuOe 4" Weld insideond outsrde Deepweld ond mochineto l OD t /r I O.O65wo ll o

I DeeDweld ond mochrneto I OD I --r-I Fr"-f (b)

Fig. 10.17. Detail of two different nickel reaction cans. Design (b) is convenientfor the addition or removalof solids.IReproduced by permissionof the copyrightholder, The AmericanChemical Soci- ety. From W. E. Tolberg, R. T. Tewick, R. S. Stringham,and M. E. Hill, Inorg. Chent.,6, 1156 (1e67). l 231 232 METALSYSTEMS

Traplll

Tovacuum throughcorrugated Teflonflexline

Trap I Trap ll

Fig. 10.18. Assemblyfor the manipulationof HF solutions.Monel Su'agelokunions are usedto join U-trapsconstructed from Teflon FEP tubing. A rigid Kel-F or Monel tube must be placedinside the Teflon tubing to make it sufficientlyrigid to hold a swage-typeseal. Similar Swagelokattach- ments are made to the valves. IReproduced by permission of the copyright holder, The American Chemical Society.Frorn K. 0. Christe,C. J. Schack, and R. D. Wilson. /rrorg. Chem..16.849 (t977).1

Sincefluorine and most volatilefluorides are corrosiveand highly toxic. the vacuum rack for a fluorine handling systemgenerally is placedin a hoodeden- closure(Fig. 10.20)and the fluorine tank is often enclosedin a separateenclo- sure which can be manipulatedremotely (Fig. 10.21).

B. Flow ReOcfors. Laboratory-scalecataly.tic reactors and reactors for the reactionof solidswith gasesare often constructedfrom metal. One of the principal objectivesin the use of laboratory-scalecatalytic reactors is the determination of rate data which can be associatedwith specificphysical and chemical processesin a catalytic reaction. Descriptions are available for these kinetic analysesas they relateto reactordesigns and reactionconditions.q eE.G. Christoflel, Catal. Rev.,24 159(1982); L. K. Doraiswamyand D. G. Tajbl, Cutal.Rev., 10, 177(1974); L. L. Hegedasand E. E. Peterson,Catal. Rev.,9,245(1974). Fig. 10.19. Spectroscopiccell for HF solutions.All internalparts are Kel-F, Teflon,or, in the case of window material, sapphire or silver chloride. A commercial Teflon valve may be substituted for the custom Kef-F valveshown here. (Reproducedfrom H. H. Hyman and J. J. Katz Nonaqueous solventslstems, T. c. waddington Ed., p. 47 (1965)by permissionof Academicpress Inc.)

233 FluorescentI qhf ln opposfe sloe

SlidrngsoterY- gloss doors

Glossend windows Electilcol -/ outlet

.'-o /9 \l--

Laboratory Planning;t'orchem- Fig. 10.20. Hooded vacuum rack. (Reproducedfrom D. R. Ward, istryandChenicalEttgitteering,H.F.Lewis'(ed.)(1962)bypermissionofthecopyrightholder' Van NostrandReinhold Co', Inc., New York')

234 Bockstop Centering brocket 1tö' \ 1t/i ongle steel l9 15'h Retoining bor. 1/ädiom steel; t- locote to hold cylinder I centeringbrocket I ogoinsl L_. 4" diom ducl lo zPortition exhousl sysien Pillow block Geor supporis Too l,/i'sieel Dlote l/r'diom hole steel shott 2"drombevel geors ; for nitrogen line Cc rirr Oge Loose sleeve To NoF scrubber Purge lrne to Centerrng l/<'copper tubing nitroqen cylinder \r -brocket instoll flored tittinqs \U B to fit cylinder T- wrench brocket Centering necX Verticol geor short Box purge to end milledto I ntee '/4 volves nitrogencYlinder 1/i'xt/ä'squore x2" Hoke M ongleI stem lengths o0tronol Connectrng.sleeve I ock stop 0oor t/zt/2 toptog hole \t/2xt/z l/ T etoining bor diom s/ri' Eoltom hole ttti't r/e" Ä I centerinq'/ | | brocket | | 2 door hondles 5'-6" I F t/d x'l t/j' steet l t;o' I t -2" l4 holes diom r/a l a-a - drill to moich Box lj' steel I l#' door I llonges oll- welded l4bolts 516'squore construction od; weld to l1r Side I top tlonges 1?', flongesi 14 woshers I I 't"x 1" ongle sleel Ll_r I '14 f humb nufs Right side Lelt sade F ront

Fig. 10.21. Safety enclosure for a high-pressure fluorinc tank N c) (rr 236 METALSYSTEMS

GENERALREFERENCES

Broker, W., and A. L. Mossman,Mutheson Gas Datu Book, MathesonGas Products,P.O. Box 1587,Lyndhurst, NJ 07071.A generaldescription of the handlingof compressedgases is given along with information on fittings and properties of specificgases. Calahan, F.1., Swagelok Tube Fittirtg und Installatiott Manual, Crawford Fitting Co., Cleveland. Proceduresfor forming and joining metal tubing are described. Canterford,J. H., and T. A. O'Donnell, 1968,in H. B. Jonassenand A. Weissberger,Eds., Iecft- niquesof Inorganic Chentist1',Vol. 8, Wiley, New York, p. 291. Generaltechniques for fluorine handling. Hagennrulfer, P., Ed., 1985, Inorganic Solid Fluorides, Academic, Ne* York. Chapter 2 of this book, "Preparative Methods," gives an extensivelyreferenced account of synthetic methods used in inorganic fluoride research. Severalapparatus are pictured and described in detail. Hyman, H. H., Ed., Noble Gas Contl>ounds,l963,University of ChicagoPress, Chicago. Many chapterscontain experimental detail. Guide to So.feHandling qf CompressedGases, Matheson Gas Products. P.O. Box 1587,Lyndhurst, NJ 07071. The safe handling, transporting, and storageof compressedgases are described. Moore, J. H., C. C. Davis, and M. A. Caplan, 1983,Building ScientiJicAppurdlr/.r, Addison-Wes- ley, Reading,Mass. Includescoverage of metalworkingand the constructionof apparatusfrom metal components. Steere,N. V. Ed., 1971,HandbookoJ Laborutory,.lc/en,,TheChemical RubberCo. Press,Cleve- land. Containsa chapteron compressedgas cylinders and cylinderregulators. Weinstock,8., RecordoJ ChemiculProgress, 23. 23 ( I 963).Apparatus for the svnthesisand characterization of xenon fluorides is oresented. A N Sofety

Many air-sensitivecompounds are verystrong reducing or oxidizingagents, and thereforecare must be usedin their manipulationto avoidexplosions and fires. Carefulplanning and executionof experinrentscan nrinimizethe dangerof reactive compoundslike diborane.However, there is an unfortunatetendency to for- get mundane hazardssuch as the fire and explosionhazards of organic solvent vaporsor hydrogengas. The chemistalso should be sociallyresponsible by never discardinghighly toxic materialsdown the drain and by chemicallyscrubbing noxiousgases from gas streamsbefore the gas is allowedto go into a hood.

1.4 coMBUsTrBLEs

The explosionlintits for vapor-air mixtures are the nraximum and ntinimum concentrationsof vapor betweenwhich a flame will propagatethrough the mixture. Large quantitiesof flammable solventsand gasesmust be handledin well- ventilatedareas so that the vaporsare dilute. Laboratoryrefrigerators present an explosionhazard because the storageof highly volatilesolvents and volatilesolu- tions in them may lead to the buildup of the solventvapor concentration.The usual householdrefrigerator is equippedwith a thermostatand a light switch which may spark and ignite solventvapors. Explosion-proofrefrigerators are commerciallyavailable. High pressuresof oxygennray spontaneouslyignite nranycombustible materials such as hydrocarbongreases and oils. Therefore,regulators, gauges, and other oxygen-handlingsystems should be strictly oil-free.

237 238 SAFETY

1.2 UNsTABLEcoMPouNDS

A largenumber of compoundsare unstablewith respectto spontaneousdecom- position. Only a few of the most important will be listed here.

'1. Acetylene may spontaneouslyexplode if its pressureexceeds l5 psig. Commercial acetylenecylinders are filled with a porous material soakedin acetonewhich maintains a safe acetylenepressure by dissolvingthe gas. Acetyleneshould never be passedthrough a vacuum pump, which will compressthe gas. 2. Acetylidesof heavymetals are often explosive. 3. Azides,diazo compounds,and fulminatesare frequentlyexplosive. 4. Nitrogen chlorides,bromides, and iodidesare endothermiccompounds which may detonate. 5. Organicperoxides are liableto detonate.Exposure of ethers,alkenes, and alkynesto air and light leadsto peroxideformation. Distillation of these solventsposes an increaseddanger due to the concentrationof peroxides in the still pot as the distillation proceeds. When present in small amounts,the peroxideis removedbefore distillation by the useof reducing agentssuch as ferrous sulfate in acidic aqueoussolution. Peroxides may be detectedby the addition of a few drops of aqueous10olo KI solution to a few mL of the ether.The presenceof a peroxideis revealedby the appearanceof the brown triiodide color. 6. Liquid or solid ozoneis explosive. 7. Perchloratesalts of metal complexesare liable to detonate.Perchlorate has been a popular counterion for metal complexes,but saferions, such as tetrafluoroborateor hexafluorophosphate,can generallytake its place.

1,3 soMEDANeERous MTxTUREs

Undiluted mixtures of strong oxidizing agentswith strong reducingagents are potentiallydangerous, as are mixtureswhich leadto unstablecompounds. A few of theseare listed below.

1. Perchloric acid forms explosive mixtures with organic compounds and easilyoxidized inorganiccompounds such as ammonia. 2. Nitric acid with organic compoundsand ammonium nitrate with metal powdersor organic materialsare potentialexplosives. 3. Ammoniacal silver(I)solutions may form an explosivecomponent after long standingor in the presenceof strongbase. 4. In the presenceof air, mercuryand anhydrousliquid ammoniaform an explosivecompound, as doesyellow mercuric oxide with ammonia. DISPOSALOF REACTIVEWASTES 239

5. Activated charcoalwith nitrates,chlorates, liquid air, or liquid oxygen forms explosivemixtures. 6. Liquid air or liquid oxygenwith organic matter is very dangerous. 7. Active metals, such as the alkali metals,alkaline earths,and finely divided aluminum, may explodewhen mixed with chlorinatedhydrocarbons, such as chloroform and carbon tetrachloride. 8. Potassiumpermanganate with sulfuric acid yields the explosivecompound permanganicacid. 9. Decaborane(and possiblysome other boron hydrides)in the presenceof carbon tetrachloride, and possibly other halogenatedhydrocarbons, forms a very shock-sensitivehigh explosive. 'l0. Similarly,an explosivematerial results when alkyl phosphinesare mixed with halogenatedhydrocarbons. 'l'1. Sodium amide (NaNHz),forms an explosivecompound upon prolonged exposureto the air. 12. The distillation of ethersfrom lithium aluminum hydride occasionally leadsto an explosion.The exact causeis not known, but CO2 may be involved. The danger can be minimized by predrying the ether with calcium hydride and then using a minimum amount of LiAlHa for final distillation. Also, the distillation should be performed behind a blast shield,and the still pot shouldnever be allowedto go dry. Frequently,a safebut powerful desiccant,such as benzophenoneketyl or sodium-potassiumalloy, may be usedin placeof LiAlHa. '13. The reaction of potassium with atmospheric oxygen leads to a surface layerof potassiumsuperoxide. When this oxidizinglayer is embeddedin the metal, an explosionmay result.Therefore, the oxidizedsurface layer must be scrapedoff beforethe metal is cut. Presumablya similar problem existswith rubidium and cesium. '14. Dimethyl sulfoxideis reportedto form an explosivemixture with BeHq-2 and with diborane. It is probablethat other boron hydridesand hydro- boratesbehave similarly. 'l 5. N2O4with somechlorinated hydrocarbonsand olefins forms shock sensitive compounds.

1,4 DrsPosALoF REAcTTvE wAsTEs

Lithium aluminum hydride wastes may be destroyed by passing nitrogen through a water bubbler, an empty trap to catch the water, and then into the flask containing the waste. Alternatively, hydride wastesmay be coveredwith rags and burned in an open area.Aluminum alkylsmay be burned in the open, or a dilute solution of the alkyl in a hydrocarbon may be run into agitated water in a vesselwhich is blanketedwith nitrogen.Variants of thesemethods are effec- 240 SAFETY tive with a wide variety of compoundswhich are decomposedby water or alcohols. Alkali metal residuesmay be destroyedby isopropylor /-butyl alcoholand then flushed down the drain with water. Sincepotassium is more difficult to destroycompletely by alcoholsthan is sodium, extra care must be used when disposingof potassium. Nitrogen halides are destroyedwith cold base. Azides and fulminates may often be destroyedwith acid, while heavy metal acetylidesare decomposedby ammonium sulfide. The removalof peroxidesby reductionhas been described above.

1.5 HrGH-PREssuREGAscYLTNDERs

Proceduresfor safehandling of pressurizedgases are given in Chapter 10.

1,6 AsPHYXTATToNBYrNERr GAsES

An atmosphereof inert gaseswill not support life; therefore,good ventilation is required.

1.7 EXTTNGUTsHTNeFtREs

Carbon dioxidefire extinguishersare widely usedin laboratoryfire fighting because the CO2 does not damage apparatus or causeelectrical shorts. Further- more, carbon dioxide is effective against a wide variety of fires and is not toxic. The National Fire ProtectionAssociation adopts the following classificationof fires: ClassA fires occur with wood. paper, fabric, and similar solids.Water and wet fire extinguishersare recommendedbecause they are effectivein quenching burning embers. ClassB fires occur with liquid hydrocarbonsand similar combustibleliquids. Foam, dry-chemical,halocarbon, and CO2extinguishers are recommended. ClassC fires occur in live electricalequipment. Clearly,water and wet-type fire extinguishersmust be avoided. ClassD fires involve strong reducing agents such as active metals (magnesium, titanium, zirconium, and alkali metals),metal hydrides,and organometallics. Specialdry-chemical fire extinguishersare availablefor thesefires (e.g., Ansul Co.). Sand is also useful for small fires of this type. Water should be avoided becauseit promotes the fire by liberation of hydrogen or hydrocarbons. GENERALREFERENCES 244

GENERALREFERENCES

Bretherick. L., 1985, Handbook of ReactiveChemicul Hazards,3rd ed.. Butters,orths,Boston. Chenricalhazards. uith referencesfor 4.900 compounds. Keith. L. H., and D. B. Wallers, Eds., 1985,Conrpendiunt o.f SuIetJ,Dnu SheetsJor Reseurch and Industrial Chenticals,3Vol, VCH Publishers.Deerfield Beach, Florida. Health hazards,first aid, recommendedstorage, and referencesfor 867 chemicals. Prudettt Practicesfor Hundling Hazardous Chenticals in Laborutories, National Academy Press, Washington,D.C., 1981.General laboratory practice for hazardousmaterials, electrical hazards, laboratoryventilation, storage of chemicals.disposal of chemicals,and thresholdlinlit valuesfor chemicalsubstances. Sai. N. I., Ed.. 1984,Durtgerous Properties o.l'lndustrial Materials.6th ed.. Reinhold,Neu York. Physicalproperties, fire and explosionhazards. toxicity, and inconrpatibilityfor about 20,000 chemicals. Steere,N. V., Ed., 1971,Handbook of Laboratory-^tdletr,, The ChemicalRubber Co., Cleveland, Ohio. A P P N D x GLASSAND GLASSBLOWING

Even though the servicesof a professionalglassblower may be available,it is often much more efficientfor the chemistto construct,modify, and repair small glass items, and most chemistsinvolved in vacuum line work are capableof much more. In addition to the advantageof efficiency, glassblowingaffords an agreeablediversion which is doubly rewarding when an aestheticallypleasing apparatusis produced.As an aid to the designof glassapparatus, this appendix presentsinformation on the properties of some common laboratory glasses,followedby instructionsfor somebasic glassblowing operations. These instructions should be supplemented,if possible,by observingan experiencedglassblower. The beginner will find practicenecessary to developthe manual dexterityand judgment which are required in glassblowing. ll,4 PRoPERnEsoFGLAssEs

The glassesin general laboratory use contain SiO2andlor B2O3as the glass- forming constituentand frequently a metal oxide modifier, which is added to lowerthe viscosityof the glassor to impart other desirablecharacteristics. Glass is an amorphous substancewhich may be viewed as a highly viscousliquid. Thus, unlike a pure crystallinesubstance, it doesnot display a sharp melting point, but despitethis, it is convenientto speakof temperaturesaround which recognizable changes in properties occur: The strain point correspondsto the temperatureat which internal stressis largelyrelieved in 4 h; more precisely,it

242 PROPERTIESOF GLASSES 243 correspondsto a viscosityof 1014spoise (P).r At the annealingpoint (10t3.0P), internal stressis substantially relieved in 15 min. The deformation point corre- sponds to a temperature at which viscousflow neutralizesthe effect of thermal expansion(about l0rr-10r2 P). The soJteningpoint has an involveddefinition, but roughly speakingit correspondsto a temperatureat which a small heated rod will slowly elongate under its own weight. This correspondsto a viscosityof approximately107 0P. Glassis generallyannealed at a temperaturebetween the strain point and the annealingpoint and is worked abovethe softeningpoint. The relationshipof thesetemperatures is brought out more clearlyin Fig. II.1, whereit may be seen that fused quartz is the most refractory of the common laboratory glasses,and Vycor, a96Yo silicaglass manufactured by Corning GlassWorks, is somewhat lessso. Becauseof the high softeningpoints of thesetwo glasses,they must be worked with a hydrogen-oxygenflame and, unlike borosilicateglass, they are generallyblown while in the flame. The ability of theseglasses to withstandhigh temperaturesleads to their use in combustiontubes and similar applications. The maximum temperaturefor continuoususe is about 900"C for Vycor, while

o $ öt I |.. oQ

I q \-+"']^, ornpornt \l -\SL. ;L;; o 612 o o t- o ,.] oi^ ; lol-tf 11n_s_pqq|. t 6

400 600 800 1000 1200 1400 1600 Tem oe roture. oC

Fig. II.l. Viscosity-temperaturecurves for some common laboratory glasses.The numbers in pa- renthesescorrespond to Corning designations.(Adapted from Corning Glass Works, Corning, Ny, Bulletin B-83, 1957.)

'These are tentative designationsspecified by the American SocietyFor Testing Materials. 244 GLASSAND GLASSBLOWING continuousheating of fused quartz aboveabout 1000'C will lead to failure due to devitrification(crystallization). Also, becauseof their high strengthand very low coefficientof expansion,these glasses can withstandconsiderable thermal shockwithout breaking. For example,a red-hottube can be plungedinto water without cracking. Another important propertyis their transmissionof ultraviolet and near-infraredradiation (Fig. II.2); accordingly,fused quartz and, to a lesserextent, Vycor are often employed in cell windows and reaction vesselsfor photochemicalwork. Finally, the high strengthof fused quartz leadsto its frequent usein fibers for the suspensionof galvanometerparts, as the helical spring for weighingsmall samples,and for spiral gauges. The majority of chemical glasswareis constructedfrom borosilicateglass, which has the advantagesfor routine use of a reasonablylow coefficient of ex- pansionand a convenientsoftening temperature for glassblowing.In additionto the oxidesof siliconand boron, theseglasses contain small amounts of the oxides of aluminum, sodium, and potassium.The trade designationsfor the glassused in most laboratoryequipment are Pyrex7740 (Corning Glass Works) and Kimax K-33 (Owens-Illinois).They are very similar in compositionand are compatible with eachother, but cannot be fused directlyto flint glassor fused quartz. Al- though the softeningtemperature is 820'C, it is unwiseto useborosilicate glass

s_ c 9

E c o

400 500 Wovelength, millimicrons 100 .{- o 6 oqo E c o F o 1.O 20 5U 40 50 Wovelenqth,microns

Fig. II.2. Transmission of Pyrex, Vycor, and fused quartz. Transmission curves for 2-mm-thick samplesof (a) fused quartz (GE type 102),(b) Vycor (Corning 7910-note that this is a specially controlled grade; the more common 7900 has an ultraviolet cutoff similar to 7740), and (c) Pyrex (Corning 7740).(Adapted from data suppliedby Corning GlassWorks and GeneralElectric Co.) Certain glassesand types of fused quartz are available which lack the infrared absorption at about 2.7 microns. EOUIPMENTAND MATERIALS 245 above500"C, especiallyif evacuatedor under stress.2Unless otherwise stated, the piecesof apparatusdescribed in this book, aswell asthe glassblowingopera- tionswhich follow, apply to Pyrcx7740or Kimax K-33. Becauseof its poor resistanceto thermal shockand low softeningtemperature, flint glassis not desirable for most laboratory apparatus.The junction of dissimilar glassesis generally performedthrough a gradedseal composed of rings of compatibleglasses which have a smooth variation in expansioncoefficient and melting point. The very usefulPyrex-to-quartz graded sealsare availablecommercially. Also, a serviceable union may be made betweenPyrex and the high-temperature-resistantce- ramics,3 The tensilestrength of glassis influencedby a sufficientnumber of variables, so it is difficult to specifyvalues which will apply to laboratoryconditions. It is decreasedby surfacescratches, moisture, and many solvents.Also, the strength decreasesfor glassunder continualload. As a result,strengths greater than 1 X 106lblin.2 and as low as 19 lb /in.2 havebeen determined. It hasbeen suggested that a valueof 1,000lb/in.2 is reasonablefor annealedglass.a Accordingly, this valuecan be usedto calculatethe valuesfor the burstingpressures of glasstubes. Any glass tube under pressuremust be treated as dangerousbecause of the highly variabletensile strength of glass.Values calculated for sealedtubes are of limited value becausetests have shownthat the weak point is usuallythe glass seal.s ll.2 EoUTPMENTAND MATERTALS

An amazing variety of glass apparatus can be constructedby using simply a torch and low-pressurenatural gas and oxygensupplies. Also, a pair of didyntium-tinted glassesis a necessityto elim'inatethe yellowglare of sodiumemission which occurswhen borosilicateglass is heated. A nrorerepresentative group of equipmentfor usein the laboratoryincludes the following items, someof which are illustratedin Fig. II.3:

Hand torchband oxygenpressure regulator Didyntium glasses Glassknife or three-corneredfiles

rA.W.Laubengayer,lrrl. Eng.Cltent.,2l.174(1929),describessomeexperimentswhichgivean indicationof the usefultemperature range for Pyrex. rJ. A. Afexander,Fusiort.3. 5 (1q56):E. R. Nagle.Fusiott.10.2J (196J). rPropertieso.l Selecttrl Contntertiul Glrrsses, Bulletin B-83. Cotning GlassWorks. Corning. N.Y. 5J.Tanaka. J. Chent.Educ..50. 4978(1972). nSurface-nrixhand torchesare availablefrom BethlelremApparatus, lnc., Flallertown,Pa. Intelnal- mix hand torchesare available fronr most laboratoryor welder'ssupply houses. A rangeof tips is also requiredwith the internal-mix torches. 246 GLASSAND GLASSBLOWING

Swiveland blowhose Tweezers Taperedgraphite rods (hexagonalor circular crosssection) Set of plain and one-holestoppers and corks Glassfiber paper and/or aluminum foil Polariscope,or two piecesof polaroid film and a flashlight Caliper scale A pair of rollers mounted on a stand A small fireproof bench top or table A reasonably dust-free cabinet stockedwith a variety of standard wall tubing, heavy-walledcapillary tubing, and rod A ring stand and clamps with woven-glass-coveredfingers Surface-mix bench burner for large items

clean glassis usedfor glassbrowingbecause foreign matter is easiryincorpo- rated into molten glass.Aside from the obviousbad effectsthis can haveon the surface and characterof the glass,specks of dirt are a frequent sourceof pinholes'To avoid picking up foreign matter, it is desirabreto usefreshry prepared surfaces joints for making and to minimize contactof thesesurfaces with any- thing but glass or cleanglass-working tools. In this connection,tubinq shouldbe storedin a cabinetto avoidthe accumulationof dust.

@ @

\ 4? ---2-1 ryh .4'-/J -t-'1 tl CAL-/J il

F€( |.l\ a,-JP t\vc=

Fig' II'3' Some glassblowing implements.An internal-mix hand torch and a seriesof tips are shoun in the upper left. In the upper right is a setof rollers.From top to bottom in the cenrerare a brass'shapingtool, a tapered carbon rod on a handle, a glassknife with tungsten-carbidecutting edges.and a verniercaliper scale.At the bottom a swiveland blowhoseare illustratedat a slightlv larger scalethan the other items. The short length of tubing on this swivelmay be connecteddirectl! to an itenror it may be attached by meansof a one-holestopper rvith glass tube. In either casefree rotation of the item and simultaneousblowing are possible. ANNEALING 247 ll.3 sEeuENcEoFoPERAIToNs

Molten glassresembles very thick molasses,so it tends to sag and flow under the influence of gravity. Therefore, wheneverpossible, the piecesbeing worked are rotated to avoid the pileup of glass. When clamping is necessary,the effectsof saggingmay be minimized by clampingtubes in a verticalfashion and placinga tube with thick walls aboveone that has thin walls. In general,it is best to finish a piecewithout interruption and to anneal it immediatelywith the hand torch. An evenwall thicknessis alwaysdesirable be- causethin glassis weak, while lumps are frequentlystrained. Before an intricate apparatus is constructed, the sequenceof work is planned so that it is always possibleto apply pressure(blow) on a joint that is being constructed.Occasion- ally it is necessaryto blow a temporary hole in an apparatus to serveas a place to attach a blowhose.For example, supposea bulb with an attachedstopcock is being constructed from a round-bottom flask and a stopcock. A small hole is first blown into the bottom of this flask (Fig. II.4c), and eithera blowhosewith a swivelis attachedor elsea temporary length of tubing is attached. Either of these provides a mechanism for sealing off the neck and then blowing another hole which will match the stopcock(Fig. II.4ä). After the stopcockis attached,it provides an opening for blowing while the temporary hole is being sealed(Fig. ll.4c). Details of glassblowing operations involved in the construction of this bulb are presentedin the following sections.

ll.4 ANNEALTNe

In the processof working glass,the thermal gradientsintroduce strains which must be relievedif reliable serviceis expectedfrom the glassware.The most sat-

-+ Swivel ond To swivel ond blow hose blow hose

Swive I ond (c) 0low nose

Fig. II.4. Somesteps in attaching a stopcockto a flask This sequenceallows the glassto be blorvn at each stage. 248 GLASSAND GLASSBLOWING isfactoryprocedure involves the use of a glassblower'sannealing oven, which providesgradual and well-controlledwarming and cooling cycles.However, large and intricate parts must be annealedwith the bench torch immediately after constructionand then placedin an annealingoven. A muffle furnacewill servewell as an annealingoven. For most laboratoryitems of moderatethick- ness,the furnace and contentsare allowedto warm from room temperatureto 570"C; this temperatureis maintainedfor half an hour, and then the furnaceis turned off and allowedto cool slowly.Many small parts may be adequatelyan- nealedwith the benchtorch alone.A cool, bushyflame is used,and attainment of the annealingtemperature is judged by the appearanceof the yellowsodium flame. Strains tend to concentrateon either side of a sectionwhich has been worked, so a generousarea should be annealed.After the glasshas been thoroughlyand evenlyheated to the annealingtemperature, the flame temperatureis gradually reduced. Some glassblowersrecommend that the last bit of heating shouldbe donewith a sootyflame; however,it is doubtful that sucha coolflame is worthwhile.For largeparts, it is handyto havea Fisherburner availableto use in the annealingprocess. After the glasshas cooled,strains may be locatedas light streakswhen the apparatusis viewedbetween crossed Polaroids. When a large apparatusis mounted on a lattice,strains are inevitablyintro- duced by the clamping operation.This is partly avoidedby using a minimum number of clamps.Also, all heavyitems, such as thosewhich contain apprecia- ble quantitiesof mercury,must be individuallysupported. The clampfingers are bestcovered with wovenglass sleeves or a layerof glassfiber paper.These covering materialshave a degreeof resiliencyand allowthe useof a torch in the vicinity of the clamp for the purposeof making repairsor alterations,and for flaming out and annealingthe apparatus.After a vacuum line has beenassembled, but before it is evacuated,the glassis softenedand annealedat selectedpoints to removestrains introduced by the clamping.

ll.5 cuTnNGGLASS TUBTNe

Glass is generallybroken and not cut. Small-diametertubing is conveniently broken by making a scratchabout one-fourthof the way around the tube and then graspingthe tube on either side of the scratchand simultaneouslypulling and bending. The nature of the scratchis quite important; it should be made with a sharp tool and with a smooth, firm motion, so that the glasscrackles. Sawing at the glasswith the corner of a dull file producesa rather ineffective scratch.The breaking operationis facilitatedif the scratchis moistened.With largetubing or with a permanentlyclamped piece, this methodcannot be used, and in thesecases the finite thermal expansioncoefficient of Pyrexis utilizedto producea strain around the scratch.The simplestprocedure is to heatthe end of a small-diameterglass rod until it is white hot and then quickly touch this to the glassjustbeyond the scratch.Ifthe resultingbreak is not sufficientlylong, it can be led around the tube by touchingthe hot rod just beyondthe end of the break. TEST.TUBEENDS AND FIRECUIOFFS z4Y

A variant of this technique is to extend the scratchabout three-fourths of the way around the glassand then to direct a small but veryhot flame at right anglesto the tube so that it grazesthe tubing along the middle of the scratch.While a smooth,clean break can be producedby the foregoingmethods, a more satisfactory surface for subsequent glassblowing is often produced by a fire cutoff, which is describedin SectionII.7. It is sometimeshandy to smoothup a jagged end or removeglass by brushingthe end with a metal screen.However, this practice is not recommendedif the end is going to be glassblown,because metal particlesadhere to the glass. ll,6 BENDTNeeLAss TUBTNG

Simplebends can be madeby evenlyheating a broad sectionof tubing and allowing the free end to sag under its own weight. For this purpose a large flame is used which is sufficiently hot to surpassthe softeningpoint, but not hot enough to melt the glass.A bend may alsobe made by evenlyheating the desiredlength of tubing to the softening point and then removing it from the flame and making the bend. Kinks or verysharp bends should be avoidedbecause they break easily under strain. It is sometimesnot possibleto avoid somecollapse of a tube when a bend is made, but its shapeis restoredby stopperingone end of the tubing, heating the sectionto be re-formedto the working point in a large flame, and then gently blowing on the open end of the tubing just after the flame is removed.With a little practice,one can combinethe bendingand blowinginto one continuousoperation. ll.7 rEsT-ruBEENDs AND FIRE cuToFFs

Both ends of a tube are graspedand rotated in a hot flame until the glassbe- comesmolten (Fig. II.5c). The tube is then pulled apart in the flame, and excess glass is removed from one half by melting the unwanted glassand pulling it out with a pieceof cool rod or tubing (Fig. II.5ä). This should leavea completely closed tube, free of excessglass. The closed end is now heated in a hot flame until it becomesmolten, and during this heating, the saggingof glassis pre- ventedby constantlyrotating the tube (Fig. II.5c). As the tube is being rotated, it is removed from the flame and gently blown out to give a hemisphericalend of uniform thickness(Fig. II.5d). Timing is important in this processbecause if the end is blown out immediately after heating, any thin regions will blow out first; but with the correct delay, thick sectionswhich cool the slowestwill be preferen- tially blown out to yield a uniform wall thickness.Failure to rotate the glass constantly is a common error, which leads to uneven heating of the end and a lopsided product. Another error is to heat the closedend too long, which leadsto an excessiveaccumulation of glass. When one is forced to work close to the end of a tube, it is not possibleto 250 GLASSAND GLASSBLOWING

/ tI\,, . -Ftr K (a, ,

(d)

Fig. II.5. Construction of a test-tube end. (c) A small sectionof the tube is melted and the halves pulled apart. (ä) A small hot flame is used to melt excessglass, which is then pulled off with a cold piece (c) of glass. The end is heated evenly, removed from the flame when it is molten but before excessglass accumulates, and gently blown. (d) A finished product. The end should be hemispheri_ cal and the wall thicknessuniform.

grasp both ends as decribed above. In this situation another pieceof tubing or a rod is sealedto the end of the tube to serveas a handle.A verycrudejunction will suffice since the handle is temporary. The preliminaries to produce a fire cutoff are the sameas for a test tube end. Instead of gently blowing the molten glass into a hemisphere, a more vigorous putf is given to producea large, thin bulb. Just as with the test tube end, even heating is necessaryto ensure a well-shapedopening (Fig. II.6). If properly blown, the thin glass is easily brushed off by use of glassrod or another piece of glasstubing to leave an even opening with a slight flare and a thin edge.

(b)

(o)

Fig. II.6. A fire cutoff. (a) A large, very thin bulb is btown out. (ö) The thin glassis brushed away END.TO.ENDSEALS 254

ll.8 END-Io-ENDsEArs

The end-to-end seal is a very common operation in constructing glass equipment. The processis aided if the ends to be joined are smoothly broken or are evenlyblown out; and it is usually desirableto start with freshly broken or fire- cut piecesbecause this minimizesthe chanceof incorporatingdirt into thejoint. When the joint is to be made offhand, the torch is clamped and a free end of one of the tubes is stoppered; the tubes are then grasped in either hand and rotated in a hot and rather large flame (Fig. II.7a). This processrequires some dexterity, sincethe rotation must be evenand the ends must not touch but must becomethoroughly molten. The heating is carried on at an evenbut quick pace to avoid a large accumulation of molten glass around the two ends. Next, the pieces are removed from the flame and pressedtogether. This is generally followed by a gentle pull and simultaneous blowing to thin out the ring of glass which has formed at the junction (Fig. ll.7b). Here again, it is necessaryto develop somedexterity so that the piecesare initially joined in a concentricfashion. If the initial union is badly skewed or if a continuous hole-free seal is not achieved, a smoother final product is generally obtained and time is savedby starting over, rather than attempting to patch up the joint. The pulling-out and blowing operations described above are not absolutely essential,because the next step is to smooth out the joint. This may be accomplished in severalways. Generally, the part is rotated in a hot flame until the glassin the joint is thoroughly melted; it is then removedfrom the flame and gently pulled to thin out the thick glassand blown to restorethe glassto its correct diameter. Closecoordination of the rotation rate for each hand is necessary to avoid twisting the glass during the heating. When unwieldy parts are

ffi (c)

Fig. II.7. Construction of an end-to-endseal. (a) A large hot flame is usedto createan evenmolten rim on both piecesof glass.(ä) The two ends are joined, which leavesa small ridge of glassthat must be worked in. (c) The finished product should have a reasonablyuniform wall thickness and no vestigesof the ridge. 252 GLASSAND GLASSBLOWING

encountered,a sightly different approach may be taken. In this case,the welt of glass at the junction is worked in by heating a small segment of the glass to a molten state and then blowing it out to the correct radius. One then moveson to the adjacent segmentand works it in. A final heating of the joint to the softening point, alignment, and blowing may be necessary;but the above processdoes avoida continuousbelt of molten glass,which may be hard to handlebecause of the bulky nature of the apparatus. An end-to-end seal may also be made by firmly clamping one of the parts, preferably in a vertical direction, and lightly clamping the other so that the edges are aligned but do not quite touch. One hand is used to steadythe lightly clamped piece and the other directs the hand torch around the two ends to give continuous molten edges.The lightly clamped piece is then pressedinto the other, and the parts are worked together as describedabove. If the glasssags too much toward the lower component, the part may be inverted and additional smoothing performed. When the two tubes to be joined are of different diameters,the task is slightly more difficult. In this case,a test tube end is formed on the largertube; then a verysmall flame is directedin the centerof this end, and only a small holewith a diameterwhich matchesthe small tube is blown out. To allow better control of the hole sizeand to yield a lip which facilitatesthe subsequentsealing, it is helpful to perform this blowing-outoperation in two stages(Fig. II.8).

(b)

(c l

Fig. II.E. Preparation of a large-diametertube for an end-to-endseal with a smaller tube. (a) A test tube end is formed on the large tube, and a small molten spot is createdon the end with a small hot flame. (ä) A bulgeis blown in the end. (6) The end of this bulgeis meltedand blown completelyout. The diameterof this openingshould match that of the small tube. RINGSEALS 253

When an end-to-endseal is made with heavy-walledcapillary tubing, the end(s)of the capillarytubing is blown out to producean openingwith a normal wall thickness.It is convenientto accomplishthis in two stages,as illustratedin Fig. II.9. Subsequently,the seal is made in an ordinary manner.

ll,9 r-sEALs

A round hole is blown in the side of a tube by first blowing a bulge and then concentratingthe flame on the end of this bulge and blowing it out. This two- step operationgives a round hole and leavesa lip which is convenientfor the subsequentsealing operation (Fig. IL10). The two edgesto be sealedare heated evenlyto the molten state,joined, and then worked in like the end-to-endseal. When a T-seal is made by joining a small tube to the side of a large one, care must be taken to avoid sudden cooling and reheating of the joint before it is finished and completelyannealed. If this is not done, considerablestrain de- velopsbecause of the unsymmetricalconfiguration around the axis of the large tube.

11,40 RTNGsEALs

There are two common waysof making ring seals.One of theseis illustratedin Fig. II.l1, whereit may be seenthat a testtube end is formed on the outer tube,

:-- -_--]r\l -- Y_/ (b)

Fig. II.9. Preparationof capillarytubing for an end-to-endseal. (a) A tube trlownout to normal wall thickness.(b) The sametube with the end blou'nout. g P tl IV tl ) | | "---l IItl tl U t^l (o) (b)

Fig. II.l0. Constructionof a T-seal./a) A bulgeis blown in the sideof the tube. (ä) The end of the bulgeis heatedand blown out 10leave a small lip. (c) A junction is made in a mannersimilar to the constructionof an end-to-endseal. 254 GLASSAND GLASSBLOWING

Asbe sl os

@ (b)

ffi (c)

Fig. II.ll. Some steps in making a ring seal. (a) The formation of a seal betweenthe inner and outer tubes. (ö) A bulge is blown, which createsan extensionof the inner tube. (c) The end of the bulge is blown out. This piece is now sealedto a tube of the same diameter as the inner tube.

and a smallertube is then slippedinside and held centrallyby glasspaper. This inner tube is butted firmly againstthe test tube end, and a sealis madebetween the two tubes by playing a small and rather hot flame on the outside of the test tube end in the regionwhere the two tubestouch. When the sealis made, a very small flame is directed in the centerof the seal,and the glassis blown out by applying pressurethrough the inner tube. This is best accomplishedby first blowing a bulge and then heatingthe end of the bulge and blowing it out. The resultinglip is then immediatelysealed to a tube with a diametersimilar to the inner tube, and the joint is annealed. The secondmethod (Fig. IL12) involvesblowing a hole in the testtube end of a large tube. This hole should be just large enoughto allow the central tube to slip through it; and it may be necessaryto use a tapered carbon rod on the hot glassto obtain the correctsize opening. A small annular bulge is then blown in the small-diametertube in the region in which the sealis to be made, and this tube is slippedthough the hole so that the bulge is on the outside.The concen- tricity of the tubes is ensured by severalturns of glass paper around the central tube or by an appropriately bored cork. A small, hot flame is directed at the bulge where it contacts the hole, and the parts are rotated until the glassis molten. The small tube is then pushedtoward the larger one to make the sealand then pulled back and blown to createa uniform wall thickness. Ring sealsare particularly susceptibleto breakagefrom thermal strains, so it METAL-TO-GLASSSEALS 255

(c '

Fig. II.12. Secondmethod for the construction of a ring seal.(c) Test tube end on a large-diameter tube has a small-diameter fire cutoff. (ä) A small tube with a bulge is inserted. (c) The two tubes are sealed. is best to make the complete seal without interruption and to anneal the final product carefully before it is allowed to cool. ll,44 cLosEDcrRcurTs

It is sometimes necessaryto make a seal between two stationary tubes. Each particular casewill require a slightly different solution, but one approach is to softenand stretch one pieceof glassso that it meetsthe other, and then make the sealby heating the glassat the joint, pulling it together over any small gaps with a small pieceof glassrod. It is alsopossible to join two tubeswhich do not meet by filling the spacebetween them. When this is done, the flame is directedpri- marily onto the glassrod which is being usedas filler and not on the openedges, becausethese tend to sag away from the joint if they are strongly heated. The samesituation is encounteredwhen a hole is beins filled. ll.42 METAL-ro-eLAsssEALsT

A small tungstenelectrical lead (1/8-in. diameteror less)can be sealeddirectly to Pyrex by the following procedure. A short length of Pyrex tubing is found

TDetailedinformation on glass-to-metalseals may be found in the following references:J. H. Par- tridge, G/ass-to-MetalSeals, (Sheffield, U, K.: The Societyof Glass Technology,1949)t W. H. Kohl, Materials and Techniquesfor Electon Zräes, (Neu York: Reinhold, 1960): Chapter 13; F. Rosebury.Handbook oJ Electron Tube and Vacuum Techniques( Reading, Mass: Addison-Wesley. 1965).pp.54ff. 256 GLASSAND GLASSBLOWING which will just slip overthe wire and which is sufficientlyshort to leaveadequate bare wire on either end for electricalconnections. The tungstenwire is heated white hot, cooled, sanded until it is bright, and then carefully oxidized by quickly passingit through a flame. The oxide coatingshould be thin enoughto givethe appearanceof gun-metalblue. The small pieceof tubing is slippedover this tungstenwire and heatedto collapseit onto the wire. If the sealis properly made, the tungsten-glassinterface will have a copperlikeappearance and few bubbles.The glasssheath may then be sealedinto a hole in the apparatus.Gen- erally, the hole is blown with a small lip which may be softenedand then col- lapsedonto the glasssheath by tweezersor a carbon rod. One of the most satisfactorymetal-to-glass seals involves an Fe-Ni-Coalloy called Kovar. The coefficientof expansionof this alloy is closeto that of Pyrex, to which it can be directlybonded; however,an evenbetter match in expansion coefficientsis obtained with a specialborosilicate glass (Corning7052, Kimble EN-l or K-650). A varietyof tubes is availablecommercially involving a Kovar tube sealedto a Pyrextube through one or more intermediateglasses. The propertiesof Kovar are discussedin Appendix IV under iron (SectionIV.l.E). Copper-to-glassseals (Housekeeper seals) and stainless-steel-to-glassseals can be made and the directionsmay be found elsewhere.8eThese seals are somewhat strainedand are generallynot suitableif the joint is exposedto wide tem- peraturevariations. It is possibleto solder most metalsdirectly to glassby use of indium metal (mp 155'C) or an indium alloy suchas In 95 % Ag 5 % (mp about 145"C).The heatedglass is rubbed with the molten solderto wet the surfaceand then heated in contactwith the metal, which was previously"tinned" with the solder.r0 A number of low-meltingglasses have been specially formulated for "soldering" glassto glass.metal, or ceramics."In general,the coefficientof expansion for the solderglass should nearlymatch that of the items being bonded. ll.'13 HEALTNecRAcKs AND PTNHoLES

Occasionallya crack will developin an apparatusbecause of mechanicalshock or internal strainswhich were not completelyremoved by annealing.Providing the glassis not shatteredor the part is not under a large, externallyproduced strain, the crack may be healedby gentleheating. The areaaround the crack is first slowlyheated, and then the soft flame (somewhathotter than an annealing

öW.G.Housekeeper,J.Anr. Inst.Elec.Eng..42,951(1923);alsoE.L.Wheeler,ScientiJ'icGlass- blov,ing,(New York: lnterscience,1958). pp. l62ff. 'qS.O.ColgateandE.C.Whitehead.Rev..lci.Iustr.,33. ll2.2(1962):J.E.BenbenekandR.E. Honig, Rev. Sci. Instr., Jl, 460 (1960). roR.B. Belser.Rey. Sci. Instr.,25. 180(1954). IrSolder Glass Kit, Owens-lllinoisCo., Toledo, OHI Quartz CenrentBinder, ArnericanThermal FusedQuartz Co., Montville, NJ. SEALINGTUBING UNDER VACUUM 257

flame) is movedgradually toward the crack. In many casesthis processwill lead to the disappearanceof the crack. If, however,the crack doesnot heal, it will slowlyopen up as the glasssags away from the crack. A pieceof cane (small- diameterglass rod) may then be usedto unite the open edgesof the crack and somefinal blowingwill be necessaryto obtain a smoothseal. A pinholeusually is sealedby melting the spot with a small hot flame and pulling away a small amount of glasswith a glassrod.

lrlr.44sEAUNG ruBrNe UNDER vAcuuM

Operationssuch as the collectionof a samplein a sealedvial or the performance of reactionsin sealedtubes requirethe ability to sealoff tubing under vacuum. This is easilyaccomplished if a thickenedsection of glasswith a moderateinside diameter(about 5 mm) was included in the apparatus(Fig. IL l3c). The thickenedsection should be sufficientlylong sothat the adjacentthinner tubing is not softenedduring the seal-offoperation. The inner wall of the constrictedportion should be free from foreign matter, and throughout the sealingoperation the

To voc uum To pump pump To pump .ll, T-7 -LL \/ v o i\ Thickened sectlon \/ fth Y€4\ t^J ntl r)l/'7\ (b) (cl

Fig. II.l3. Vacuum seal-off.(a) The tube is evacuated.If a volatilesubstance is being sealedinto the tube, the lowerend of the tube is immersedin liquid nitrogen.(6) Thickenedsection collapsed by a softflame. (c) A hot flame is playedon the collapsedsection, and the sealedtube is pulledaway. (d) Not shown. The tube end is gently annealed. 258 GLASSAND GLASSBTOWING vesselis pumped on to remove gaseswhich boil out of the glass. A seal may be made by directing a soft flame evenly around the middle of the constricted section. To avoid sucking a hole in the glass, care is taken to move the flame off a section as it begins to collapse. After the tube has been collapsed in an even fashion, one is left with a small, nearly solid section, which may still contain a threadlike openingbetween the two halves.Next, a small, very hot flame is directed around the nearly solid section, and while the flame is on the glass, the tube is separatedfrom the apparatus by pulling it away. Finally, the sealedend is annealed with care to avoid further collapseof the tube.

GENERATREFERENCES

Barr, W. E. , and V. J. Anhorn, 1959, Scientific Glassblowing, Instruments Publishing, Pittsburgh. Heldman, J. D., 1946, Techniques of Glass Manipulation in Scientific Research, Prentice-Hall, Englewood Cliffs, N.J. Laborutory GlassBlowing with Corning Glasses,l96l , Bulletin, B-72, Corning Glass Works, Corn- ing, N. Y. Moore, J. H., C.C. Davis, and M. A. Coplan, 1983,Building ScientificAppararzs, Addison-Wesley, Reading, Mass. Glassblowing is coveredin Chapter 3. Parr, L. M., and C. A. Hendley, 1956, Laboratory Glassblowing, G. Newnes,London. Wheefer, E. L., 1958, Scientific Glassblowing, Interscience, New York, Available from E. L. Wheeler,P.O. Box 4833, Chico , CA 95927. A N D x PLASTICSAND ELASTOMERS

Many recent improvements in apparatus have resulted from the availability of new high-polymer materials. These substancesexhibit a wide range of physical and chemical properties. Therefore, it is frequently necessaryto exercisecare in the choice of the rubber or plastic to be used for a particular application. Rubbers and plastics have a much more limited range of useful temperatures than do metals or glass. Most polymeric materials undergo a low-temperature transformation to a brittle glassystate which often limits their utility at reduced temperatures. In addition, plastics lose their strength at high temperatures. Small changes in formulation may significantly alter the usable temperature range of a polymer material, so the glasstransition temperaturesand maximum usable temperatures quoted in this appendix are only approximate. Elastomers and, to a lesserextent, plastics tend to swell in the presenceof solvents.Frequently, this swelling is accompaniedby a lossin strength. In addition, someplastics are dissolvedby certain solvents,and all-polymeric materials may be chemically destroyed.It is in the areasof solventand chemical resistance that most problems are encounteredin the laboratory. The permeability of high-polymermaterials to atmosphericgases and solvents is much greater than for metal or glass. This is often a significant factor when air-sensitivecompounds are being handledor when a high vacuum is desired. It is evident from Table III.1 that permeabilities may vary greatly from one material to the next. The rate of permeation decreaseswith an increased cross section of the plastic or elastomer, becausethe amount of gas which will passthrough a membrane of thickness d is given by the equation q:QA(+),

259 260 PLASTICSAND ELASTOMERS where,4 is the membrane area, Pr - Pz is the differencein partial pressuresof a particular gas on the two sides of the membrane, / is the time, and Q is the permeability.rValues are presented in Table III.1 for the permeabilityQ of various materials to atmospheric gases.In most cases,the permeability increases with temperature; and it may be decreasedby greater cross-linking or greater crystallinity. From the data in Table III.l it may be seenthat cellophane and cellulose acetate have very large permeabilities to water; also, the solubility of water in these materials is great, so they are clearly unsuited as moisture barriers. Of the elastomerslisted, silicone rubber has the highest permeability to air. lll, 4 pLASTrcs:GENERAL pRopERTTES ANDFABRtcAIoN

Most plastics may be classifiedas thermosetting or thermoplastic. At the molecular level the former are characterizedby a three-dimensionalcross-linked net- work. These thermosetting plastics soften progressivelyas heat is applied, but they do not exhibit a true melting point, and often the maximum usabletemper- ature is higher than for a comparable thermoplastic. The thermoplastics,which are composed of high-polymer chains without cross-links, exhibit reasonably well-defined softening ranges and are often more susceptibleto solventsthan similar thermosetting polymers. The method of fabrication for plastic items is influenced by whether or not one is dealing with a thermoplastic or a thermosetting plastic. In general, the first group may be heat-sealed,heat-molded, and solvent-cemented,but these possibilitiesare not availablefor the thermosettingresins. Both groups generally can be machined. Irradiation of thermoplastics leads to cross-linking and thus imparts the propertiesof a thermosetting plastic. Tubing which has been expandedafter the radiation treatment has a "memory" of its former sizeand will shrink to its original size when heated. Shrinkable tubing is available in a number of different plastics.2 Heat-sealingis routinely usedin the "bagging" operationfor the disposalof radioactive and/or highly poisonous materials from a glove box. The general approachin heat-sealingis to heatthe film to the meltingtemperature and press the molten surfacestogether. To accomplish this, a tool with a heated Teflon- coatedroller is availablecommercially, and an accessoryheat-sealing tip is available for many electricsoldering guns. It is possibleto weld substantialpieces of thermoplasticby the useof a hot-

rWhile reasonablyaccurate for the permeation of simple nonpolar gases,this equation is lesssuit- able for water vapor, so the permeability data quoted for this substanceare of qualitative signifi- canceonly. 2Ravchemlnc.. Menlo Park. CA 94025. PLASTICS:GENERAL PROPERI|ES AND FABRICATION 261 gastorch (Fig. IILl).3 Theseoperate by electricallyheating air or nitrogen;this hot gas is directed on the seamto be welded while a rod of the sameplastic is fed into the molten seam (Fig. III.2). This procedureis effectivefor joining poly(vinylidinechloride) (Saran), rigid polyvinyl chloride, and polyolefins.The heat gun is alsouseful for joining metal or glasstubing to plastictubing, suchas polyethylene.aTo construct a vacuum-tightjoint, the glassor metal tubing is trealeaabove the melting point of polyethylene,and the polyethylenetube is softenedand slippedover it. The joint is heatedwith the hot-air gun, and the poly- ethyleneis worked into the joint with a cold metal tool. A satisfactoryend-to-end ,.ui -uy be made with polyolefinand similarthermoplastic tubing. The endsof the two parts to be joined are evenly melted with the hot'air gun and then pressedtogether. while still molten, the welt of plastic at the seal is pinched iogetherwith pliersor tweezers,and the resultingthin, circularband of plasticis later trimmed away. Thermoplastictubing may be sealedoff by a simplecrimp seal.This involvesrotating the plastictubing in the jet of hot air until an even molten ring results. This sectionis then crimped together with tweezersor pliers' and the two halvesare cut apart at the seal.For small'diametertubing, a "test tube end" sealmay be achievedby drilling a shallowhole of the samediameter as the tube in a metal plate. This plate is then heatedon a hot plate to the melting point of the plastic,and the end of the plastictube is forcedinto it' A remov- able collar of glass or metal tubing may be slipped over the plastic tube to prevent bulging abovethe seal and a film of talc or siliconestopcock grease may be usedto preventsticking to the heatedmold. A simplealternate method of joining and sealingthermoplastic tubing such as Kel-F or polypropylene,is illustrated in Fig. III.3. The plastictubing (1) is forcedtogether inside a glasstubing mold (2), which is gently heatedby a cool flame (4), and a rod is insertedto shapethe interior of the weld (3). This is an excellentprocedure, since it pro- ducesclean, strong welds and the necessaryequipment is readilyavailable in the laboratory.s To bend thernroplastictubing, a btoad areaof the tubing is evenlyheated in the hot-air streamand then bent. Justas with glasstubing, unevenheating leads to a sloppy bend. A much more satisfactorybend can be obtained by heating the tubing in hot wateror air, bendingit with a metal-tubingbender (Appendix lV), and. while it is still in the bender, quenchingthe tubing in a stream of cold water. Also, a flare, which is suitablefor joints, may be constructedby heating the tube end in hot water or air, shapingthe end with a flaring tool (Appendix IV), and quenching. Sheetsof thermoplastic material may be hot-formed into a variety of smooth shapesby heating the sheet in an oven to a temperature at which it becomes plia-ble.The sheet is then bent over a form. In the laboratory this method is

rPlastic welding torches are available from tool suppliers. aWhenwelding polyethylene and polypropylene,clean. freshly cut surfacesshould be prepared'and nitrogen should be used in the torch becausea thin film of oxide preventsa satisfactorybond. sNeil Bartlett kindly supplieda descriptionof this technique' N o. N Ioble lll.'1.Permeobilify O lin {0-r0 cm2/(s-torr)lfor SomeCommon PolymericMoleriolso

Temp Polymer "C H2 Oz N2 COr HIO

Celluloseand cellulosederivatives Cellophane(cellulose acetate) 25 0.0021 0.0032 0.0047 47-169.000 Cellulose acetate, plasticized 2l 4 25 I 1.000-35.000 30 0.78 0.28 2.38 Cellulosenitrate 25 t.7 l.95 0.12 2.2r Ethylcellulose,plasticized 30 26.5 8.4 41.0 Elastomers Natural rubber, vulcanized 2s 48 23 7.9 130 2,300 Butadienerubber, vulcanized 25 42 19.2 6.5 139 Buna S, vulcanized 25 40 17 6.2 122 4,400 Buna N, vulcanized 25 16 3.8 1.0 30 6,100 Neoprene,vulcanized (polychloroprene) 25 13 4.0 1.2 25.8 910 Butyl rubber, vulcanized 25 7.2 1.3 3.3 5.1 Thiokol B, vulcanized 25 r.6 0.3 3.r 65 Silicone rubber 30 91 (270) 460 Ethylene-propylenerubber 30 (air...... 11) Fluorocarbon polymers: Teflon (polytetrafluoroethylene) 20 4.7 Teflon FEP (tetrafluoroethylene hexafluoropropene copolymer) 25 4.5 1.9 l0 Kel-F, crystalline (polychloro- trifluoroethylene) 25 0.040 0.005 0.21 < 0.3 Polyamidesand polyesters: Nylon 6 [poly(6-aminocaproic acid)l 20 0.088 25 40-4,000 30 0 038 0 009.5 Myhr Ipoly(ethyleneterephthalate)] 30 0.045 0.01r 0.r5 Polycarbonatepoly(4,4' -isopropylidene diphenylenecarbonate) 25 1.4 0.3 8.0 Olefin polymers: Polyethylene,Iow density 25 (4) 2r-66 30 3.95 1.36 16.7 Polyethylene,high density 30 0.51 0.18 2.1 Polypropylene 30 2.3 0.44 9.2 Polystyrene 25 (ls) 920-r,300 30 I.l 0.29 8.8 Polyvinyl chloride 25 130-260 30 0.3 0.1I 1.5 Saran; polyvinylidene chloride 30 5xl0-r 9x10-4 0.03 Pliofilm, plasticized; rubber hydrochloride 25 I 3-330 Acrylics: Poly(methyl methacrylate) 25 r.300

*These data are taken from H. Yashuda, "Polymer Handbook," J. Brandup and E. H. Immergut (eds.),V l3ff, Intersciencepublishers, New york, 1966; G.J. van Amerongen,"Elastomers and Plastomers,"R. Houwink (ed.),vol. I, pp. 3lOff, ElsevierPublishing Company, Amsterdam, 19501R.p. Bringer, paper presented at Societyof AerospaceMaterials and ProcessEngineers, St. Louis, May 7-9, 1962 (fluorocarbon data, in part), Ethylene propylene "Nordel rubber: an EngineeringProfile," E.l. du Pont de Nemoursand Co., ElastomerChemicalDept., Wilmington, DE., and Du pont N bulletin T-38 (Teflon FEP). (.)o. 264 PLASTICSAND ELASTOMERS

.f------1 i ) /-,t-

Fig. III.l. Plasticwelding torch.

Lop fillef weld DoubleV buti Corner weld weld

{o)

(b)

Metal clamPtngstrrPS---. a- \ aPrast,cl ) \ vilw\nz/ ,z A-JIP ,-Hot ptate t------T tl ll (c)

Fig. III.2. Plastic welding practice. (a) Some typical welds. (ä) Technique for feeding rod into weld. With the rod bent back into a 45o angle, it is easyto heat and the rod is forced into the seam. The torch should be fanned between the rod and the parts being welded, with somewhat greater concentration on the latter. (c) An edge seal accomplishedon a hot plate.

suitable for the construction of simple, smooth shapesand is particularly suc- cessfulwith poly(methyl methacrylate) sheet stock. As mentionedearlier, many thermoplasticmaterials dissolve or becometacky in the presenceof a solvent,and this providesthe basisof solventcementing. The edgesto be joined should be well mated; one of the edgesis then soakedfor about 5 min in the solvent. The part is removed from the solvent, and excess liquid is allowedto drip off. While still damp, the part and its mate are lightly CELLULARPLASIICS 265

Fig. III.3. Joiningand sealingthermoplastic tubing. (a) End-to-endseal between tubes of identical diameter; (b) end-to-end seal betweentubes of different diameter: (c) closed-endsea!.

clamped together.When clear plastic is used, the joint should be transparent and nearly bubble free. Solvent sealing is especiallyuseful in the fabrication of parts from cast poly(methyl methacrylate) sheet stock. Most of the common machining operationscan be performed on plastics which are not too soft or too brittle to withstand working. Plasticsdo not dissi- pate heat as effectivelyas metals, so care has to be taken to avoid overheating.In the caseof Teflon, poisonousfumes may be given off by the excessivelyheated plastic; and many of the thermoplasticscan be heatedto the point that they flow and gum up. In general,overheating can be avoidedby employingsharp drills and cutting toolsand by appropriateadjustment of working rates.Heat dissipa- tion can be increasedby drilling with an in-out motion, and inert coolants,such as water or water-oilemulsions. mav be used.

lll.2 cELLUTARPlnsrcs

At one time or another practically everyplastic and elastomerhas been pro- cessedin a cellular form. Only two of the most commonlyencountered foamed plastics will be considered here: styrofoam and foamed polyurethane. Both of 266 PLASTICSAND ELASTOMERS thesematerials have low thermal conductivity and are very useful as low-temperature insulators. While unaffected by water, styrofoam is dissolvedby many organic solvents and is unsuitablefor high-temperatureapplications because its heat-distortion temperature is around 77oC. Molded styrofoam objects are produced commercially from expandable polystyrenebeads, but this processdoes not appear attractive for laboratory applications becausepolyurethane foams are much easier to "foam in place." However, extruded polystyrenefoam is available in slabs and boards which may be sawed,carved. or sandedinto desiredshapes and may be cemented. It is generally undesirableto join expandedpolystyrene parts with cementsthat contain solventswhich will dissolvethe plasticand thus causecol- lapseof the cellular structure. This excludesfrom use a large number of cements which contain volatilearomatic hydrocarbons,ketones, or esters.Some suitable cementsare room-temperature-vulcanizingsilicone rubber (seebelow) and solvent-freeepoxy cements.When a strong bond is not necessary,pol)ryinyl-acetate emulsion(Elmer's Glue-All) will work. Urethane foams may be rigid, semirigid, or flexible dependingon the ingredients and their proportions. The rigid urethane foams generallyswell in the presence of organic solventssuch as benzene,carbon tetrachloride,and acetone; however,exposure to thesesolvents and subsequentdrying has little effect on the foamed plastic. Someof the flexible foams are more solventsensitive, but this doesnot preclude the useof most cements.Flexible expandedurethane tubing is commerciallyavailable in a varietyof sizes.6It providesa simple and efficient method for the insulation of tubing which carries refrigerants. For example, it has proven successfulfor the insulationof liquid nitrogenlines. Foamed-in-placepolyurethane is preparedby allowinga polyolIpoly(ethylene glycol), polyesteralcohols, etc.] to react with a diisocyanatein the presenceof an amine catalyst. The gas which creates the foam may be a dissolvedmaterial, such as a Freon, which volatilizes during the exothermic polymerization reaction.? A second method involves the use of water in the reaction mixture; this hydrolyzespart of the isocyanateto produce an amine and CO2gas. The Freon- formed material is preferred for the insulation of low-temperature apparatus becausethe thermal conductivity of the foam is greatly reduced at low temperatures by the condensationof the Freon in the cells. It is probable that the long- term effectivenessof this phenomenon must be maintained by surrounding the foamedplastic with an airtight enclosurewhich will preventdiffusion of air into and Freon out of the cells.

bPolyurethaneand polyvinyl foamed tubing for insulation are available from refrigeration supply houses. TThe ingredients for the preparation of polyurethanefoam are availablefrom many companies,including the Perlon Corp., Lyons, IL, and American Latex Products, Hawthorne, CA. PROPERTIESOF SPECIFICPLASTICS 267 lll.3 pRopERIrEsoFspEcrFrc plAsTrcs

A. ACrylics. This group of clear thermoplastic materials is frequently encountered under the trade name Plexiglas(Rohm and Haas). The most common member of the series,poly(methyl methacrylate),has a softeningpoint of l24oC, at which temperature sheet stock, rods, and tubing may be formed into special shapes.In addition, the plasticmay be machined;however, care has to be taken to avoid overheating.Cast poly(methyl methacrylate)sheet stock may be bonded by means of a solvent such as methylene chloride or 1,2-dichloroethane. Giauque and co-workers used a cement composedof equal volumes of methyl methacrylate monomer and dichloromethane. This is used exactly like the pure solvent cements. After the lightly clamped parts had dried for a few hours, the joint was further cured and annealed by heating the part to 50oC for about 1 day. It was found that a joint of this sort gavereliable vacuum-tight performance at liquid helium temperature.s

B. Chlotinoled Hydtocorbon Ploslics. Polyvinyl chloride is often fabri- cated into sheetsand tubing. Some formulations are reasonablytransparent. Generally, plasticizersare included in the formulation to increasethe flexibility, and tubing of this sort is a familiar laboratory item under the Tygon trademark. A number of formulations are available, but one of these, Tygon R-3603, is recommended for general laboratory use. It makes a good seal with glass tubing and is claimedto havea vapor pressureof 10-7 mm at 21'C. The amount of gas desorbed by polyvinyl chloride is very low in comparison to rubbers. Further- more, the data in Table III.1 showthat polyvinyl chloride has a lower permeability to atmospheric gasesthan rubber, so healy-walled Tygon tubing is to be preferred to rubber when a flexible vacuum connection is required. While this tubing is less susceptibleto deterioration than most rubber tubing, it tends to stiffen and becomemilky in appearanceafter long exposureto water. It is essentially inert with aqueous acids and alkalies but is attacked by most organic solvents,as well as Cl2,HCl, and BCl3.The R-3603formulation becomesbrittle at -45oC and loses much of its strength around 93"C. Rigid polyvinyl chloride pipe is availablefrom hardwareand plumbing suppliers.It is easilycut with a saw and may be joined to elbows, T's, and other fittings by means of a special cement. The grade which is made to carry drinking water has a low content of volatiles and has been found suitable for rough- and medium-vacuum systems.e Polyvinylidinechloride (Saran) is a tough plasticwhich is extensivelyused in laboratorydrainpipes. This form of the plasticis rigid, but flexibletransparent films are usedwidely in food packaging.Polyvinylidine chloride becomes brittle at l0"C and losesmost of its strengthat77oC.It has unusuallylow permeability

8W. F. Giauque, T. A. Geballe,D. N. Lyon, and J. J. Fritz, Rev. Sci.Instr., 23, 169(1952). eR. L. Hartman, Rev. .Sci.Instr.,38,83! (1967). 268 PLASTICSAND ELASTOMERS

to gasesand is chemically attacked by only very strong oxidizing or reducing agents.The solventresistance is fairly good, and thereforesolvent bonding is not easy.Both edgesto be bonded should soak in the solvent(preferably warm) for an extendedperiod of time beforethey are joined. Cyclohexanone.o-dichloro- benzene,and dioxane are suitable for solvent bonding. Epoxies form string bondsto vinylidinechloride, and weldingor heat-sealingis quite successful.

C. Epory Resins. The epoxy resins are thermosetting plastics which have great strength and the ability to form tenaciousbonds with most surfaces.Fur- thermore, the cured resin is resistantto many solventsand chemicals.(Some epoxy resins are decomposedby acetic acid, and all are attacked by very strong oxidizingagents.) Because of this combinationof properties,epoxy cements are frequentlyused to bond metal, glass,wood, and plastics. Epoxy resins tend to outgas under vacuum, primarily through the slow desorption of moisture and low-molecular-weightorganic material. However,good epoxy cements which are compounded without filler materials or solventshave acceptableoutgassing rates for high-vacuum applications.r0Another property which must be anticipatedfor someapplications is the high thermal expansion coefficient of the cured resin. Becauseof this property, a glasstube which contains a solid plug of the cured resin will often break when heated or cooled. The basic ingredientin the epoxyresin is a viscouspolymer which generally contains two epoxide groups o (-o-cH2-cH-iH-l per molecule.The further polymerizationof this resinto a hard infusiblemass is brought about by mixing it with a curing agent (also called a hardener or a catalyst)just prior to application.The curing agentsvary in compositionand mode of action, but one common type involvestertiary amines which catalyzethe attack of one epoxidegroup on the next to interlink the original resin through -O-(CH2-CH(R)-O), groups.Reactive curing agents,such as primary and secondaryamines and alcohols, are also employed and are incorporated into the polymer during the cure. The proportions of resin to curing agent recommended by the manufacturer should be followed with reasonableaccuracy to avoid an incompletely cured product or an excessivelyfast and exothermic cure which

'oTheAraldite resins(e.g., Araldite I and l0l) manufacturedby Ciba ProductsCorp., Summit. NJ. and the Epon Adhesivesmanufactured by Shell Chemical Co., Pittsburgh, PA, are widely used in vacllumapplications. K. S. Balain and C. J. Bergeron,Rev. Sci. Insrr., 30, 1058(1959), found that Stycast2850 GT, made by Emmersonand Cumming Inc., Canton, MA, gavea sealwhich was suit- ableforvacuum and pressureapplication at low temperatures.W. R. Roach.J. C. Wheatley,and A. C. Mota de Victoria, Rev. .9ci./rrsrr., 35, 631 (1964)used Epipond 100-A(Furane Plastics,4516 Brazil St., Los Angeles,CA) for the constructionof vacuum-tight,low-temperature electrical-feed throughs.It shouldbe notedthat the opaqueepoxy cements which are sold in hardwarestores often containfillers. PROPERIIESOF SPECIFICPLASTICS 269 leavesno time for application.The uncuredresin and hardenershould be handled in a well-ventilatedarea, and contact with the skin shouldbe avoidedbe- causethe aminesemployed in the hardenerare toxic skin irritants, and the resin may cause dermatitis or an asthmalike condition with sensitiveindividuals. "One-component"epoxy preparations are alsoavailable in which the catalystis activatedby the applicationof heat.rr

D. FluorocolbOn Polymets. Four differentfluorocarbons account for the bulk of the laboratoryapplications: polytetrafluoroethylene, Teflon PTFE; poly(chlorotrifIuoroethylene), KEL-F; tetrafluoroethylene-hexafluoropropylene copolymer, Teflon FEP; and tetrafluoroethylene-perfluorovinylether copolymer, PFA. Thesepolymers are inert with most chemicalsand solventsat room temperatureand exceptionallyinert with oxidizing agents.They also have an exceptionalresistance to temperatureextremes. However, they are decomposed by liquid alkali metals,solutions of thesemetals in liquid ammonia,and carban- ion reagentssuch as butyllithium. Teflon retainssome of its complianceat liquid hydrogentemperature. The maximum temperaturewhich is recommendedfor continuousservice is 260'C for Teflon PTFE and PFA. and about 200"C for Kel-F and Teflon FEP. Teflon is an opaque, flexible solid with a waxy feel. It has a self-lubricating quality which makes it a useful material for the packing in valves.However, it tends to cold-flow, and must be well supportedon all sidesif it is to be used under pressure.For this reason,Teflon O-rings havenot beenparticularly suc- cessfulin high-vacuumapplications; but other typesof gasketswhich are supported better, such as simple flat gasketsbetween flanges, are serviceable.The flexibility and tendencyof Teflon to cold-flow may lead threaded parts in Teflon to strip when they are under much force. Conventional Teflon PTFE can not be heat-moldedor heat-sealed,and cementingis not very satisfactory.The principal method of fabrication in the shop is machining. Teflon FEP is similar in most respectsto the conventionalmaterial; however,it is more transparentand may be readilyheat molded and heat-sealed.Both typesof Teflon tend to outgas when usedin high-vacuumapparatus. Kel-F is a somewhatmore rigid plastic than the Teflons and has much less tendencyto cold-flow.Therefore, it will bear a continuousload and is preferable to Teflon for threaded items. As with Teflon FEP, Kel-F may be heat-formed and sealed(330 to 400 'C). It is somewhatmore susceptibleto swellingthan the Teflons when it is contactedwith halogenatedand aromatic hydrocarbonsat elevatedtemperatures. Also, it is slightly more susceptibleto oxidation at elevated temperature. However, at room temperature it gives satisfactoryperfor- mancein the presenceof solventsand strongfluorinating agents.Kel-F is useful in vacuum apparatusand is an excellentseat material for metal valves.Porous, sinteredfilter disks of Ket-F and Teflon are availablecommerciallv.r2 The rrCibaProducts Corp. Sunrmit, NJ. rrPallTrinitv Micro Corp., Cortland, NY. 270 PLASTICSAND ELASTOMERS former may be heat-sealedinto Kel-F apparatus. When heated in air, the toxic gasesCOF2 and HF are evolvedabove 400oC for Teflon PTFE and above350oC for Teflon FEP. When machining either of these polymers or heat-sealingthe latter, care should be taken to avoid overheating, and good ventilation is ad- vised.

E. Nylon. The most common member of this group of polyamide plastics is nylon 66 (polyhexamethylenediamineadipic polyamide), which has high strength and a very low tendency to cold-flow. It has a self-lubricating quality and is used for small bearings, gears, cams, and threaded parts. It has a greater tendencyto outgas under vacuum than most plastics. It is easily machined and may be cementedwith epoxy resinsbut not with solvents.It is dissolvedby phe- nol and phenolic compounds and by concentrated acids. Nylon should not be usedfor long periods above 149oCin the air, and it softensrather sharply about 100"C abovethis temperature.

F. Polyeslet Resins. Polyesterresins are made by the esterificationof poly- hydrolylic alcoholswith polybasiccarboxylic acids. High-molecular-weightpoly- esterswith OH end groups are used in conjunction with isocyanatesto produce many of the urethane plastics. When the polyester contains some unsaturated sites, polymerization may take place to cross-link the polyestersand produce a thermosetting plastic. This cure is initiated by a catalyst, such as an organic peroxide, and acceleratorsare also included to promote the action of the catalyst. Fiberglass-reinforcedpolyester items have high impact resistanceand good chemical and thermal resistance.Therefore, this material is used in the construction of fume hoods, dry boxes, and tanks for chemicals.The ingredientsfor making polyester-reinforceditems are available from boat shops. Clear polyestersheet stock and rods are availablel3and, like reinforced poly- esterplastic, may be drilled, sawed,and machined.This clear plasic is harder than poly(methyl methacrylate) and much more solventresistant than either poly(methyl methacrylate)or polystyrene.As with all thermosettingplastics, it may not be heat-formedor solvent-bonded.However, bonding with epoxycements is satisfactory.This plastic is claimed to give continuous serviceat 80oC and inter- mittent serviceup to 150"C. Transparent polyesterfilms such as Mylar (Du Pont) are much stronger than most other plasticfilms. However,Mylar is not as resistantto oxidizing agents and basesas are polyolefinfilms.

G. Polyolefins. The thermoplastichydrocarbons polyethylene and polypropylene are flexible, inexpensivematerials with good chemicalresistance. Two types of polyethylene are available: low density and high density. The former containsbranched polymer chains which impart flexibility. The maximum usa- r3A seriesof materialsof this nature is producedunder the Homalitetrade name by G-L Industries, Inc., The Homalite Corp. (a subsidiary.),ll BrooksideDr., Wilmington, DE. PROPERTIESOF SPECIFICPLASTICS 271 ble temperature is about 80"C. High-density polyethylenecontains linear chains and is more rigid, higher melting, lesspermeable, and more solventresistant than the conventional material. The maximum usable temperature, about 120"C, is stronglydependent on the syntheticdetails. Polypropylene is similar to, but slightly more brittle than, high-density polyethylene.Polypropylene also is useful at higher temperatures than polyethylene. All the polyolefinswill swellin the presenceof aromatic,aliphatic, and chlorinated hydrocarbons;this swellingincreases with temperature, and at sufficiently high temperatures dissolution results. They are attacked by strong, warm oxidizing agents, but are resistant to strong reducing agentslike sodium in liquid ammonia. Since they are not dissolvedby solventsaround room temperature, polyethyleneand polypropylenecannot be solvent-bonded.Also, adhesivesdo not generallyadhere well; however,as describedearlier in this appendix, heat- sealing is very successful. The aliphatic polyolefins are translucent to visible light and contain some strong absorptions in the medium-infrared, but they are transparent through most of the far-infrared and are therefore used as cell-window material for far- infrared spectroscopy.The use of low-density polyethylenein vacuum systems has been describedby Duncan and Warren, who note that a l/s-in. wall thickness is sufficient to prevent collapse of tubing up to t/z-in. They found it relatively easy to evacuatetheir system to 10-6 torr after an outgassingperiod of severaldays.ra In addition to the releaseof previously dissolvedgases, the vacuum is impaired by the permeation of the plastic by atmosphericgases; however, theseauthors claim that this factor is not too serioussince a vacuumof 10-{ torr could be maintained on their polyethylene system when it was left overnight without pumping.rs Polyethylene is not desirable for low-temperatute traps partly becauseof its low thermal conductivity and alsobecause of its high brittlenesstemperature, which is about -50-- 120" and -37-- 120"Cfor low-density and high-density polyethylene,respectively. If a polyethyleneitem contains internal stress,it is liable to break below the brittleness temperature. Polystyreneis an inexpensivetransparent plastic which is often usedin industry for the fabrication of parts by injection moulding. However, the tougher acrylic plasticsare preferablefor the constructionof laboratory apparatus. Poly- styrene is soluble in many organic liquids and, if strain free, may be solvent- bonded by the use of chlorinated hydrocarbons, benzene, or toluene. Special impact-resistant grades are available which are lesssusceptible to solventsand thus a little harder to solvent-bondthan the conventionalmaterial. Polvstvrene also may be welded.

raJ.F. Duncan and D. T. Warren, Brit. J. Appl. Phys., 5,66 (1954). rsFrom calculations based on permeability data and some laboratory tests, the authors believethat the pressurerise quoted here is lessthan can be expectedwith low-densitypolyethylene. The permeability data in Table III.I show that considerableimprovement is possibleby using high-densitypolyethylene. 272 PLASTICSAND ELASTOMERS lll.4 ELAsToMERs

It will be noted from Table III.I that the elastomersröare generallymuch more permeableto gasesthan are plastics.Also, there is a greatertendency for elasto- mersto swellin the presenceof solvents.In addition to the basicpolymer, most finished-rubberproducts contain fillers, such as carbon black, and curing and vulcanizingagents, such as sulfur. Other additivesmay be includedto improve the flexibility (plasticizers)and decreasedamage by oxidation.The sulfur which is used as a vulcanizingagent can lead to contaminationof chemicalsystems. For this reasonsome sulfur-freerubber goodsare available.It should also be noted that siliconerubber is generallyvulcanized without the useof sulfur. lll,5 pRopERTrEsoFspEcrFrc ELAsToMERs

A. Buno N (Nifiile Rubbel). This rubber is a copolymerof butadieneand acrylonitrile.As the nitrile contentis increased,the resistanceto hydrocarbons increases,but the low-temperatureflexibility decreases.In general,nitrile rubber swellsmore in the presenceof polar solventsthan nonpolar solventsand is not usuallysuitable in contactwith ketones,nitro compounds,and halogenated hydrocarbons.lt is resistantto dilute inorganicacids and alkalies.The brittlenesstemperature of formulations which contain low percentagesof acrylonitrile (about 20%) is about -55oC, while 36 % acrylonitrileleads to an increasein brittlenesstemperature to -27oC. On the other hand, softenersmay be includedin the formulation which allow the brittlenesstemperature to be reduced to about -54"C for the high-nitrile-contentrubber. Use above120"C is not recommended. Nitrile O-rings and gasketsare extensivelyemployed for applications which require resistanceto hydrocarbons.From the data in Table III.l it willbe notedthat the permeabilityof Buna N to moistureis high, but Buna N O- rings are used with successon vacuunl systems,and both static and dynamic sealsare possiblebecause this rubber has good resistanceto abrasionand cold- flow.

B. Butyl Rubber. Butyl rubber is a copolymerof isobutylenewith a small amount of isoprene. The outstanding characteristicsof this rubber are its low permeabilityto gases,high strength,and resistanceto oxidation.Because of the low permeability,butyl rubber O-rings are useful in high-vacuumservice, and butyl rubber glovesare desirablefor use in inert-atmosphereglove boxes. Butyl rubber tends to stiffen rapidly as the temperature is loweredso that it losesmuch of its resilienceabove the brittlenesstemperature, which is about -45oC. Use aboveabout 100oCis not recommended.Butyl rubber swellsexcessively in con-

röAdditional information on the propertiesof specificelastomers may be found in J. Brandup and E. H. Immergut, Eds., PolymerHandbook,2nd ed., (New York: Wiley. 1975). PROPERTIESOF SPECIFIC ELASTOMERS 273

tact with aliphatic, aromatic, and chlorinatedhydrocarbons. Its resistanceto ketonesis satisfactory,and contact with siliconeoils and greasesdoes not lead to excessiveswelling. It is attackedby hydrogensulfide, halogens, and basesbut is reasonablyresistant to acids.

C. Neoprene (Polychloloprene). Neopreneis a polymer of 2-chloro- 1,3-butadiene.It has good resistanceto aliphatic hydrocarbons(not as good as Buna N, however).Much more swellingis noted with halogenatedhydrocarbons, aromatic hydrocarbons, and carbon disulfide, but satisfactory performanceis possiblein the presenceof thesesolvents. This rubber may be exposed to all concentrated acids except nitric without extensive damage. Neoprene swellsexcessively in the presenceof ketones. The brittle temperature is a sensitive function of the amount of monomerother than chloropreneused in formu- lating the rubber; also, plasticizersare sometimesadded to lower the brittle point, which is ordinarily about -40"C. The upper usefultemperature is about 150oC;however, it is inadvisableto heat neoprenegaskets above 90"C, since they tend to take a permanent set around this temperature. Neopreneis still used as an O-ring and gasketmaterial in high-vacuumsystems, but other elastomers have taken its place in most vacuum and laboratory applications.

D. Ethylene-Ptopylene Rubbel. Ethylene-propylenerubber, as the name implies, is a copolymerof ethyleneand propylene.This particular rubber hasvery good resistanceto polar organiccompounds like ketones,ethers, acetic acid, and amines.It alsowithstands silicone oils and greases,dilute acids,alkalies,and metal solutionsin liquid ammonia.However, it swellsconsiderably and losesits strength in aliphatic, aromatic, and chlorinated hydrocarbons.It is claimed to be serviceablefrom -54 to 149"C. This elastomer is very attractive for generallaboratory O-ring ware. It also has good abrasion resistanceand tensile strength, so ethylenepropylene rubber O-rings are suitable for dynamic seals.The permeabilityof this rubber is fairly high (Table III.I).

E. Fluolocorbon Rubber. The most familiar rubber in this seriesis Viton- A (DuPont), which is a copolymerof hexafluoropropyleneand 1,1-difluoroethy- lene. This material is the best generalelastomer for O-rings and gasketsto be usedin high-vacuumwork. It will withstandtemperatures from -29 to 205"C; and it is resistantto acids and halogenated,aromatic, and aliphatic hydrocarbons, and many metalloidhalides like BClj. However,it swellsand breaksdown in contact with oxygenated and basic solventssuch as ketones, ethers, esters, amines, and ammonia. Acetic and chlorosulfonicacids also attack Viton-A. This rubber is not recommendedfor continuoususe in aqueousbasic media. It will be noted that Viton-A and ethylene-propylenerubber complementeach other rather well, sincethe former is resistantto hydrocarbonsand many oxidizing agentsbut attacke.dby certain polar organic solvents,while the latter rubber has the opposite characteristics. 274 PLASTICSAND ELASTOMERS

A fluoroelastomer manufactured by Du Pont called Kalrez, has mechanical properties and resistanceto oxidants which are similar to those of Viton. In contrast with Viton, Kalrez has good resistanceto polar moleculessuch as amines, ethers,ketones, and esters.Kalrez is unique among the elastomersin its toler- anceto both polar and nonpolar solvents.The cost of O-rings made from Kakez is very high, but for certain critical applications this cost can be justified because of the outstanding range of solvent tolerance.

F. Notulol Rubber. Natural rubber products have low resistanceto hydrocarbonsand relativelyhigh permeabilityto gasesand moisture.Natural-rubber goods are often more flexible than those made of synthetic rubber and have excellent tensile strength.

G. SilicOne Rubbel. Siliconerubber hasoutstanding flexibility at low temperatures coupled with good resistanceto heat (about -95-230"C). Brief service up to 300oC is possiblefor most silicone rubbers. Plasticizersare not used with this rubber, which is a contributing factor to the very low weight loss of silicone rubber in high vaccum. These rubbers are generally resistant to nitric, acetic, and hydrochloric acid but are attacked by concentratedH2SOa, concentrated base, and HF. Resistanceto aliphatic, aromatic, and chlorinated hydro- carbonsis variable.The principal weaknessesof siliconerubber arehigh permeability to gasesand poor resistanceto tearing and abrasion. Room-temperature-vulcanizingsilicone rubber (General Electric and Dow Corning) is available at hardware stores and is very useful as an adhesiveand sealant. Atmospheric moisture is necessaryto effect the cure, so broad areasof impermeable materials should not be cemented with these preparations. The uncured material evolvesacetic acid, and the cured material appears to lose someweight in high vacuum; but if usedwith moderation, it can be considereda satisfactoryvacuum sealant for most chemical vacuum systems.

GENERALREFERENCES

Data sheetson the solventresistance of various plastics and rubbers are availablefrom the primary manufacturers. In addition, a number of O-ring manufacturers publish information on the solvent and chemical resistanceof elastomersused in O-rings, For example, the Parker Seal Company, 17325Euclid Ave. , Cleveland,OH, publishesa Seal Compound Manual which contains this information. Diels, K., and R. Jueckel (H. Adam and J. Edwards, trans.), 1966,Leybold Vacuum Handbook, Pergamon, New York. This is an English translation of the secondGerman edition. It contains information on the gas desorption and mechanical properties of plastics and elastomers. Evans, V., 1966, Plastics as Corrosion-resistantMaterials, Pergamon, New York. Newmann, J. A., and F. J. Bockhoff, 1959, Welding of Plastics, Reinhold, New York. SPI PlasticsEngineering Handbook, 1976,4th ed., Van Nostrand Reinhold, New York. This book is concetnedwith the commercial production of plastic items. However, it containssome information which is useful for the fabrication of plastic items in the laboratory or shop. A P N D x METALS

When metal apparatus is designedfor chemical applications, it is usually necessary to consider corrosion and heat resistanceas well as easeof fabrication. In this appendix these topics ate discussedat a levelwhich should help the experimentalist to specify the correct materials and construction procedures.No details of shop practice are given. The interestedreader may pursue this topic in the general referencescited at the end of this appendix, and in Chapter 10. Except for a few very hard and very soft metals, intricate shapesmay be machined from heavy metal stock. Parts with thin metal cross sectionsfrequently can be constructed from tubing or sheet stock which may be bent and formed into a variety of shapes. Permanentjoints may be formed by solderingor welding. Soldersmelt below the melting temperature of the parts being joined, and must wet the surfacesof theseparts if a bond is to be achieved.A flux is employedto promote this wetting process,and the residual flux must generallybe removedbefore the parts may be used. For example, a borate flux is frequently employed for hard soldering (brazing and silver soldering). This flux forms an adherent glassydeposit which will slowly outgas in vacuum. Welding is performed by melting the parts to be joined at the seam and simultaneouslymelting a "filler" rod of the sameor very similar material into the seam. Arc or gas welding may be used with most metals, but the least porous welds are obtained by inert-gaswelding (Heliarc). In this process,an electric arc createsthe elevatedtemperature, while a stream of helium or other inert gas blankets the molten area. When possible, inert-gas welds should be specified for vacuum apparatus. When the apparatus is large enough to be welded from the inside, this mode of welding should be specified becauseit avoids the presenceof rifts and voids which may slowly outgas. Of necessity,small items must be welded from the outside, but this is often quite acceptablebecause the material is thin. When it is not thin, a bevel should be 275 276 METALS provided so that the seamis thoroughly penetrated. Somegood and bad welding practicesare illustrated in Fig. IV.1. Often an oxide film or scaleis left by welding or soldering; this should be removedfrom parts which are used in high vacuum becausemetal oxides slowly outgas, becauseof the desorptionof moisture. The fabrication from seamlesstubing is describedin Section10.1. lV,4 PRoPERnEsoFsPEcrFrc METALs

A. Aluminum. Aluminum(mp 660"C),is a tight,soft metal with fair resistanceto corrosionby laboratoryfumes except hydrogen halide vapor. It hasex- cellentelectrical and thermalconductivity. Many aluminumalloys are used; somemay be softenedby heatingto 550'C and quenchingin water.The metal subsequentlywork-hardens or hardensupon standing for a fewhours (that is, 24 ST and 14ST alloys), and all aluminumalloys are easily machined. These alloys

+__, l- r----rt'------l

tr vo cuum a Vocuum \ tJ --] L-J ä Yl"iiJl ^ :l #jjI{-l tr- Vocuum 5 "';\1*1---tl -l *9 vn::::)J_ u"j"r^fL Ira , --S" +==-

\rConlinuousweld Nlntermrtient weld Q Troppedvotume I Dirf trop lncorrect Correct

Fig, W.1. Welding practice for vacuum apparatus. Note that the general approach is to weld on the inside and avoid dead spaceswhich may present leaks that are extremely hard to locate. PROPERTIESOF SPECIFIC METALS 277 consistof more than 90% aluminum. Copper,magnesium, silicon, and transition metals are the most common alloying agents.Pure aluminum and most aluminum alloysmay be welded,but the techniqueis not easy.Aluminum soft solders are generally unsatisfactory,but certain aluminum-containingeutectics make suitablehard solders.Electrodeposition on aluminum is not practical,but a tenaciousoxide coating may be formed by the anodizingprocess, which in- volveselectrolytic oxidation. The resultingcoating may be dyed(e.g., black dyes are frequently used on parts used in spectroscopicwork). The chemicalresistance of aluminum is fair, but any chemicalwhich destroys the protective oxide coating will lead to rapid corrosion; therefore, strong acids, alkalies,and mercury must be kept out of contactwith aluminum.

B. Coppet. Copper (mp 1,083"C), is a moderatelysoft metal which has a high electrical and thermal conductivity. Electrolyticcopper, 99.9% pure, is usedfor electricalwire; and free-cuttingalloys, containing small amountsof sulfur or tellurium, are commonlyused for sheetor bar stock. Coppermay be machined,brazed, and soldered.However, because of its toughness,it is much less easyto machine than brass. It tends to work-hardenbut may be annealedby heating,followed by rapid quenching. Copperis amalgamatedby mercuryand attackedby strongoxidizing agents, suchas nitric acid, chlorine,and fluorine. However,the bulk metal forms a pro- tectivefluoride coatingand is suitablefor apparatusused with fluorine and oxidizing fluorides.The presenceof ammoniapromotes the air oxidationof copper, so copperand brassfittings shouldbe avoidedaround NH3. Copperis attacked by many sulfur-containingsubstances and is slowlyattacked by most strongac- ids in the presenceof oxygen. Alloys of copper and zinc are called brass,while bronzesare composedof copper and tin. These alloys are generallyeasily machined, brazed, and soldered. Their chemicalresistance is somewhatbelow that of copper.For example, brass is slowly attacked by fluorine and oxidizing fluorides. Brazedjoints are much strongerthan soft solder, and when used on well-matchedsur{aces, the brasstends to penetratethe joint and form a good.vacuum-tight seal. On the other hand, the highly fluid nature of moltenbrass makes it more difficult to fill gaping holeswith brazing rod than with soft solder.

C. Gold. Gold (mp 1,063'C), is a soft, inert metalwith good electricaland thermal conductivity.It is easilyplated onto metalsand vacuumevaporated onto various surfaces.Except for fused KOH and similar bases,strong oxidizing agentslike aqua regia, and strongfluorinating agents,gold is chemicallyinert.

D. Indium. Indium (mp 157'C), is a soft metal which wets many surfaces and retainsits ductility at verylow temperatures.This combinationof properties makes indium an excellentgasket material betweendissimilar materials. For example, a gasket made of indium wire will give a vacuum-tightseal between 278 MEIALS

quartz and metal from room temperature to below 4 K. Indium is also used in somespecial-purpose solders. It is attackedby cold dilute mineral acids,halogens, and other oxidizing agents, but is not affected by solutions of KOH.

E. lrOn. Iron (mp 1,535oC),is softerand somewhatmore corrosionresistant than the commonly encountered alloys. Cast iron contains a separateiron carbide phase as well as carbon dissolvedin iron; in addition, other elementssuch as silicon, manganese,sulfur, and phosphorus are generally present. Gray iron and severalother grades of cast iron contain graphitic carbon as a secondphase dispersedthoughout the casting. The presenceof graphitic phasesleads to slow outgassing, which may be objectionable for certain exacting vacuum require- ments. Iron castings may be somewhat porous becauseof rifts and voids in the granular structure. Such a casting is not suitablefor vacuum work. Iron and steelare not amalgamated or appreciably dissolvedby mercury; so iron or steel containers are used to transport mercury, and steel is used in some mercury- diffusion pumps. Steelcontains some carbon, about2To, but considerablyless than cast iron, which contains over 5 % . Steeltends to becomebrittle at low temperatures,so it is not recommencedfor high-pressurecylinders which will be cooled to liquid nitrogen temperature. Slight variations in the constituents of iron or steel make them resistant to strong bases,nitric acid, and so on, but the judicious choice of irons and steels for specific chemical resistanceis not practical in the laboratory. Stainless steels are iron-based alloys which contain more than l2To chromium. A common compositioncontains l8% Cr and 8% Ni, and is designated aseither 18:8or type-304stainless steel. Unlike ordinarycarbon steel, the stain- lesssteels in the 300 seriesdo not becomebrittle at low temperatures. Stainless steelhas a rather low thermal conductivity.It may be welded,brazed, or soldered and is machinable with somedifficulty. Type 303 is the easiestto machine. While the chemical resistancevaries somewhat, stainlesssteel is fairly resistant to most acids and bases,is not amalgamated by mercury, and is generally resistantto oxidizing agents.While it can be usedin fluorine handling, Monel and nickel are much better for this purpose. The resistanceof stainlesssteel to atmospheric corrosion is an advantagein vacuum work becausea corroded surface tends to outgas. Certain alloysof iron, nickel, and cobalt (Kovar, Fernico,etc.) havethermal expansioncurves which nearly match thoseof borosilicateglasses, and a good bond may be formed between the two. Kovar is similar to carbon steel in its chemical properties. For example, it oxidizes when heated in air and is not wet by mercury. It may be machined,welded. copper brazed, and soft soldered.Sil- ver solders should not be used with Kovar since they may causeembrittlement. At low temperaturesKovar undergoesa phasetransformation, and the change in expansioncoefficient below this temperature may be sufficient to causefailure of a glass-to-Kovarseal. The transformation temperature usually is below PROPERTIESOF SPECIFIC METALS 279

-78.5'C. The exact transformationtemperature varies from one batch of the metal to the next and somesamples of Kovar havetransformation temperatures below - 196"C.Another significantproperty of Kovar is its low thermal conductivity.

F. Leod. Lead (mp 328'C), is a soft metal which finds use in gaskets,soft solder,and radiation shields.While leadtank linersare usedin someindustrial processes,this metal is not attractivefor laboratorycontainers.

G. Nickel. Nickel (mp 1,453"C),finds its primary usein the constructionof apparatusto handlefluorine and volatilefluorides. In this situationthe metal is renderedpassive by a fluorine coating. Nickel plating is easilyperformed and providesa means of imparting corrosion resistance.The metal may be machined, silversoldered. copper brazed, or welded.However, the weld shouldbe performedon cleansurfaces because the presenceof impuritiescontaining lead, sulfur, phosphorus,and variouslow-melting metals leads to embrittlementand failure at the weld. Monel is a type of alloy containing about 70To nickel, with the remainder mainly copper. Exceptfor susceptibilityto nitric acid, Monel is generallysupe- rior to stainlesssteel in corrosionresistance. Monel is similarto stainlesssteel in machinabilityand is weldedlike pure nickel.

H. Pollodium. Palladium (.np 1,552'C), is soft and ductile but work- hardens.At elevatedtemperatures, the diffusionof hydrogenthrough palladium is rapid, which forms the basisof a methodfor the purificationof hydrogen.The best performanceis obtained from a palladium-silveralloy containing about 18% silverbecause, unlike pure Pd, this alloy doesnot undergoa phasetransi- tion in the presenceof hydrogen.Palladium is not as inert as platinum and is attackedby sulfuric and nitric acids. l. Plolinum. Platinum(mp 1,769'C),is a malleableand ductilemetal with high chemicalresistance. Because of this resistance,it finds usein somelabora- tory ware.lt is attackedby aqua regia,and, at somewhatelevated temperatures, by sulfur, phosphorus,halogens, and cyanide(in the presenceof air). The coefficientof expansionfor platinum nearlymatches that of softglass (flint glass),and an adequateseal between platinum wire and soft glassmay be obtained.

J. Silver. Silver(mp 961'C), hasthe highestelectrical and thermalconductivity of any metal. It is usedin making electricalcontacts and in the construction of some laboratory ware. It is easilyelectrodeposited, and both chemical and evaporationcoating with silverare possible.Silver is generallyless resistant to attackby oxidizingagents than is platinum or gold. However,it is resistantto fusedalkalies and fusedalkali-peroxide mixtures. Therefore, it is usedto nrake 2BO METALS

cruciblesfor NaOH-Na2O2fusions. At elevatedtemperatures oxygen diffuses through silver, and this property is occasionallyused to purify oxygen. Two typesof silver solderare available.The soft-silversolders are generally alloysof silverwith lead, which, like the commontin-lead soft solders,melt below 400"C. The soft-silversolders have the advantageover the Sn-Pbvariety of greaterresistance to creepunder load. The hard-silversolders generally contain copper as the primary alloying constituent.These solders generally melt above 600'C. One common type of silversolder, AWP 355, is resistantto fluorine and many fluorides.

K. Tonlolum. (Tantalum mp 2,996'C). is an extremelychemically resistant metal which is hard but ductile. Becauseof its high melting point and goodcor- rosion resistance,tantalunr is frequentlyused as a containerfor high-temperature melts.It is attackedby HF and otherfluorides, as well as sulfur trioxide and nitrogenoxides.

L. Tungslen. Tungsten(mp 3,410"),has the highestmelting point and low- estvapor pressureof the nretals.The commonlyavailable form of the metal contains trace impurities which impart brittleness.Tungsten wire is occasionally fibrous and thereforesomewhat porous along the axis of the wire. Very pure forms have some ductility. Tungsten is oxidized in air but is otherwisefairly chemicallyinert. Mineral acids have little effect. The expansioncoefficient is similar to Pyrex, so tungsten is frequently used in electricallead-throughs for glassapparatus. It is not wet by mercury.

GENERALREFERENCES

Hoke CorrosionChart, Hoke Inc.. I Tenakill Park. Cresskill,NJ. A compacttabulation for common metalsand plastics. Lee, J. 4., 1950,Materiuls ol Co,rstructiotr,lorChemical Prccess Industries. McGraw-Hill, Neu York. Infornrationon the corrosionresistance of nraterialsarranged according to the corrosive agenr. Mettls HundbooÄ.9thed.. Vols. l-8. AmericanSociety for Metals.1978-85. Moore, J. H., C. C. Davis,and M. A. Coplan. 1983,Building ScientiJicAppuraras, Addison-Wes- ley, Reading.Mass. Oberg. E.. F. D. Jones.and H. L. Horton, l9lt4. Muchinen"sHandb

Vapor pressuredata are important in the identification,separation, and general manipulationof known compoundson the vacuumline and for the characterization of new compounds.This appendixwas preparedwith theseapplications in mind. It is introduced with a discussionof the use and limitations of several analy'ticalexpressions for the representationof vapor pressuredata. A description of a least-squarestreatment of vapor pressuredata for fitting to the Antoine equation is then presented.Finally, a table of vapor pressuresat convenient slushbath temperaturesis presentedtor 479compounds.

V,'1 ANALvTTcALREpREsENTATToN oF vApoR pRESSUREDATA

Most of the widelyused vapor pressureequations have as their basisthe Clapey- ron ecuation dP AH (1) dT TAV which is an exactthermodynamic expression. AH is the molar heat of vaporization, and AV is the changein molar volumebetween the condensedand gaseous phases.If it is assunredthat (l)the volumeof the condensedphase is negligible by comparisonto that of the gas,(2) the gasexhibits ideal behavior, and (3) the

28tl 282 VAPORPRESSURES OF PURE SUBSTANCES latent heat of vaporization is constant over the temperature interval of interest, Eq. (l) may be integratedto yield the simplerelationship rogP:-ffir*u (2) or _A logP:;*u (3)

When convertingto the absolutetemperature scale ?, it is important to recog- nize the conventionOoC : 273.15 K. The constantsA and B in Eq. (3) are determinedempirically from experimentaldata by plotting log P versus| / T and taking the slopeas -A and the interceptat | /T : 0 asB. Equation(2) is found to yield a fairly accuratefit to vapor pressuredata for highly volatilesubstances and is often perfectlyadequate for moderatelyaccurate data below the boiling point. The heat of vaporizationvaries slowly with temperatureand eventuallybe- comeszero at the critical temperature.In addition, the assumptionswhich were usedto approximateAV (ideal gas behaviorand negligiblevolume of the condensedphase) are inaccurateat high pressures.However, the assumptionsare adequatefor data of moderateprecision (about + lYo) in the I -760-torr range, and in these cases the heat of vaporization may be determined from the .4 parameteras indicatedin Eq. (3). Of course,different,,4 and B parametershave to be determinedfor each particular phase(e.g., for the liquid, and for each solidphase, if more than oneexists). lf A andB areknown for one phaseand the heatof transition(fusion or solid-statetransition) is known, the heatof vaporization and its equivalent,the,4 valuefor the secondphase, may be calculated.The new valueof B is then found by taking advantageof the fact that the vaporpres- suresfor the two phasesare identicalat the transitiontemperature. When accuratevapor pressuredata are plotted as log P versus1,/T over an appreciablepressure range, it is usuallyfound that thereis somecurvature to the plot. This defect in Eq. (3) is largelyovercome by an empirical modification proposedby Antoine: B logP:A- (4) t+c The introductionof a third constantC leadsto an improvedequation which has beentested in somedetail and found to be the bestthree-parameter vapor pressure equation for generaluse.r'2 Usually the temperatureterm in Eq. (4) is in degreesCelsius. Because of its simple form and generallygood accuracy,this equationhas beenchosen for usein someof the most extensivecompilations of

lC. W. Thomson.Chenr. Rev., 38, I (1946). rM. Kh. Karupet'yantsand Kuang-YuehCh'ung. Chent. Abs.,53. l76l3d (1959). ANALYTICAL REPRESENTATIONOF VAPOR PRESSURE DATA 283

vaporpressure data (see below).Equation (4) is found to givea generallysuitable fit between30 torr and 3 atm, and it givesa much betterfit between50 and 760 torr' Thomson notesjh{ the accuracyis poor when the reducedtemperature exceeds0.75 (?..d : T/T*). However,it is often much simplerto usea second Antoineequation above this temperature,adjusted so that the two coincidenear ?."a : 0.75, rather than fit the entire set of vapor pressuredata with a singre, more complex expression.The drawbacksof the equation in the high-pressure region are of little consequencein vacuum line work, where pressuresgreater than an atm are seldom attained.The deviationswhich occurtelo* l0 torr are of more importance because it is often necessaryto extrapolatedata very far into the low-pressureregion to estimatethe temperaturewhich must be usedto trap a component effectively. under these conditions, an extrapolation based on (3) Eq. is generallyreriabre and can be readilyaccomplished graphicaily. The c value in Antoin-e'sequation appears to be the teastciiticat parameter, and someworkers usea fixed valueof 230 for all compounds.However, Thom- son has found that there is a correlationbetween c and the boiling point of a substance.For elementswhich yield monatomic vapors, and foi subtances - which boil below l50oC the correctionleads to C : 264 - 0.03416 where/5 is the normal boiringpoint in degreescelsius. For other compoundshe finds

C : 240 - 0.19 r,.

The relationshipsare not exact,so if the data are good it is better to determine C directly. Another rather simpre semiempiricarmurtiparameter equation has been used to fit vapor pressuredata:

-A logP=f+BT+CT2+D (s)

Multiplying through by ? and rearrangingleads to

- -A TtogP + DT + BT2 + cT3 The parameters.4 through D in this equationare easilyfit by meansof a least- squaresroutine. In severaltest cases it wasfound that the ur" of fou. parameters in Eq' (5) gives a slightly poorer fit to vapor pressuredata than does the three- parameterAntoine equation. It appearsthat the variation of the heat of vaporizationwith temperatureis one of the primary sourcesof inaccuracyof Eq. (2), and the extra empirical parametersin Eq. (4) introducea variationof afl with temperature.In a somewhat different approach, it is assumedthat the heat of vaporizationis a rinear function of temperature, and the remainingassumptions invorved in the deriva- 284 VAPORPRESSURES OF PURE SUBSTANCES tion of Eq. (2) are retained.With theseapproximations the Clapeyronequation may be integratedto yield the Kirchoff equation

logP: (6) +*B-ctogT Nernstproposed a somewhatmore elaborateequation, which may be written

togP: (7) +*B-CtogT*DT He found that C frequentlyis closeto 1.75,and it is the practiceof someworkers to usethis valuefor all substancesand vary only,4, B andD . While Eqs. (6) and (7) give a better fit to the vapor pressuresof somecompounds than the Antoine equation,the accuracyis more often not quite as good. Also, the estimationof vapor pressuresby the extrapolationof Eqs. (6) and (7) beyondthe highestpres- sure of the original data appearsto lead to more error than one would obtain upon extrapolationof the Antoine equation.Finally, Eqs. (6) and (7) are much more difficult to usewhen onewishes to find the temperaturecorresponding to a given pressure. Many other vapor pressureequations have been used; the interestedreader may refer to Partington'streatise for someof these.3One of the most successful equationsfor the faithful reproductionof vapor pressuresfrom low pressuresto the critical pressurewas devisedby Frost and Kalkwarf.a

logp:- A+B=*Clog T++ I t' This equation is appropriatefor iterativecomputer calculation. Simplifications havebeen proposed by Thodos.s

V ,2 LEAsI-souAREsFrrTtNG pRocEDURE FoR THE ANToINE EOUAIION

When precisevapor pressuredata are available,it is desirableto employa least- squaresfitting procedureto the Antoineequation. The formulationof this problem is availablein detail in the literatureand will be summarizedhere.b rJ. R. Partington, An Adtunced Treutiseon PhysicatChentistry, Vol. 2 (London: Longmans, Green, l9sl), pp.265ff. {A. A. Frostand D. R. Kalkuarf,J. Chen. Phys.,2l,264 (1953). 5R. C. Reid and T. K. Sherwood.The PropertiesoJ Gusesuntt Liquids,2nd ed. (New York: Mc- Graw-Hill, 1966),Chap. 4. Referencesand a discussionof the Frost-Kalkwarfequation nray be found here.Also, a rathercomplete comparison of variousreduced equations is presented.These are most usefulat high prcssures. oC. B. Witlinghamet al.,J. Res.Nat. Bur. 9td.,35,219 (1945). LEAST.SQUARESFITTING PROCEDURE FOR THE ANTOINE EQUATION 285

A. Detivolion of Equolions. Equation (4) may be rearrangedto the form (A-togP)(C+t)-B:0 (8)

If the left sideof Eq. (8) is multiplied out and a changeof constantsmade. this equationbecomes ut*h*clogP-rlogP:0 (9) - wherea : A, b (AC - B), and C: -C. SinceEq. (9) is linearin the constantsa, b, and c, data mayfit to this equation using leastsquares. To reducerounding errors, it is easyto make initial estimatesof a, b, and c by usingEq. (9). Theseinitial estimates,which will be calleda1y, b6, and c6,mä] be calculatedfrom threeexperimental points, preferably spreadout overa substantiaIpressure range. This resultsin the generationof three simultaneouslinear equationsof the form of Eq. (9). Substitutinges, bs, and c11into Eq. (9) gives Fo: aot+ äo + colog P - r logP: 0 (10) which may be addedto and subtractedfrom Eq. (9) to obtain at*ß*7logP*Fo:g (11)

- - wherea : (a ai, 0 : (b bd,? = (c - co),and FpisdefinedinEq. (10). Equation(ll) is the form of the Antoineequation used to setup the normal equationsfor the least-squarescalculation: -t aE(ti)2 BDti * "yDrilog Pi: E76ti qDtt + 0(1) * 'yElog Pi : L.f'n (12)

aDti log P' * BDlogPi * 7I(log Pi)2: L.f slogPi where.l'iy: estt + lr{r+ c0 log Pt - ti log Pi .

Theseequations are solvedsintultaneously for a, 6, and'y, the resultingval- uesused to find a, b, andc, and finally thesevalues are usedto find,4, B, ard C. The entire procedureis easilycarried out on a hand-heldcalculator, as demonstratedin the examplebelow. If many calculationsneed to be done,these calcu- lationscan be done on a computer.

B. ExompleColculofion: Ihe AnfoineEquotion for Woter. TableV.1 fiststhe vapor pressuredata for water from 20 to 80oC.Values of as,b6, and c6 are calculatedfrom the data at 20, 50, and 80oCby solvingthe followingthree simultaneousequations: ao(20)* bs * cs log(17.535): 24.878 ao(50)* b0 * colog(92.51) : 98.309 ao(80)* b0 I co log(355.1) : 204.028 286 VAPORPRESSURES OFPURE SUBSTANCES

ao: 8'07577 bo : 154.140 co : -233.761

Next, the summationsappearing in Eq. (12) are found for alr of the data points. This leadsto the setof three simultaneousequations: - a(87,420) + P(1s50) + {3224,87) - 19.2937 a(1550) +B(1) +^y(60.1940):-0.10986 a(3224.87)+ 0(00.1940)+ y(121.536):-0.51109 e : -0.00307 0 : 0.00002 ^Y= 0'07716 Fromthis weobtain o : 8.07270 b : 154.140 c : -233.684 Finally,reversing the first changeof constantsyields the Antoineconstants A : 8.07270 B : 1732.32 C : 233.684 and,therefore, the Antoineequation 1732.32 logP:8.07270- t + 233.684

By comparingthe secondand third columnsof rabre v.r. it is seenthat the agreementbetween the experimentaland calculatedwater vapor pressure vatues is quite good.

V,3 coRRELAnoNAND EsTtMATtoN oFvApoR pREssuREs

occasionallyone has availablea singlevapor pressurepoint-for example,the normal boiling point-but wishesapproximate vapor pressuresat other temperatures.some of the simplestschemes are basedon Eq. (2). If the compoundis not likely to self-associatethrough hydrogenbonds or otherspecific interactions, the Trouton constant(aH,.uo/T:6,,,1in ) is approxim ately 2l catlmolo. Substitution of this valueinto Eq. (2) showsthat the vapor pressureis relatedto normal boiling point T5 by Eq. (13).

logP",n, : +.0 - (13) (r +) CORRELATIONAND ESTIMATIONOF VAPORPRESSURES 287

Ioble V.t. ExperimenfolondColculofed Vopor Pressureof woler

P".o(torr) P."1,(torr)

20 17.535 t7.541 22 19.827 19.836 24 22.38'7 22.389 26 25.209 25.224 28 28.349 28.366 30 31.824 3r.843 32 35.663 35.684 34 39.898 39.919 36 44.563 41.584 38 49.692 49.712 40 55.324 s5.343 ^1 61.50 61.51 AA 68.26 68.27 4b 75.65 75.66 48 83.7I 83.72 50 92.51 92.5r 52 102.09 r02.08 54 112.51 112.48 56 r23.80 123.78 58 136.08 136.04 60 149.J8 149.32 62 163.77 I63.69 64 179.31 179.21 66 r96.09 195.98 68 214.t7 2r4.06 '70 233.7 233.5 72 254.6 254.5 74 277.2 2'77.0 76 301.4 301.2 78 JZ / .-'t 327.2 80 355.r 355.0

While very approximate,this relationshipis usefulfor order-of-magnitudeesti- mation of vapor pressures,u'hich is often adequatein establishingtrial condi- tionsfor trap-to-trapfractionation. For this purpose,a family of curvesbased on Eq. (13)is presentedin Fig. V.1. Another useful approximationis the Ramsay-Youngrule, which statesthat for two relatedsubstances, the ratio of the temperaturesat which they exert the samevapor pressureis constant.TThat is,

-The natureof the approximationinvolved here is describedby S. Glasstone,Textbook ttl Phvsicul Chentistry,2nded. (Princeton,NJ: Van Nostrand).p. 454. 288 VAPORPRESSURES OFPURE SUBSTANCES

/T \ /T '\ (j1)p:('o \p, \rBl \ rB / Vapor pressuredata often can be found for a substancesimilar to the one for which a singlevapor pressure is available,and the tabulationby Stull (seebelow) is handy for this purpose,since the data are given at a seriesof fixed pressures. A better estimateof vapor pressuresfor a varietyof organiccompounds can be made by meansof the correlationsof Hass and Newton. This procedureis easiestto use if the normal boiling point is known, but it may be used in an iterativefashion if the vapor pressureis known at an arbitrarytemperature. The descriptionis availablein the Handbook of Chemistryand Physics,so it will not be repeatedhere.8 Finally, we note a simple but crude rule which is usefulfor quick estimates: For every l0oC rise in temperaturethe vapor pressureapproximately doubles.

350 ,Z- 300 e co / o (c -l 250 -a {'/ ,-- % ^ _l 200 )< ,6 ffi 150

100 t 'z -/

50 z2 z7 o 50 100 150 200 zso 300 350 400 450 500 Ta,oK

Fig. V.l . Approximate relationsh ips between the vaporpressure at an arbitrarytemperature f and the boiling point Is.

8H. B. Hassand R. F. Newton,Hundbook ol Chenristn,untlPht,sics.64th ed., (Cleveland.Ohio: ChemicalRubber Publishing Conrpany, 1983-81), p. D-189.This informationis presentedin earlier editionsand is indexedunder: "boiling points,correction to standardpressure." TABLEOF VAPORPRESSURES 289

V .4 TABLEoF vAPoR PREssuREs

The followingtable of vapor pressuredata (pages290-31I ) is suppliedas an aid to the planning of experimentsand identificationof compounds.When vapor pressuredata are employedas a criterionof purity. the investigatormay wish to evaluatethe original work critically and obtain a preciseinterpolation of this data to the temperatureof interest;therefore, references are includedat the end of the table(pages 312-313). Most of the vaporpressures tabulated here were calculatedon a digital computer using parametersfrom the referencescited. In thesecalculations OoC : 273.15K. Sincemany of the originalreports may have employedslightly different values for the ice temperature,a small error is some- timesintroduced. Calculated values which knowinglyrepresent an extrapolation or areotherwise suspect are enclosedin parentheses.When an analyticalexpres- sion was not availableor the given analy.ticalexpression was obviouslyerrone- ous, the original data werefit to Eq. (9) by leastsquares. The slushbaths which correspondto the giventemperature are methylcyclohexane, - 126.59'; carbon disulfide,- 111.95';ethyl acetate, -83.6'; chlorobenzene,-45.2"; carbonte- trachloride,-22.9"; ice water,0'C. All temperaturesgiven in the tableare in degreesCelsius and pressuresare torr. A subscripts meansthe condensedphase is a solid. \oN o Tobleof vopor pressures

Tenperalure, oC

Compound -teo.s:tl_rrr.usl -$.6 l-t5.etl-zz.75l luu.oo bp("c) mp("c) Vapor pressure, torr Aluminum: Aluminum borohydrideAl (BII{) 3 87 459 -64.5 I Trimethylaluminum (C[Ir)rAl . r24 7 l5 LB Antimony: Antimony pcntachloride SbCl5 1.2 2.8 LB Antimony pentafluoride (SbFs) 14',2.6 8.3 LB Triethylstibine (CrI{s)rSb. . . 3.8 161.4 -98 2 Trimethylstibine (CI{r)3Sb. . . :J) (l0) 3ir 109 806 -62.0 ,) StibineSbtIr 1.6 2l 629 (-18 4) -88

Arsenic pentafluoride AsFr. . . . - 52.8 -79.8 LB Arsenictriehloride .{sClr...... l6 1313 -16 LB Arsenietrifluoride AsFr...... - ,'- 4t) 622 5.9 LB Arsine AsHr. .JD -62.3 - 116.9 l)imethylarsine (CI{r)zAsI{. . . l6 178 492 37.1 LB Methyldichloroarsine CH rAsClr ,, l0 134.5 LB Methyldifl uoroarsine CII:AsFr. i). t 22 87 76.I LB Trimethoxyarsine As(OCIIT)r. . 2.0 l0 LB Trirnethylarsine (CHr)rAs. . . . . AD 30 1)8 295 504 LB tris(trifluoromethyl)arsine(CFr),As l5r 58 187 55r (33.3) ä Beryllium: Beryllium borohydrideBe(BIIn)2. . . 9r.3" 6 Diethylberyllium(C2H 5) 2Be 194 l" LB Bismuth: Trimethylbismuthine(CI{e)aBi. . . .. 2.6 l07 l - 85.8 Boron: 1,2-Bis(dichloroboryl)ethane (BClr)rcrH. l3 6.1 (t42) - 28.5 1,2-Bis(dichloroboryl)ethene ,2 - crHr(BClr), 9.4 ( 144) 130 8 1,2-Bis(difluoroboryl )ethane -31 CzH,(BFr)2. 9.9 44 r56 507 (35) 5 8 1,2-Bis(difl uoroboryl)ethene (BFz)zCzHz. 2lt 380 l5 -82 Bis (dimethylarnino)borane BH(N(CH3)r)2. . t7 8.5 105.7 Bis (dimethylanrino)chloroborane ((CHr)rN)rBCl.. . .. l, 5.8 r46 LB 1,2-Bis(dimethylboryl )ethane (B(CH3)r),CrH(. l2 98 10 Bis (perfluorovi nyl ) chloroborane (CzFrtzBCl 27 ll 42 100.5 -57.5 ll r)< qar Borane carbonl'l BII3CO...... -64.0 - 137.0 LB '262 Borazino BrN3ll6. 60 ilir )J. J t2 Boron tribromide BBrr. 4.:l l9 69 90.9 -46 LB Boron trichloride B('lr 50 175 476 124 - 107 LB Boron trifluoridcRFa... .. 75 :JT}I -99.9 13 - Bromodiborane BzI{ rl}r . 2.5 ,tl l4l 16.0 104 LB - l)iborane(6) Brll6...... -93 165.5 l4 I)iboron tetrachloride BrCl{. . . . ll (65 5) -92.6 7 I)iboron tetrafluoride BrFn. . . . . I l" 378 -34 - i)t) 29 l)ihydroxyrnethylborancCH3B(OH ):l 25 co.100 20 Dimethylamine-borane I (cH3)rNrIBI{3. öo 16 I l)inrethylarninodihorlnr. I BzHrN(CIIr)2.. . . 1 6. ii 50.3 -47.5 tl

.oN t\)€ N Ioble of vopor pressures(Conlinued)

T emperalure,

-te6.lel- -8e.6-/,5.el1-es.75l ,.*, bp("c) mp("c) Compound IIt.ssl I 1 Vapor pressure, torr

Di m eth yl am inod ic hlorobo ran e I,B (CH3),NBCl, (1123) I)imethylarsine-borane (8,:r.5) (CIlr)zAsllBIIr... . B,B'-I)imethylborazine (107) I8 Brll (CH3)rNrIIr. . . N,N'-l)imethylborazine ( 108,) l9 B3H3N3(CH3)2. -2 6 I,B Dimet,hyldiborane(CHr)zBrI{,... . 87 ll0 ,4') ') 20 I)imethylfluoroborane B(CII3)rF. . t2 6.0 bt) 657 I )i m ethyl phosph i ne-bo rane l8 (174) I,B 1Qfl.1,PIIBHI l)imethylphosphine-dimethylborane LI} (CH3),PHBI{ (CHr)r. l)imethylphosphine-trimethylborane I,ts (CHr)'PIIB(CIl3r3. 5.8 :t6 l)imethylpropenylborane ,) /')')| (76) (242) | Cr[Is(CHr)zB. (4 e) ,)i ta 2'2 . (01) 1,3,2-I)ioxaborolane (CIIzO) rBII 22 (CIITS)rBII . . 4.1 1,3,2-Dithiaborolane -62 rr.l Li) L:) 3l :l Hexaborane(l0) 86II ro. I\Iethoxydimeth ylborane /.ltl,)i 2l LB (CHr)zBOCHr 1)6 84 (84) l1) N-Methylborazine BrI{rNrHrCII3 . |4 0.7 I\Iethyldifluoroborane BCHrFr...... ö.t 18 2) - 130.5 20 trIeth1'ldivinylboranc (C.H').CIlrB. (31) (rl3) (344) 1-63 2l NI eth yl phos ph ine-bo r an e CH3PH:BII3 (2) 158 B-Nlonomethylborazine 83ll:cH3N3IIr. 4.9 20 70 (87) -59 18 2a Pentrborane(9) BsII,. . l8 65 209 (57) -46.8 25 I ) B5Ilr. 3.1 lrl 52 170 Pcntuborane(l (63) -122 ,24 Perfluorovinyldichloroborane CrFrBCl:. 6.1 ,7 48 - 108 Perfluorovinyldifl uoroboranc C,F3BF2 -14 -96 ll Phosphorustrifluoride-borane PF, B II (-62.2) - 116.I ',7 Tetralrorane(l0; BnII'o 388 l8 - 120 l5 Tetraborane(8) carbonyl BoHrCO. . (219) (5e 6) - I14.5 28 Tetraboron tetrachloride B{Cl4. . . . ,, (140)" LB Tetranrethoxl'diboron B:(OCIIT)r . I IJ ( 130) -26 30 Tetramcthyldiborane (CIIr){BrIJ? . 47 t:) I 68.6 -72 5 LB Triethoxl'trorane B (OCzH r) r (3 t4 ll8 3l Triethylboreneß(C:Hrtr...... l5 l0 49 102 -ot o 32 B, I)', B" -T riethylborazine Ba(CzllrrrNrHr. 30 (173) -46.4 33 Trinrethoxyborane B(OCH3)r. . . . . 40 146 663 t5 Trimethylamine-borane (CII r) 3NB Il 0.9 94 l6 Tri nr ethy ltrrsine-boran e (CIIr)rAsBIIr (l.5)" 154 LB Trimethylborane B(CI{r) r _20,l -tot s 32 B, R', B " -'l rimet h ylborazine Br(CIIr)rNrIlr 10, (l2e) 31.5

\o19 a .oN 5 Tobleof vopor pressures(Confinued)

Temperature, "C

- 126.5t)]-111 .sll - tt.o - 2s.751o.oo ss.oo bp("c) mp("c) Rel. Compound l-,,0.u,| I Vaprtr pressure, torr

Trimethylboroxine Br(CIIr)rOr. . . . . (4 8) 2l 80 (7e) 20 Trimethyldiboranc (CI{r)rBzHr. . . . 9.6 38 r22 JJ / 45.5 LB Tris (dimethylamino)borane B(N(CII3)-)a 4.3 152 34 Tris(pcrfluorovinyl)borane (C?Fr)rR 50 23 (104.5) ll Trivinylborane (C:IIr) rB. (2 9l (t5) (64) (235) (55) 2l Cadmium: l)imethylcadrnium (CI{:):Cd., 9.8 36 105.7 , One carbon: Bromomcthane CIITBT 3tt 7l 66r 3.6 -93.t) MCA Carbon dioxideCOz.. . . 3.9" ,'7 -/ö.o, LB Carbontetrabromide CBrr...... 1':" (0.8), 191.9 90.i LB _t, Carbon tetraehloride CClo. . . . . 8.3 JÖ 76.7 LB - 128 - 183. LB Carbon tetrafluorideCF{...... :^^ l" Carbonyl chloride COClr. (2 6) 56 200 aoJ 7.6 -t27. 8 D Carbonyl fluoride COFz. . 2a t24 /:)r - 83.4 - l14 LB Chlorodifluoromethane CHClFr. . . . (4 6) (()2) 617 -40.8 - 160 35 Chlorofornr CHClr. (3.1) 60 6l .7 -63. D o2 -97 Chloromcthane CHrCI 279 lu lnt -24.22 . MCA -' -81 - . . . . 1)l 107 667 .2 r8l. LB Chlorotrifluoromethane CF3Cl. .), Dibromomethane C I{:Brz ll 45 96.95 -52. MCA I)ichlorodifluoromethane CFzClz. . . 2.7 36 376 -29.9 - 160 LB I)ichlorofluoromethane CIIClrF. . . . (2 2) (51) iss 531 , 8.9 - 135 öo I)ichloromethane C I{:Clz. 8.2 40 (138) (435) 39.8 -95. MCA Difluoromethane CHrFr. 26 13 t26 - 51.6 MCA Fluoromethane CHrF. l9 76 coJ -78.4 - 141.8 MCA Formaldehyde CH:O. . l4 207 646 -19.1 -ot MCA Formic acid HCOOH 428 r00.6 8.4 MCA Iodomethane CHrI. . ''''"1. 42 140 406 42.43 -66.5 MCA MethaneCHr... (10mm at - 196.5) - 161.5 - r82.5 D Nlethanol (CH3OH) at 2S t25 64.7 -97.7 MCA Trichlorofluoromethene CClrF. . . . . (l 5) (27) 103 302 23.77 -111 35 Trifl uoroiodomethane CFrI . 1.9 24 260 753 -22.5 ot Trifluoromethane CHFr. ll4 -82.4 - 147 LB -95.0 -215 Trifluoromethyl hypofluorite CFrOF IJ 251 1ii < 38 Two carbon: Acetaldehyde CHsCHO. 1 l z8 109 20.4 - 123 MCA Acetic acid CH3COOH. "l l5 117.9 16.7 MCA AcetylcneCrHr. ... 12" 67" 76r" - 84. -80.8 39 Bromoethane CzHsBr. (12) iuor (163) (469) 38.4 -118.6 MCA Bromoethylene CzHrBr (2.6) (47) 157 424 15.8 - 139.5 D l-Chloro-1, l-difl uoroethane CzH rClF 1.1 l3 t52 444 -9.8 40 (, Chlorocthane C:HtCl . ,\ (46) (164) (468) 12.27 - 136.4MCA ChloroethyleneCzllrCl. . . . t4 l8l (tl - r3.37 - 153.8 D Chloropentafluoroethane CrClFr. . . . 59 574 . -39.2 -99.4 LB CrH2ClFi. . . . 28 3l 331 -27 .9 - 158 4l Chlorotrifluoroethane .. l, l-Dibromoethane CrHrBrr ö.c 26 108.0 -63 MCA 1,2-I)ibromoethane CzHrBrr 12 l3l 4 9.79 D 1,2-Dichloro-1,2-difiuoroethylene CtFtClt l.l te 108 20.6 - 112 LB l. l-Dichloroethane CzHrClz ,.t l9 228 57.28 -97 MCA 1,2-Dichloroethane CzHrClz (4.e) 7S 83.5 -35.7 D I , 1-Dichlorotetrafluoroethane CF3CFCI'. (7.1) (87) 266

N 9 (rr t\) \o o. Ioble of vopor pressures(Confinued)

Temperalure, "C - -as.o Compound 1e6.ssl-1r 1.ssl l-r,u.ntl-ee.zslo.oo I s5.00 bp("c) mp("c) Ref. Vapor pressure, torr

1,2-I)ichlorotetrafl uoroethane CzClrF,. 7.1 87 680 30 -94 35 l,l-l)ifluoroethane CzHrF:. . . I 2U3 -24.7 - tt7 MCA l, l-I)ifluoroethylene CHrCFr . (48) r52 - 85.7 40 Dimethyl ether CzIIoO I -24.8 - 138 MCA EthaneCrHo...... 54 176 - 88.6 - 183 D BthanolCrHsOH..... 20 l2 60 78.29 - I ta _ I N{CA EthyleneCrHo...... 156 459 - 103.8 - 169 Ethylene oxide CzHnO. . . . 2l 172 r0.7 - lll LB FluoroethaneCrlliF. 4l o,t 534 -37 .7 MCA IlcxafluoroethaneCrFe.... . ,, 93" b/t, -78.3 LB Iodoethano C:HsI . . 20 ll 4l r36 72.3 MCA Tetrafluoroethylene CrFr... . . l5 62 4tt3 -76.3 36 l, 1,2-Trichlorotrifl uoroethane C:ClrFr. 334 47.57 -35 35 l, l, l-Trifl uoroethane CHTCFT (2 8) (12) 106 -47 .6 40 Three carbon: AcetoneCrHoO. 3.4 l8 o/ /r9t\ 56.5 -94. LB Cyclopropane CrHr. . . 30 42 437 -33.I - 126. LB Methyl acetateCrIlrOr. .. .. 30 l6 6l 211 57.8 - 98. LB .l\lethyl aeetylene CrH,. . . . l8 260 -23 2 - 102. D Methyl ethyl ether CsHaO. . . . r68 554 7.4 MCA PropadieneCrHn. . . (1 e) (45) 48r -34.5 - 136 D z-PropanalCrHrCHO...... 5.ö 28 r02 318 48.0 -80 MCA Propane C.Ha. . . (l 3) (7.1) 76 660 -42.l - r87. D -126.2 l-PropanolCaH'OH.... 3.3 2l 97.2 |MCA -88.5 I 2-Propanol CTHzOII.. . 1.2 8.3 45 82.6 MCA -87 2-PropenalC3II{O... . . (6 6) (27) (8e) 52.5 .7 LB -47.7 - Propene C,Hu . . (2 0) 10 ion lrunl 185.25 D Four Carbon: - 1,2-ButadicncCrllo. . . . . (2 e) r78 496 r0.85 136.19 D -4.41 - 1,3-Butadiene C,He. . . . (7.3)llr 350 108.9 D -96.4 n-Butanal CsHzCHO. . . I 3l t12 74.8 MCA - - n-ButaneCnHro...... (6.l) 94 299 0.5 r38.4 D - 2-ButanoneC,IIaO.... I i.l 30 100 79.6 85.9 LB -6.26 - l-ButeneC.Ha...... (8 3) 123 380 r85.4 D - cz's-2-ButeneCrIIe. . . . . (1.1) IJ 244 658 3.72 r38.9 D -50 CyclobutaneC,Hr.... 2.5" 50 167 460 12.g LB q(t -32.26 Dimethylacetylene CrH o 80 26.97 D - Diethyl ether (CrHs)zO. DI 185 534 34.6 I16.3 MCA -69 1,2-Dimethoxyethane CrHroO:. . . I' t7.4 65 85.2 42 1,4-l)ioxaneCrllaOz .. 3S l0l. t 10 LB Divinyl ethcr ColloO (17) (72) (234) (672) 27.8 LB - Furan CnHrO. 19 70 2r5 604 31.I 85.6 LB - - Isobutane CnHto. . l3 164 484 11.73 159.6 D - - 2-Methylpropene CrI{ s. (8 7) 126 391 6.9 r40.4 D Methyl z-propyl ether CrllroO. . . (4.1) (34) (145) (457) 39.I MCA -6.6 -40.2 Octafluorocyclobutane CrFr. . . . 4.0. l0l, 376 LB Tetrahydrofuran CrH a(). It 48 163 ca.63 43 lrazs-2-Butene CnHa. . (5.3) 87 280 734 0.88 -ios.o D Five carbon: -93.88 Cyclopentane CrHro. . (7.0) 31 t07 3t7 49.26 D - CyclopenteneCslle. . . (9.l) 39 r30 380 44.2 r35.1 D 2,2-Dimethylpropane CsII rr (neopentane) t\ 9.5 - 16.55

h)\o ! N\o @ Tobleof vopor pressures(Confinued)

Temperature, "C -1s6.5e1-11r.ssl-8s.6l-t5.ptl-ee.zsl p,.oo Compound o.ooI bp("c) mp('c) R"l.

Vapor pressure, tom

2-Methyl-1,3-butadiene CslI g (isoprene.l (l6) (63) (le8) (550) 34.07 - 145 D 2-NlethylhutaneCsllrz.. . 87 259 688 27.9 - 159.9 D n-Pcntane CrII rr . . l4 5ö 183 512 36.07 -r29.7 D Six carbon: Benzene (CeIIo) . 24, 95 80.r 5. D,J ChlorobenzeneCoIIrCl (l2) 131.7 - 45.21 CyclohexaneCrH r,. . ..'.n, t':' 98 80.7 6 D CyclohcxanoneCoHroO 4.6 155.6 -45 LB CyclohexeneCuHto. . (1.0) (6.0) 25 89 82.98 -rffi.5 D Diethyleneglycol dimethyl ether CuH',Or. (4) t62 -64 42 Di-n-propyl ether CoI{rrO 50 ,^ 70 89.5 -122 LB n-HcxaneCrH,,.. (2 2) (12) 45 l5l 68.7 -93 D Seven carbon: BenzaldehydeCtH.O. (1.e) 179 -26 LB n-HeptaneCrHto.. (2.3) (ll) 46 98.4 -90.61 D 1\{ethylcyclohexane CzH r r (2 7) 12 46 100.9 -126 D Toluene CrHr. . . (l 3) (67 28 110.6 -94 D Eight carbon: Cyclooctatetrene (CrHr) (1,5 (7.8) 140.56 -4. D n-OctaneCrH,r.. (29 t4 r25.67 -56.8 D Styrene CaHe. . (l.r (6.0) t45.2 -30 D 2,2,4-Trimethylpentane CslI 1g (isooctane) (2 e) l3 49 99.2 - 107 D m-XyleneCrHro.. (l o (8 2) 139.I -47.87 D o-Xylene CrH,o. . (l J (6 6) r44.4 -25 18 D p.Xylene C.Hro (8 8) 138.35 r3.26 D Gallium: Triethylgallium (CzHs)rfla 1.5 6.8 t42.4 -82 LB Trimethylgallium (CHr)rGa 65 218 55.6 _16 LB Germanium: Bromogermane GeBrHr. o< 87 272 -32 44 Chlorogermane GeClHr l8 234 689 (28) -52 44 Chlorotrifluorogermane [.ieFrCl. . . . l0l 653 -21 -66 LB l)ichlorogerrnane fieOl: H:. 21 l0 39 133 69.5 -68 44 I)ifluorodichlorogermane GeF:Clr. . . 79 ,o, -0 -52 LB l)igermane Clerlle. (1 5) (26) (8e) (247) (623) (31) ca. - 109 LB I ) i m ethylc h lorogerm an e (CHr)rGcllCl (2 4) (s.7) 3l (n3l (8e 4) _76 45 I)imethylgermane(ClI3)rGeIIr... . (5 3) 83 (27e) - 0.6 - 149 45 FluorogermaneGeFHr. 358 (15.6) -22 46 GermaneGoHn. . 48 182 (-e3) - 165 7S (iermanium tetrachloride GeCln. . . . JO 24 87 85.8 -50 LB (iermanium tetrafluoride (ieFo. . . . (s e) (337), ( - 35), 47 Nlethylchlorogermane C H rGeI{zCl. . \t . t ) 26 aü (le0) (70.e) - l0l 45 Methyldichlorogermane CH rGeIICl, (2 8) ll (36) (113.2) -62 45 Nlethylgermane CH rGeIIr. 44 48 (470) (-35.1) - 158 45 Trichlorofluorogermane (leFClr. . . . (s 7) (30) (r20) (435) 37 -50 LB Trichlorogerrnane Ge HCl3. 4.9 24 100 74 LB Trigermane CeaHs.. (2 8) (ll) (3e) 111.1 - 106 LB Halogen BromineBrr...... 13, 66 2t5 58.8 -7 .1 MCA IJromine pentafluoride BrFs. . I 2a l3t) 407 40.9 -60.6 MCA Bromine trifluoridc BrFr. . . 1.3 7.7 125.8 8.8 I\(CA Chlorine Clr . D< 44 453 -34.1 - r0l MCA

\o19

Tentperature, "C

('ontpountl 25.00 bp\"c) mp("c)

Vapor pressure, torr

Chlorine dioxide CIO: . 34 155 10.9 -59 MCA Chlorine dioxygen fluoride ClOrF. . 5.0 104 ,tD) -5.7 -l15 MCA Chlorine fluoride ClF. . 50 173 -90 - 155.6MCA Chlorine pentafluorideC1F5...... (1 7) l9 190 D.' J -14 - r03 78 Chlorine trifluoride ClFr. . . 139 451 11.8 - 76.3 MCA Chlorine trioxygen fluoride CIOrF (perchlor5'l fluoridet |.4 7.9 90 -46.7 -147.7 MCA l)euterium chloride ])Cl. . . . 28, t'20 -84.8 - tt4 .7 MCA l)euterium fluoridc I)F 47 146 385 18.6 - 83.6 MCA I)ichlorineheptoxide (Cl:O')...... 5.l) ao 84 -9r.7 MCÄ I )ichlorineoxido ('lzO. 3 69 246 696 ,1 - 120.6 MCA l)ioxygen difluoride FzOr. . . 45 20 173 -56 - 163.5N{CA FluorineF2..... - 188 - 219.6MCA :,. Ilydrogen bromide HBr. . . o.öt 28" 299 -66.7 -ö/ MCA Hydrogen chloride HCI . . . 30" 124 -85 - tt4.2 MCA Ilydrogen fluorideIIF., l3l 19.5 -83.4 MCA Hydrogen iodide HI 2.0" 38" 498 - 35.6 -50.9 I\ICA Iodine heptafluoride IF7. 1.7" 179" 580" 6 6.0 MCA Iodine monochloride ICI ,'7 97.8 r3.9MCA Iodine pentafluoride IFr. 4.O 26 102 9.4 MCA Oxygen difluoride Fz0. . . - 144.9 -223.8 MCA Indium: '7' Trimethylindium (CIIr) rln r35.8 88.4 LB at 30" Lead: Tetraethylplumbane (C:Hs)rPb. . . . 0.4 183 LB Tetramethylplumbane (ClI3) 4Pb 1.7 76 30 (ll0) -27 .5 LB Nitrogen: Acetonitrilc CIITCN 28 (e6) (816) -45.7 LB -77 Ammonia NHr .. lOt 408 .7 NICA Analinc C6H7N. 0.8 184 -6 LB BenzonitrileCTlIbN 0.8 l9l LB Carbonyl cyanide CO(CN), 6.9 31 124 65 -38 LB cis-Difl uorodiazinc N:Fr . r57 494 '.,- - 105 7 <-195 48 rtn Cyanogen bromidc CNBr. 5r.8 LB Cyanogen chloride CNCI . . 456 t2.5 -5.2 LB Cyanogen fluoride CNF. . . s.z" ,, -72.9, LB -31.05 -74.3 I)eutcroammoniaNI)3. 19" .JO,' IUCA f)ic.vanogenCzNz.. 4.7" 163" 707 -21.3 -27.9 LB Diethylamine (CrHs)rNH 40 l9 70 235 55.7 -50 8l I)imethylamine (CHr)rNH 44 179 562 6.88 -92.2 80 N,N-I)imethylforamide CTHTON . . 4. 149 -60.5 D l,l-l)imethylhydrazine (CHr):N'IIz. (1.5) 9.3 4l -58 LB 1,2-l)imethylhydrazine (CHr)rNzHz. (2.e) l6 70 LB Dinitrogen pentoxide NrOr. . 5.5, aö! 413. 4l MCA Dinitrogen tetroxide NrOn. . . 263 2r.2 - 9.3 T{CA Ethylamine C?II5NH, 26 112 366 16.58 -81 MCA ( 1,2-diaminoethane)Ethylenediamine c,H4(NHr), 12 tt7 .2 ö.1) LB Fluorine nitrate NOrF. l0 95 731 -44 - l8l MCA HydrazineNzHn...... t4 113.5 1.5 MCA -80 Hytlrogen azide HNr 183 512 JO MCA Hydrogen cyanide HCN. . 265 742 25.7 - 13.29 49 N{ethylamine CHTNHz -6.45 -93.5 NICA

G, o (,) o N Ioble of vopor pressures(Conlinued)

Temperature, "C

Compound. - t 26.6sl-rt t.sll-s.e.6 - /+s.el -ze.zsl o.oo bp("c) ,np("C) Rel I I Vapor pressure, torr

Methyl hydrazine CHrN:Hr. (50) LB N-Methylhydroxylamine C H3NHO H 6.5. 115 42.5 LB O-Methylhydroxylamine CH:ONHz . 84 293 48.r LB :.' : Methyl isothiocyanate CH3NCS. . . . . 8. 24, ll9 JJ.C LB Methyl thiocyanate CHISCN... . 2.6 t2 132.9 -51 LB Nitric acid HNOr. 2.6 l4 63 83 -41.6 MCA Nitric oxide NO. . . . -151.8 - 163.6 MCA Nitroethane CrH5N02 495 114 -90 LB Nitrogen trichloride NClr. . 9.0 37 (71) _27 MCA Nitrogen trifluoride NFr. . . - 129.06 -206.8 MCA Nitromethane CH3NO, 1.6 r0r -29 LB Nitrosyl chloride NOCI . . 4.6" 345 -5.4 -59.6 MCA, Nitrosyl fluoride NOF. . t.7 175 -59.9 - r32.5MCA Nitrous oxide NrO. 14, - 88.48 -90.8 MCA Nitryl chloride NO2CI l0 573 _ r5.3 - 145 MCA Nitryl fluoride NOrF. . 393 -72.4 _::: MCA Phenyl isocyanate C6H5NCO 26 165.5 LB Piperidine CtHrtN. 8.1 32 106 LB Pyridine CrH'N. I' 4.1 20 115 LB Pyrrole C.HrN. (2.0 (l l) l3l LB Tetrafluorohydrazine NrF.. . (478) co. -73 50 Tetramethylhydrazine (CHn).Nr. . . . 1.6 8.9 73 LB trons-Difluorodiazine NrFr. . . - 1r1.4 -172 48 Triethylamine (CrHr)rN. s.z 2l 89.5 -114.7 8l Trifluoroacetonitrile CFrCN 7.l -ol-t -r44.4 51 Trifluoronitrosometh&neCFINO. . . . 32 -84.5 LB Trimethylamine (CHr)aN 29 -117.1 82 Trimethylhydrazine(CH:)rNrH. . . . . r96 -72 LB Oxygen: Deuterium oxide DzO. 2l 101.4 3.82MCA OzoneOs. - 111.3 -251 MCA Water HzO. 24 r00 0.0 API Phosphorus: 1,2-Bis(trifluoromethyl)diphosphine PzHz(CFr)2. (2 0) l1 43 (6e.5) MCA BromodifluorophosphinePBrFr. . . . . 12 184 567 :li1l -16 - 133.8MCA ChlorodifluorophosphinePClFr. . . . . 3.6 t2l -47.3 - 164.8MCA DibromofluorophosphinePBrrF. . . . . 1.5 8.0 32 r09 78.3 _ 115 MCA DichlorofluorophosphinePClrF. . . . . 2 47 163 448 13.9 _r44 MCÄ DifluoroiodophosphinePFzI...... l9 /ft 243 710 (26.7) -93.5 52 DifluorophosphinePF:H -64.6 -124 53 Difluorophosphoricacid HPOzFr. . . . 2l 32 I16.4 -96.5 MCA Dihydrogen phosphorustrifluoride PH2F3. ot 207 640 3.8 -52 54 Dimethylphosphine(CHs)zPH. .... (2) 34 rt7 334 ... 20.9 LB DiphosphinePrH.... 4.L 20 7T 224 59 -99 MCA Hydrogen phosphorustetrafluoride PHF{.. (4.4)

Temperalure, "C

Compound bp("c) mp("c) ne|.

Vapor pressure, tom

Phosphoruspentafluoride PFr...... 48" - 84.5 -93.8 MCA Phosphorustribromide PBrr...... r73.2 -40.5 MCA Phosphorustrichloride PClr...... 9.4 76.r -92 MCA Phosphorustrifluoride PFr...... ra+ l0r .2 - l5l .5 MCA Phosphorylbromide chloridefluoride POBTCIF. 6.6 100 7S MCA Phosphorylbromide dichloride POBrClz 9.9 136 l3 MCA Phosphoryl bromide difluoride POBrFz. t4 60 199 582 32.1 -84.8 MCA Phosphorylchloride difl uoride POCIF,, 68 240 672 3.1 -96.4 MCA Phosphoryldibromide fl uoride POBrzF. 3.0 l2 lr0 -rr7.2 MCA Phosphoryl dichloride fluoridc POCI,F. .)a 4.8 84 52.9 -80.1 MCA Phosphoryl trichloride POCI3. . . . 105.5 l.l MCA Phosphoryl trifluoride POF3...... 7.6, -39.5 -39.1 N,ICA Tetrafluorodiphosphine PrFo...... 8.1 367 (-6.2) -86.5 57 Tetrakis (trifl uoromethyl ) cyclotetra- phosphine Pn(CFr)n. g2 (135) 66.4 5ö Trifluoromethylphosphorus tetrachloride CFBPCIn t3 (104) -52 58 Trimethylphosphate (CH aO)gPO . (.e) 191 LB Trimethylphosphine (CII3)3P. . . . l3 I l)ö 459 38.4 Tris (trifl uoromethyl) phosphine (CFr)rP. (3.3) (46) 149 400 (17.3) I ,2,3-Tris(triffuoromethyl )triphos- phinePrll:(('Fr)r... 3.6 ca. 123 59 Iladon: lladon Itn. (4.l), (21)" (217)" -62.O -71 MCA Selenium: Carbon diselenide CScr. . . 4.4 l8 12l.8 -45.5 LB Carbonyl selenide COSe. . 2.1 24 2;4 -21 .9 -124 LB Ilydrogen selenideII2Se...... t) r- 5t" 6;-r4 -65.7 MCA I\lethylselenol CH rSel I (1.4) (25) LB Sclenium hexafluoridcScFe. . . .. 1 ti" -46.3, -34.8 TICA Seleniumtetrafluoride SeFa... . .>a 16 105 -9.ir I\(CA Selenyl fluoridc Sr'OF, . 4.2 t26 l5 MCA Silicon: AllyltrichlorosilaneCrIIsSiCl3...... la (116.8) 60 1,2-Bis(trichlorosilyl )-ethanc (sicl3)rcrII4 (r.3) (2o2) 60 Bromodichlorofl uorosilane SiClr BrF l7 a;> 8{) 2r6 f\43 - ll2 LB BromosilanoSillrBr 6.2 83 26; l I -94 6l Bromotrifl uorosilanc Si FrRr 65li -41.8 -70.5 LB i-Butylsilane (i-C4Hr)SiIl3. (7 l) (32) tioet (322) (48.6) 62 a-Butylsilane (n-CrI{g)SiIIr...... (4.2) l'), \ (7e) (242) (56.4) 62 .)< ChlorosilaneSil I3Cl. tt t) 393 - 30.4 -tte t 6l I)ibromochlorofl uorosilane SiIlrrCl F :-t.4 22 73 2l{) 59.3 -98 LB Dibromodifluorosilane SiFrBr:. . . . . (3.6) (.i,2) (r67) (452) -67 LB I )ibro mosilane Si I I: Brz 3.0 l3 c0 t4'2 74.I -70 LB I)ichlorodifluorosilaneSiFrClr...... 44 4 ltt -32.2 - 139 LB I )ichlorosilaneSi I l rclr. 3.ll ir9 198 i)48 (8.3) - lrt 6l

(^, o (rl (.) o o. Toble of vopor pressures(Conlinued)

Temperalure, "C

Compound o.oo st.oo bp("c) mp("c) Rel. I

Diethyldichlorosilane (CrH')sSiCl'. . (2 6) (13) 60 Diethylsilane (CrHu)zSiH:. (4 8) 83 254 1t.ro'] 62 Dimethylc hlorofl uorosilane (CH3)'SiCIF. l2 51 t7r 500 36.2 LB Dimethyldichlorosilane (CH r)rSiCls. (2.3) ll 43 r42 70.5 60 Dimethyldifluorosilane (CHr)rSiFr. . (3.4) (67) 239 ruln] 2.1 LB Dimethylsilane (CH')zSiHr. I.ir t? 253 686 -20.1 - r50 6r Disilane SizHo.. t.4 18 195 548 14.5 -r32.5 6l l)isiloxane (SiHr)rO. l5 193 563 -r5.2 - r43.6 61 Ethyldichlorosilane CzHsSiHCl'. . . . lt 38 t22 75.5 60 Ethylsilane Crll 5SiH i. (l4) (182) (sle) (- 13.7) -r79.7 62 Ethyltrifluorosilane CrHiSiFl (6.2) (e7) 325) -5.4 LB Ethnylsilane C'HSiH.. 263 746 -22.4 -öo.z 63 Hexafl uorodisilane SizFc 71" JOU! -19.r LB Hexamethyldisiloxane (CHr)uSi,O. . 1.7 8.3 (37) s9.2 _l?i LB Iododisilane SirHsI 3.3 l3 nu. 8] 6,4 Methylchlorofl uorosilane CH3SiHCI 58 83 (267) (722) 1'o2 LB Methyldichlorofl uorosilane CH,SiCI,F. (le) 74 227' 643 25.4 LB Methyldichlorosilane CHsSiHClr. . . II 47 150 429 (40.e) 60 Methyldifluorosilane CHTSiHF'. . . . (3.7) 44 (475) LB Si-MethyldisilazaneH NSi H $i H:C H l4 60 189 544 34.0 LB MethylailaneCHrSiHr. 4.8 23 195 -56.8 6l Methyltrichloroailane CH$iClr. . . . (2.6) iioj iiir i iozr (66.4) 60 Methyltrifluorosilane CH3SiF3. . . (l.e) 28 350 -30.2 LB Silane SiH. 304 760 -lll.9 _ 185 6l no Silazane (SiH3)rN öz 109 315 52 - l0ö.6 6l Silicon tetrabromide SiBrr...... 7.6 153 5 LB Silicon tetrachloride SiClr...... (4.8) 2; ;; 237 57.3 -68.8 60 Silicon tetrafl uoride SiFr 18, 1r, - 95, LB Silylcyanide SiHTCN l).v 4l 250 49.6 32 LB Silylphosphine SiHrPH, 77 ato 506 12.l <_135 LB Tetramethylsilane (CHr)rSi...... t.l 24 ot (276) (738) 26.2 - l0l.7o 62 - 99.5f TetrasilaneSi{Hro. . 1.7 8.1 33 (r0e) ca. -90 6r Tribromofluorosilane SiFBr:. . . . . 1.5 LU 26 86 83.7 -82.5 LB Tribromosilane SiHBrr. ,, 8.8 32 rt2 _74 LB Trichlorofluorosilane SiFCl3...... 4.1 56 177 472 12.6 - t2l LB Trichlorosilane SiHCls. t7 70 218 598 3l .8 -126.5 61 Trifluorochlorosilane SiFaCl. . . . . l3 49 JDö -70 _,:, LB Trimethylchlorosilane (C H r)rSiCl (4.7) 2l 76 234 57.6 60 Trimethylfl uorosilane (CH3) rsiF . (2 0) 37 12t 388 16.4 LB Trimethylsilane (CHr)3SilI.. .. 4.1 67 22r 594 (6.7) - 135.9 62 Trisilane SirHa. . 6.5 28 96 28it it2.9 -tr7.4 6l Yinylsilane CzHaSiHr. (1.it) (24) (280) (7ö3) ca. -22.6 -111- 179.la 62 Vinyltrichlorosilane CzHrSiClr. . . (4.6) lg oo (e0.6) " Sulfur: Bis (pentafl uorosulf ur) peroxide SzFtoOr 5.0 a;t 9ö 305 49.4 -ii' 65 Bis (trifluoromethyl)disulfide (CFr)rS' l5 5ö r83 529 (34.6) 66 Bis(trifluoromethyl)sulfide(CF3)rS. . 1.3 l9 240 -t9 , 66 Carbondisulfide CSz. . . . (e 6) 40 t27 362 47.3 -lll.95 D Carbonselenosulfide CSSe. . . (t.2) (6.5) (26) (8e) (8ö.3) -85.2 LB I

(.) o (^t o @ Tobleof vopor pressures(Confinued)

Temperature, "C

Compound - 1p6.lsl- 1 r t.sll - ffi.6 - 45.p1l- ee.rslo.oo 25.00 bp("c) mp("c) Rrt. | | Vapor pressure, torr

Carbonsubsulfide CrSr. . . , 0.4 LB Carbonyl sulfide COS. -50.2 - r38.2 J Diethylsulfide (CzHr):S...... (3 2) I;) 58 92.r - 104.0 D Dihydrogendisulfide HrSr...... l.J 7.6 32 111 76 -89.8 MCA Dimethyl disulfide(CHr)rS, (1.3) (6.7) to r09.7 -84.72 D Dimethyl sulfide(CHr)zS . . 51 lb/ 485 37.3 -98.3 D Disulfur decafluorideSrF'o...... au 23r 05/ 28.9 _o9 MCA Disulfur dichlorideSzClz. . 1.9 9.5 137.6 -80 MCA Disulfur difluorideSrFr. . . 2tl -91 - 120.5MCA EthanethiolCzHrSH. 57 184 35.0 -tzl API Hydrogensulfide HzS to 200" -60.3 -öo.D MCA MethanethiolCH'SH. (3.0) 61 213 5.96 -t2l ÄPI Nitrogen sulfur fluoride NSF. . . . D.J lI) 263 co. 3 -89 67 Nitrogen sulfur trifluoride NSFr. . . . 307 -27.r -72.6 67 Pentafluorosulfurhypofluorite SFsO 45 482 _35 - 86.0 68 Peroxydisulfuryl difluoride SgOoFz.. (7.2) (36) ino 67.I -55.4 68 l-PropanethiolCaHsSH (2.2) t2 46 r54 67.7 -112 API Pyrosulfuryl difluoride SzOrFz.. . . . 6.1 28 98 296 51 MCA Sulfinyl bromideSOBrr. l.l 6.3 140 -52.2 MCA q Sulfinyl ehlorideSOClr. . 2.0 öt r20 75.6 -lli MCA Sulfinyl chloridefluoride SOCIF.. . . 2.1 44 159 463 t2.3 I MCA Sulfinyl fluorideSOFz. . . 4.0 64 710 -43.9 MCA Sulfur dichlorideSClz. 4 59 -78 MCA Sulfur dinitrogen difluoride SNrFz. . 160 47r -11.1 - 108 MCA Sulfur dioxidcSOz. . . . 4 .9, 416 - 10.0 -/o.i) MCÄ Sulfur hexafluorideSF6. . . 2.l. 13" 186, -63.9 -50.5 MCA Sulfur tetrafluoride SFo 6.1 68 601 -40 - 124 MCA Sulfurtrioxide SO3(a, stable). .... o.a" 54 74" 62.2 IlICA Sulfur trioxideSOr (€, mctastable) 3.4, 2t 233" 32.5 MCA Sulfur trioxideSOr (r, metastable) 6.0" 45" 16.8 I\{CA Sulfur trioxide SO, (liq.) 8.5 260 448 MCA Sulfuryl bromidefluoride SO:BrF. 8.4 39 139 428 40 MCA Sulfuryl chlorideSOzCI:. l.t 9.9 40 140 69.4 -54.1 MCA Sulfurylfluoride SOzFz. . I t4 l4l -55.4 - 135.8T,,ICÄ Sulfuryl tetrafluorideSOF{...... (l D' (8.7) (e8) -48.5 _99.6 MCA Tetrahydrothiophene(CHr)rS. . . . (4i (18) (121) -97 LB ThiophcneCoHoS. (4 8) 2l 80 84.16 -38.2 t) TrifluoromethanethiolCFTSIL . . . . 48 56 543 -38 ( - l5e) 69 Trifl uoromethylsulfuryl fluoride CF3SO'F. (1.5) (20) 240 724 -2t.7 LB Trimethylenesulfide (CHr)rS. . . . 4.6 tf 9l-r .,:", LB Tellurium: I)itellurium decafluorideTerFro. . . l9 69 218 59.0 -33.7 MCA Hydrogentelluridc II1Te. . 82 293 _46 NICA Tellurium hexafluorideTeF6...... I .0" 494" -38.4" -37.8 MCA Thallium: Triethylthallium(C,H5)3Tl . .... (le2) -63 LB Trimethylthallium(CH:)rTl .. . (r47) öö. 1) LB

Tin: StannaneSnlln... (4.6) -53 -49.7 LB Tetrameth-t'lstannane(CI{r)oSn . . . r.7 8.7 78.0 LB Tin tetrat'hlorideSnCl. 1.0 t24 ;- LB

(.) o .o (., o Tobleof vopor pressures(Conlinued)

Temperature, "C

Compound - 126.ssl-r 1r.sll -ß.61_$.s11_ee.zll o.oo pt.oo bp("C) np("c) Ret. I Vapor pressure, torr

Transitionmetal: Cromyl chlorideCrOrClr. 4.3 20 116 _95 LB Cobalt nitrosyl tricarbonyl Co(CO)rNO. ,a 95 77.8 (-r12) LB llafmium borohydrideHf (BHr)r. . 2.0 15" 118 28.8 LB Iridium hexafluorideIrFo. . . . , .4rr 60,r 226,, 53.6 43.8 70 Iron dinitrosyl dicarbonyl Fe(CO),(NO)2. . 4.8 26 107.6 l8.4 LB fron pentacarbonylFe(CO)5. /.o 30 r05 -21 LB Iron tetracarbonyl dihydride Fe(CO),H, 1.8 6.1 t7 43 -70 LB Molybdenum hexafluorideMoF5. . . . U.l"r 37,r 168,, (DD/J 34 17.4 70 Nickel tetracarbonylNi(CO),...... o.0, 43, r35 394 43 -22 7l Osmiumhexafluoride OsFo. . , .9rr lgrr 84" 313., 47.5 33.4 70 Platinum hexafluoridePtF6...... n.0tt 26or 112,, 69.14 61.3 72 Rheniumhexafluoride ReFs...... 4.7, öörr 172,1 546 33.8 18.7 70 Rhenium oxypentafluoride ReOFs. . . 3.9, ,9 109. 73 40.8 73 Titanium tetrachlorideTiCl4...... 2.5 (11) (138) _23 LB hexafluorideWF...... 37", 373", ' L7.r 2.0 70 Tungsten :': Vanadiumtetrachloride VCI{...... 1.8 ,.D 152 _26 LB Zirconium borohydride Zr(BH)t...... 1.0 8.2, r23 28.7 LB Uranium: Uraniumhexafluoride UFa...... 2.1, 17, I 10, oo.or 6,{.I LB Xenon Xe. -lll.9 MCA Xenon difluoride XeF:. . . 0.6, 4.5" r2g 74 Xenon hexafluorideXeF6. 2.6 29" 46 75 " Xenon tetrafluoride XeFl . 0.3, 9< rt7 74 Xenon oxygen tetrafluoride XeOFr 7.9 to _28 76 At 23"

Diethylzine(CzHs)zZn. . . . . ö.t) l6 (117.6) -30 2 Dimethylzinc (CHs)zZn.. .. 9.1 r23 37r 43.8 -29.2 LB Di-n-propylzinc (CzH t) tZn . . 1.9 ö.1) (139.4) -81 2

(.) 312 VAPORPRESSURES OF PURE SUBSTANCES

Referenccs for table of vapor Pressurcs: D to Dreisbach'sbooks, ,4p1 refers to the American Petroleum Institute Tables, ./toJordan,sbook,MC,4totheManufacturingChemistsAssociationTables,arrd sourcesare given in this .LB to LancloltBornstein. The conipletecitntions to these follorving references(f) aopendix under Solrces of Vapor PressureData' ln the nie^ansthat the originaldata wasfit br Eq (\"9) (1940)' 1. Burg and Schlesinger,I' Am'Chem' Soc',62:3425 Soc',1946:468' 2. Bramfordet al.,"J. Chent. 3. Berkaet al.,J. Inotg' NucLChem',14:190 ( 1960)(f)' ( 4. Shermanand Ciauque,I ' Am. Chem' Soc, 77:2154 1955)' 5. Benettet al., ,J.Chem. Soc, 1953:1565' ( 6. Schlesinger,et al.' J. Am' Chem Soc, 62t3421 1940)' 7. llrw et ;1., /. Am. Chem' Soc.,76:3293 ( 1954) ' 8, Ceronet al., J. Am.Chem' Soc''8l:6368 ( f959 )' 9. Burg and Sandhu,lnorg. Chem',1:1467.(l^9-61 ) 10. Urr| et al.,/. Am.Chem. Soc., 76:5299 ( 1954) ' (1960)' 11. Staffordand Stone,I. Am.Chem. Soc., 82:6238 Press,Ithaca, N'Y', iä. S,""1, "Hydrides of Boron ancl Silicon," Cornell University 1933. (1532)' 13. Pohlandand Harlos,Z. Anorg.AIIgetn Chen',207:242 14. Wirth anrl Palmer,!' Phys.Chem ,6Oz9Il (1956)' Table 39D' 15. Holtzman et al., "Proclirctionof Boranesand Related Research," AcademicPress, Inc., New York, 1967' 16. Alton et al..J. A.rn.Chem. Soc, 81:3550( 1959) 17. Burg and Randolph,l. Ant.Chem soc',7I:345I ( 1949)' f 8, Burgand Schlesinger,J. Am.Chen' Soc',58:'109(f 936)' 19. Schi-esinceret al.,/. Am.Chen. Soc' 6O:1296(1938)' 2O. Burg, I.-Am' Chem. Soc, 62:2228 ( 1940)' 2L, Pariow et al.,I. Am.Chen' Soc.79:5091 ( 1957)' 22. Egan et al., lnorg. Chem.,3:1024 ( 1964) ' 23. Bure and Kratzer,lnorg. Chen',1:725 (f962)' 24. Spielmanand Burg,lttorg. Chem,2:1I39 ( 1963)' 2S. Wirth and Patmer,J. Phys.Chem., 6O:914( 1956)' 26. Burgand Schlesinger,I. Am.Chen Soc,55:4009 ( 1933)' 27. Parryand Bissot,J Am Chem.Soc ,78:1524 ( 1956)' 28. Burg and Spielman,J. Am.Clrcm. Soc, 8l:3479 (1959) 29. Finchand Schlesinger'I. Am.Chen. Soc',8O:3573(1958)' 30. Brotherton,et al.,J. Am.Chem. Soc.,82:6245(1960)' 31. Wirshburnet al., Adc ht Chertt.,\et ,23"129 ( 1959) 32. Stockand Zelder,Chem. Ber.,54:$f (f921)' 33. Haworthand Hohnstedl,l. An. Chen Soc.,82:3860(i960)' 34. Burg and Randolph,I An. Clrcnr.Soc., 73:953 (1951)' 35. Benningand McHarness,lnd. Eng. Chem.,32:197(19'10)' 36. C. F. Furukawaet al.,J. Res.Naf Bur' Std.,51:69(1953)' Soc.,1948:2188. 37. Bankset al., "1.Chem' 38. Ducllel et al.,/. An. Chem.Soc., 7O:3986 ( 1918) (f )' 39. Stull,lnd.Eng.Chen.,39:517 (1947) (f). 40. Mearset al., Ind. Eng.Chen , 47:1449( 1955). 41. Boothet al.,/. Am.Chen. Sor:.,55:2231 ( 1933)' 42. C. Kubas, rrnptrblishedobsen ations, Northwestern Universitv, 1968; Anstrl Co. Data Sheet. SOURCESOF VAPORPRESSURE DATA 313

43. Kolski and Schaeffer,l. Phys.Chem.,64:1696 (1960). 44. Dennisand Judy,I. Am. Chem.Soc., 5l:232I (f929). 45. Ambergerand Boeters,Agnero Chem.,73:'114 ( 196l ). 46. Sravastavaand Onyszchuk,Proc. Chem. Soc., 196l:205. 47. Fischerand Weidemann,Z. Anorg. Allgem. Chem.,213:106 ( 1933). 48. Colburnet al.,/. Am. Chem.Soc., 8l:6397 ( 1959). 49. Giauqueand Ruehrwein,I. Am. Chem.Soc.,6L:2626 ( 1938). 50. Colburn and Kennedy,l. Am. Chem. Soc.,8O:5004 ( 1958). 51. Paceand Bobka, I. Chem. Phys.,35:454 ( 1961). 52. Budolphand Parry,lnorg. Chem.,4:1339( 1965). 53. Rrrdolphet al., Inorg. Chem.,5:L464(1966). 54. Holrnesand Storey,lnorg. Chem.,5:2146(1966). 55. Zeffert et al., /. Am. Chem. Soc.,82:3843 ( 1960). 56. Rudolph et al., J. Am. Chem. Soc.,88:3729 ( 1966). 57. Lustiget al., /. Arn.Chem. Soc., 88:3875 (f966). 58. Matrler and Burg, I. Am. Chem. Soc.8O:616I ( 1958). 59. Burg and Peterson,lnorg. Chent.,5:943 ( 1966). 6t0. Jenkins,lnd. Eng- Chem., 46:2367 ( Igil ). 61. Stock,Z. Elektrcchemie,32:Ml ( 1926). 62. Tannenbaumet al., I. Am. Chem. Soc.,75:3753 ( 1953). 63. Ebsworthand Frankiss,J. Chem.Soc., 1963:661. 64. Ward and MacDiarmid,I. Am. Chem.Soc.,82:215I ( 1960). 65. Merrill and Cady, I. Am. Chem. Soc.,8399B ( l96f ) ( f ) . 6i6. Brandt et al., /. Chem. Soc.,1952:2198. 67. Glemserand Richert,Z. Anorg.Allgem.Chem.,307:313 (1961 ) (f ) 68. Drrdley et al., ,1.Am. Clrcm. Soä.,78:1553 ( 1956) . 69. Dinney and Pace,J. Chem.Phys., 32:805 (l%O). 7O. Cady et al., ,1.Chem. Soc.,1961:I563. 71. Anderson,I. Chem.Soc., l93O:1653. 72. Weinstocket al.,/. Am. Chem.Soc., 83:4310 (1961). 73. Cadyet al.,/. Chent.9oc.,1961:1568. 74. Schreiner et al., Äbstracts of Papers, l53d ACS Meeting, April 1967, Sec. R, no. 127. 75. Weinstocket al., Inorg. Chern.,5:2189( 1966). 76. Chernick et al., "Noble Gas Compounds," p. 106, University of Chicago Press, Chicago, 1963. 77. Lamb and Roper,I . Am. Chem. Soc.,62:806 ( 1940) . 78. Pihpovich et al., Inorg. Clrem.,6:1918 ( 1967). 79. Finholtet al., ,I. Ant.Chem. Soc.,69:2692(1947) (f ). 8O. Astonet al.,.l.Am. Chen. Soc.,6l:1539(1939). 81. Pohlandand Mehl, Z. Physik.Chem., A164:48 (1933). 82. Astonet al.,.I. Am. Chem.Soc., 66:l l7l ( 1944) .

SOURCESOF VAPOR PRESSURE DATA

Boubfik, T. and H. E. Vojitech, 1984, The Vapor Pressureso.f Pure Substances,Physical.9crences Data. Yol. 17. 2nd ed.. Elsevier.Amsterdam. Dreisbach, R. R. , I 955, PhysicalProperties of Chemical Compounds, Vols. I , 2. and 3 (Advancesin ChemistrySeries, Nos. 15,22 and 29). AmericanChemical Society, Washington, D.C. Antoine parametersare givenfor organiccompounds in thesebooks; frequently these have been taken from other compilations. 314 VAPORPRESSURES OF PURE SUBSTANCES

Gmelin Handbook oJ Inorganic Chemistry, Springer-Verlag, Berlin, While not specificallydevoted to vapor pressures,equations and referencesto data are availablein this multi-volume compen- dium. Jordan, T. E., 1954, Vupor PressureoJ'Organic Contpound.s,Interscience, New York. Vapor pressure equations, tabulations, and graphs for organic and organometalliccompounds. This book contains a fair number of errors and inconsistencies. Stull, D. R., 1947,Ind. Eng. Chent.,39,5l7, 1684.Reproducedwith minorchanges inHandbook of Chemistry and Phvsicsand in Chemicul Engineers' Handbook, Stull presentstabulations of temperatures correspondingto vapor pressuresfrom l-760 torr for 1,500 compounds. In addition, short tables of data are given for the I -60-atm region. Even though 40 yearsold, this is a valuablecompilation. Wilhoit, R., and B. Zwolinski, 1971, Handbook o.f Vapor Pressuresand Heats of Vaporization o.f Hydrocarbons and Related Contpounds, College Station, TX: Texas A & M. PRESSUREAND FLOW CONVERSIONS

Conversionfactors for variouspressure units and flow units are given in Table VI.1. TableVI.2 listsvalues of the ratio d,/dofthedensity of mercuryat a tem- peraturet dividedby the densityof mercuryat 0'C) overthe temperaturerange 0-99'C. Capillarydepression corrections for mercuryin glasstubes are givenin Table VI.3. The completeset of correctionsfor a pressuremeasurement is made as follows: P(mm): h.u,(g/gd@,/di + C,- Cl wherefto5, is the observeddifference in heightof the two mercurvcolumns, 9/96 is a correctionfor the local accelerationdue to gravity(where g is the localvalue of the accelerationdue to gravityand 96 : 980.665cm/s2). d,/d()is a correction for the densityof mercury(see Table VI.2), C" is the capillarydepression correction for the upper column of mercury (seeTable VI.3), and C1 is the capillary depressioncorrection for the lower column (seeTable VI.3).

315 toble Vl.,l. ConversionFoclors for PressureUnils ond FlowUnifs

Pressureunits: I atm : 760 torr : 1.01325bar : 101,325Pa (Nm 2) : 1,013,250dyne/cm2 : 1033.23g/cm2 : 14.6960lb/in.2 : 760 mm (Hg at 0"C)

Flou'units:I L/s :0.06 mjlmin : 2.11880ftrlmin : 15.850342gal/ntin

316 Ioble V1.2.Rotio of lhe Densityof Mercuryof TemperotureI Dividedby the Densifyol OoCo

dt/do

OC 3

0 1.000000 0.9998t8 0.999637 0.999456 0.999275 0.999094 0.9989r2 0.99873l 0.998550 0.998369 t0 0.998188 0.998007 0.997826 0.997645 0.997465 0.997284 0.997r03 0.996923 0.996742 0.996562 ln 0.996381 0.996201 0.996021 0.995840 0.995660 0.99s480 0.995300 0.995r20 0.994939 0.994759 30 0.994580 0.994399 0.994219 0.994040 0.993860 0.993680 0.993501 0.993320 0.99314r 0.992961 40 0.992782 0.992602 0.992423 0.992244 0.992064 0.99r 885 0.99r705 0.991526 0.991347 0.991168 50 0.990989 0.9908r0 0.990630 0.990452 0.990273 0.990093 0.989915 0.989736 0.989557 0.989379 60 0.989200 0.989021 0.988842 0.988664 0.988486 0.988307 0.988r28 0.987950 0.987771 0.987593 70 0.987415 0.987237 0.987059 0.986880 0.986702 0.986524 0.986346 0.986168 0.985990 0.985812 80 0.985634 0.985456 0.985278 0.985r00 0.984922 0.984744 0.984566 0.984389 0.98421I 0.984033 on 0.9838s6 0.983679 0.983501 0.983323 0.983146 0.982968 0.982791 0.9826r4 0.982436 0.982259

'These density ratios are based on the densitiesgiven by P. H. Bigg, Brit. J. Appl. Pfrys., 15, I I I I (1964). This referenceshould be consulted for valuesin the range -20 to OoCand 100to 300'C, along with estimatederrors.

! TobleV|.3. CopilloryDepression Coreclion for Mercuryin GlossTubeso

Tube Meniscusheight, mm diameter (mm) 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8

2 2.52 4.51 3 1.14 2.r3 2.93 4 0.63 r.22 r.73 2.12 2.47 5 0.39 0.76 l.l0 1.41 t.64 1.84 6 0.26 0.51 0.75 0.96 1.15 1.30 1.42 7 0.l8 0.37 0.53 0.69 0.82 0.94 1.04 1.13 8 0.13 0.26 0.38 0.50 0.61 0.70 0.78 0.84 0.90 9 0.10 0.20 0.29 0.38 0.45 0.52 0.59 0.64 0.69 l0 0.08 0.t2 0.21 0.28 0.34 0.39 0.45 0.49 0.53 ll 0.06 0.1l 0.16 0.20 0.26 0.31 0.35 0.38 0.41 l2 0.04 0.08 0.13 0.16 0.20 0.24 0.27 0.29 0.32 l3 0.03 0.07 0.t 0 0.13 0.16 0.18 0.2r 0.23 0.25 IA IA 0.03 0.05 0.07 0.10 0.12 0.14 0.16 0.r8 0.19 t5 0.02 0.04 0.06 0.08 0.09 0.11 0.r2 0.14 0.15 l6 0.02 0.03 0.05 0.06 0.07 0.09 0.l0 0.11 0.12 l7 0.01 0.02 0.04 0.05 0.06 0.07 0.08 0.08 0.09 l8 0.01 0.02 0.03 0.04 0.04 0.0s 0.06 0.07 0.07 19 0.01 0.01 0.02 0.03 0.03 0.04 0.05 0.05 0.06 20 0.01 0.01 0.02 0.02 0.03 0.03 0.04 0.04 0.04

'From G. W. Thomson. Techniquesqf Organic Chemistry, Vol. I , Pt. 1, 3rd ed., A. Weissenberg, Ed., Interscience,New York, 1959,o. 410.

3.18 INDEX

Acetone,purification, 92 Q sealant,145 Acetylene: vacuumgrease, 155 generation,92 vacuumwax, 156 purification,92 Argon, saeInert gas Acrylic plastics,267 Aromatichydrocarbons, purification, 91 Alcohols,purification, 92 Arseniccompounds, vapor pressure, 290 Alkali metals,sampling, 206-207 Aluminum: Baggingradioactive wastes. 61-62 gaskets,222 Bendingtubing: generalproperties, 27 6-277 glass,249 resistanceto fluorine,228 metal,274-215 Aluminumcompounds, vapor pressure of, plastic,26l 290 Berylliumcompounds, vapor pressure of, 290 Ammonia: Bismuthcompounds, vapor pressure of,290 purification,93 Boron compounds,vapor pressure of,297-294 vaporpressure of, 301 Boron halides,purification, 93-94 Ampule: Borosilicateglass: opening,34-35 ir-visible-uvtransmission, 244 sealing,32-34 resistanceto fluorine,227-228 Analysis: tensilestrength, 245 gaschromatography in, 199-2N thermalproperties, 242-245 hydrides,27 ,30,200 seeaßo Glassblowing hydrolysisin,27,30 Brass: pyrolysisin, 200 generalproperties, 27'7 Annealing: resistanceto fluorine,228,277 glass,243 Breakseals, 202-204 plastic,267 Bubblermanometer, 129-l3l Antimony compounds,vapor pressure of, 290 Bubblers,8-12 Antistaticdevices, 65-66 Buna-N,272 Antoine equation,282 Buret, gas,27, 29-30, 108 Aprezon: Burstingpressure of glasstubing, 245 diffusion pump oil, 122-124 Butyf rubber,272-273 319 320 INDEX

Cadmium compounds,vapor pressure of, 294 Elastomers,see Rubber Calibration of volume,l0g_i09 End-to-endseals: Cannula,see Syringe techniques glass,251-253 Carboncompounds. vapor pressure of: plastic,26t,265 one carbon, 291-295 Epoxy resins, 268-269 two carbon,295_296 Esr samplepreparation, 190_191 threecarbon, 296-297 Ethers,purification, 9l four carbon,297 Erhylene: five carbon,29i-2g| purification,94,20g six carbon, 298 vaporpressure of, 296 sevencarbon, 298 Ethylenepropylene rubber, 273 eightcarbon, Z9B-299 Explosionhazards: Carbondioxide: acetylene,92 purification,94 dangerousmixtures, 239_239 as refrigerant, 112-ll3 liquidair, 10.103,127 vaporpressure of, 112_113.294 liquid oxygen,10, 103,127 Carbon disulfide,vapor pressure of, 307 organicvapors, 11,237 Carbon monoxide,purification, 94 perchlorates,Tl, 23g Cariustube, see Sealed tube reactionvessels peroxides,36-87,239 Cathetometer, I3Z-133 pressurizedglassware, 11, 105, ll0 Cellularplastics, 265-266 slushbath, lll Centrifuge tube,cappable, 4l unstablecompounds, 23g Cesium,sampling, 207 Chlorocarbons,purification, 9l Feed-throughs,electrical, Clapeyron throughglass, 255_ equation,2gl 256 Codistillation, 193,195 Filtercannula,22-23 Columnchromatography, 37_3g Filtration: Conditioningfluorine apparatus,22g fluorinecompounds, 232 Conductance of tubingroward gases, 127_1Zg underinert gas,22-23,30_32. Copper: 35,3g_41 of liquefiedgases, 35, 39_41,102,190-192 gaskets,222 low temperarure,35, 39_41, generalproperties. 102,1g0_Ig2 2'/7 vacuumline, 190-192 resrstance to fluorine,Z2g,277 Fire curoff, 249-250 Cryoscopyapparatus, 3g, 39 Fire extinguishers,240 Crystallizarion, 35-37 Flint glass,2,15 Cvlinder,withdrawal of liquidfrom, 20_21 FIow reactors,232 Fluorine: Degasing: conditioningapparatus with, 22g freeze-pump-thaw,l0.l corrosionof variousmaterials by,2?7_22g liquids,85,104 cylinderenclosure, 235 Desiccants,70-72, g5-gg precaurionin handling,232 Diffusionpump: pressuremeasurement, 137, 227 designof, 121-123 vacuumline manipulation, 227_232 fluidsfor. 124 Fluorocarbon: Distillation: grease,155 fractional,low-temperature, 193_195 plasticapparatu s, 269-27 0 rnertatmosphere, 12_13, g7_gg polymers,general properties, 269_270 trap-ro-trap,105_107 rtbber,273-274 Droppingfunnel, 8, 30 sealingcompoun

Fusedquartz: fire cutoff, 249-250 ir-visible-uvtransmission, 244 healingcracks, 256-257 resistanceto fluorine,227 healingpinholes,255 thermal properties,243-244 metal-to-glassseals, 255-256 Fusedsilica, see Fused quartz ring seals,253-255 sealingevacuated tubing, 257-258 Galliumcompound, vapor pressure of, 299 sequenceof operations,247 Gas: test-tubeends, 249-250 cylinders, 166,210-212 T-seals,253 generation,207-208 Glovebag, 45-46,62-63, 64 generator,automatic, 25-26, 28 Glove box: measurement,26-27 , 29 antichamberdoors, 52-53 samplingtube, 26 commonoperations in, 65-66 separation,115, 105-107, 190-200 contaminationof atmosphere,51-56 storage,2m-202 evacuable,63 transferof: gloves,59-61 condensable,25, 27, 104-105 hazardousmaterials containment, 61-62 noncondensable,24-26, 113-1 16 maintenanceof atmosphere,54-56 seeaßo Inert gas materialsof construction,63-64 GaschromatograPhY: monitoringimpurities, 56-59 gasinlet valves,197-198 pump-and-fill,48 generalreferences, 209 purging,49-51 hydrides,200 Gold,27'7 permanentgases, 199 Grease,vacuum, 153-155 preparative,198 reactivehalides, 199 Halogencompounds, vapor pressure of.,299- sampling,194-198 300 Gauge: Heat-sealingplastics, 260 Bourdon,136 Helium, ultrapurification,82-83. Seealso cold-cathode,140-142 Inert gas diaphragm,137 High vacuum: electronicpressure transducer, 136-13'l definitionof, 118 high vacuum,140-143 measurement,140-142 hot-cathode,142 Hot-tubereactions, 42-43 ionization,140-142 Hydridewastes, disposal of,239 Mcleod, 13'7-139 Hydrocarbons,saturated, purification, 90- mediumvacuum, 137-140 91 Philips,see Gauge, cold-cathode Hydrogen,purification, 94 Pirani,139-140 Hydrogenchloride: spiral,136 purification,94 thermalconductivitY, 139-140 vaporpressure of, 300 thermionic,140, 142 Hydrogenfluoride: thermocouple,139 corrosionof glassby, 227-228 Germaniumcompounds, vapor pressure of, plasticapparatus for , 230,232 299 spectroscopiccells for, 233 Glass,properties of , 242-245 vaporpressure of, 300 Glassblowing: Hydrogenhalides, purification, 94-95 annealing,247-248 Hydrogeniodide: bendingtubing, 249 purification,94-95 closedcircuits, 255 vaporpressure of, 300 cuttingtubing, 248-249 Hydrolysis: end-to-endseal, 251-253 analysisby,26-30 equipmentfor, 245-246 apparatusfor, 27-30 322 INDEX

Implosion of evacuatedbulbs, 200 virtual, 14,3 Indium, 277-278 Liquid, transfer: Indium compounds,vapor pressure of, 300 betweenflasks,22-23 Inert gas: from metaltanks,20-21 detection of impuritiesin, 56-59, g3 Liquidair, 109-ll0 impurities in commercial,6g_69 Liquidnitrogen, 109-110 purification, 69-80 Lithium,sampling, 206 purificationsystems, 80-g3 Low-temperaturebaths, 109-1 13 Infraredcells: Low-temperaruredistillarion, 193-lg5 gas,184-185 liquid, 23-24 Manganeseoxide: low temperature, 186 finely divided,prepararion, 7g-79 specialized. l39 supported,preparation, 79-g0 Infrared transmissionof glass and qtartz,244 Marlifold: Iron,278-279 fluorine, 228-230 IR samplepreparation, 23-24 glass,high vacuum,100-102 Isoteniscope,175-176 for inert gasand vacuum,9-10 roughvacuum, 119 Joints: Manometer: ball-and-socker,l5Z-154 designs,129-131 cone high pressure,220 reading(s),132 flange,218-219, 221-Z2Z correctionof , 132-134,315, 317_3lg flare,216 Mediumvacuumr measurement, 13j-140 greasefor, 155 Meltingpoint determinations, lg3-1g5 greasrng!153-154 Mercury: knife edge,222 capillarydepression of, 132,134,315. 3lg O-ring, 154,156-160 cleaning,135-136 pipe thread, 220-221 cleaningup spills,134-135 Solv-Seal, 157,159 densityof, 315.317 standardtaper, 152-154 generalproperties, 134 swage,217-218 manometers,129-l3l wax for, 156 solubilityof metalsin, 134 toxicity,134 Kabez,274 trappingvapor,722 Kel-F,general properries, 269-270.See also vaporpressure of, 134 Fluorocarbon Metal alkyl wastes,disposal of,239_240 Kimax glass,see Borosilicateglass Metalhalides, anhydrous, purification, Kirchoff vaporpressure equation, 2g4 95 Kovar: Metaltubing: gen€ral properties,27 8-279 bending,214-2t5 seals,256 cutting,214-215 flarefitting, 216 Lead,279 O-ring fitting, 159,2t8-2t9, Z2\-ZZ2 Lead compounds.vapor pressure of, 301 sofder fitting, 215-216 Lead-throughs, seeFeed-throughs, electrical, swagefitting, 217-2lg through glass weld fitting, 215-216 Leak detectors,145-146 Methane: Leaks: purificationof, 208 dry box, 51-52 vaporpressure of, 295 locating: Molecularsieves: in glassapparatus, 143-146 gaschromatography with, 199 in metalapparatus, 146 low temperatureadsorption on, j2_.13, real,143 I 1-s_116 repairof, 144 wateradsorption, 70-73. 85-g6 INOEX 323

Molecularweight determination: removal: boilingpoint elevation, 38 from inert gases,74-80 freezingpoint depression,38-39 from solvents,8T-89 isothermaldistillation. 179, 180 Oxygencompounds, vapor pressureof, 303 vapordensity, 177 vaporpressure depression, 177-179 Palladium,279 Monel: Perfectdisplacement of, 49-50 generalproperties, 279 Perfectmixing, 49-50 resistanceto fluorine,228 Permeability: Mylar.270 dry box gloves,52-54, 59 glovebags,52-54 plasticsand elastomers, -260, Naturalrubber, 274 259 262-263 Peroxides: Needlesizes, syringe, 19 detection Needlevalves: of, 86 removalof, 86-87 metal, ?22-224 Phosphoruscompounds, vapor pressure Teflon-in-glass,164-165 of, 303-305 Neoprene,273 Pinholes: Nernstvapor-pressure equation, 284 detection Nickel: of, 145 repair.257 generalproperties, 279 Pipe-threadjoints, 220-22. resistanceto fluorine,228,279 Plasticizers,16,267 Nitrile rubber,272 Plastics: Nitriles,purification of , 91-92 bending,26l Nitrogen: cellular, 265-266 impuritiesin, 68-69 fabrication,260-261. liquid,109-l l0 264-265 generalproperties, 260 purification,69-80 machining,26,5 reacrivity,68, 206 permeability, scavengers,80 259-260, 262-263 thermoplastic, seealso Inert gas 260-261, 264-265 thermosetting,260 Nitrogencompounds, vapor pressure of, 301- welding. 303 260-261, 264 seealso generic Nmr samplepreparation, 23-24, 188 name of specific plastics Plastictubing: Nylon,270 bending.261 crimpseals, 261 Oil, diffusionpump. 122, 121 end-to-endseals, 261-26-5 O-ring: end seals,265 chemicalresistance of, 1-58-1-59,272-274 Platinum,279 joint, 156-157 Polyamideplastics, 270 propertiesof elastomersfor, 158 Polychloroprene,273 solventresistance of, 157-158 Polyesterresins, 270 Outgasing: Polyethylene,270-27 1 of asbestos,5l Polyfluorocarbo ns, 269-27 0 of cloth.51 Polymerpressure bottle, 230 of corrodedmetal, 51 Poly(methylmethacrylate), 63, 261, of elastomers.1.13 267 of glass.1,13 Polyolefins,270-271 of paper,5l Polypropylene,270-27 1 of stopcockgrease. 1.13, 162 Polystyrene,271 of wood,51 Polyurethane,foamed, 266 Oxygen: Polyvinylchloride, 267 detectionof, 56-59 Polyvinylidinechloride, 26'7 -268 preparation.207-208 Pop-bottletechniques, 41-42 324 INDEX

Potassium,sampling, 206_207 Safety: Pressure: disposalof reactivewastes, definitionof unirs,316 239_240 extrnguishingfires, measurement,129_134. 240 136_143 implosion Pumpingspeed: of evacuatedbulbs, 200 seealso Explosion calculationof pump_down hazards rimefrom. {g Sampling: olrruslonpumps, 122 alkali metals, limitationby appararus, 206_207 l2j_I2g gasmixrures, mechanicalpumps, 197_l9g 120_122 volatile rhroughput liquid mixrures,196-197 _ calculationwith, 12.1 Pumps: Saran,267-269 Schlenkware: arrangementof, 127 assembly, diffusion,l2l_124 3l_32 basicpieces, 30 mechanical,122, lZ4, 126_127 H-rube, Toepler,ll3_l15 39_41 purglngair from, Purgingair from apparatus: 31 rube,30_32 drybox,49_51 Sealedtube reacrion initial purge,7_g vessels,42_43,202_206 Sealing openvessels, g_9 evacuatedtubing. ZS7_25g Seals: Schlenkware, 30_31 glass: synnges,l0_11 end-ro-end, Pyrex,see Borosilicate giass 251_253 graded.2.15 Pyrolysis,analysis by, 2-00 ring, 253-255 gfass-to-meral. Quartz,see Fused quartz 255-256 glassT, 253 plastic.end-to-end, Rack for vacuumline, 103 265 Seleniumcompounds. Radon,vapor pressure vaporpressure ol, 305 of, 305 Jepta, Ramanspectroscopy, rubber,l4_17 lg7 Serum Reactionvessels: bottlecap, ree Septa, rubber Shortcircuit,4g-50 for anionradical generatron, 190_19i Siliconcompounds, for fluorine, 230_231 vaporpressure of, 305_ hot rube,42-43 307 Silicone: rnertatmosphere, 30 diffusionpump sealedrube, 43_44 oil, 122,124 grease,155 vacuum_linefiltration, 102, lg0_1g2 rubber,274 for vaporpressure titrations, _ 16g,lj2_l:/3 Silver,279-280 Reactivewasres, disposal ot, 239_240 Ketflgerants: Slushbaths, ll0-ll2 Sodalime Dry lce. 112-t13 ftap. Z2g_230 Sodium.sampling, 206_207 Iiquidnitrogen, 109_l l0 Soft glass,see Flint glass liquid nitrogenboil_off, 193,195 Soldering: slushbaths, 110_112 glass,256 Residualgas analyzers, 142_143 metal, Ring seal, 253-255 I 15-116, 228, 275_2.76 Solid, Roughvacuum: transferof, 3l_3-5 Solvents: apparatus,llg_119 cryoscopy,112 definitionof, 11g Rubber: detectingimpurities, g9_90 purification,84-g9. 90_92 generalproper ties, 272_27 4 storage,89,200_202 permeability,262_263 Solv-Seal, sepra,14_17 157,i59 Spacevelocity, 70 genericname ol specific ^t:l :lto rubbers Stainlesssteel: Kuotdlum.sampling, 207 generalproperties, 27g INDEX 325

resistanceto fluorine.228,278 Transrtronmetal compounds, vapor pressure Steel,278 of, 3l0 Stirrers: Traps: reciprocating.174 fluorocarbon.232 rotary,S glass.124-125 Stockvalve, 165 for low-temperaturegas adsorption, I l5- Stopcocks: 116 designof, 161 metal,229 greasing,162 soda-lime,228-230 improvingfine control, 164 volumecalibration of, 108-109 lapping,163 Trap-to-trapdistillation, 105-107 retainer.163-164 T-seal.253 Storage: Tubing: gas,200-202 metal,ste Metaltubing solvent,89.200-202 plastic,see Plastic tubing Styrofoam.265-266 Tungsten: Sublimation.36-37 generaIproperties, 280 Sulfurcompounds, vapor pressure of, 307- to glassseals, 255-256 309 Tygon,267 Sulfurdioxide: purificationof, 95, 208 Ultraviolet: vaporpressure of. 309 cells,2,1 Swagefitting, 21'7-218 transmissionof glassand quartz.244 Syringetechniques. 13-24 U-manometer,129-131 Uraniumhexafluoride, vapor pressure of. 310 Tantalum,280 Teflon: Vacuumgauge, see Gauge generalproperties, 269 Vacuumline: sleeves,l53 arrangementof components.100-i03 tape. 220-221 generalpurpose, 99-100 seealso Fluorocarbon greaseless,l02 Telluriumcompounds, vapor pressure of, latticefor. 103 309 metal,22'7-232,335 Tensimeters.168-175 plastic,119 Teslacoil, i45 simple,99-100 Test-tubeends: Valves: glass,249-250 attachingto apparatus,225, 227 plastic,26l ball.224-226 Thalliumcompounds. vapor pressure of, bellows,223-225 309 diaphragm.223-224 Thermaltranspiration. 17 0-17 I gate.224-225 Thermistor,180-181 needlevalves, 222-224 Thermocouple,182-183 packedmetal,223 Thermometer: Teflon. 233 mercury-in-glass,179 Teflon-in-glass,164-166 pentane-in-glass,179 Vapor pressure: vaporpressure, 179-180 characterizationby, 113 Thermoplastics, 2ffi-261, 264-265 correlations,286-288 Thermosettingplastics, 260, 265 estimation,286-288 Three-needletechnique, 17-18 measurement,113 Throughput,124 of purecompounds, 289-311 Tin compounds.vapor pressure of,309 tabulations,290-311 Titration,tensimetric, 172-17 4 thermometry,179-180 Toeplerpump, 113-ll5 titrations.1'72-175 326 INDEX

Vaporpressure equation: Wastes: Antoine,282 radioactive,bagging.62 four-parameter,283 reactive,disposal,239-240 Frost-Kalkwarf,284 Water: Kirchoff,284 detection,56-58, 89-90 least-squares,derivation,285 purification,90 Nernst,284 removal: two-parameter.282 from inertgases,70-73 Vibration: from solvents,85-89 effecton gauges,137 vaporpressure of, 287,303 reductionof,102,121 Wax,vacuum, 153-154, 156 Visible: Weighingtubes, micro, 31-32,34 cells,24 Welding: transmissionof glassand quartz,244 metal,275-2'16 Viton-A, 273 plastic,260-261, 264 Vycor: Xenoncompounds' vapor pressure of' 311 ir-visible-uvtransmission. 244 thermalproperties, 243-244 Zinc compound,vapor pressure of, 311