ALUMINIUM NITRIDE and RELATED MATERIALS a Thesis Presented

University of Plymouth PEARL https://pearl.plymouth.ac.uk

04 University of Plymouth Research Theses 01 Research Theses Main Collection

1970 THE FORMATION AND REACTIVITY OF ALUMINUM NITRIDE AND RELATED MATERIALS

COLES, N.G. http://hdl.handle.net/10026.1/1953

University of Plymouth

All content in PEARL is protected by copyright law. Author manuscripts are made available in accordance with publisher policies. Please cite only the published version using the details provided on the item record or document. In the absence of an open licence (e.g. Creative Commons), permissions for further reuse of content should be sought from the publisher or author. ALUMINIUM NITRIDE AND RELATED MATERIALS

A Thesis presented for the degree of

DOCTOR OP PHILOSOPHY

of the

COUNCIL FOR NATIONAL ACADJMIC AWARDS

London

No G„ COLES, MoSCo

Depajrtment of Chemistry^ The Fblytechnic, Plymouth, August. 1970 " ^.500214

CLOSS T Fk^. l-U CoL No. Abstract

The preparation and properties of aluminiuin nitride are reviewed v/ith special reference to the nev/er production methods and fabrication techniqueSo

Information so far available on the sintering of materials is summarised. For nitrides the sintering is influenced by additives or impurities such as oxides formed by partial hydrolysis and oxidationo

Resistance to oxidation is increased by sintering and hot-pressing the refractories.

The kinetics and products of oxidation of nitrides so far studied depend mainly on the intrinsic reactivity of the material and available surface at whi.ch oxidation can occur.

In the present research conditions are investigated for preparing aluminium nitride from ammonium hexafluoroaluminatCi, The x-ray characteristics and the thermal stability of a new compound, ^-AlP^ are established. Attempts to study the kinetics of the commercial methods of aluminium nitride formation are summarised. The reactivity of aluminium nitride is examined by correlating changes in phase composition, surface area, crystallite and aggregates sizes with hydrolysis and oxidation time and temperature. The kinetics and rates of reaction are influenced by the crystallite and aggregate sizes of the aluminium nitride, by differences in type of crystal structure, by the molecular volume of the oxide products, and by fluoride additives. Ageing and sintering of the aluminas are additional factors* The activation energy of the oxidation of aluminium nitride in air is determined as 53 k>cals/molec Acknowledgements

I wish to thank Dr« A« Bo Meggy for the helpp comment and general

supervision of this worko I also yrish to acknowledge the helpful discussions I have had with Dr* D© Ro Glasson, Thanks are also due to

Miss lo Gratton^ the Polytechnic Ldbrariarip and her staff, for their patient and willing cooperationo The help of Mr, Tapper with the

computation has been gratefully appreciated., I would also like to

thank Mrso Eo Adams, JoAoCa^ A, Down^ Dro So A. A, Jayaweera and

Mai^garet Sheppard for their assistance and cooperation. I am indebted

to the Governors of the Polytechnic for the research award and the

facilitieso

Finallyp I would like to express my thanks to Anne for her

understanding and encouragement throughout this work*

ii Ta.bles

1. The effect of vajrlous media on aiijjniniujn nitride^ 9

2. The lattice parameters of alujiiira.\iin nitrideo 11

3« The heat of forniation of aliJininium nitride. 13

The decomposition temperature of aluminium nitride„ 15

5» A canparison of the mechanical p.roperties of al^jminium

nitride with certain ceramcs, 17

6. The tiierraal expansri.on of certain materials- 19

7o A compari.son of the cr^'stal structures of certain

materials. 20

8« Ammonium hexafluoroaluminate heated at 220°G in dry air. 63

9« Ammonium hexaflucroaluminate heated at 3hO^C in dry air, 64 lOo Comparison of the observed and calculated d-spacings for ^ -AlP^o 66 11. Comparison of d-spacings of ammonium hexaifluoroaluminate heated in moist air for various times with Y-AlPjj, some basic fluorides and aluminium hydroxide» • ^ 68 12- Ammonium hexafluorcalumi.nate heated at "lO'^C for 18 hours in dried air. 71

13*> AmmoQium hexaiT-uoroaluminate heated^in dried ammonia at 960"C for 1 hour and cooled to h-00 C in ammonia. 75

14. Compari.son of the observed x-ray intensities of ammonium he.xafluoicaliiminate heated at 960 C in variou;3 flow rates of ammonia. 79

15- X-ray data of basic fluorides and alumir^Lum fluoride hvurates. 83

16. Comparison of the d-spacings of tiie reported S -AlF,

and I^ -AIP^. I du IJo Lattice parameters of some complex hexafluorides* 86

XIX 18. (a) Infra-red analysis of the thernial decomposition of

ammonium hexaLfiuoroaluminatea 58

(b) Density of some aluminium compounds • 89

19. Intsratomic distances in (j^..-aluminium fluoride and related compounds. 93 20o Comparison of the crystal properties of AIN v/ith

possible impur-ities in the Serpek pnDcesSe 99

21* X-ray analysis of hydrolysed aluminium nitride. 118

22. Infra-red analysis of hydrolysed aluminium nitride. 119

23o Activation energies of aluminium nitri.de and related compoiinds^ IZ4.3 24- A comparison of the rate constants of milled samples

at various temperatures. 149

2^. Aluminium nitride heated at 900°C for 96 ho^jx-s« I56

26. Silicon nitride heated at 1000°G for 96 hoi:rs. 157

27o Variations in aggregate sizes during the conversion of

AIN to iX -^-^2*^3 at 1000*^0 in air. l62 280 Free energy of formation of aluminium carbide from the reaction of alumi.n-a and car^bon. 130 1. The change in conductivity of AlP^ solution when adding NH^F solution, 192

2, (a) The Van-Arkel arrangement a

(b) Determination of the knife edge angle of a 9 cm povrcLer camerao

3« The percentage v.-eight loss of aruj:onium h'.y r-Quoroaluminate h-?att^ "in dried air for various tefnoeratures and times. 39

I it 13 \J. t - .0

(b) Differejitial -uheraal ar-.^aiy:^!of V|'-..i^'\..

6o The -ihtinnal decomposition of amironiv-^ hev'^fX>Jorcgallate, 7-

.-,mi:".c

(a)- (d) The fijTimoni'jir. rctrafluororoiumin^ire/-aluminium flucjri.oe o-.y'.t-ll-:^-j--:>iic - j..'^ ti'.:.. ^1,

atcr.-dc arror:gan'cnt ino<^-/'l?^o

9b (b) The atomic arr.-»xif;cr-ent in .'Jl.o

IG. (a) Electron diffraction pattern of the aluminium fiirr, lev (b) :ile:;tron dj.ffraction pattern of th-: ' r.7z*-]^. dr-c' aluninium .filrPo

(a) Electrrjr^ mi'::r:.

1'h-: ci-r.r;- ^r. , -^.r.j '-'U- 3'^riace during trie nrdxiing of alun^^ r.iMi:; --iit :d d^c 115

(b) m±il-'.ng of aluminj'^m r.itrldec

13. (a)- (d) Comparison of the -specifa.c surfac-i. surface are; and average CiystaJlits si^'.r. \7i:;h perr:^r.-^ag^: h>'droIysi£. lit-. The percentage conversion of aluminium nitride to oC-alumir^ at various temper^tursso 132

15. The percentage conversion of alumini-am nitride heated at 930 C for 3 hours. I36

16• (a) A plot of fi.rst-order kinetics v/ith time for vajrious temperatureso 138

(b) A plot of log t (time) wi.th log x (x is % conversion)^

17. A plot of y against timeg t, at 905*^C. 139

18. A plot of 2^ and y against timej, t, for periods up to 30 hours, 141 2

19o A plot of Z against timer t, for various teinperatures. 1A4

20» Arrhenius plot for the oxidation of alumini--^ nitride. 145

21. The effect of milling on the oxida.tion of aluminium nitride at 872 C. I5I 22. The effect of milling on the oxidation of aluminium nitride at 905 C. 152

25o The effect of aluminium fluoride on the oxidation of aluminium nitride. l^h-

?.L*~ Srrnie electron micrographs of alumijiium and silicon 158- 27, nitrides and oxidised samples. I6I

28* Comparison of the rate of oxidation of AlN at lOOO^^C with the change in (i) specific surface, (ii) the number of crystallites^ (^'/g) p (iii) the average cr^'stallite size. I63

29. Comparison of the oxidation of aluminium and silicon

nitrides,. I66

30. The free energy of formation of some nitrides. 173

31. A comparison of the free energy of formation of AlN from its elonents. 175 32. Free energy of formation of AlN from various methods of

preparation. 177

33. Plot of against oC (p^^ or V-^) * > 178

34. Comparison of the free energy of the formation of oC-alumina and silica from the nitrides. 184

vx OONTmTS

Abstract mo oo o <> .o oo o <> oo oo oo o. i

Aclaiowledgements •<> o* co oo r. .<> co «. •<> ii

Tables oe ou oo o o o o .o OD oo o> oo oa oi Hi

Figureso. o« o* «. , <, .o v

CHAPTER 1 Literature survey of alijminium nitride and related rna-terials

1,1 Tj}^_formation and chemical properties of aluminium

nitride »c .e «• en oo oo oe

I^lei The formation of aluminium nitride .o o - * 1

I»lc:i(a) The formation of aluminium nitride from its elements 1 I,l.i(b) The formation of the nitride from the decomposition of alumina v/ith caxbon in the presence of ammonia or nj.tmgen lo .o o. o. «« »» 2

I.l.i(c) The thermal decomposition of ammonium hexafluorc-

aluminate in ammonia oo .o c ^ oc c 4

I„loi(d) l.iiscellaneous methods of preparation <>• «o ». 3

1*1.ii. The chemical properlles of aluminium nitride .* 7 I^2 The cryatalloaraphy and the heat of formation and thermal, stabi3.ity_of^ aluminium nitride lB2oi The crystallography of aluminiiom nit ride«« 10

Ig2oii The heat of formation and thermal stability of aluminiiim nitride oo .» oo .o .o .o 12

I«3 The physical and mecb^anlcal proper-bies of aluminium nitri.de and related materj.als

Io3oi The physical properties of aluminium nitride oo lit-

1*3*31 The mechanical properties of aluminium nitride and related materials .o ... ,o .o o. 16

I«4 The fabrication and uses of aluminium nitride and related materials

Io4oi The fabrication of aluminium nitride .o .. 21

I.4oii The uses of aluminitim nitride and related materials 23

I^eferences to Chapter loo oo -

II. 1 The preparation of ammonium hexafluoroaluminate 34

II.2 Chemical Analysis ... «o oo 35

II o3 Thermal Analysis

II.3«i Thermogravimetric analysis .o •« .o .» 35

II.3.ii Differential thermal analysis .„ .„ .« <,* 36

II.4 Infra-red Analysis oo o. o. oo .. •• 37

IIo5 X-ra,y Analysis

II.5«i Powder diffractometry c- o. o. 38

II.5cii Powder camera .. o - <.« . <. •» <. 40

II.5»iii Errors in powder photographs •„ .<> o. .o «c 40

II.6 Electron micrxjscopy oo oo .« co .o »o 43

II .7 Estimation of particle size

II*7«i Electron microscopical technique o^ 44

II.7»ii 'Optical microscopical techni.que .«. oo e. .o 45

11.8 Surface area measurgnentsa. o* oo oo oo «• 45

11.9 Ba31 millinR oo o. 47

11 ^ 10 Experimental techniques used in prepaiinp^ aluminium nitride

II. lOoi Preparation from anmcnium hexafluoroaluminateo» *. 48

IlolO.ii Preparation by the Serpek reaction •« .c 50 n.lOoiii Preparation of the nitride from its elements oo .o 54

References to Chapter II .- .» 56-

CHAPT-ER III The formation of al.umin.ium nitride

III. l The thermal decomposition of ammonium hexafluoroaluminate in_ various atmospheres Illol.i The thermal decomposition of ammonium hexafluoro• aluminate in air oo oo oo «o o. •« 58 Illol.ii The thermal decomposition of ammonium hexafluoroaluminate in aanmonia .<> oo .. .• «. 72

Ill.loiii X-ray analysis of ammonium hexafl-uoroaluminate 85

Illoleiv The structural rearr-angonents during the formation of aluminium nitride by the thermal decomposition of ammoniimi hexafluoroaluminate .o o. «« 85

111,2 Th.e formation of ^aluminium nitride^by the Serpek process 96

III o3 Th_e fbrmatLon of aluminium nitride from its elements 101

III.3.i Kinetics of metal nitri.dation .» o. .<> 101

III^3-ii The formation of the nitri.de from its elements .„ 102

References to Chapter lllo» 108- 110 CHAPTER IV The reactivity of aluminium nitride

Ij^-troduction .o .o .o Ill

IVcl*i The hydrolysis and oxidation of nitrides.. 113

IVol.ii Materials e. .o on oc 11^

IVo2 The hydrol.ysis of alumini.um nitride

IV.2.i The hydrolysis in water ©. .o 116

IV.2oii The hydrolysis in steam .« .„ 122

I\r^3 The oxidation of al.uminium nitride

IV.3^i The oxidation reaction .» 124

IV«3oii The rate laws of oxidation •<> 125 r/.3.:_ii The kinetics of the oxidation of aluminium nitride.. 126

IV.3*iv The effect of particle size on the rate of reaction IZ^B

IV.3.V The effect cf impurities on the oxidation 150

IVo3,vi The change in surface properties during the oxidation of SLluminium and silicon nitride .. «. 153

References to Chapter IV ,«, .o .o ... 167- 169 CHAPTER V Therroodvnamical aspects of the formation and reactivity of aluminium nitride

V.l The formation of alujniniujn nitride o o o o »<, «« 170 v.l.i The formation from the elements o» oo 172

V.l.ii The formation from the Serpek reaction . „ <>• 17^

Volciii The formation from the aluminium halide derivatives 179

V.2 The reactivity of alumi.nium nitride

V«2.i The ox±dation of aluminium and silicon nitride 183

References to Chapter V co .o -o «o 186

CHAPTER VI Concluding summajry and sufi^estions for fur^er v/ork 187

APPEN-PICES

Appendix I Preparation of ammonium hexafluoroaluminate 189

Appendj.x II Methods of Chemical Analysis 19^

Appendix III Computer program (NGITO) in Fortran IV for the lEM 1130 - Estimation of cry stall ographic parajTieters 205

Appendix IV Computer program (FODH) in Fortran IV for the imA 1130 = Estimation of surface areas 208

Appendix: V Computer Program (NICKIT^ETIC) in Fortran IV for the im JI30 - Estimation of kinetic paj?ameter3 212

Appendix VI Reprint- The formation and reactivity of nitrides pELTt HI, BoroHj aluminium and silicon nitridesj^ J.Appl.Chem., 1969, 19, 178 2124-

Appendix VII Thermochemicai Data 219 CHAPTER I Literature survey of aluminium nitride and related minerals

The survey is divided into four sections as listed belov/:

1. The formation and chonical properties of aluminium nitride.

2. The ciystallography and the heat of formation and thermal

stability of aluminium nitride.

3o The physical properties of aluminium nitride.

4. The fabrication and uses of aluminium nitride, lol The formation and chemical properties of aluminium nitride

I.loi The formation of aluminium nitride

The preparation of aluminium nitride is confined to four main processes;

(a) The formation of the nitride from its elements.

(b) The fonnation of the nitride from the decomposition of alumina

with carbon in the presence of nitrogen, i.e. the Serpek process.

(c) The thermal decomposition of ammonium hexafluoroaluminate in the

presence of ammonia.

(d) The thermal decomposition of the aluminium halides^ hydride and

sulphide with ammonia.

I.l.i(a) The formation of aluminium nitride Vvom its elements

The solubility of aluminium for nitrogen has been discussed by many authorsj, and it is the key factor to this method of fomation.. Pitcher

(l) and others (2-43: 139 157) have reported that at temperatures between 530 and 820^0 aluminium absorbs nitrogen to give the nitride, although the reaction appeared to be more vigorous at 1300-1400°C. These statements were contradicted by Claus (6) and Laffite et al (8) who concluded that nitrogen was almost insoluble in aluminium both in its liquid and solid state* Rontgsn and B.rau^i (7)..j hov/ever,^ stated that although nitrogen i.s almost insoluble in aluminium in the crystalline state'^ the absorption increases v/ith temperature* The preparation of the nitride using ai/imonia inste.ad of nitrogen has also been studied (l5)- The use of ammonia to nitride steels is well knowr^ and th*^ resultant formation of aluminium nitride in fully-killed steels has been established.

The earliest reference to formafion of the nitri.de from the elements is the v/ork of Briegleb and Gerjther O-O) i-i"' 186^ v/ho stated that EtLuminium nitride is formed when "aluminium tu.mings are heated in an atmosphere cf nitrogen"- Arous (ll) stated that if aluminium is heated by electrical current in the presence of nitrogen^ aluminium nitride is formed,

Ali.jninium nitride was formed (l2) when ali^minium was burnt in oxygen^ and nJ.trogen sabstltuted for oxygen v;hile the aluminium is still burning.

The pu.ri.ty of any nitride formed by this method is questioned„ as the presence of al'jmina is anticipated., The formation of crystals of the nitride from its elements at elevated temperatures is reported (l20).

The use of a catalyst v/as introduced in 1953 (l6), Finely-divided alumijiium was heated v/ith 1- 3 wtopercent of a fluoride catalyst in the presence of nitrc-gen to give alirniinini.tride* Long and Foster (l7) have stated that high purity nitride can be made by striking an arc bet\veen tv/o pure aluminium electrodes in a nitrogen atmosphere^ vdth a final treatment in argon to increase its stability towards water*

1.1, i (b) The formation of the nitride from the decomposition of alumina

vrith carbon in the presence of ammonia or nitrogen

This method v/as extensively investigated by Serpek (45) in 1914^ and was later to be known as the Serpek process. Prior to Serpek^s v/ork^ Caro (30) using aluminium carbide prepared the nitride^ Although this process proceeds efficiently at high temperatures^ it was found that very little nitride was formed at l600*^C and sulphur dioxide was detrimental to the process (3l)» The Serpek process has been discussed by a number of authors (32-43)5 Prankel (44) stated that when using producer ga^ instead of nitrogen^ a higher temperature is required.

The nitride, according to the Serpek reaction, is best formed by a mixture of nitrogen and hydrogen (45). Carbo-nitrides have been formed during this process (46)0 The earliest reference which is related to this method of preparation is reported in I876 by Mallet (47)o Aluminium was heated in a carbon crucible and impure aluminium nitride was formed.

Various additions to alumina in the process such as zinc chloride, ferric oxide (43)5 and iron (49) used as catalysts, have been reported as benefiting the formation of the nitride. A vitrified refractory consisting of alumojia and aluminium nitride has been reported v/here the method used was to heat the materials in a graphite crucible at about one hundred degrees above the softening point of the refractory (50) <,

Crystals of aluminium nitride have been prepared according to the Serpek pzx)cess (51)- The revival of the process by Pechiney (52, I64) in 1956-73 led other people (56) to re-investigate the processo The nitride has been prepared by this method using calcium aluminate as a binder (53-55). V/hen alijmini'om nitride is prepared by zhe Serpek process „ the product is impure and has been known to contain up to 12^ carbon (102)« Methods have been described for removal of such impurities (101-5)c

More recently the Serpek process has been adapted using a nitrogen plasirasourcs (59;, 9Sc, 99) c I.l.i(c) The thermal decomposition of ammonium hexafluoroaluminate in ammonia

AmmorLium hexailuoroaluminats ( (Ml, )-,AltV) can be oreoared from molar

scV;.tions of aluminium chloride and ammonium fluoride (78).

6NK,^P + AlCi^_ {m^)^AJI'^ + 3NH^C.l.

Th_is ariimonlixn complex can also prepared from ammonium fluoride and

freshjy preclpitattd aluminium hydroxide (79^ 96. 97)= The salt has

been mentioned as a by-product of va^^ious other reactions, such as the

anrnionation cf phosphoric acid (Bl) ^ anion exchange in clays (82)5 the

formation from alumina and ammonium fluoride (89, 83)? the formation

from aluminium nitrate and ammonium fluoride (79).'! and the formation

from ammoni.um al-am and hydrofluoric acid (5) , The complex is the

ammonium salt of flucrcai^-iminic acid cr hydro-fli^-roaluminic acid^ as it was previously known (83)o Desnite its obvious association with

cryolite (Na^AlF^), ammoniijm hexafluoroaluminats is related to perovskite

and the potassi>m:i hexaflucroplatinate (K^PtCI^) in its structure (8if).

The exi.st'ence of ammoni.um hexafluoroalumina-*-* has been verified by

a r;.^ber of authors (85-39^oWien heatc-d in amn* a it decomposes in stages

to alumi.nium rd-trideo The stages are summarised as follows:-

(NK^)ÂIF^ ^!}bs> ^îÂlF^ (1)

NH^AIP^ ]^ AJF^ (2)

AlF, AUJ (3)

In Lhe pr-asent work« th*? temperatures at- v/hich these reactions occur

i.3 found to differ from the results of Shinn et al (90) and Maak (9l)-

Rear-tlon temperatures according to Shi.nn et al:

(1) 1-0°C (2) 300°C (3) 720°C Reaction temperatures according to Maak:

(1) 300°C (2) 600-700°C (3) 800°C

Shinn et al also reports the existence of *|^-A1F,.

The decompositioncf thefluoroaluminate to form aluminium nitride

has also been s udied by i^'unk and Boehland (93).

I.l,i(d) Miscellaneous methods of preparation

There have been reported various methods of preparing aluminium nitride

which do not appear to have a wide commercial application, but are reported

here ^.s nossible alternatives the more common methods. Perhaps the most noted of these methods is the reaction of aiihydrous aluminium chloride v^th

ammoniaj knovm as the Grov/i.. ^i-ocess. This method is princip.ally used

to prepare sin^e crystals of aluminium nitride which are to be used for

electronic devices,

Tiede et al (57) reported that when animonia is passed over pure

aluminium chloride the monoammoniate is formed, and when the salt is

decomposed onatungsten spiral at 1000°C aluminium nitride is produced.

This process has been studied more recently by Renner (58), v;hose results

confirm the work of Tiede and others. This method can also be used to

prepare the nitrides of silicon (63* 66), boron, gallium and indium (!8',

and it has been adapted by Bopper (60) , in his study of the formation

of non-oxide coatings by pyrolysis. The method has also been used to

coat various ceramic materials with aluminium nitride. If the temperature o

is raised to 2500 C, it is reported that al-omdnium nitride of high purity

and desired particle size can be prepared from the chloride and ammonia

(62). It has been observed (6k-) that if aluminium is reacted with the

aluminium chloride mono-ammoniateg an aluminium chloride-aluminium

nitride complex is foimeds

AlC.l^I'JH^ + Al AiCl^. AU'I +

which is apparently so stable that it does not decompose when strongly

heatedo It therefore may v/ell be that this compound is more resistant

to oxidation than the pure nitrldeo

V/iberg and May (65) have reported that aluminium nitride can be

produced from the addition compound of aluminium hydride and amnonia.

The reduction of hydrides using ammonia has recently been studied by

Berg et al- (66) using silicon hydrLde^ Components v^hich sLre corrosion-

resistant and v/hich possess mechanical strength have been prepared from

alumir_ium hydride and amnonia or nitrogenp using such processes as slip

casting^ extniding, or hot pressing (67)0

Aluminium nitride has been prepared in a non crystalline form by

passing dry ammonia over aluminium phosphide at 1000-1100 C (68).

AlP -f. m-^ AITJ + +

The phosphorus produced by this reaction-condenses in the system. It is

removed by passing an excess of nitrogen through the system at 1375-

1600°C, The phosphorous is carried away., separated fixan the nitrogen,

and reacted vn.lh aluminium powder at 1250°C to give aluminium phosphide.

The phosphide can be returned to the system^ thus making the process continuous (69)*

If ammonia is passed over aluminas heated at a lOOO^Cj aluminium nitride is formed (70)« However^ the product is in5)ure due to formation of oxy-nitrides (7l)o This preparation is questioned as it is

thermodynamically unfavourable at a 1000°C« There have been early reports that if aluminium sulphide is heated in nitrogen^ aluminium^nitride is formed (72^ 73)o Borchers aJid Beck

(7^) have reported a process involving electrolysis. Impure nitride is formed when mixtures using pov^dered aluminium are nitrided (l8); when liquid suLuminium is nitrided (iS) g and also by the themial evaporation of aluminium in vacuo (2), presumably due to the presence of residual nitrogen* Aluminium nitride can be prepared industrially by nitriding a mixture of aluminium powder with ^Ofo aluminium nitride

(20). High purity nitride has been prepared by nitriding aluminium, aluminium nitride and aluminium fluoride mixtures (22-24). The fluoride o is used as a carrier or catalyst and volatilises at 12^00 C. Aluminium nitride is formed by nitriding aluminium alloys, principally iron- alumini\im (Zk) p silicon-aluminium (26), aluminium-zinc (27)5 and lithium- aluminium (91) alloys. The combustion of aluminium with nitrous oxide

(28) and a nitrogeneous organic chemical^, such as the thiocarbamide (29) to form the nitride have been reported. Aluminiiim nitride has been rormed from aJLumina using a nitrogen plapma jet (lOO) or by heating aluminium phosphate and carbon (75)2 ororthoclass (76) in an atmosphere of ni.trogen. Jander and Weiss (77) have reported that stannous nitride and alumi nium bromide react together to form aluminium nitride.

I.l.ii The chemical properties of eiluminium nitride

It has been reported that when aluminium nitride is heated in air i.t turns grey. It was also reported that aluminium nitride hydrolyaes to give the hydroxide (56114) s and the action of dilute sulphuric acid results in the formation of aluminium hydroxide. Hardtung (IO5) reported that hydrogen does not react with aluminium nitride. The origi.naJ. observation of Mallet that when aluminiinn nitride is heated to rridnizss it deconiposes to give aluminaj was confirmed by Pitcher (l06)c

Pitcher and SpengeL (IO7) in 1925 reported that dry halogens reacted slowly th aJ-uminiiim nitride- and in fact at 760°C aluminium nitride forms ^he chloride in the presence of chlorine. Bromine is observed to reacb slowly wi th Ihe nitride only at high temperatures (56), Contrary to these reports 3 Flament (IO9) has observed that the halogens do not r^ac*. vri.th aluminixjJD nitride, but no physi.cal conditions were given^

Bradshsw and Matthew (110) reported in 1958 that the nitride o?ddize3 ir. oxygen at temperatures greater than a thousand degrees,

Taylor and Lenie (ill) have studied the properties of aluminium nitride extensively (see Table l)^ and have reported that it is not highly resi.stant to corrosion by mineral acids, and it starts to oxidise in ciir at 600°Ct A review of the oxidation of aluminium nitride in different atnespheras and teraperatureSjj and for varying intervals of time^ has been dsscribed (112), and will be compared \7ith the present \Jork. later*

AlJiniiiijja nitride has been produced v/hich is in fact stable to moist air (115)0 The oxidation of the nitride was investigated in 1962 by

Cooper .^t ,al (1^5)5 'our the act^ varion energies for oxidation vary ccni^di=:T-ab';y even for the sane specific surface^ The oxidation is said

-.0 follow a parabclic law.

8. Table 1

The effect of various media on aluminium nitride

'"ater Acid Alkali Miscellaneous !\ef erence rfecomposes Attacked by D'rcomposes Gaseous chloiine (177)

concentrated caitpletely. at nomal pressure

sulphurrlc. decomposes it acid» completely.

Hydrolyses ( 78, llO

easily with

NaOH.

Resistant to Decomposed (:82'

comjnon acids. by NaOH.

Partially Resistant to B^O^ (111)

resists molten aluminium

lineral aci ' 3 and cryolite T-Ia-^AIF^,

Deccmposes Ko effect v/ith (ISO ^ 18^)

P --^'imposes in hot chlorine, bromine

in hot coi c ' JaOK or iodine.

liNO^, ^3^4 Unaffected by (117)"

molten aluminium,

Iran or silicon.

9. To2 Tiie^j^rvst^lJ-O^r^ th^_ beat^ of fonp-atiof. and thennal stability of

ajujainlun: nitride

I • 2oi The :^'^".^^^\p_fi^"^P^ aVjmi.niAun nitri.de

The c}"ystal sfcr'.ictiire of aJvjn.Lnluin nitride was first studies by Ott ilPy) ir, '}3?.U.o Ha reports thar it crystallizes in the hexagonal system wi*}\ a c/a ::^tio of 1.601 anr5 an aLvimin:3.iun''nitrogen inter-atomic distance of IQS'P^. ji. The ionio charges In single cr/stala of aj.uminiura nitride he.vt b&e-ii s';-j.di*id (130)^ and *.he ele.?ironic structure has been discussed

{'LM)O The uii;:.t cell dimensions were later repoi-ted by a number of wo-yer5 (733 lil^ 122, 128y 132-6)(sse Table 2). The term^ ideal wurtzite

r-;oi;jr^^^ (l,»e. hexagonal stmcture of zinc sulphide), }ias been used to desc.r^.be aluminium nitride by several authors (ll7j, 123)^ but I^irry et al

(157) frcm thei.r structural invesTii.gatic'ns of a2.uminium nitride, confirmed trie early proposals (129) and revealed a distortion along the c-axis and the s:'--ro.cr,ora of the rJ.tri.de has latterly been compar*ed with the ZnO

sr.r^^^U-ii^. The influence of the bonding i'oixies on this deviation from an ideal atrjotar^ r^s been 3tudi.ed by Zndanov and Brysneva (136).

Da^a ^las been published on the existence of cubic aJ.uminium nitride

la - UlOu X) form-^d by nitriding a steel containing aluminium (94)9 but

the formation cf a cable nitride is questioned by Kohn et al (iJ.S).

HCT^/evsv-j when the nitride is subjected to high static and dynamic pressures a modificat;lon of the str.icbjT^ is observedo but no conclusive evidence of a possible wirt-zite-sphal.erite transfcmation is reported (9). Table 2

The lattice parameters of aluminium nitride

a CX) c a) c/a ratio Reference .-. 3.113 1.601 (132)

4.965 1.599 (132)

1.600 (133)

^;.\0 * 0.1 4.963 0.01 1.601 (134)

3olO + 0.01 4o968 + 0.01 1.602 (122)

z,„980 1.601 (111)

%110 + 0.002 4.980 ^ 0.002 1,601 (135)

3.05 + 0.02^- 4o93 ± Oi06 1.601 (128)

/,.968 1.595 (78)

11 I«2«iX J^^:^£x^^.L jlpJ'mation and thermal stability of aluminium nitride

The heat of formation of alinniniian ni.tride has been studied by a number of v/orke.T-s exteiding over a period of some Tifty years, Matignon (139) in was the first to look at tbis featitre., Six years later, Moldenhawe

(lAO) again locked at the heat of formation, but no results are given in the literaturfio Prescott and Hencke (li+l) quote a figure of "80»43 k.cal/mole

(see Table 3). Mellor (97) gives a value for the specific heat of aluminium nit rn.dc a=>

0 0.1803 + 2.750 X 10 ^ T + lo93/ x 10 ^ T^

TJV5.3 tsrm i.nvclves a power cf 10 ^ and later expressions do not involve any Verms smaller than 10 Prom Table 3 there is a wide range of values for the heat of foimati.ono This is probably due to the experimental methods used by each av:thor. For example Weugebauer et al (147)s using a bomb oalorimeter, gives a value which is in agreement with Sato (143)5 whereas

Ne:.'iiimamm ^t_al (1^2) vised sodium fluori.de as a "catalyst". Apin et al (I48) usftd alijmini'im and lead nitrri.de in an explosive method to determine the heat of formation* Schissel and V/illiaras (149) deduced their value using the mass"specti:i::metry third lawo Fran Table 3 a statisti.cal analysis suggests that the heat of foTTnation is in the region of -7b koCals/mole.

Y/smer (ihB) for the reaction of the elements to give aluminium nitri.de at 1800°G reports a value of the equilibrium gas constant (Kp) as log K.p :^ l^hBo Kubaschewski and Evans (I50) equated the free ener^ of for.mation of All^ ass

G -^154,000 ^ 44.5T for the eqiiaticn 2A1 + --^ 2A1N.

12 Tabj.e 3

The heat of fonnation of aluminium nitride

AHp^g kcal/mvol« Referen.-^e

80.^,3 (lU)

-3'.^ (142)

-?..7 (143)

^6L,0 (144)

-64o0 (145)

-:-fS,i.7 C.20 (147)

-5"o6 (lifB)

-63.0 (149)

^76.5 1 1-0 (150)

7i.O (180)

13. Olette and ^^me.Ancey-^^oret (l5l) in a recent article have

studi-d the variation of free energy of formation of the some oxides and nitrides, among them aluminium nitride.

It has been reported that aluminium nitride has no melting point and dissociates in the range of 2200-2400°C in agreement v/ith the equation:

In fact, no melting has been observed as high as 2700^0 (158). The vapourisation behaviour of aluminium and boron nitride has been studied using an effusion method (132)^ This method appears to be complex and not totally relevant to the present studies, llah et al (153) have shown from their thenriodynamic calculations, that aluminium nitride is stable at 1727^0 (2000\) which agrees vrith established facts. The vapourisation pressure (l54) and the decomposition of aluminium nitride - (154» 160, l6l)

have been studied. The activation energy of sublimation for gallium nitride has been studied using mass spectrometry methods (l55). The vapourisation behaviour (155, 159) and the kinetics of vapourisation of aluminium nitride have also recently been discussed (156).

1.3 The physical and mechanical properties of aluminium nitride and related materials

1.3." The physical properties of aluminium nitride

Several nitrides including aluminium nitride have been placed in a diamond shape pattern and theories put forward to relate their properties v/ith reference to their positions in this table (l24).

llatignon (37) stated that aluminium nitride does not melt, but in fact dissociates at 2200°C. Herzer (II5) in 1927 reported that it decomposes at greater than 1400°C, and since then various research v^orkers (106, 111, 117, 14^ have reported the decomposition temperature

14. Table 4

The decomposition temperature of aluminium nitride

Decomposi^n-on Temp. Preference

2i30^"c © 4 almoanheres (108)

2230-2240^'c (138)

2i.C0''c (111)

2200'^C © 4 abnospher-es (ll6)

223G°C (117)

15. of aluminium nitride. The density of aluminium nitride has been reported as 3.0Z,9, 3.004 (115), 3.25 (ll7), 3.30 (123), and 3.26 (ill).

CrystaJ-S of aluminium nitride have been reported as white (108, 122), pale yellow (97), and blue (97, 108, 122, 134), and in fact the giovrth and properties of single crystals of aluminium nitride has been studied by V/itzke (119) and Matsuraara and Tanake (l20). The occurence of blue crystals has been attributed to cobalt impurities (121).

The electrical properties of aluminium nitride have been studied

(l24r 126-128). It has been reported that aluminium nitride is a

"typical dielectric" (125), and the epitaxial growth on several single crystals subtrates of aluminium nitride has been studied (l28).

I.3.1i The mechanical properties of euLuminium nitride and related materials

Ceramic materials have such desirable properties as resistance to wear, mechanically hard, good electrical insulation, and resistance to corrosive envi.ronmentp but the machinability of the ceramic is such that to produce articles vri.th close dimensional tolerances requires an expensive operation.

However, a material has been established which not only possesses the reputed ceramic properties, but also has resistance to thermal shock and is capable of being produced vd.th an improved degree of dimensional accuracy. This new material is silicon nitri.de. A con^jarison of the foimabili-t^y^ with respect to mechanical characteristics of aluminium nitride, with silicon nitride and other ceramic materials (see Table 5) suggests the possible use of aluminium nitride in a similar field.

16, Table 5

A comparison of the mechanical properties of aluminium nitride with certain ceramics

Ttinsii e Shear Knoop ftiodulus of :oeff. Strer.f^: .h Str^MPi.h fiaxdness .Rl o.-i f.v of Temp. Material Temp. kg/rmn^ Temp. kg/nTrn^ Temp. Phermal. of E-xponsion Stab- °C % X 10-^

al 'niiitivjn 27 25 1230 33030 25 3.64 1 n .trifle (lOOg) 2400 16.93 ] 000 132300 ICOC 4.03

12.7 28100 140c

1 silicon 20 16 1.3- 20 3337 2+360 30c 2 1900 [ nitrid- 2.73 (I20g) 14.7 1200 • 4600 HOC 2.3

tanteT3.um 2-3 29100 6 ca "bi

tioaniijin 24o3 20 34000 6 2980 b s.i.Oe

molybdenum 28 980 21 980 733 43000 8 2030 di l.licide (50g) 29.4 1200 6 .100 9.2

17. It is reported (ill) that aluminiiun nitride has high thermal conductivity^ lov/ thexroal expansionj and good thennal shock resistance.

It is observed that the mechanical properties of aluminium nitride and silicon nitiide decrease with temperature, but when compared vrlth molybdenum disilicide, the drop in shear strength is not so drastic.

Hcwever-, the tensile strength of molybdenum disilicide increases sli^tly with tsnperature. The difference in crystal structure is noted as a possibility for the explanation of these observations (see Table 7).

The knoop hardness figures suggest that aluminium nitride is not so r^esistant to mechanical deformation as silicon nitride. Aluminium nitride has a lower modulus of elasticity than most of the ceramics considered, but is nevertheless compatible with the materials in terms of its elastic deformation. The bending strength5 however^ reduces rapidly with respect to temperature for aluminium nitride as values of 38^500 p.s,i. at 25*^0 falling to 18,000 p.s^i. at 1400°C are reported. The thermal stability range of aluminium nitride, however, is reported to be higher than that of silicon nitride, but not so high as titanium boride.

A comparison of the coefficient of thermal expansion of aluminium arid silicon nitrides shows that with respect to temperature, aluminium nitride wiJl e:xpand more than silicon nitride. However, this is still less than that of the other ceramics considered (see Table 6).

The thermal shock characteristics of aluminium nitride are better than all the ceramics considered5 except silicon nitride, and it is concluded that the use of aluminium nitride as an engineering material has distinct possibilities, especially as the properties could be enhanced by hot pressing the material as observed with boron nitride. In fact.

18, Table 6

The theimal expansion of certain materials (92)

Material Percentage expansion from 250^0 to

l) 500 2) 1000 3) 1500^0

a-uminium nitride 0.23 0.54

- silicon nitiide 0.10 • 0.28 0.54 i.

^ ~ silicon nitride 0.07 0.22 0.46

molybdenxim silicide 0.37 0.83

o<.--quartz . 0.92

alumina 0»36 0.83 1.37

19. Table 7

A comparison of the crystal structures of certain materials

Crystal Lattice Parameters Material Type Structure a(g) c(g) ^^a

al.urainium nitride hexagDnal Z nS 3.104 4*965 1.600 (XnO)

oC"Silicon nitride 7.76 5c64 0.725 hexagonal

^ -silicon nitride 7-59 a.92 0.385

tantalum crabide cubic NaCl 4.456

titainium boride hexagonal 3.026 3.213 I0O62

molybdenimi tetragonal disilicide MoSi^ 3.203 7-887 2.463

20. it has been showm that the thermal shock parameters of aluminiimi nitride are improved by this technique.

I.i*. The fabrication and uses of aluminium nitride and related materials

I.ii.»i The fabrication of aluminium nitride

Rey (117) suggested the possibilities of aluminium nitride as a refractory material, and it was established that aluminium nitride could in fact be used as a container for aluminium up to 2000°C (=-?). Sintered aluminium nitride objects (I62) were produced by placing pov;der around a graphite core and heating the assembly to 2000-2500°C. The shape of the article was determined by the design of the core. Porous refractory bricke. and nitrided articles were also obtained by heating a mixture of corundum, coke, calcium alurainate cement, and water or bauxite at l60O°-1800*^C in nltrogenm The products were found to have density of greater than 1 and contained more than 30^ nitiogen. Compacted aluminium nitride crystals bonded by aluminium nitride and containing small impurities v/ere heated to 1500°C in a pure nitriding atmosphere, resulting in sintered objects, details of con?>osition and conditions being given (I63). Aluminium nitride powders were heated as a compacted mass to 200O2500°C in a nitrogen atmosphere. The vapour phase of aluminium niti^de is formed ar.d on cooling

AlN reciystallizes Eiround the grains of• the compacted mass. Another method of producing a moulded article, was tc adc e suitable or^ganic binder to the powderec mixture of aluminium nitride and a small amount .of mineraliser.. The mixture was heated in an oxidising ^.^ -^ere below :;00^C to eliminate the binder and maintained in ammonia to remove the oxygen, ,and the tsnperature raised.

a. Conii'ary to the report of Rey (ll?)j that the conductivity of al-ji2.1rii-jin nitride up to l^OO^C is so low that it could be used as an

-ijisulaiing material, electrodes of aluminium nitidde nave been prepared

(l65)y and could be substituted for graphite in trie Hall process (l?5

166). A refractory material similar in somposition to these electrodes was produced by hot pressing a titanium carbo-nitride - aluminium n:.*:-ri'Ie mixture to give a bt'lk density of 2.6 gram.cc and an electrical resistance of 250-3000 x lO"^ ohm^ins. (16?).

Objects of al^jminium nitride v/ere prciduced by calcining aluminium

aluminium nitride powders together v/ith a cat^jlyst in nitrogei: atmosphere (l68)c Aluminium nitride articles were prepared by mixing alummium vn.th 7-50~A cyanam-ide^ dicyanamide or melamine and heating for

30-90 minutes in nitrogen at 1200-1400*^0 (lb9)o To stabilise the niti-ide against water^ the product v/as heated in oxygen before or aVter pressing and sintering at 2030-2150'^C.

Sirtersfd refractory mixtures of aluminium nitride and titani-um borlde ha^^c: been prepared (l70)o riefractories were obtained from a mi,xt\jre of alum^n.ium ajid .'silicon powderi? v.d ch ;:'-10;-c paraffin binder and a fluoride

\'i^J:^3^y^t in a nitrogen atmosphere and hcati.ng in stages to irV20°G (184)0

/_l^^:iiii«jm nitride and a solid solution of alumlni-im nitride and silicon oarbidej together v/ith approximately 2% vra.ter v/ere hi'drostatically pressed to give- a hard danse and strongly bonded refr-actory (l7l)» Silicon carbide is also raported to benefit the properties of aluminium riitride

(1745 lS'0„ 191)* Crucibles were formed by extruding thie pradu-ct aTter it b^d been sJ ov/iy heated to remove the v/ater« The sintering of the aluminium riltvile-alui.LirLiuin ryr.iem \v.\s rv^ceritjy been studied (1..'/')- '^'^"^^ re3\3lts WCTT^

22. applied in the manufacture of aluminium nitride crucibles. The mechanism of sintering in general and factors influencing sintering has recently been reviewed (173). A vitrified refractory composed of alumina and aluminium nitride was made 'ly fusing the two compounds in a graphite crucible at 2000-2300*^0 (IS3 . Care was taken not to exceed 2300°C5 because the nitri-de may stai c to decompose in this terrperature region,

I.4«ii The uses of aluminium nitride and related materials

Since the discovery tiuit silicon nitride has properties similcir to bo-th a conventional cerajnic material and a semi-conducting material ^ the interest in the possible applications of aluminium nitride has grcvric

Silicon nitride from the vii-tue of its physical, chemical and mechanical properties, has been used as high temperature electrical insulators, refractory for aluminium, engineering components, Ajmace linings and barings, vrfiere the coeffic ent of friction compares with such materials as P^T.F.E. and glazes (l"/^ ,

Aluminium nitride is -esistant to most common acids and alkalis and in fact artic" ^s specifically to be used in corrosive environment have been made (176

The appi j-c at ions of aluminium nitride have generally been directed

1" producing refractory articles of aluminium nitride (.V 118, 183, 194#

186 such as crucibles, or combining aluminium nitride —1;.- .,.M^_...ias

Acanium cr •-bon-nitride (182-, silicon nitride (l85 18?) and silicon carbide (2O4 to form such ..rticles. Aluminium ii^-idc .as been used to coat graphic*- (l3), quartz (61), and alumina (188). and other refractory materials (133), to improve the surface propert..^o of the ceramic matrix.

Silicon nitride has been used as a binder for refractory oxides (I89) and there is possible use of .aluminium nitride in this field.

Aluminium nitride has been used as a carrier for molten aluminium (l?) and in this respect is more resistant to cryolite-alumina melts than silicon nitride or some metal borides and carbides (l90),

- 23 - As aluminium nitride in compact form is non-reactive up to l600°Cj, it has been developed for use in connection with nuclear reactors (l92p 193) and has a high temperature insulation material (196)« Aluminium nitride has been used in the production of radioactive isotopes (194, 195).

Titanium salts have been added to improve the conductance of aluminium nitrldCo The resulting cermet has been used as electrodes to produce aluminium by the Hall process (l97r 19B). Semi-conductors have been produced using co-axial films of aluminium nitride with the elements of compounds of germanium and silicon when the difference in lattice parameters is less than i^Ofo (199)» The precipitation of aluminium nitride in low carbon steel benefits the deformation characteristics of that particular steel (200), Aluminium nitride has been used as a slow-working fertiliser

(203)3 as a secondary accelerator in the vulcanization of a co-polymer

(200)3 and in the production of aromatic hydro-carbons (2OI). Thin refractory layers of aluminaj aluminium nitride and silicon nitride have been used as covering layers for electronic devices (173)« Aluminium nitride has been used in connection v/ith reinforced filaments (5, 95) „

In this thesis the author has studied ajid compared existing and nev/er processes for the production of aluminium nitride, viz.

(a) Seipek process; the preparation of the nitride from its elements; the reaction of ammonium hexafluoroaluminate in aimionia.

The formation of aluminium nitride has been investigated thermodynamically using the available thermal data* The reactivity of aluminiimi nitride has been examined with regard to atmospheric oxidation and possible hydrolysis by steam or liquid water, particularly for samples of size ranges possibly suitable for sintering or hot-pressing. Changes in phase composition and crystal structure on milling and oxidation or hydrolysis of aluminium nitride have been investigated by X-ray, optical and electron-micrographic methods. Surface area deterrninations have been made by gas sorption and correlated with changes in crystal structure and crystallite size on oxidation or hydrolysis. Some compariscns have been made with the reactivity of silicon nitride.

- 24 - 1. Fitcher^ P.^ Z.anorg.Chem. . 190?^ 54s 332o

2. Fitcheri F.. & Oestei-held,, G... Zeit.Elektrochem. . 19155 21^ 50,

3. '.Yolf. J., Z.anorg.Chem^,. 1913:, "iJ., 159*

4. Fitcher, F., & Spengej.,; A.Z,anorg,Chtn., 1913^ ^2^^ 192-

5. Forratt. F., French Patent No., -.,33?i,343, 1-963.

6. Claus, V/., Z.MetalIkunde, 1929, 21^ 268.

7. Rontgen, P., & Braun. H.- luetallv-drtE-h^ 1932. 11, 459-

8. Laffete^ P. , KlcharduS;, A. - & Grandadam P., Rev= IndoMiJierals-. 1936 No. 375:, S61, 7.

9c Vereshchagin, L.F,. et al;Doklad, A^No Soviet Riysics. 1969^ 13^ (9)- 869o * '

10. Briegleb;. F.^ & Geuther- A.^ Liebig's Ann., 1862;, 123., 238.

11. Arousj L., Natur.vc "^jnd^o 1899^ 14^ 453-

12. Zenshelis, Z .RiyScChem«. 1903= h6» 287 =

13. Iv/ase^ K., 3cx,-iepoTohok-,'.Univ. ^ 1926^ 13, 531o

14- Biesalky, E. ^ ^-Van Eck H.^Zeitc anorg.Chem. ^ 1926^ 156 26 „

15« V/hite^ A.H., ... I^.IL lun. L„ . J.Amer.Chem.Soc, ^ 1908^ _ , 1343.

16. Charlton, J.C, & Kvans^ C.Co^ British Patent No.. 784^126; 1954-

1?. Long^ C.G., & Foster- L.M. . J.Amer.Cerajnic.SoCo . 19595 42^ 53*

18- Pepkin- Yu.D, „ Sz Samsonovp G.Vc^ Ibroskovaya Met.Akad.Nauk . Ukr« SSR. , 1963, (5)/68

SaitOj T., & f.Iaruya, K. ^ Bull.Resea2x;h Inst.Mireral Dressing i.let..T 1952, 8, la. '

20. Grana^ Yu.M. , S: Sabanova^ L^-N.^ Simp,Profsessy Sin.Rosta.Kri.st^Plenek. Poluprov.Mater. p Tesesey Eokl.,, Novosibirsk 1965^ No. 8,

21. Iblishchuk, V-,S., Zh.Prikl.Khim., 1963;. 36, (5), 1142.

22. htandorf, v., U^.Patent NCc^ 35307p907, I967.

23. Union Cr -bide Co , British Patent No., 896^766^ 1960c

24. Mandorf V.,Ger. - Patent No<, 1,131,195, 1962,

25. 23. K-Tase, H.J.p et al J ,Ind, Eiig.Chem., 1926, 18- 128?.

26, Kobos-",. H.I.. Eroreevj PcT,^ JcGen.Chem.. 1933^ 3... 872o

2-^. Bifilips, N.V.,NethoAppl, - 6,602.899; 1966.

28. Smolensk!;, D« - & SuveryniakM. , Bull/;/cj^kowey Akad^Techc , 1963:, 12, (L), 43.

29. Voumasos; A.C B'jlloSoCoChem.^ 191I.n 9^ (4); 506c

30. Caro. IU3 Z-agn* VoChemo^ 1910^; 23,., 2412,

31< lYicker. S.. S: Rt a-J^ He" TranScAmeroElectrochem. , 1912. 22. 37.

32o Norton^ T,H, ^ "Consular Re:iort on the Utiliza.tlon of Atmosp-ieric Nitrogen"p Washington. 1 p. 138.

33» Ijinathj Eo p & Indrap Aoj "Die Oxydation d-tjs Amnomaks zu. SeJ tpel Ars und Saltpetzair-e"^ (Stuttgart)41- 19-12.

34. ilsseu^ 0.5 Chem«Ind,Eng. . 1918., 19',,, 808.

33. Richard,, J.Y/.. J.IndoEng.Chem^.. 1913. 3.. 191.

36. I^laxted, E.B. ^ J.Soc.Chem.Ind., 1916, IO3T.

3?. Matignon, C.p Chem.Ztg. ^ 1909:, 38, Ql4i.o

380 !.Ia2re- F,, Genie Civile, 1912^ 6i._, 3O0

39. Bouger^s, O.L, „ Mcnit.Sclent. ^ 1911. 1.^ (3)s 361, i^. Von Escher, Chem,Ztg,, 1918, 42, 353c

41.. Bronnetp E. „ Bull.SocoInd.Mulhouse. I9O9, 29.^ 39^

42c Shneld;, M., U,S, Patent No., l,34^,133r 1920.

43o ife-man. G., Ger-P-tent No.- 3195O46. 1914* it4o Frankelp V/., Z ii^lek-crochem. ^ 1913- 362.

43- Serpekp 0,, 'Z .omp.Tnisf-^.a3^=». lit 33-

46. Peacock, -clu Ibnt E ' U.S. i^atent Noso j, l,031i»38l5 l3033:,727p 1912

47. Mallet, J.v/.^ ^nem. Ne;-^ , lo76p JJ^ 23&.

43. Tsumura, Y.p Japan Patei. o179 ..269^ 1949.

Brit. Ritent 1^0., 21 p366, 1913.

26. 50. Johnsonj A.F,, U.S. Patent Nc^^ ^80^4735 1949«

51. Klebero Y/., & HoD.^ ZaKri-sto, I96I., 116^ 126^

52« Peohiney Co. „ Brit. Patent No., 868.301, 1956.

53. Perievssj R., & Bollack- R. ^ UoSoPatent No.^ 2^962^359i.962.

5^ Bri.t. Patent Nc^ 893?l6A^.. 1962.,

55. Claxrp G., Ger. Patent No,., 1,0.765099? 1960.

56. Repenko, K.N. _^ EfunenkOj R.Lo . Oul-ko. rl.V. ^ Nauot a.. Sb<, ^ FroUo:. Naucha - Issledpy[n3t<,pgneupoix Vj 1962., 63 I2O0

57. Tiede., E., Thirrann., M. ^ & Sensse^ K.. Bev.., 1928^ 6iB_^ 1568»

58. Rennerp T., Z^anorg.Chem* P 19595 298,. 22.

59. MatsumotOj, 0. ,, KiniiokUg I9605 5^^, K '^^'JS <=0 *

6O0 Popperr P., ProcoSymp.Bj'itoCeram.Res.Assoc. 5 1962^ p. 157 o

61. PlP.tyhishkinp AoA. , £z Slavina^ N.Go . UoS.S.R» Patent Noo^, 1.80^936^ 1966.

62. Heymer, Go. 6^ Plarznisch. H.5 Ger. Patent lic^ l_a93.^48?. 1965o

63o Comprehensive Inorganic ChemistTy^ Vol. 5, (Van Nostrand^ D. j)_. New York.

64o P-lotnlkov, V.A«5 & Kaiita; P.l\, JoGen.Chem.„ (U.S„SoRo),, 1933.. 3o 872.

65» V/idebergo E. ^ & Uay^ A.^ Naturforsch. 1955;= 106, 229.

66. Bergn D.^ Lev/is, D.W^^ DaJcin^ T.V/.. Sestrichj Ssposito.; J.^'.. Re^. & Technol. Div. UoS„ Air Force Sy:^:.. Commandc T-^jh, Rep. ^ A P M L "T R-32O,, (X). 1966.

67. M^.tallvrork.PIansee . A. G.^ Neth. Ai:.pl. ^ 63600.870,, 1966.

68. Addamianc, A. p J. Ele. brochem. SoCr;: 1961, 1_03. 10':'2,

69. IvIanko\aGh, V.I«, U„S. latent No. 35147.076^ 196^.

70. Gilles^ J.C. Le.jiSp A.M. 5 Ther>'p J.5 & Coilonguesj R. ^ Corapto Rend. 5 1962, (1), -.5'.

71. Gi.l."].es. J.C._, LejjSp A.M., Sz Collongues^ R.Corrosion /vnti-Corrosion^ 1964, 12, (3), 99-

72. Kaiser, K., Ger. Patent No., 181,657;, 1904.

73. Bunet. Elec.Eng. ^ 1935, 54, 1320.

7o 74. Borchers^ V/., & Beck, E. ^ Ger. Patent >Io. , I963323:, .1906.

75. U.S. Patent No., 1,134,U4.<, 1913.

76. Peacock^ 3., U.S. Ritent Mo., 129-721, 1915.

77. Jander^ G., & V/eiss^ J. 5 Z.Electrochen., 1959? 63^5 1037.

78. A»S.T.M. X-ray RDv/der File, (Philadelphia), I96O,

79. Tm-ner, K.C., & Rice, Soil Sci., 1952, 7Z(., IZO..

80. August^m, V/,, Firlus^ L« . & Prackowiak„ K, , Preznystchem. , 1961^ ho, 255.

81. Ando., Omura, U,, & Akujama^ To, Kogyo Kayak^u Zasshi „ 19f^6, GQ^ (12), 2327.

82. V/eiss. A., Mehler, A., Koch. A. ^ & Hcfmann, Vo, Z.anor-r Chem.,1956, 28^t, 247-

83- Dej.vjlle, H. Stc Anrio Cliemo Phy?.5 (France), I86I, 6I, 309-

8^, V/ells, A.F. 5 *Strac cajraH. Inorganic Chemistry" (Clarendon Press), 1962.

85. Barteczko, P. ^ Ueber Doppel Fluoride, (Hamburg)^ 1909.

86. Menzer, G., Z.Krist., 1930, 21^ -^3.

87. Novoselova, A,V.., Zhur.Obschei.Khimo « 1940, 10, 1547.

88. Si'ddl.ovski, Zh. Piz. Khim., I962, 36, 1173.

89. Schvrarzmann, S., Fortsthr. Mineral., 1966, 42^ (2), 231.

50„ Shinn, D.B., Crockett^ D.S.« & Haendler, A.M., Inorg-Chem., I966, 3^ (11).

91. Maak, D. , unpublished.

9; Krikorian, 0. H., UCRL Report Noo, 6132, I96O.

93. Funk, H., & Boehland, H., Z.ano— Chan., I964, 33^-, (3-4) 155.

94. Koch, V/., Hscheuar^ C, & Gersch^ R.K., Arch.Ei.sen. , 1956, 701.

95. Reinhart., T.J., Stabil.Flast,Soc.Flast.riig. , Reg.Tech.Conf .5 (Washington) , 1967, Fl.

96. Caj-ter, R.H., Ind.Eng.Chon., 1930, 22^ 68.

28, 97. Mellor^ J.V/. .'Comprehensive T.reati.se cn Inorganic and Theoretical Chemistry, (Longmans. London),, 1924*

98. M^tsumoto, 0., Denki Kagaku, 1967^ 35, (lO), 697.

99. ?.iatsumoto, 0., ShiratOj Y. ^ & Hujazaki, M., Denki KagaJcu^ 1963^ 36, (1), 41.

100. Athavale, V.T., Awasthi, ScP. & Sunderasan, IvU , Talanta. 1965^ 12-s (1), 7.

101. Brit. Patent NoJ ^Oll^,^10, I96?.

102. Noble. H., & RueJle., L„A. . U.S« Patent No. 3.^248.171.. 1966.

103. Per2hiney Go.,. Neth.Appl.. 6^611 .,17].. I967.

10k. Shapirel, I-.[.M. . Sb.Tr.Tresntr.Nriu :ha - Iss3 ed. Inst oCherr.oi Met.. 1960^

103. Hardtung, H., Beit, zur Kenntris der Metallnitride. CHannov-r). 1912^ 34.

106. Fil-cher, H., Helvetica Chim.Actao,- 1922, VH8.

10:'c Pitcher, H. . & Spengel. A.^ Proc.Hcy.Soc., 1925:> 109A, 186^

108. Lange, N.A., "Handbook of Chanistiy", (Handbook PUb.Co.J, I946.

109. Plament, P., Compt.Rend. 27.Congr.Intern.Ghim.Ind, . (Brussels). 195^^-" 2; Industrie Chirn.- (Beige), 1955.. 20. 372. no. Br^dshavr, V/.G., & Matthe-.v, C<,0.„ Props, of RefractcT^ Materials, LJ.13D-2466, 1958.

111. Taylor^ K.M. , & Lenie. C.J^Electrochem.Soc., I96O. ICT. 3O8.

112. Shaffer- P.T.B. ^ Tlenuni Press HaJidbook cf Hi.gh Temperature Materials« " No. 3. Materials Index p. 259 (Plenum Press).

213. Edelstahlv/orke- A.G.^ BrLt. Pb^tent No., 899^,398, 1963.

114. Foryst^ J., et al, Hutnik^ 1966^ 33:> (^2), 519.

L15. Herzer^ H., Bei1 . zur Kermtris der Nitride. (Hannover), 1927.

116. I'Vi.ederich, E.^ & S-jLttig^ L.. riorg.Chem.1925 5 143^ 293.

117. Rey, M. , Silicates Inds. ^ 1958., 22. 435. lir. Kinse, M., Galvano technik, 1968, 58, (4), 350.

119. W'itzke, h.i^., r-/ J--^^^^^

29. 120. Matsumara, T,, & Tanabe, Y., J.Fhys.Soc.Japan.I96O, 15, 203.

121. Klebe^ W., &:Witzke, H.Dc, Z. Kilst»I96I, 116, 126.

122. Myers, 1^. , ViiU'uniiL.i l.itride iij. u^-rature Search'^ (^arborunduirj^ 1937^

123. Lagrenaudi, J., J .ChemcPhys, ^ 1956> 3^? 222.

124. Solid state phys. rHectronics Tele-communic.Proc. Intem.Conf. , (Brussels), 1953, (2), 645-

125- Andreeva, T.V., Barantseva, I.G,, Dudnik, E.M., cS: Yupko^ V.L.., Teplofiz. Vysokikh. Temperatur. Akad. Nauk S.S.S.R.^ 1964p 2,"(3)s 829

126. Richards, N.E., Berry, J.S., & Johnston, T.J.5 U.S. Patent No., 3,328,280, 1967.

127- Cox, G.A., Cummins, D.O., Kawabe, K. , & Tredgoldp R.H.<, J.Hiys.Chem. Solids, 1967, 28, (4), 343.

128. Fb.stemak, J., Roskovava, L., Riys^Status. Solidly 1963s 9. (2) p K73.

129. Ott, H., Z ?hysik., 1924, 22, 201.

130. Neissen, Ehys.Zeit.p 1926, 27, 299.

131. Hume-Rothery, W., Grimm, H.G., & Sommerfieldp A., Phil.Mag., 1927, I, (3)p 301.

132. Stackelberg, M.V., et al. Z. .-jhysik.Chem., 1925^ A173-^ UjO.

133. Parry, G,B., & Jeffrey, G...., .^hem.Phys. , 19355 13^ 456.

134. Koln J.A., Cotter, P.G., & Potter, RoA., /\mer.tiineral.1936, Up 335.

135. Cooper, C.F., George, CM., & Hopkins, S/'V.J.y Spec.Ceram.Soc.Syir.p. p 1962, p. 427.

136. Zhdanov, V.A., & Brysneva, L.A., Izvest.Vysshikh. Ucheb. Zevedeni. Piz., 1961, 3, 93.

137. Parry, G.S., Jeffrey, G.A., & Mozzi, R., J.Chem.i^ys, , 1936s 25^ 1024-

138. Hest, M.K., Perg. v. Ferguson, Technol .Chem.Eng. , 1937i 237.

139. Matignon, C, Chemische Zeit. - 1914, 38, 894.

140. Meldenhav/e, V/., "Die Reaktionen des f reienstickstoff s", (Berlin), 1920p p. a.

141. Prescott, C.H., & Hencke, T/.B., J.A.C.S., 1928p 3228.

142. Neumann, B., Kroger, C, &• Haebler, Z.anorg-Chem^, 1932, 202^, 81.

30. 143. Sato, S., Papers Inst. Hiys.Chem.Res., (Tokyo), 1936, 295 No. 624, 19o iVi-. Roth, V/.A,, Z.Elektrochem., 1942, 4§, 267.

145. Brev/er, L., Bromley, L.A., Gilles, P.V.'., S: Lofgron, NoLo, "The Chemistry and Metallurgy of r.ii seel Ian ecus feterials" . (McGraw Hill), 1950.

146. V/emer, G., Metalurgie. V. Gussereirech, 1953? 3, 324-

147. Neugebauer, C.A., & Margrave, JoL,, Z .anor^f'. Chem. , 1957s 290, 82.

Iii8. Apin, A.Ya. , Lebedev, Yu.A., & Nefedova, O.I., Zhur.Piz.Khim. , 1958. 12, 819.

149. Schissel, P.O., & V/illiaras, V/.S., Bull.Am.Phys.Soc. , 1959^ 4, (2), 139.

150. Kubaschevrski, 0,, Evans, E.L.L., cS: Alcock, C.B., "J.Ietallurgical Thermo• chemistry", (Pergamon Press), 1967-

151. Olette, M., cS: Ancey-Moret, M.F., Revue de Mettallurgie, I963, 570.

152. Hoch, M., Sz V/hite, D., Ohio State University Research Foundation, Oct. 29th, 1956.

153. Mah, A.D., King, E.G., V/eller, V/oV/., t5c Chris ten sen, A.O.^ UoSoBur. Mines Rep.Invest., No. 5716. 1961.

154- Dredger, L.H., Dadape, V.V.^ & Margrave, J.L., JoPhys.Chem,, 1962, 66, 1556.

155. Mun-.r, Z.A., N.S.A., I963. 17^ 23307.

156. Hildebrand, D.L., & Hall, V/.F,, J.Phys.Chera., 1963, 67, 888.

157- Sthapitanonda, P., & Margrave, J.L., J.Phys.Chem. , 1963s 60, I626.

158. Fisher, A., Phys Verb., 1957, 8, 204-

159. Knippenberg, K.F., unpublished.

160. Guiochon., G. , cS: Jacque, L, , Bull. -Soc .Chemiciue de France, 1963, 863.

161. Bhat, I.R., & Khan, I,A'., Indi£ J.Chem., 1967, 5, (lO), 499.

162. Pechiney, Co., Ger. f^tent No,, ±,023,717, 1958.

163. Bollack, R., & Rey, M., French Patent No., 1,149,539, 1957- l64o Pechiney, Co., French Intent No., 1,123,3035 1956c

31. 165. Ceramic Abstr., 1960, 193a.

166. Ricker, R.Wo, & V/allace, P.P., U.S. Patent No., 3,0115983, 1959.

167.. Madek, EoA., & Ricker, R.V:., U.So Patent No., 3,011, 982.

168. Morganite Research & Development Ltd., Belg. Patent No., 620,323, 1962.

169. Bartlett, H.J., Laipp, D.T., & Watson, G.R., U.S. Patmt No., 3,141,737, 1964.

170 Mandorf, V., U.S. Patent No., 3,251,700, I9660

171. Morganite Research & Development Ltd. , French Ratent No., 1,422,049, 1965.

172o Matsuo, S., Komeya, K., & Matsuki, Y., Yogyo Kyokai Shi., I965, 73y (2), 34.

173. ThumniLer, P., & Thomm.a, W., Met.Mat., (Met.Rev«), 1967, 69.

: -Tli^S^efVJ^^' & Hx^tedVJ.H.', BDv/derMetSTlurgy, 19 61, 8, 196.

175. Pletyushkin. A.A., & Slavina, N.G., Izr.AkadcNauk. S.S.R»N. Mater., 1968, i, (6), 893-

176. Schraiger, M.T., Za^olskaya Lab., 1960, 26, 1223.

177. Beeghly, H^,,Anal.Chem., 1949, 21, (l2), 1515.

178. Beeghly, H.P., AnaloChem., 1952, 24, (7), 1-095.

179. Duboyik, T.V;. Kaaakov,. V.K'i , Refractones, (U.S.S.R.)» 1967, 32, 3, 1311.

• • 180« Hildenbrand, D.L,, & Theaid, L.P», U,S,Dept.Comm,,Office Tech.Serv., - AD-258,,410, 1961.

181. Liaduk, J.A., & iiicher, R.W., U.o. -atent No., 3,011,982, 1959.

182. Bollack, R., & Rey, M., French Patent No., 1,149,339, 3 '57.

183. Matsuo. S., Konseya, K., & Matsukin, Y., Yoyyo. Kirokai Shi, 1965, 73, (2), 34.

184. Chemical Abstracts, 1966, 6^, 15043c.

185. Moi^ganite Research & Develop. Co. Ltd« , Belg. Intent No., 620,323, 1962.

186. Burykina, A.L., & Evtushok, T.M., Vysokotemp Pokiytiya Tr. Seninara, (Leningrad), 1965, 6, 145-

187. Tokyo. Shibara Electric Co., Brit. Intent No., 1,098,867^ 1968.

32. 188* BrLt. Patent No«, 717,463p 1955.

189« Matkovichp V.I., Cotton, E,^ & Peretp JoL». U»S« Intent No.^ 3p259,509p 1966.

190^ Naumchik, NoG,, Samsonovj G.V„5 Naumchik.) A.N., & lapin^ A.A. Izv. Vyssh, Ucheb^ Zaved. Tsvet. Met* 5 1966^ 9^ (6)^ 57c

191. Mutech ChCTi. Eng. 1964j, 9* 45.

192. Austria PSit&it No.p 242^3775 19^5^

193. Bei:gp D., Lewis, D.Y/c 5 Dakin, ToY/,, Sestrick, D.E, ^ & Esposito, JCN^P UcSo Air Force Syst. Command Tech. Rep« p APJa>-TR-66,(l)s I966.

194. Charltonp J.C., & Evans, CpC., Brit.Intent No,, 84^25* 1954.

195. Kihryp I.G., & Adolf ^ J<,P,, Ball,Soc.Chim.Pr. , 1967^^ 9, 3414.

196. Itlcher, R.'A^, & Wallace, P„F., U,So Patent No., 3,011j,983,» 1959o

197. U^Sc Patent No., 3,328^280, I967.

198. Ruchravein. ReA., French Intent No., I,371s868, I964.

199. Leslie, V/.C. ^ et al. Trans. A.S.M., 1954, ^6, 1470.

200. Byms, A.C., & Von Stroh^ G., U.S. Patent No., 2A59,915p 1949.

201. Coupard, C.I., & D.P., French Patent No., 870,636^ 1942. .

202. Sato, S., & Trokava, H., Repts. Sci. Research. Inst., (Japan), 1953, 29 , 439.

203. Chiv, T^L.n Ihg, D.V/o; & Noreika, A.J., ISlectrochem. Technol., 1968, (1-2),.56.

33. CHAPTER II. =bcperimental Techniques

This ciiapter is devoted to the experimental techniques used in the present, worko Reference will be made to this chapter when the results of a particular section are considered^

The methods observed werej

1- The foimation of ammonium hexafluoioaliominate.

2. Chemical analysis.

3. Thermal analysis,

4» Infra-red analysis«

5« X-ray analysis.

6. Electron microscopy techniques.

7. Particle size analysis.

8» Surface area deteimination.

9i ' Ball • milling.. lOg. Methods of nitidde preparation.

II.l The preparation of ammoniijm hexai'luoroaluminate

Ammoni.um hexafluoroaluminate was prepsired by the following methods,

(l) Reaction of aqueous ammonium fluoride v/ith an aqueous suspension of

Bayer hydrate**, «Alg0^.3H20. (2) By reacting aqueous ammonium fluoride with aqueous solutions of aluminiiim fluoride, and aluminium chloride.*

(3) By reacting alcoholic amnonium fluoride with alcoholic aluminium bromide or.aluminium nitrate.

The method .selected was to dissolve aluminium foil in aqueous HP to give a solution of aluminium fluoride^ and after filtration to react the solution with aqueous ammonium fluoride. Details are given in Appendix I,

3if II.2 Chemical analysis

The chanical analysis of the ajnmonia content in ammonium

hexafluoroaluminate was carried out using the Kjeldahl technique (3).

The nitrogen content in aluminium nitride v/as determined using the method of Passer et al (4)- The fluoride content of ammonium hexafluoroaluminate was determined using the V/illard-?/inter technique on a micro-scale. This method was found not to be satisfactory for the fluoride analysis of

aluminium fluoride and a method based on the report of Bognar and Negy (6) v/as adopted. The aluminium content of all the compoimds was determined by precipitating the aluminium as aluminium oxinate (2, 7).

Details of the analytical methods are given in Appendix II.

IIo3 Thermal analysis

The thermoanalytical techniques used in the present study v/ere

(a) Thennogravimetric Analysis, (b) Differential Thermal AnalysiSo

II.3.i Themogravijnetric analysis

Thermogravimetry is the continuous or frequent measurement of weight at a particular temperature, or as a function of temperature change. The measurement of weight and temperature as the specimen is being heated is not 3in?)lep several errors tending to distort the system (2l)o

The balance used in this analysis was based on a suggestion of Gregg and Winsor (22)p using a null point thermo-halance design. The balance

(Stanton's A49) could record weights to an accuracy of 0.2 mg and was supported on a dexion frame above the fXimace. The furnace was constructed in the following manner. Nichrome windings was placed in double turns round a grooved silica tube of 1 inch I.D, The tube was supported in a mixture of vermiculite and asbestos contained in a cylindrical stainless steel case. One end of the silica tube was sealed. The nichrome windings

35 - were attached to a temperature controller (Sunvic (AJl^I^))., The

specimen to be heated was suspended in the furnace by nichrome \v±rG connecting the base of a weighting pan to the nichrome crucible holder^

Nichrome v/as used, as it does not begin to oxidise appreciably in wire form until llOO^C (24)o The specimen was placed in a 10 c.c„ porcelain crucible^ placed in the crucible holder and suspended in the furnace^

A chromel-al.umel couple5 capable of recording temperatures up to a llOO^C was placed a few centimetres from the specimen.

The furnace was brought to temperature aoid the weight changes were observed at a particular temperature.

II.3.ii Differential thermal analysis

Introduction

Differential thermal analysi^ is a technique by which thermal effects are measured, usually as the sample is heated or cooled. In basic technique it is related to calorimetry. As heat is added to a calorimeter or isolated systan, the temperature of the system will rise approximately linearly. V/ith a specimen present, the specimen has to be heated as well so there will be a decrease in the rate of tenq^erature increase. If the specimen undergoes some tr^sformation^ additional heat must be added to the system to change the specimen to its new form.

If a reference jmction is present within the system, the temperature difference after the transition will be zero. If the temperature difference was plotted against temperature instead of heat input, and if the thermocouple was inserted in the specimen and reference thermocouple in an inert material, this v/ould result in the essentials of differential thermal analysis. The thermal transformation taking place can be detected by such a system from the plot of temperature difference against temperature,

36 - The sample shape and size v/iU affect the shape of the plotp or peak a as it is known <,

An account of the e3q)erLmental factors which affect the shape of a differential ciirve has been given elsewhere (2l).

Apparatus

The apparatus used was based on the design of Grimshaw et al (l8)»

28 gauge v/ire thermocouples (nichrome and alumel) v/as placed in the double holder vath each section containing a common lead v^ich was placed in identical position to its neighbour.

The sample under test vias packed into one of the two cubical compart• ments (l cm wide) of the thin walled refractory holder^, the other being filled with inert material. This holder was fitted into the lower half of a refractory blockp the upper half forming the covers V/hen assembledg the cylindrical block v/as placed in a tube furnace (Griffin & Geoi^e) of similar diameter. The thermocouples were connected to a recording instr\unsnt (Cambridge Instruments Ltd,), The temperature of the specimen was measured by inserting a similar refractory block in the other side of the furnace o The block contained the same inert material as used in the sample block and the temperature vreis read by placing a nichrome thermocouple in the block and connecting it to a directly calibrated temperature recorder^ using self compensating thermocouple leads.

The rdse in temperature was recorded for three temperature settings and for a heating rate of 10-13°C per min a furnace setting of 180 V v/as usedo

11,4 Infra-red analysis

The instrument used for this work was a Unicam SP 200 double beam spectrophotometer* The instrument had an aar cooled Nemst glower as its

- 37 - source of radiation., and a monochromatcr of the Lxttrcw arrangement. The

detector v/as a Golay pneuma.tic type. The chart recorder v/as of the flat

bed. type. The instrument operated over a range of 65O cm to r-.m vath a change in scale at 2000 cm "~. Sodium chloride prisms were used

thrc^oghcut this work.

Sample preparation

Several techniques have been developed for obtaining infra red

absorption spectra of solidso These include mulling or suspending the

solio :in a liquid medium and the pressing the sample in a3.kali h^O.idesc

The liquid technique v/as employed throughout this v/ork - The comnicti

technique is to suspend a few milligrams in a commercial Nu.iol mull.

Ho'.vever; the reported values of the absorption spectra of the ammonium

fluori.de and its complexes are in the range 1420 - 1490 cm "^^ and ,5000 -

3300 cm o Nujol gave strong absorption peaks at I46O cm and 2850 cm ^•

Tetrachloroethylene gives strong absorption peaks at 780 cm so it was

decided to use the Nujol mull in the range 65O - I'P.OO cm and

tetrachloroethylene in the range 1200 - 5000 cm .

A fe-,v milligrams of each specimen were ground in an agate and mortar^

A fe-.Y crops of the solvent was added and the mixture was reground and placcjd between the sodium chloride plates= The plates were mounted in

the holder and the assembly placed in the instrument using a reference

beam of air.

11*5= X-ray analysis

Two methods of identification were used; po\'/der diffractometiy and a 9 cm x-ray powder camera,

-'^'5 * - B;>v/der dif f ractometry

In the present work most of the compounds could, be indexed on orthogonal axes.

- 38 " From nX = 2 d sin 0 (l)

ana = h^a- . -^^b- . l/c-(2)

where hj, k^, 1 and the ciystal indices and a^ and c and the crystal

parameters and by substituting equation (2) in equation (l)^ it is

possible to show a relationship between the Bragg angle and the intrinsic

crystallographic properties of a particular system, the length of the

' equation depending on the symmetry of the crystal system

i^e. sin^ Q = ^ 1^ ^ ~ •** "2 * ~ a b c 2

The agreement between the calculated sin 9 values or d-spacings

and those observed will indicate the accuracy of estimating the cell

parameters a, b, and c.

Intensity of radiation emitted by an element is proportional to

the atomic scattering factor f and f = 3, the atomic number of the element,

when 0 is zero, but falls off as Q increases* In the present study

compounds such as aluminium nitride, aluminium fluoride and alumina were

x-rayed and as Z i'or alijminium is 13, the observed intensity will decrease

with increasing ©• Conseqaentlyp it was anticipated that the d-spacings

at high 0 angles would be too vfeak to make accurate measurements» For low

0 angles greater accuracy is obtained with the recordings of a

diffractometero

Sytmple preparation and instrumental technique

Techniques for sample preparation have beeri given (23)» but as the

identification of the sample only is required, a fair less complicated

technique than those described was used.

39 To a sample of powder placed on a v/atch glass v/as added a small

amount of "durofix" and acetone. The presence of these two substances

did not alter the x-ray characteristics of the sample and serve to

coalesce and maintain the powder on a flat glass slide. This glass

slide was supported in the x-ray beam and rotated from to 2^0°. The

refracted beam was collected by a geiger or proportional counter and

translated to the chart recorder by means of a panax ratemeter or

Berthold rtitemeter/discriminatorj, depending which diffractometer was

used. The chart was calibrated in intervals according to the speed of

rotation of the sample, from v/hich a direct reading of 0 could be made.

II.5.ii Powder camera

A 9 cm-radius Unicara powder camera was used with the Van Arkel

arrangement (see Fig. 2a)•

A powder film (Kodirex 3.5 cm x 2o8 cm) was cut to the required dimension using a guillotine (Unicam So6l) placed around the sample in

the camera support and the lid. set in position. The camera was mounted adjacent to the x-ray tube and ^evacuated for two to three minutes before

the x-ray generator was switched on. A working voltage of i^O kV and 6 mA • was'used in all cases for e3q)Osures of 2 to 4 hours.

After exposure, the powder films were developed for 4 minutes, (Kodax

D19b), rinsed in water and fixed for 4 minutes (Kodax PX40)p washed for half an hour, and left hanging to diy.

II.5.iii Errors in powder photographs

The possible errors in powder photographs are (a) the non-coincidence of the axis of the camera and the rotation axis of the specimen; this error can be easily accounted for and will be discussed later, (b) the finite height of the specimen; in a 9 cm camera only approximately 2mm of specimoi is irradiated and hence this error was neglected,

- 40 - I o I

FigiVan Arkel a r rang erne nt (c) absorption and diver^gence of the x-ray beam? the errors produced by

these effects are similar, for with absorption only a specimen in which

this error is negligible can the centres of the pov/der lines be taken as

the correct positions, and usually the measured value of 0 is too large

(91)« Hence the observed d-spacing will be too small v/hen compared vri.th

the standards. The opposite of this effect is true with divergence of

the x-ray beam*,

From the equation

n X =2 dsin© when considering first order v/avelengths

d =: ( V2) cosec 9

Ld = A/2 cosec 0 cotOo 0

Ad = - d cot Qo LQ

Now in the Van Arkel arrangement 0 = 90 - /l^R where S is the distance between corresponding diffraction arcs and R is the radius of

the camera. So when S is large AQ v/ill be large. An extensive mathematical survey for this error has been cited (9)o To compensate for the errorn a plot of the unit cell parameter against the Nelson-Riley function could be

(8)9 (d) film shrinkage; when the film is developed depending on3 among other factorso the temperature of the developer^ the film may shrinkc To compensate for this it was assumed that the shrinkage was uniform throughout the film and the error could be calculated if the knife edge angle (0^) was known for the camerao

Measurements were made using micrometer callipers of the knife edge at the point opposite to the emergent x-ray beam termed as C in F .g* 2b, and of the camera radius.

h2 From Fi-g. 2b

= sin 29j^

4 = 2 sin""^ ^/2R

. = 36C5 - 2 sin"^ V2R

, , 0^ = 90 - i sin"^ ^/2R

/ Jfj^ = 86o40 + 0.01°

from which the film constant will be • • V

Measurement of the film

The powder films were measured using an instrument constructed from

two metre mles separated and ribbed together by varnished three plywood*

Adequate allov/ance was made for placing the film between the two metre

rules and a plastic cursor was placed over the rules* Any tolerance in

the cursor was compensated by a small piece of watch spring between the

rule and the cursor. A vernier scale of 1 mm intervals was made in the

cursor enabling measurement to be made to the second decimal place.

Accuracy of measurement was + 0,01 cm©

As a result of careful measurement the estimation of the crystallographic parameters were made using a computer program based on Ito's method

(see Appendix III). 11,6. Electron microscopy techniques The microscope

The Philips Qd 100 B electron microscope v/ith a resolution of 25 2 was used in this study. The microscope is usually operated at 80 KV, The pumping system consists of a prevacuum lotaiy pump, a mercury diffusion pump and an oil diffusion pump. The magnification is altered by adjusting

- 43 the currents to the electromagnetic lenses* Focussing of the image is controlled when varying the strengths of the magnetic fields^ by changing the currents generating them. The image of the sample is projected onto a fluorescent screen directly in front of the observer^

There are facilities provided for photographing this image with a 35 mm

Camera which can be lov/ered into position immediately in front of the screen. Generally^ a four second exposure is used and the magnification of the photomicrographed image obtained from comparing the instrumental and the illumination settings with calibrated standard tableso The camera constant XL is calculated using a compound of known unit cell dimensions^ but if the same accelerating voltage is maintetined then A L remains constant,is the effective camera length.

Sample preparation

Specimens were prepared by placing a film of carbon on a copper grid in the normal manner, '^^he grid v/as supported under an infra red lamp, A few milligrams of the sample were placed in distilled water or acetone in a test tube and placed in an ultra-sonic medivun to ensure that the sample was thoroughly mixed, A single drop of the suspension was placed on the gridp the heat from the lamp evaporated the water leaving a dispersion of the sample on the carbon film.

Finally the grid was placed in a specimen holder to be introduced into the microscopeo

II»7 Estimation of particle size

The particle size was estimated using electron and optical microscopy,

II»7,i Electron microscopical technique

Electron micrographs of the relevant samples were taken using a 35 mm camera. From the print obtained and knD-/n.ng the toird magnification (i.e.

the m,--xgnification of the microscope and the magnification characteiistics of the enlarger), an equivalent distance to lyUm could be measured on the photograph. The dimensions of the irregular particles were measured with

respect to the M'l m equivalent distance and the mean given to represent

the particle dimension. As the particles v/ere ill-fomed^ a range of size is quoledo

II»7.ii Optical microscopical techniques

The method has been described in great detail (lO). The instT-iment

•js^'i was a Vickers polarising microscope v/ith magnifications 400x and l600,y. T'he samples were spread on a glass slide and placed on ti.e microscopCo

The sizes were estimated by corig^aring the particles v/ith standanl dimensions on an eyepiece graticule (ll). The graticule dimensions v/ere calibrated

to represent different ykjn sizes for each magnification. Again, as the particles are irregular, a range of size is quoted.

V/'i.th both techniques of measurement, care must be taken v/hen measuri.ngj

that, the sample is representative of the total mass. This involves precise and careful observation of the sample characteristics.

II08 Surface area measurements

.Cias sorption measurements give information as to the specific surface and the average crystallite size of a powder* A general treatise of the

subject has been given by Gregg and Si.ng (l2).

The method used to determine surface areas was due to B.runaer_n Kmmett

& Teller and is knovm as the B.EcTc procedure (l3). The B.EoTo equation givess

P ^ c - 1 ^ p ^ _J_ / \ X c ** — x c x (p^ - p) m p^ m

45 where p is the pressure of the adsorbate vapour in equilibrium with absorbent! p^ the standard vapour pressure of adsorbate vapour; x is the

amount of vapour adsorbed s is the capacity of filled monolayer^ c is a constants

Adsorption isotherms are classified into five types of which type

II isotherms give the best agreanent with the BoE«,To equation over limited

ranges of vapour pressure (14)- Thus a plot of —against ^/p^ would give a straight line of slope — ~-r^ and intercept -~- . From the X C X c

m m quantities a value of x^^ can be founds The specific surface 3 is related

to x^ by the equation;

S = ^m . N . A^ M v^here M is the molecular weight of the adsorbate

N is Avogadro's number A is the cross sectional area of an adsorbate molecule in a m

completed monolayer*

The specific surface is related to the average particle size 1 byj s= i- vrfiere ^ is the density of adsorbent*.

Apparatus

The sorption balance is based on the design of Gregg (15s l6)c The balance arms are made of glass and supported on needles. One arm of the balance supports buckets for the sample and counterweights^ the other arm either a solenoid or magnet enclosed in glass and surrounded by an external solenoid. The whole assembly is enclosed in glass and connected to a system of evacuation pumps and gas reservoirs. The pressure readings were made

IS with a graduated mercury manometer. The current in the external solenoid is

va.ried to obtain the balance point, which is noted by comparing the position of a horizontal metal pointer with a reference pointer- The instrument is calibrated by measuring the current required to observe the null point for knov/n weightSo Buoyancy corrections wer^ made to the readijigs again by comparison vrxth a standard material.

Technique

The sample was placed in the specimen bucket and out-gassed to remove physically adsorbed vapour* This was carried out at 200° by surrounding the balance liinb with a furnace {U)^

k Dewar flask containing liquid oxygen v/as placed around the balance limb. The absorbate was nitrogen gas« The isotherms were measured at o

-183 C. The weight of the sample v/as determined in vacuo* Nitrogen was introduced into the system and equilibrium v/as achieved before si.multaneous readings of sample weights and gas pressure v/ere taken*

From the results the surface area measurements were found with the aid of a computer program devised by F* OM^Jeill and Denise Harris (5) in

Fortran IV using an loB^M* 1130 computer as detailed .in Appendix IV*

11,9 Ball milling

The al.uminium nitride v/as milled in cylindrical porcelain pots containing a number of balls of the same material. The pot had radiused ends to present a smooth interior surface free from comers and crevices*

Having placed the material in the pot^ the open end was secured v/ith a lid and quick-release bar* The pot was placed in a jig and lay in a horizontal position^ and mechanically rotated so as to ensure effective contact v/ith the porcelain ba^ '

47 Following the milling period, the process of recovery was as follov/s:

The pot was held vertically above a sieve positioned on a large disho The

porcelain baJ.ls were collected on the sieve and the powdered nitride

collected in the dish. The balls and the inside of the pot were brushed

vigorously to remove the nitride. Any remaining nitride was brought out

by jDtating the closed pot with a portion of acetone, v/hereupon the ni.tride

and acetone were removed from the pot and the nitride was freed from

acetone by drying in an ove/i at 70^C overnights

8C^- recovery or better vras achieved \vith this operation.

II• 10 Experimental techniques used in prc-parinp( .•.li-iminium riitridg

IlolOoi Preparation from ammonium hexafluoroalt-iminate

The preparation of aluminium nitride v/as attempted by the thennal

decomposition of ammonium hexafluoroaluininate in gaseous ammonia,

Ttie :removaI of gaseous impurities

Vvhcn decomposing the- htxafJuoroalumin-^ite compound in air it v.-as noted

that aftf-jr periods of an hour at hiigher temperatures (> 500^C) the

formaf.ion of compounds similar in x-ray cliaracterlstics to basic fluorides

(24) were formeda The removal of the moisture in the system v/as therefore

vi tal. c

Tht: air v/as passed throur^h tvro r.lreschel bottles and a hoj*i cental glass tube containing potassiLim hydroxide pellets* The glass l^ube v/as \i3ed to improve c:ont,.T.ct between t;he hydroxide and the air* As a consequ eiice p the removal of moisujrc from the system appeared to be effective^ for in .18 hours at

62^^C no basic fluoride v/as I'onned v/hen decomposing tlie hexaflui^roaJamnatee

The presence of a sm^Ui percentage of ox^'gen v/as anticinatod an the nitrogen ^-'^as used and to- remove it the gas v/as bubbled through pyrogallo.l solution. To prepare' pyrogallol solutions 15 grams of A.Ro pyrogallol v/ere acJued to a quickfi t test tube. A t)jbe was inserted via a side arm piece

and 100 mis of 4Q/o aqueous potassium hydroxide was added ijnder nitrogen.

The solution v/as prepared in this manner because of its actii*e affinity

for oxygen. The nitrogen v/as bubbled through the pyrogalLol solution and

passed through a U-tube containing magnesiimi perchlorate, prior to passing

it through the drying system.

Furnace

The furnace v/as a horizontal tube t.^-pe using chromel-alumcl

thc-rmocouples v/ith a maximum temperature of 1000 C,

V/hen ajnmonium hexafluoroaluminate is thermally deccmposed, amm.onium

fluoride is present. At temperatures above 520*^0 it vrill exist in its dissociated state as ammonia gas and hydrofluoric acid gas^ Hov/ever, the recombination of these tv/o gases takes place at temperatures less than p20°C giving ammonium fluoride which condenses on the colder parts of the purox tube. It appeared to condense in one particular region and the bui-'id up of the compound v^as stifficient t( vigorously attack the purox until t.he tube fell apart. Kence the tube li.fe is drastically shortened^ To overcome this problem,, the tube end v;as maintained above the decomposition temperature of ammonium fluoride in the follovriiig manner. The tube end v/as wound v/ith several tu.mings of ni.chrome wire on a layer of paper asbestos, A thick layer of alumina cement v/as placed on the windings a.nd left to sc-t hard. The ends of the v/indings were connected through aji avometer to a viiri.a.c v/ith a majtimum current of six ampso The excess load on the tube vas compensated by supporting the tube below the alumina cemeni: ]ayer.

The variac v/as set just below its nELximam rating and a temperatur-e of 600^0 v/as observed in the furnace end. This initially upset the therrrtil equilibrium and the discrepancies v/ere accounted for by allav/i.ng the gas to

49 be used5 to pass through the system foi- a period of some 30 minutes.

The ammonium fluoride condensate v.^as therefore collected in a six

Inch length of copper tubing which v/as rigidly set in the purox tube v/ilh

a.laTina cement. Less than half of the copper txibe v^as cooled by placing

a few turnings of thinner copper tubing around it and passing ^vater

through them.

After each run, the copper tubing where -Jie ammonium fluoride v/as

nc.v observed to condense v/^is cleaned v/ith a small brush.

The exit gases were passed through (a) a plastic bottle containing

glass wool, (b) a dreschel bct.tle containing potassium hydroxide pellfrts,

arid (c) a plastic bottle containing distilled ^'.-ater^

The fi.rst plastic bottle was inquired to prevent any fluoride attacking

the dreachel bottle which in turn was required to prevent moisture: diffusing

back into the system. The a-nmonia exit gas was partially dissolved in the

distilled water; any excess was passed to a furne cupboard.

The ammonium hexafluoroalioml-nato and its deri.vatives v/ere placed in

a pt:r\::x boat which v/as inserted into the horizontal tube furnace and placed

m the hot zone under the gas in question. The rate of gas flow v/fis measured

using calj.brated flowmeter r/jbeso

Il.lOoii Preparation by the Serpek reaction

There are enumerable problems^ such as temperature control and

fluctuaticnsj thermocouple materials and syston designs v/hen studying chemical reactions at elevated temperatu reso iThe possj.biMty of designing a, high

'•?mper?iture furnace was considered-, but for the reasons stated above, an altf.mative method v/as desirable.

50 The use of optical microscopy appeared to offer a suitable method

for examining the reaction*

Tht: n^icroscope used in the investigation was a Gri f fin-Tel in hot

stage microscope which has the following advantages^

(a) Elaborate v/ater-cooling arrangements for the protection of the micrrs^jpe are unnecessary and the instrumait can be adapted to examine

thf. bshaviour of na.teraals at high temperat'ure by x-.r3,y diffraction as

W-T:]! as by optical microscopy*

(b) The' method of mounting the sample makes provision -^or examination of the internal str-.ioture by transmitted light- CrystaJ.s present in a r^r;;^: oan be viewed in normal and in polarised light.

(c) The instrument provides specifically for very hi^h fcemperatrxre cbs'^r'/aticns and reprc-ducibility cf results ' reported to be within

± ^=G.

The instrament is composed of a pov/er supply,which incorporates a

3 inch scal.e meter calibrated directly for use vrith 20?5 Rh-Pt/595 Rh-Pt-

• h^nnocouplfc^ and a leek petrological binoctilar-type microEcope.

The instroraent i^ provided wi.th a gas tight cell which houses the

thfjrmocouple elements and at the same time permi.ts the use of any desired atmosphere* At high temperatures oxidation of the thermocouple iTiay ccciT* and iJri^ volatd lisation of the thermocouple v/ill impair visior. of th& sample* Passing of nitrogen rb^d^tes this effect and the use of this gas is also desdjrable for the Serpek reaotion.

The inlet and outlet posts of de cell v/ere guarded. f.roiii moisture by U-tubes containijig oalclum chlorideo

The thermccoupls *^ni.t3 are provided with necpr^ne gaskets vrtiich make ar. efficient seal v/hen the retainir.g nuts on the gaide rods are tightened.

- 51 - The cel3. was attached to the microscope stage by means of slotted

armsj; which in the locked positi.on exert a slight pressure on the cell

t*. ensure good thermal contact with t;he revolving microscope stage^ and

sc any heat radiated which is smallp v/ill be ccnducted away and dissipated

in the body of the instrument*

The aligrjnent of the instrumen*^ was checked before each cperat.cn

t-o snsure optim^jni \rislbility-

W^en using the instrument the b-^avaour of any material and the

aCT^racy of tempezB-tuj-e mea3uxem?-nt is dependent on two factors,, (a) the

ccrTzrct fabrlca+iort of the mlcrof'-tma'js assembly,, (b) temperature

gradient within the sample.

(a) Fabrication of the themccouple elements

The cptimum performarce of the micro furnace assembly is dependent upor> the thenjio^iijinctions being formed in en eract and reproducible manner.

A length of 5^ Rh~PL alloy (approximately 3 cm) is placed in the negative terminal designated by a ?mall red dot and sec^jred by the clampJjig screw. The other extremity of the v/ire was such that when placing the thermocouple ^^nit i-nto the ceil^ it extended just to the edge of the windovj aperture. A eimilar length of 0.5 mm diameter

20fc Rh-Pt alloy wire- wa£ damped tc the pr*sitive terminal. These two wir^s form the supports for the heater element proper, which is composed of 0.2 nan diameter wires of ths same alloy composition. To join the two rsspaotiv^ v?lreB togetharc the operation requires a small oxy-coal gas flams. The thinner diameter wire is fi.rst placed in flame and a small bead concparlble in dijnension to the diameter of the thicker wire is formed*

52 The "bead io placed adjacent to the head of the thicker wire and the ^virea

pl.aced in the flame ujitil fusion is complete. The operation, which

requires a cei-i:ain amovint of skill, is repeated with the other two v/ires

of differing diameters. The fine wires are then trimmed to approximately

lo5 cm and the supporting v/ires turned inv/ard until the fine wires are

crossed. The fine wires are trimmed in this position using a guillotine

and jig and the v/elding of the juxtaposed fine wires is completed in the

flame. Any final trimming may be done using the guillotine. Finally,

the fine v/ires were squeezed together in the heighbourhood of the junction

over a length of 5 mm, A rigid observation of the procedure enables

repi^ducible results to be obtained,

(b) Tgnperature gradient in the sample

Dae to a finite v;-idth between the thermocouple wires adjacent to the

point of junction of the 0.2 mm diameter wires, and the presence of the

sample in this region, there will be a temperature gradient v/ithin the sample,

This is reported to be of the order of 4°G (i.e. - 2^C from the junction

point at which the actual temperature is measured. It is therefore necessajry not to overload the thermocouple with the material to be investigated. The materials v;ere ground to less than 200 mesh.

To calibrate the thermocouple A.R potassium sulphate was used as it has a sharp and reproducible melting point at 1072°C. It also under• goes a polymorphic transition at 580°C,

To moiu-it the standard and materials to be examined, the thennocouple was dipped in solution of an inert solvent and placed in p^JV/dered . sample. It was found that a coliamn of appro^c^r^tely 0*5 mm gave the optimijm results with the standard, and this dimension was adopted with the materials to be examined.

53 - The thermocouple and sample were placed in the gas tight cell and

the assembly mounted on the microscope stage* Nitrogen at a moderate

flow rate was passed through the system for a few minutes to remove any

air present. The rate of gas flow was found as in the previous technique

using a flowmeter. The connection betv/een the power unit and the thermo•

couple was made and the heat input increased gradually until the temperature

required v/as obtained.

After the run, carefVil removal of the sample was made, A smaJ.1

amount of collodian was added to the sample and it was moiinted on a very

thin glass fibre and left to dry for 30 minutes. The fibre v/ith the sample

v;as then placed in the 9 cm povider camera and a powder photograph was taken

as previously described.

The thermocouples were cleaned by inserting them first in concentrated

hydrochloric acid and drying them and placing them in water, then acetone,

and a final drying in an oven at 60*^C.

Il.lO.iii Preparation of the nitride from its elements

Reports that aluminium can be nitrided belov/ its melting point, i.e.

above 400*^ were investigated. The microcrystallinity of aluminium films

and their changes on attempted nitridation were studied by electron

microscopy and diffraction.

The aluminium film was prepared by first depositing a carbon film on

mica. The mica plate was then fixed inside the high vacuum unit at about

10 cm from a helical tungsten filament. Aluminium powder was placed in the

filament and the system evacuated. The filement cutrent was increased

sufficiently slowly to avoid rapid temperature changes, thus avoiding any unnecessary stresses in the film. After the aluminium had evaporated, the

resultant film and carbon base were stripped from the mica plate and placed

34 on a copper grid in the normal mannero The film was observed under the microscope and a diffraction pattern vjas taken.

The copper grid with the deposited aluminium film was placed in a glass vessel which was flushed with nitrogen gas at room temperature.

The nitrogen pressure was reduced to 0,2 atmospheres by pumping out the excess gas from the vessels The whole assembly v/as laz/ered into a furnace preset at 300°C. The films v/ere heated for 3 hours and re-examined under the micro scope,»

55 !• V/illardj, H.H, , & Winters^ O.B., IndpEng.Chem.Arial.Ed., 1935, 1, 7o

2- ' Vogel, A,Iftj> "A Test Book of Qualitative Inorganic Analysis", 2nd Ed., 1931, (Lon^ans).

3. Linstead, R.P., Elvidge, JoA,, & V/alley, M,, "A Course in Modem Techniques of Organic Chonistry", 1935* (Butter\M3rths, London).

4. P&sser, R«G., et alo Analyst, 19^2, 87, 301«

3. O'Neill^ P.5 & Harris^, D^^ PODH, (Fortran 'IV)p Plymouth PDlytechnic, 1969•

6. Bognar, Jo, & Nagy, L., Koliaszati Lapok, 1938» 91p 338.

7. Hejduk, Jo, & Novak, J,, Z.Anal.Chan. 1968, 23^, (5), 327-

8. Henny, NoF.M,, Lipson, H.j, & V/ooster, Vi'oA«, "The Interpretation of X~ray Diffraction Hiotographs", (Macmillan & Co.)^ 1960»

9. Klug, HoP,, & Alexander^ UE., "X-ray Diffraction Procedures for Polycrystalline and Amorphous Materials", (j.V/iley), 1934.

lOo B,S. 4306, F^rt A, 1963.

11. B.So 3623, 1963.

12. Gregg, S.Jp, & Sing, K.S.VJ.^ "Adsorption, Surface Area and Porosity", (Academic Press), I967.

13. Brunaer, S. , Bnmett, P.H., cS: 1 eller, E. j, JoAm.Chem.Soc, , 1938 , 60 , 309

14. Gregg, S.Jo, "Siirface Chanistry of Solids", (Chapman* Hall), 1951.

15o Gregg^ S.J., J.ChQDoSoCo, 1946, 36I0

16. ibid., 1933, 1438.

17. Glasson, D.R., SoCI. Monographs, 1964, No. 18, 4OI.

18. Grimshav/, R.V/., Heaton, E. , & Roberts, A.L., Trans.Ceram.Soc., 1945. 44. 76.

19« ShJ^-nd. Bo, Crockett, D.S., A Haendler, H.M., Inorg.Chem., I966, 5, (11), 1967.

20^ Haendler, H^M. , Johnson, F.A., & Crockett, D.S. , J. Am.Chem.Soc., 19383 80, 2620

21. Gam, P.D., "Therrooanalytical Methods of Investigation"^ (Acadanic Press), 1963.

56 22o Gr«gg, S^J.p & V/insor, G.V/op Analyst^ 1945p JO^ 336.

23. I^raerj H.S<,5 Rooksby, H.P.p & V/ilson, A.J.C, "X-ray Diffraction by Iblyciystalline Materials", (Chapman & Hall), 1960<,

24. Cowley, J , & Scott, Mo, J^A.C.S., 1948, JO, 105.

57 - CKAFTER III '^he formation of aluminium nitride

In the present research, three methods for the formation of

aliiminixim nitidde were tried. They were (l) themal decomposition of

ammonium hexafluoroaluminate in ammonia^ (2) the formation of the

nitride from an intimate mixture of oc -alumina and carbon in the

presence of nitrogen, and (3) the nitriding of pure aluminium.

III.l The thermal decomposition of ammonium hexafluoroaluminate in

various atmospheres

The thermal deccmposition of the ammonium-aluminium-fluorine

complex was studied in air, dried air, and dried ammonia.

m.l.i' The theiToal decomposition of ammonium hexafluoroaluminate in air

Approximately 0.25 grams of ammonium hexafluoroaluminate v/as weighed

out in a purox (recrystallised alumina) boat ajid placed in the tube

furnace as described in Chapter H. Air was pumped through the furnace

at a moderate rate to allow sufficient ranoval of any volatile matter,

V/hen the air was to be dried it was passed through a potassium hydroxide

dxying system. The complex was heated in air at various tenperatures

-for set intervals of^ime and subsequent weight losses were determined.

A plot of percentage weight loss against time for different temperatures

was made (see Fig, 3). At various intervals in the heating cycle,

samples were removed for x-ray analysis to determine the phases present

(see Fig. 4). The thermal and x-ray analysis gave the following results'.

Ammonium hexafluoroaluminate is stable in, air up to 130*^0, v^en a

weight loss of' ^ was observed. This decomposition is probably due to

loss of water present in the system. From the results of the differential

thermal analysis a small peak is recorded at 100*^C (see Fig. 3a). At o 220 C the formation of ammonium tetrafluoroaluminate begins to take

58 Fic.3. 'f'-i^ vvvcei\t-^t:e v;t. loG" of an::.or.iu:^ hexfifl-'V;rop3viuinate hei-ted in

c.i^ied r.ir for vc iicr.r- te:nr*e-; r tv.res :^ncl tinov-.

Z2o"c

-X. G place. The weight loss at this teniperature is therefore due to the

volatilisation of annionium fluoride. The characteristic d-spacings for

(NH^)^AIF^ are 5-2 and 4-A-7. From Table 8 the d-spacings are 5.0? and o if.A- respectively a.fter 5 hours at 220 v/hich suggests that the number of moles of ammonium fluoride present in the sample is slightly less

than three. After 4 hours at this temperature, the tetrafluoroaluminate phase is prevalent (see Table 8). As the temperature is increased the loss of ammonium fluoride continues and at 340^0 d-spacings intermediate between those recorded for ammonium tetrafluoroalwmi nate and those of a phase identified as >j'-aluminium fluoride v/ere observed (see Table 9,

Fig. 8). This intermediate compound exists even after 5 hours at 340°C.

The thermal analysis curve at 420°C confirms the existence of this intermediate as the percentage v/eight changes for ammonium tetrafluoroaluminate and "j^-aluminium fluoride are 3^ and 5^° respectively, and a weight change of 51»^^ is observed after 4 hours at 420*^C. To verify the nature of the intermediate, infra-red analysis gave peaks at 1430 and 3240 cm which are due to NH."*" ions and hence this intermediate is 4 of the type AIF.^ (NH^F)^. TO determine the stoichiometry of the compound, a chemical analysis of the ammonia content was made, ^he perxientage ammonia present was detemiined as 4-32^ and the theoretical aimipnia content of ammonium tetr^fluoroaluminate is 14.0^. The formula of the intermediate observed was therefore AIF^.0.3 (NH^F) v/hich is in agreementhermal analysit with sth eo f 51.2?ammoniuo weighm hexafluoroaluminatt loss. Furthermore.e a , peafrokm ove ther differentiathe l temperature range 200 to 420°C vdth a maximum at 335*^0 is observed.

Ammonium tetrafluorostluminate therefore does not appear to exist as a

- 62 Table 8

Ammonium hexafluoroaluminate heated at 220*^0 in dry air

3 hours 4 hours d (NH^)3A1F^ - ^^AlF^ d I d I

6o284 11 6o231' 4i 6.40

3.07 4 5.2

4o398 2 4.47

3.377 13 3.349 2 3.60

3.122 11 3.080 2 3.14 3.13

2o523 4 2.496 2 2.57 2.54

2.343 4 2.328 2 2.36

2.218 4 2.197 2 2.22

2.104 3 2.090 2 2.03 2.11

1.97. 2 1.958 1 1.99 1.98

I08I3 4 I.8O5 3 1.82 1.83 lo788 8 1.778 5 1.80 lo723 2 lo708 2 1.71 1.73

1.61

1.396 3 1.591 2 lo59

1.378 2 1.571 ] 1.38

1.549 3 1.542 3 1.56

63 Table 9

Aimnonium hexafluoroalumiriate heated at 340°C in dry air

^ hoiir 5 hours 'NH. AlP, 5'.A1F3 d I 4 4

6*224 3 6olU 4 6.4 6.029

3.535 ras 3o620 9 3.60 3o5Al

3.083 m 3.039 2 3ol2 3.042

3 = strong

• ins = moderately strong

m."=:-. moderate©

64 stable phap.*? in the decomposition, but may be considered the end member

of tht series MF^.NH^F - ^-AlFy Shinn et al (12) concluded from x-ray •

results that the tetrafluoroaluminate is a distinct phase in the

deccmposition even though dynamic thennogravimetric angilysis reveaJed

a point of inflection corresponding to a weight loss of 2.1 - 2.25

moles of ammonium fluorideo Other vjorkers (l3, I4) also report the

existence of stable tetrafluoroaluminate phase in the thermal decompo•

sition and it seems that their conclusions are wrong.

Differential thermal analysis of the starting coirplex revealed a

peak with a maximum at 470^0. X-ray ajialysis gave d-spacings comparable

to those of Shinn et al (12), Hov/everj. Shinn ,et al (12) were not able

to make full che nical analysis of -AlP^ due to the resistance of the

compound to decomposition. They managed to prepare an impure form of

-aluminium fluoride by passing gaseous hydrogen fluoride over aluminium

bromide or chloride at temperatures from I50 to 500°C, as indicated by

the x-ra> pattern. The x-ray pattern however, v/as generally amorphous,

but the transition to OC -aluminium fluoride was observed when the impure

fluoride was heated in nitrogen at 730°C, In the present work infra red

analysis showed the absence of any ammonium ions in the compound Jj'-AIF^.

A chemical analysis for eiluminium and fluoride was made (see Appendix II) ,

and the compound was therefore unequivocally established as ^-aluminium

fluoride. The x-ray characteristics of the compound will be discussed later.

V/hen the temperature was raised to 530*^0 the formation of ^-aluminium

fluoride vras evident after a quarter of an hour. However, at 620°C after

1 hour the formation of a phase which gave a number of spacings which did not fit with the previous data was observed (see Table 11), To

65 - Table 10 Comparison of the observed and calculated d-spacings for ^-AlP^

(a = 3.53 ± OoC lS; = 6o02 + OoOl 2)„ ^

^obs ^alc ^ 60O3 6.02 001

3.54 3.53 100

3.03 3.04 101

2c0 2o01 003

1.92 1.92 112

lo76 lo76 200

lc70 I069 201

1.54 1«33 211

1.50 lo50 004

1.38 1.38 104

1.33 1.32 203

1.24 1.24 213

66 establish the nature of this compound the sample was x-rayed after 4 hourSy 18 hours and 65 hours at this temperature. The results are given in Table 11. A comparison of the d-apacings observed with those reported for basic fluorides (15^ 16) revealed the possibility of a basic fluoride being formed due to the moisture content in the air. A fluoride analysis of the specimen heated for 18 hours at 620*^0 gave a percentage fluoride content of 41.7^ which corresponds to a formula AlP ,q. Hence to the balance the stoichiometry OH ions v/ill substitute in the lattice to give the emperlcal formula Al OH F., v/here x = O.8I5 and as the time

X J —X of heating in increased the loss fluor-ine increases and x in the emperlcal formula will increase. A formula in v/hich x = 2 (i.e. A1(0H)2F) for a basic fluoride has been reporLed (15)» Prom Table 11 as the time of heating is increased the ionic fraction of (OH) increases and peaks are observed after 65 hours which are not present in the previous cases of 1, 4 and to a lesser extent 18 hours. The Ai-F bond lengths in aluminium fluoride are of the order of 1.7 S and this is increased to

1.84 ^ for the basic fluoride Al(OH^ ^^F^ ^^) l.OS.H^O, so the introduction of hydroxyl ions will weaken the crystal lattice, and will finally result in the total removal of fluorine. This forms the basis for the analytical, method to determine the fluoride content of aluminium fluoride by pyrohydrolysis (17^ 18). There are conflicting reports as to the temperature at which the thermal hydrolysis of aluminium fluoride initially takes place, but temperatures as low as 300°C have been reported (19). It is noted that as the time of heating in moist air is increased the d-spacings respectively descrease and there is significant change after 63 hours (see Table ll). Furthermore, the density of the fluoride heated in moist air for 18 hours was measured as

67 Table 11

Comparison of the d-spacinfis of ammonium hexafluoroaluminate heated in

moist air at 620°C for 1, Us 18 and 65 hours v/ith Y -AlP^, a basic

fluoride, aluminium hydroxide and al.umina

1 hour 4 hours 18 hours 65 hours d - I . d d • ' d ^^-AlP^ obs obs obs • - .olis X ... ^ z

6.029 5.93 w

5.32 w 5.31 vs 5o29 s 4.90 s 5.53 4.72

3.8/4- w 4.36

3.547 3.51 VSl 3.46 ms 3.46 mw 3.52 m 3.4B

3.36 ms 3c37 s 3.28 m 3.19

2.999 3-05 vw 2.93 3.08

2.84 niw 2.83

2.68 WW 2.67 w 2.67 m 2.70 m 2.69

2.300 2.53 vvw • 2.52 w 2.58 mw 2o55

2.39 WW 2.43 2.43

2.37 2.34

2.28

2.270 2.2 m 2.18 w 2.28 vw 2.25 2.21

2.18 w 2.19 vvw 2.16 2.14

2.129 2.11 m 2o09 w 2.09 VI 2.08 2.00 2.06

2.003

1.915 1.97 w 1.96 1.97

1.773 1.83 w 1.89 1.83

1.736 1.75 nT7/ 1. 74 mv/ 1.74 1.73 1.76

1.707 1.60 1.65 1.68

1.382 1.58 w 1.55

I0532 1.51 1.50

1.40

1.379 1.37 1.38

lo332 1.25 w 1.28 1.28 / m i 1 - 68 - vs = veiy strong = ^-^2^3 s = strong m - n>oderate • V = ^W^.H^O w = weak = Al(OH), (Bayerite) w/ = very weak etc.

- 69 2.Vf + 0.06 g.cc vrfiich cccipares well with the reported values for basic aluminium fluorides (15)3 i^e* 2.25 and 2.45 + 0„2 (20)»

When the sample was heated in carefully-dried air (see Chapter II) at 620*^0^ the specimen was identified as ^-AlF^. The d-spacings of a

sample heated at 700*^0 no longer agreed with those for ^-aluminium

fluoride, A comparison v/ith the values reported for -aluminium fluoride (2l) shov/ed that in fact a crystallographic transformation had taken place. K-fferential thermal analysis also showed this change and a small peak was established at 690°C (see Fig. 5a). To check this fact a sample analysed as ^-AIF^ was heated under similar conditions

(see Chapter II) and a peak v/as observed at JOO^C (Fig, 5b). Chemical analysis of the product concluded that ©(-aluminium fluoride was formed at 695° i 5° c.

There are several reports in the literature that aluminium fluoride undergoes a phase transition at 445°C (22^ 23) and 46O + 4°C (24).

Repeated experiments between room temperature and 700°C with ammonium hexafluoroaluminate and ^-aluminium fluoride gave no evidence of a phase transformation for aluminium fluoride other than that at 695° + 5°C as previously described. It should be noted that the existence of

^-AJ.F-j over a v/ide region of temperature (420-695°) <. The alviminium fluoride transformation is irreversible as a specimen of oC- aluminium fluoride was heated at 600°C and the d-spacings of QC, -aluminium fluoride v/ere maintained. The presence of OC-aluminium fluoride is observed at temperatures up to 880°C, However, when (p(-aluminium fluoride is heated for 18 hours at 710°C in dry air^'d-spacings other than those for OC-alurainitmi fluoride are observed (see Table 12). This is probably due to removal of fluorine from the fluoride and substitution by oxygen.

70 Table 12

Ammonium hexafluoroaluminate heated at 710°C for 18 hours in dried air

4o79

3.67

3.50 3oS2 3.48

2.65 2o55

2ol7 2ol2 2.16

lo86

1.5 1.51

1.45 1.46

1.4 1.36 1.40

71 - The themal decomposition of ammonium hexafluorogallate is said

to take two cour-ses (see Figo 6)0 Pijrstly gallium flizoidde can be formed

as 13 observed -with the aliimini\im compound or the second course i^.sulting

in galli'om nitride^ Tirf?ich was proposed by Kannebcru-i & Klemm (46) to explain

the weight changes observed when heating the sample in vacuo o In the

/present vfork when ammonium hexafT-uoroaluminate was heated in vacuo at o

4-50 a white x/^ray amorphous compound was fcimed for which no chemical

analysis v/as madCo This investigation was not continued as means of

qualitative identification of the product was not possible.

Two different forms of galliijim trifluoride are reported to exists

orxe obtained as above and one by the fluorination of galliiam oxide as

600°C (25)« Recently a crystal structure of galliijm fluoride has been

reported (5)»

It was concluded that the decomposition of ammonium hexafluoroalimiinate

ia air took the follo;ving courses (NH^)^ AlP^. V f^^y, o<-AlF3 i^20-330°c 695°

Illolcii The theii3:ial decomposition of amnonium hexafl^oroaluminate in

ammonia

It has been reported (13.) 26) that aluminiiim nitride is formed when

annnonixim hexafluoroaluminate is heated in ammoniac Due to the ease of

formation of the fluoride complex and that fact that aluminivnn fluoride

is a waste product in the phosphate industryg and could therefore be

subsequently converted to a useful source^ this method of fanning the

nitride was extensively investigated.

72 - TheiTual decomposition cf ammonitDn hexafluorcgallate (^^^^.^3 ^6

WH,GaP. GaP,

•2EP

-HP •HP Ga(NH2)^2 Ga(NH)P GaN

- 73 As in the decomposition of the complex in air the complete removal or emmcnl-jm fluoride was not observed ^_Jitil 330°C v/hen an x-ray trace of a sample heated for 2 hicars at this temperature was positively idsntified fis ^-AlF^e ^''hen the tonperature was increased^ the thermal decomposition

,in cartifully dried ammonia v/as analogous to decomposition in air© At

620*^0 1^-aluminii-un fluoride \va.s observed which converted to -aluminium fluoride a.t JOO^C in aninonia ,, TheoC-phase was still observed at 840 and.

8S0"C» The temperature was raised to 5^0 C and the specimen v/as heated

Per on hour and cooled to hOO^C under a flav? of ajnmonia to prevent oxidation of the sample when removing it fj-om the funiacs. An x-ray trace of the product, I'eveaJ.ed aluminium nitride in the presence of aluminium fluoride

(see liable 13). To study the effect of the rate of flov/ of ammonia on the reaction at this temperature ^ half gram samples were weighed out and placed in the tube furnace under a curr-ent of ammonia at 96o^C.

A plot of percentage weight loss against rate of flow of ammonia was made (see Figo ?)• ^ v/eigJit los^i of 6le58^ ^vas recorded v/hen the flov/ rate of amjnonia v/as zero* The theoretical v/eiglit loss for the transforrrB.tion of ammoni'jm hexafluoroaluminata to aluminium fluoride is 3"/^e According to the i-eacti.on

(NH^)^ kW^ + im^ AIN -r- 6NH^F the theoret.ical v/eight loss for the formation of alumi.nium nitr^ide is

78«9fi?o« An x-ray trace of the product rsvealed twc- peaks which gave d-spaciJigs comparable with those established for aluminium ni.tride,, The presence of aluminium nitride in a zero flew rate of ammonia can be exr)lai.ned as follows^ Table 13

Ammonium hexanu 0 roal.umiriat e heated in d i-i ed ammorj-i and cool ed to 400°C in ammonia.

d. . Intsn iiity* ODSo ^A.1JI

5.48 2 5o52

2.68 3 2o70

?c53 3 2o51

2.46 1 2o49

2 2.37

2.07 3 2.07

..8.1 1 1.83

^^"!'^ .1 1.76

1.^9 4 lv59

1 1.56 1.56

1 1.46

* Intensity measured as the peak hei^t»

75 .1^, -

Pig. ?• The thermal deconposition of anmoniuia hexaflouroalunina in various flow rates of ammonia.

3 - 76 - AramonrrAui fluoride sublimes at 520 o C to give ammonia and gaseous hydrofluoric acid according to the reaction

NH.P NH^ + HP

Hence the fomation of aluminium nitride in this case will be a result

of the reaction of al.umim,um fluoride and ammonia according to the

reactions (NH, ), AlP. —»^ AiP, -i- m^F L 3 ^ J

NH, + H P

A.1P, + NH,—^ AIM + 3HF

To verify this statement an independently prepared specimen of X,-aluminium

fluoride was heated in ammorj.a at 9Sd^C and aluminium nitride was positively

ider.tlfiedo

Prom the reaction

AlF^ +• NH^ ^ AIN 3H?

the equilibrium constant v;ith respecr. to partial, pressure of the gases

present K^-^ w.iJLL be given by

\- PHF ^

^NH^

Reducing the partial pressure cf gaseous hydrofluoric acid in the system vrill therefore promote the formation of the nitridcc I'he ammonia gas

flowplng through the system yii.ll therefore remove the gaseous KP as the condensate ammonium fluoride and hence the increase in rate of flow of

ammonia vdll result in increase of the nitride fomation which is observed as an increase in weight lo3s= A comparison of the peak intensities of

diffractcmeter traces of samples also shov/ed the relative increase of

- /( nitride with respect tc fluoride as the flow mte of ammonia is increased

(see Table I4) - At a rate of 50 cc/mi.n a \ve±g.ht loss of 78^ is observed*

This corresponds to 98^6^ conversion to aJ-i^mi.niiim ni.^ridsu A nitrogen aralysis (see Chapter II) of a sample heated in airmonia at a rate of

48 cc/min gave a nitrogen content of 33*6l%5 v/hich corresponds to 98^5?^ alumi.avjn nitridec As the rate is Increased there is a marginal increase in nitride content as is shown in T'^g« 7o At a rate cf I60 cc/min a nitride content of 98.7?d was analysed., Further increase i_n rate did not increase the percentage conversion of the complex to aluminium nitride.

A specimen heated for 4 hours at 120 cc/min was analysed and gave a nitride content of 99.1/^«

It appears th-at the thermaa. decomposition of ammonium hexafluoroaluminate in dry ammonia gives a nitride yield of the order of 99/'"" Aluminium, fluoridej prtisent here as an impurity,, is reported to be used as a binder when sintering the nitride so the p-resence of the fluoride v/o'old not be detrimental v/hen the ni.tride is to be used in this marinero Ho//ever^ the presence of the fluoride i.s shown to increase rapidly the r^te of oxidation of aluminium nitride (see Chapter IV). The only disadvantage of the preparation is the rapid attack on the purox rube by ammonium fluoride seric^a3."]y reducing the furnace tube life. If this problem could be over• come the successfV'-l industri.al application of this method may be possible.

Reports that al.uminium nitride is formed frcm ammonium hexafluoro- al^ominate in ammoni.a af 50C°C (26) are not verified. These v/orkers report the presence of brown and graven aluminium nitride which would suggest

UTidesir^ble impurities present in the nitride^ In the present study the nitride formed was a white cr^-stalline po^jider of excellent purity.

- 78 Table 1

Ccnt-parlson of the observed x-raj^ in ten si t±ea of_ anmoniujii hexaTiuoroaJ-uminate

heated at S60*^C in various flow rates of ammonia.

Rate (cc/min ) 5 8.1 23.5 43 71 96,7

I I ^^AIN I I I I

3.48 12 8 8

2.70 2o69 12 12 28 36

2.51 2.49 2o5i 12 12 12

2c46 4 16 16

2.3?2 2.37 4 4 6 6 16 18

2oli9 2.12 12 12

2 c 074 2.07 16 4 2 1 1 1

2 = 019

1.S29 I08I 2 6 8

1M7!)^J 1.73 * 4 4 4 1

1.6C6

lo59 8 8 4- 2

1«560 lo557 lc36 4. 4- 6 12

1.48

1.414 1.40 2 4 8

1.353 lo343

•70 It hias been reported chat gallium and indium nitride (2?) are

formed v/hen the corresponding hexafluorcmetallate compound is heated, in

ammoni.a at bj^gh temperatures» Gallium nitride is also r-eported tc be.-

foiTned from ainmoni-.:un hexafluorogallaue at lower teinpoxatures Thr.

complex is heated in argon at 175^^ initisJ ly t;o ammonium trr-trariuoio--

gallaf.. The tetraflucr-cgallate is heated in ammonia at 130^0 to form

the aad.:ct ammoni'wm tetrafluorogallats :ro;:o-/•-in.T.o.nifvJ;--', As the temperafj.re

is rai.sed , monc-.'jjrino °alli!.^: fluoricJe (CaP-, .I'Jti.^) is forneri wttich lose^

gas'.^ous hydrofluoric acid in the px^esence of ammonia at 300*^0 to form

galli-.m niLrideo As this offers a lov/ r.anporatur? aiteLTiaf:ive to

formation of' nitrides fix^m their corr-esponding hexaflLiOi'omet.aliates^ a

sijidlar pTX>gram v/as adopted for a^^.oni.um hexai'luoroalumlnatec

Aminoni-jm tetralluorcaluminate was mride acccrcing tc ti^s reaction

HBP; + Al(OH):; + NH, OH --^ NH, Ali"-' + H .BO, + H^O details are given in Appendix Ic

Ajnmoniw. tetrafl-joroaluminate was heated in ammonia at 110 C i'or

periods up tc 30 hours^ but no difference in structure v/as detected by infra-red and x-ray anal^^siso To continue the method of Merm^unt et al^

(28) attempts were made to prepaj:*e aluraJnium fluoride monoammoni.atee

The ammoniates of vhe chlorides (2.9) r bromides (30)^ and jcaid^^-

(39) cire known^ and it is reported that the mono-anrnoniate can be prepared by adding aluminium fluoride very slowly to liq;jid ammonia (3i)'»

To pr-epare the alu/ianium fluoride mono-ammoniate„ liquid ammonia was prepared by passing dried ammonia gas into a quickfit test tube placed in an ice trap (a dev/ar containing solid GO^)» Tc the oti-er side of the trap was connected a dr>''ing tube contaiiring potassium hydroxide

80 - pe?tlo.xF. to prevent moisture from entering the sye^tem*.

(p2^pai'ed by heating ammonium hexafiuor^aJ.imdnatrT in purified nlti-ogen at.

7.U-0~G) was very slov/ly added zo the liquid animonia anc the ml-xtv.^vas

left in a f.-me clipboard tc reach equilibrium. The quicK: fit test zxihe

v/as gmdually removed from the ice trap ^urh that indL05d tcinp-:rai^-^re

difference v/as sufficient to remove any excess jiquid a'!!-ni:*r.ia „ '-h'-r whi*.o

cov/der v;as examined using x-r^iy and inf ::^-red oji-al V5ji s anri no zt'r ^" '' "-...ra'L

differ-ences from oc -altomini-jm fluoride v/erd obser-ved. Henc:: th-: wcrk o*

Clark (51) v/as not confirmedo

Attempts v/ei^ made to prepare trie monc-- ammonia te by ])a35;inK a-Timo-.if.

g.^.s overo^ -al.Jiniriium flucride a*i; .1 lO'^ and l60^C for period--, up 1.0 .00

hours but no svructural changes v/ere obse:rvod<, It wai, er-tncii-atecj that,

^-alumirj.um fluor.ide liad a more open structui-^j, but no mor.::'-^;iPr;;no f' l-r-:.-1

adduct v/as observed usi.ng the above methods.

Using the Sehomaker-Stevenson relationsliip {32} the bcn-'ii^i^^j fo'r '^hf."

kr.ov/n OL--ali^minium fluoride structu.;:^ (33) v/as calculated as 6b/-. ionic in character^ whereas alimini^jm chloride^ iodide and bromides ar--^

prevalently" ccvalenc in cha_ractero Boron trtflucride ir.ono-^irriTior.iav i^^

readily formed from borcn triflucride and ainmo.nia and the r^^sultrixg chemi.cal bonding in the adduct is characterisi.j.cally ccvalenic rViri:-h£r!ri:;r?r,

aiuminium fluoride is repx^rted to have the rd.ghest lattice energy ot' the gr-c:;p Illb metal trihalides (34). The absence of i*orTP.at.i.on of a2iiiTj.ni:um flucride mj^no-amm.oniate is therefore attributed to inl-ierBnt chcirdcaJ na.tp^^re of ai.'.^minium flucride bonding*

Other routes for the formation of aluminium nitride from ammoraum hexLafJuorc-aJ-uminate than those established ax-e not possible^ and ihe

- 81 method of formation einalogous to the v/ork of iAermant et al (28) on the

gallium compo'ond is not confinned.

IXje to the similarity between animonolysl?= and hydrolysis a stU'dy of

the solubility of aluminium fluoride in distiJ.led v/ater was inadec Also

the structure of ^-aluminium fluoride is not yet evaluated and the

formation of any hydrates vdth the compound may give infornfiation about

the lattice space vachin the fluoride. The solubiliiy of aluminiijm

fluoride In v/ater is reported as 0^35% (2) presumably as the (A -trihydravec

The hydrates of aluminium fluoride are numerous (see T£Lbl6 15) arid

Ecgachov and Myasmkov (36) shov/ed that 0-19^o v/ater of crystallization v/as present in alumirdum fluoride v/hen left in air of var^a.ng relative

humidityc There is a report that v/hen alumi.nJLum I'lv-.oride trinydiiite is dehydr-atedj a nevf catalytic form of alumj.nium fluoride (y^-AlF.) is

formed (37). A comparison of the d-spaclngs of -al-.mnr:ium fluoride v/i.th

those reported for this catalytic fluoride (see Table 16) shov/s certain

similarities.., but contains a number of lines not present in ^-al--jro.ni.;)m

fluoride. The possible hydrolysis of the aluminium fluoride to t'oijn a basic fluoride may also occur.

It has been proposed (12) that this -aliuni.nium fluoride is in fact an open |^ structure with a residual amount of water ptesent.

To stijdy the solubility of the fluorides v/eighed amounts were placed i-n two separate 100 ml quickfit conical flasks. 50 mis of distilled v/ater v/ere added to each flask and the flasks sealed v/ith firmly fixed steppers.

The flasks v/ere gently shiaken iji a water bath set at 25^0 I'or 17 days.

Intermittently samples were extracted^ carefully dried by v/ashing in acetone and placing in an oven at 50^0 and v/eighed. X-ray and irifra-r-ed

- 82 Table 13

X-ray data of basic aluminium fluorides and aluminium fluoride Kydrates

Compound a (X) b (fi) c (2) ' Ref,

AIP^.SH^O 4A- AlP^.H^O 3.610 20

AIP^1.33H20 11»42 2ia8 8.54 41

AlP^ 3.H2O . 9o20 9.30 43

A1P^.3H20 7.734 7.330 44

7.734 3.665 45

Al(F^^^3,OH^^25)Vl6H20 9.83 15

Al(^1.65'^"l.35^'/^^^2° 9.849 15 9o87 15

- 83 - Table 3 6

Comparison of the d spacings of the reportedy^^-AlF^ (37) and ^-AlF^o

^j-AlF3(calc) ^-AlP^

6o02 6.002

3.53 3.563

3.04 3-063

3.001

2.4Sit

2 c 295

2.161

2.01 2.001

1.92 i<,914

1.76 1.782

1.732

1.69 1.708

1.665

1.585

1.53 lv532

1.50 j .500

1.38 1„377

1.32 1.310

1.284

1.24 J.242

1.2_16

1.200

1.188

l.^i48

3.134 - 84 - Analysis of the dried sangjle were madee After the period of 17 days^

there was no overall change in weight and no structural differences were

observedc It appears that ^ and oi -alvnninium fluorides are resistant

to hydrolysis under these conditions. However, basic fluorides are

formed as shown at higher temperatures*

III l,iii X-ray analysis of ammonium hexafluoroalumlnate

To determine the lattice parameters of the canplex a powder

specimen was ptrepared and placed in the 9 can camera (see Chapter II)^

After a 2 hotir exposure, the developed film v/as measured as previcusiy described. The intensity of the powder lines are dependant on the arithmetic mean of the scattering factor (f), (i.e. f is the ratio of the ajnplitude of scattering of an atom to the amplitude of scattering of a

single electron) and as th^ Bragg angle (0) increasesj, f deoreases*

Cor^sequentlyp for an accurate value of the lattice parameter^ Cohen ^s least sqixares method was enployed (8)^ as this method reduces the statistical error involved when using a small number of powder lines^

The lattice parameter of ammonium hexafluoroaluminate was determined as 8.93 + 0,01 X, which agrees well with established values (see Table 17)

Ill.l.iv The structural rearrangements during the formation of al^jminium

nitride from the thermal decomposition of ammonium hexafluorc-

aliiminate-

Aramonium hexafluoroaluminate has a tetramolecular unit cell cf dimension 8»93 + 0,01 2. The space group has been assigned as Fm3m-0^ with atoms in the positions:

NH^ (1) : ikh) h> h

• (2) : (8c) h id, h

85 - Table 1 7

Compound ^^^^ ,0, Ref ^ Dimensions (A) '

i^lJfoF^ 9-17 I,

(NH^)2^gPe.P^^O.i4H^O 9.10 4

Na,PeP 9.26 4

K^FeP^ 9o93 4

Rb^PeP^ 10.23 4

(NH^)^SiP^ 8.39 4

Rb^SiP^ 8oit4 10

(NH^)^AIP^ 8.90 40

(NH^)yilPg 8o93 Present vrork

Na^AlP^ 7.80 5.61 5.46 90^11' 41

Na^^AlPg. (500^6) 7.95 42

AlFg 8 . 468 5-944 41

K^Al P^^^ O.IH^O 8o435 41

(NH^)3lnP^ 6.53 9.49 40

(NH^)^GaPg 9.04 9

86 Al s (Aa) 0, 0, 0.

F ; (2ife) xÔÔ; O^x^C; 0«0,xs xÔÔ; O^XpO; OpO^x^

v/here x -• 0,23 =

There is an octahedral arrangement of fluorins atoms aicund each aj.umirKlum

atom with face centred cubic distributiono

The first thermal transition of the above system is the r^joval of

ainnscnxvm fliioride from the system^ If it is considered bha:: at any instant o

below 420 C in the decomposition*, the phase ammoni^jm tt^trafiuorcalT-jiiir.ate

exists then the following observation can be made.

Ammonium tetrafluoroaluminats has been assigned to space group

VL/mm - 'A with atoms in special positions

AI t (Id) '

F (1): (2e) 0,^,h i.O,^.

P (2)s (2h) ^^i^jz; -^^i/Z, where z = 0.21.

From structural considerations the removeil of t wo moles of ammonium

fluoride woiold be followed by contraction of the cubic lattice in tv/o

directions to form layers of AlF^ cctahedra Joined by shared comers (if?)*

The major adsorption in the infra-red analysis has been assigned to

The sharing of the fluoride ions does not distort the AlF^ oczahedin. as

the 2 band is not appreciably affected (see Table 18a). Th.e NH. grc-^jps would lie betv/een these layers^ The removal of the tvTO molea of amsaonium

fluoride distorts the H-F and P-F octahedral interatomic distances by less

than 2»5^ which suggests the AiP- octahedron is not unaffected in the initial deconiposition. Thus it wCTiild seem possible the amncniuin atcms associated with special position (8c) in ammcr.ium hexafiuorcaluminate

87 - Table 18a

Infra-red analysis of the thermal decomposition of axninoniiim hexaTluoro-

alianinate

Compound ^ ^ \ ^\ •^2^+ \ "^^ Rs^**

(NH, ),A1F^ 3240 3050 lii.30 Present ^ ^ work.

Heated 2 hr. 3240 3050 1435 at 220°C

Heated 4 hr,

at if20°C

NH.P 1484 (4) 4

$ffi^)^AlF£ 3250 3060 1428 (4)

NH^AIP^ 3230 3120 2905 1800 1435 (4)

88 Table 18b

Densities of some almniniuin compoxinds

Coinpoiind Density (gccc"''")

1.98

3.25

2.17

A1P3.3^2° 1.914

AIN 3.. ?

3.97

89 - are initially removed in the deconpositiono Hov/every these supposit-icns

are not conclusive»

The total removal of ammona'am fluori.de results in the, y^/-.].?-. ^-t r..'..^ cv-- v/hich indexes satisfactori.ly vrlth a tetragonal cell oV unit cslI. diicen.si.oi:-

a =: 3.53 + OoOl X C ^ 6.02 + 0.01 X (see Table lO). The basic i?i.rucv.i;rc

of tetrafiuoroaluminate is unchanged in the decomposition iz- '^-A.lF,o ^tr:.

contraction of the lattice is essentially concerTied with the r>-ayis

shc\'m by Figs* 8a and 8bo A greater distortion of the ^qqj- spa:;ir.g v;:.tn

increasing temperature is observedc The removal of ammcniiain fluoride fixm

the tetrafluoroaluminate phase by the ammoniimi atoms and one of* -L'he r.o-:-

bridging fluorine atoms v/ould result iji a structuj^e composed pU-r a-

AlP, g.roups with four fold co-ordination, sharing comers wfi th each

aluminium atom being connected by an unsh-ared fluorine atom {s'-je Pigs* 3c

and 8d)c V/hite and Roy (^8) have proposed a formula connecting th': irJ*:-;a-

red spectrum v/ith the metal--fluoride interatomic distance 2 P where F =

wher^ ') = mad.n metal-fluoride frequency

^= reduced mass of the metal-fluoride ion pair

^^Z^ = product of the effective chaise

r = metal-fluoride interatomic distance.

By comparison with interatomic di.stances in --aluminium fluoride

(see Table 19) and using the reported metal-fluori.de vibrations (l2; for

1^ and -aluminium fluorides an Al-P interatomic distance in ^^-AlF-^ Is

calculated as lo77 2*

- SG 0

• L.

^1 i:

too I.V:S i-i

U4 3.0

loo 300 400 6co

Fig. 8. (a^) The aanonion tetrafloaroaluainate^«>alualiiiaB flourlde uystallographie tranaitloh^ r 91 - Table^_19

Interatomic distances in -aluminium fluoride and related conq^ounds

Compound Ref. Al-Al interatomic Al-F interatomic F-F interatomic distance distance distance

(NH^)3 AlF^ 6.31 1.76 2o49

NH.AIF, 38 4 4 6.35^5o07,3.59 1.79 2«54

33 3 c 508 1.79 2=503 present v/ork 1=77, 3.-01

Al UH 15 1.84 1.35 1.65

L^ . l.'.l

- 93 - The calculated x-ray density of 'j^-alijminium fluoric3e Is 1*96 goco

\7hich ag.rees well v/ith the observed value of 1^92 -i- O.O4 g.cc~'^. This

agreement suggests that tlie proposed aluminium-fluorine coni'iguration (see

Fig. 8d) is four planar fluorine atoms at a distance lo77 ^ from the

aluminium atom and two flu.orQ.ne atx>ms at a distance of 3»01 ?. from the aluminium atom. The Al-F configuration in -^AlF, is a regiuar octahedron of Al-F interatomic distance 1.79 8. The collapse of the ^ Vaz-e-:jenlre6

tetragonal structure to form the rhomhedral <^ -AlF^ stnjcturs is agfd.n probably associated v/ith the c-axis and a contracticn of the Al-F spacing

of 3o01 2 to 1.77 X v/ould result in a cube of side 3o54 2 ar^d a calculated density is 3.48 g.cc The reported density of -A.IF^ is 3^25 and *:ho lattice parameters is 5-029 X ( c< = 58'~' 31 \)so the transition toc^-AlF^

in'A)lves a slig.ht distortion of the pseudc-cuV io cell. This rearrangeme-nr.

of Al'-F configuration is also shown from the results of differential thermal, analysis. The resultant -AlF- 3::ructure is represented in Fig. 9ao 'I'he

splitting of the band (see Table 18) is attributed to the presen^'.e of

the tvvc octahedra. Moreover the difference in densities of the ^and. the

oC modification of aluminium fluoride suggests that ammonia or water mighr;

be substituted in the moi^ open ^ -AlF^ structure. This v/as not e>::periment-

ally verified at 25 and 60^o However the ^-AiF^ is seen to take up mcr-^tur-e.-ncre readily than ^-aluminium fluoride at elevated tempera cures.

Moreover attempts to fcxm alumini.um nitride from ammonium hex*3.f.lucroaluminate and gaseous ammonia at 520°C \7ere unsuccessful, Thes-3 obser^raiicns would

suggest that the kinetics for tlie reaction

AlF^ + NH^ —AIN -r 3HP as v/ell as the themcdynamics (see Figo 33) are unfavourable^

94 10)

© (b)

t.ttSA

a) MF^ - 95 i») AiN Ill,2 The fonnat-ion of aJ-uminxum nitride by the Serpek process

Serpek (49) patented a process of making al-uminium nitride i'crmed f r-om

ths?. reaction of gaseous nitrogen v/ith an intimate mixture of al^-imina and

carbor.;t

Al^O^ + 3C - —> AIN + 3C0

This method of nitride formation is now known as the Serpek prorje.'ts.

Other workers have studied the reacti.on and there is great conflict in

the literature as to the exact process variables required to bring about

the optimum aluminium nitride yielde

Tucker and Read (50) reported the absence of aluraini'-jm nivrid'5 I'rcm

the above reaction at iSOO^Cj but Frankel (5i) £hov;ed that 10)1 ni.triae

formation is observed as low as l^OO^C.. and thi3 percentage nitrogen

fixation initially increases with increasing temper^iti^re o

The presence of impurities is reported to catalyse the rsacti.on

according to Mellor (32) such that the nitride is formed at .13^0°C using bauxite ±n place of alumina, but Repenko et_aj o (53) ^id not

confirm this reports

Peacock and du Pont (54) concluded that the reaction at 1300^0 ana

500 mm Hg was

The compound ^^2^Jf^6 ^''^'^'-^'^ contain 42^ nitrogen arid I'^rankel usiiig

the same conditions as Peacock and du Pont observed 19-4?^ ni.t,rcgen fixation at pressures as low as 100 mg Hg»

It has been previously stated that increasing the reaction temperature increases the yield but too high a temperature appeajTs to be detrimental.

96 This v/as observed by Pechiney (55) from an analysis of the reaction

product. The residual alumina content decreased with increasing

temperature to a minimum of lo^'o at 1725*^0 but increased to h-^2yo at

1825^0 in three quarters of the original time. Residual carbon was

also present in the charge which was removed by roasting in air at

700 to 800°C o From the present v/crk 1^% conversion to pC-aJumina i.s

observed in 5 hours at 800°C and this suggests that the residue al*amir.a

content v/ould be increased by roastingo Furthermore at temperatures in

the region 1600-1800^0 the side reaction

AIN + C ^=dfc AlCN

is reported (56)* 0o2;G aluminium sub-cyanide content is analysed at

1600°C and this increases to 1% at l800°Co Nevertheless Tucker and Read

(51) stated that the reaction is best completed in the temperature range

1800-2000^0.

The presence of other impurities than aluminium sub-cy6.nlde is

expected. Accordingly Frankel observed that aluminium carbide (Al^C^)

is formed as a sublimate when alumi.na and carbon are heated together in

air from the reaction

2 Al^O, + 9C —Al.C, + 600 2 3 ^3

Thi.s vrould suggest that the reaction is strongly exothermic a.s the

sublimation temperature is reported as 2100''C, Also compounds of the

general formula (AlN)^.Al^C^ v;here n-1 to 6 are formed when alumiriiiim

nitri.de is heated in a carbon crucible in the presence of nitrogen (57)»

Repenko et al. (53) reported that a spinel of the typ^ AlO.ft-l^O^ is fomea

in the reaction. Yamaguchi & Yanagida (58) ho-vvevsr reported that a spin^^l

of the type AlM.Al^O^ is formed in a reducing atmosphere above 1650*^0 (see

97 - Table 20), Oxycarbides are also reported to be formed in the reacbiono

Pechiney (59) have reported that better than a 39/o yield of alumiriiuj-n'

nitri.de is observed after a purification process which involves a final

chlorinating stage at 450-650°Co Chlorine is reported to attack al-oTr-:isi±<:m

nitride at 900 C forming aluminium chloride ana so unecessary xmpuritie.-,

may be introduced by this purification stageo Hence the irH'.er'rnt

impurities likely to be p:^fesent as a result of the reaction ar=- detrimental

to the process^ However Repenko et alp (53) has shown, that unrfer the

same experimental conditions a greater percentage of nitride :is I'orrnea if

the initial reaction mixture contains the spinellide AlOcAl^^^. rather

than al'jmana. They also showed that prolonged heating incr^eased the

ni.trade content v/hich is a direct contradi.cti on of the results of Franl-iel (f;l)

It wo^jld seem that temperatures in the rv^glon 1700-1?50'^C give tr.i-,

optim'jm results, especially as it is reported that the reaction velocity of

alumina reduction by carbon increases at a faster rate than rhe dif.fusicn

velocity of nitrogen in the diffusion mass above 1750°C„

Frankel (5l) was able to show that in fact the Serpek prcces? is

reversible and thus the equation can be v/ritten

Al^O^ + 3C + N^.*-^ ^• 3C0

He assumed that the solids aluminar, carbon and alumini.um ni'-.ride ex±3Z in

there standard states and hence the equilibrium is a function of the

part.i^ pressures of the gases in the system, such thai

However, due to impurities discussed above, this assumption is to a ijrsL approximation only valid for lower temperatures In the cunsider-sd

~ 9B - Table 20

Comparison of the crystal properties of AJl^ with the possible imparities in the Serpek process

Compound Refractive Index Unit Cell Pararaetersj, S Densix:y Ref.

a o

AIN 2.13 - 2.20 3cll 4c98 3o20 57

AlNoAl^O^ 1«80 7.490 3.73 58

AlNoCAl^O^)^ 64

Al^C^ 2o70 3.330 24o89 3.00 57

^•(Pf2 ^'^'"^

Al^O^ 1.770 - 1.795 53

AlgO 53

AlCN 55

Al^CO 57

AIO.AI2O3 1.99 - 2.03 53

99 temperature range. Moreover Frankel (51) has stated the equilibrium

constant incorrectly as K = C /C^ where C is concentration. Hence by 2

studying the effect of a gaseous mixture of carbon monoxide and nitrogen

on an intimate mixture of alumina and carbon as evaluation of the

chemical equilibrium could be made.

It has been reported (53) that the equilibrium constant can be

calculated from the equation

log Kp = 14.71 - 27743/T (2)

Consequently, at 1600°C and atmospheric pressure the gaseous mixture v^ill

contain up to 3^° N^. At I7OO the nitrogen concentration would be

expected to be 1^1 from the equations (l) and (2) assuming ideal conditions.

These results agree with those of Frankel (51) v;ho reports a gaseous mixturs

of 50-65% carbon monoxide at l600°. Frankel also established a v/eight

ratio of 2 : 1 (Al^O^iC) v/as satisfactory to form the nitride. He also

concluded that the rate of reaction is dependent on the form and reactivity

of the carbon in the process.

From the above observations an attempt was made to carry out the

reaction using the Griffin Tellin hot stage microscope described in

Chapter II. A fine mixture of alumina and carbon in a v/eight ratio of

2:1 was made. To a small quantity was added a drop of sodium silicate,

which moistened the mixture. The Pt/Rh thermocouple was inserted into

the mixture and very carefully extracted to ensure that sufficient

material was present in the thermocouple tip (see Chapter II). Any

spuiious material v/as carefully removed v/ith a fine brush.

The thermocouple v/as inserted into the gas tight chamber and nitrogen was passed over at a rate of 50-60 cc per minute. The temperature was

100 - grad'oally raised to 1700*^0. Temperature fluctuations v^ere noted. This is probably due to the strong endothermic reaction when aluminium nitride is formed in this manner. After 1 hour at 1700 - 10*^0 the sample was removed and submitted to x-ray examination*

Aluminium nitride was observed but due to the very smal.l quantity of material the povfder lines were very weako Some other weak pov/der lines were observed, but these could not be positively identified. It was hoped to study the gaseous equilibrium in the reaction by passing CO/n^ mixtures over the alumina/carbon sampleSj but inherent p.robleras ariose concerning the chemical analysis of the reactants and products« Due to the small quantity of sample (less than 10 mg) quantitative analysi.s of solid components of the reaction proved impossible with the techniques available.

It v/as intended to use an optical crystallographic to identify the amounts and the composition of the phases present^ Mt this v/as not successf'iL partly because of poor crystaQ. fom^tion and partly be-^ause the material was opaqueo A total aluminium determination e^go spectrographicallyp v/ould not have yielded any useful information. The most profitable line would have been to develop a micro-method for the determination of conbined nitrogen but there was insufficient time available at this stage of the work. Hence;; due to the pz-c-blems of chemical analysis,, no further observations of the Serpek process could be made.

III,3 The fortriation of aluminium nitride from, its elements

Intnriduction

III.3-1 Kinetics of metal nitrldation

Jietal, rd.tridation is expected to conform to the principles applying to oxide growth. As discussed in Chapter IV^ the oxidation of metals

101 follov/ linear, parabolic5 and logarithmic relationships and as is obs-brved for the oxidation of alum.inium (61)3 any combination of these laws may be used to describe a nitridaticn curve. The kinetics of the ni.tri.dation of alumini\im i.s :reported (62) to be ini.tially linear but wi.th increasing temperature becomes parabolic«

Factcr-g^ affecting the rate of react.ion

V.'hen a nitride is formed from a metal and its gaseous environment5 the i^ni.tial nitride layer may act as a bair^ier and for further reaction to take place the reactants mijst pass througii thi G barrier^ Therefore^ factors which eiffect the overall rate of reaction are (a) the supply of ga5ec;j3 reactant to the initial nitride layer and (b) treLnsport of the reactants through the nitride layer. Each of these fa.ctors are governed by the effect of temperature, pressure and any defect structtire in the nitri.de layer.

The mechanical stabili.ty of the nitride layer is also important in determining the exi:ent of reactionc The strength of the nitride layer depends on the difference in molecular volume ard type of crystal lattice of the product layer compared with the original metal (63)«

Sintering of the nitride layer can also cause a ch^ge in lattice dimension e*g« Ca^N^p the lattice dimension falls from 11^42 to 11,33 X on sintering (33)-

For nitridation of al'ominium there is a fractional volume change of

+ 0,19 and hence a stable nitride film is anticipated,

III*3*i.i The fonnation of the nitride fron its elements

On heati-g alumini.ijn fil.ms prepared as described in Chapter II in ra.trogen :.inder the described conditions^ no nitrddation appeared to take

102 place at temperatures up to 500^C= The raic:ro3ccpical examination revealed that crystallite gro\'irth had occured to a limited extent as can be seen by comparison of Big* ] la and b. However-^ the rings in Pig, lOb index for f „o.c Al ac-in I'ig. 10a.

The growth is nucleated at points ?uch as a and b as shov/n in Figo lib,

The fil:n appears to have sintered as can be cbser-ved friv-m the electiron diffraction patterns of the "nitrided'' film (rig. 10b), The pattern is more spotty and this observation is consistent v/ith previ cus v/ork on metal fi."lms (60-

According to other v/orkers the formatlcn of aluminium nitride is reported to commence appreciably at 530 (6z) and 600-650 (60) both at a partial pressure of 100 mm of mercury (0^12 atm-) • '^"he kinetics of nitridation are initially linear bji.t change tc parabolic in the temperatui^ range 580-590'^Co Attempts to nitj^ide alumirilum at i^.50°C were made by the same authoi^ but wi.th success^ v/hereas aji^riinium is reported to oxidise at this temperaturCe Metal films v/hen prepared^ have a large surface area to v/eight ratio and are inherently unstable and highly defective in structurcc

As is cbseived in the case of iron fi!lms (ll)^ the sintering of the aJumiXi-iiyn film is probably due to the structui^xl defects such as vacancies diffusing through the biil.k material to the metal s'arface and reducing the overall crystallite area^ This mode of dif.fusion is possible as the temperatures considered are v/ell above the Tamman temperature^

This sintering minimi.ses possible initiation of the reaction v/ith nitrc-gen on the alumini:;m sur-face at 500^0. At '-4-75^0 and 515*^''-; v;eight cl-ange.3 of Ool and 0.25 ^g/om' for the nitridation of aluminium have been report^ed (62)« A comparison of the rates of nitridation and the t^ces of

103 Pig 10a* Electron diffraction pattern of the eaxixainAiun film.

Pig. 10b. Electron diffraction pattern of film heated in nitrogen. Pi^ lib :;ic;ctron nucro-raph of the filr^ heatsu

in nitro-en.

Pi:; Uu Electron i-iicro-i-aph of the cil-a..ur.iun f ilr..

• ••:-. \ ^• ,.:-^^•'J•^•'•i^•>•:••::^^^: y •<•^^^ oxidation (6) show that aluminium reacts more i:apidly in the presence of oxygen^ even at temperatures approaching the melting point of alumijiium.

The formation of aluminium nitride from its elements has been studied in the temperatxire range 600-1800°Co At 600"C chemical analysis revealed that the powdered lump was saturated with nitrogen aind yet the formation of aluminium nitride v/as not observedo Certain authors (3) consider that even at low nitrogen content (at JOO^C 0«.0064 - 0.0070^^^, at 850° 0.0058-0.Ol43?a^) the compound AIN is distributed on the surface of the molten metal as a very tYiln film. Repenko et al, (53) reports substantial nitride formation at temperatures greater than 1700°C where the high concentration of ELluminium vapour and nitrogen gas is sufficient to produce single crystals of aluminium nitride*

The formation of alumini-om nitride from molten aJiuninium and nitrogen gas has been described also by Cooper et ai, (l). They emphasise the need for preventing the reaction being irliibited by layers of nitrade formed on the surface of the molten metalc

An attempt to prepare aluminium nitride as previously described was made (see Chapter II). A portion of finely-divided aluminium powder was placed in a horizontal tube fumace at lOOO^'C under purified nitrogen«

After tv/o hours the sample v/as removed and cooled to room temperature. The surface of the sample v/as obser--/ed to be sintered. The sample was ground and replaced in the fUmace under nitrogen at 1000°C fcr a further two hours. The cooled samp].e v/as x-ray amorphous and no appreciable weight change v/as recorded. Even with repeated cycling of the routing no nitride forrriation v/as observed.

106 It has been reported that alunnj-.vam nitride is formed from aJijminium

pov/der and nitrogen at cemperat^jres as lov/ as c30°C [GOj^ '^he same autiior;

report increasing the particle size of the aljmini'jm pov/der decreases tiie

rate of reaction to form the nitridco However., orily at temperatures above

lOOO'^C are yields of better than 90^^ obb-ervedo Thes^ obse: vations are

not ccnfirmed from the present v/orkr. and it woi:ld therefore appear thiat

the formation of the nitride from the e.l.-men^s is besc faciJ.itated at

ej.evated temperature v/hsre the reacLion take£ place in the vapour state

(fci.p. PA ~ 2467°C), HcFweverr, at temperatures in the region of the boiling

point of aluminium^ any nir,ride v/i.].l bi unstable and dissociate into its

e.iexents^ thus making the reaction reversible and temperatures of IJrOO-

iBOo'^C are recommended as it ohse-n/ed in the worx of l

- 107 lo Cooper^ CaFe:; et al. Proc.Symp.Bri.t XeramoReSoAssoc. ^ 19^2 r, 4-9y (Academic Press),

2, NovGselcvas AoV, ^ J.Gen.Chem. o (U.S.S.R.). 1940, lO^ 1547»

3c KlyachkOj Yu.A.^ Zhpkh., 19U., 14^ (l)s 84.

4. Cox., B*^ & Sharpe^ k,0, . J.Chem,Soc.,-, 1954s 1798p

3q Brev/er^ F.H.^ Ciartcn^, Go<, cS: Goodgame« DeH.Lop JoInorg.Nucl.Chem. , 1959, 9. 56,

7. Tananayev, I.V. ^ & Talipov^ Sh. ^ ZhOkhc ^ 19355 9 5 1155-

8<^ KlTig. H.P. p & Alexanderp L.E.^ 'TC-ray Diffrar-tion ^cedures for Polycrystalline and Amorphous Materials" j (j,\7iley)^ 1954*

9* Schwarzmann^ S.,, Z.Krist. ^ 196/+. 120r (4-5):. 286.

10. Ketelaar^ J.A.A.., Z^Krist. , 1935^ 92., 155o

11» Hoberts, M,\V, , Trans.Pamday Soc. ^ 1960^ (l)^ 128.

12. Shinn^ D»B», Crockett. DeScp & Haendler.- H,Mo ^ Inorg.Chem.^ 19663 5^

(n), 1967.

13-- Maakr, D. ^ unpublishedc

14. Thilo, E., Natur^.'/isseno. 1938^ 26^ 529.

15. Co^.vleys J,Hep & Scott^ 1\R« ^ J-AmcChem.Soc. ^ 1948^ JO;, IO5. I6p Vanderherder^ D.Bo 5 I>amlerj, J,T. ^ Allen^, D.R. 5 & Allen. A.S.j LndoEngcChera.Prcd.ReSoDeveiopc 5 1968^].^ (3)^ 220.

17» Harrington, D.Ec p & Dorsett^ PoS, A.EcC. Accession Noo 12765s Repto No»p DP - 1004, 1965c

18. Henry, J.L., & Dreisback, S.Hop J, Am. Ghera.Soc o1959^ 81. 5274.

19. Locseip B., Natura, 1962p 19^;^ 177o

20. Chandross, R., Acta Cryst.p 1964^ 17. 1477c

21. StaritskypE., & Asprey^ L.B.p Anal.Chem. ^ 19573 29, 984.

22. Thakurp R.L. . Rock. EoJ. 5 & Pepinsky., R., Ajn«I.iineralogists 1952, 37, 695.

23c Douglas^ T.B.p Sz Ditmar^ D,A., J.Re3 = Nat.Bur.Stand. 5 1967, A7I5 (3), 185.

- 108 2L. Rcy^ JoAmeroCeram^SoCo , 1954^ JJ^ 381.

23. Hebecker. G„ ^ & Hoppe^ Ro „ Natiu-wissen-^ 1966^ 104*

26. Ponk, H»p & Bohlandj, Ho ^ Z.anorg•Ghem. 5 1964-:, (3-4)? 153.

27. Ju2ap R.3 & Hahnj K. ^ Z.ar-org.Chemo ^ 1940 ^ 21^.^ 111.

26. Mermantj G.^. Be^.lnskij C.^ & Lalau-Keraly ^ F., C oR.Acad.Sci. ^ (Pari?.)i» Series I967, 26^, (4) ^, 238.

29. Rerner^ Z.ancrg.Chemo 5 1959:r 298^ 22,

30. Fov/leSy ti.Vf.A^p PxTDCoSymp.Chemo Co-crxii.natioa Compounds^ (A.gi'aj India) J, 1960. 2^ U.

31- Clarkj, G^L,, Amer.Journal Science^ 1924o 2^

32. Schomaker cSc Stevenson^ "Advanced Inorganic Chemistry", Cotton & WUkiriSon.;, p.943 1962.

33. Hanic^ F., Stempelova^ ^ Metiasov&ky.o K c 5 ci Malinovskyj M. 5 Acta.Chem.Acad.ScioHang. p I962. 3_2. 309-

34P Yatsimirskiij K^B.. J.GenoChemo, 1956 j, 26-^ 2633.

35. Jayaweera, S.A.A.^ Thesis. I969.

36. Chemical Abstracts, I968, 68^ llC885b.

37- UoS. latent Noo, 3,17Qo'-r^^!> '^963o

33, Brosset, C, SB vl 1938, 18, 95.

39. Watt^ G.W., & Braun^ J.H, ^ J^Am.Chem.Soc., 1956, 78, 494-

40. V/ykoff, R.V/.Go^ "Crystal Structures"^ Vol. 3 flntersciences New Yo.rk)^ 1963 o

41. A,CoA. Monograph No. 3? Crystal Data^ (2nd Ed.) 5 1963.

^4.2. Stev/ardp EoG., & Rooksby^ H.Pc 5 Acta. Cr-yst., 1933, 6, Z.9.

43c rxiioky A. 5 MoSc, Thesis^ 1969.

44- Ehrt^to V/.A.^ & Fr^re, F.Jo, J.Am.Chem<,Soc., 1945. 67<7 64.

45o Freeman, R.D., J.Phys.Chemo, 1936, 60, 1132o

46c Hannebohn, O^, & Klemm, Y/.^ Z.anorg-Chem., 1936^ 229, 337.

47. Wells, A.F., "Str-:ctural Iricrganic Ghenilstr>'" „ 3^ Ed. (Claredon Press)3 1962o

109 - ifSo V/hi.te:, WoB, 5 & Roy^ R. ^ AmeroMineral <> ^ 196/^^ I67O.

49. Se:rpekp 0., Zeitokorapofhiss.Gase. 16^ 55«

50„ Tucker5> S.A.^, & Read., H.L. , Trans,AmeroElectrochem* ^ 1912, 57.

52. Franke:., W., Z.Elektrochem. „ 19^, 362.

52o Mellorp J.V/.j,'A Comprehensive Treatif?e on Lnorganic and Theoretical Chemistry", (Lon@nans)y 1947*.

53. RepenkOp N.K., et_aj-«. Sb^Nauch.Tr.UkroNaucha-Issled Inst. Ogneuporv.

1962, 6y 120.

54. Peacock, S., dv, Pont, E.I.,, L^S.Patent No., 1,0315581, 1912.

55^ Pechiney, Brit.Patent Nooo 868,3013 3956=

56. Pt:rieros, R„ , & Bollack,, Re., UoS. Patent No., 2,962,359^ 1960.

57. Jeffrey, G.A., & V/u, V.Y^, ActacCrys^.„ 1963, 16,^ 559c

56. Yanegjchi, G. , & Yanagida.. H. BulloChem.Soc. Japan, 1959 s 1264o

59« Pecriiney, BritoPratent No.y 10158^6285 1969. 6O0 Vol, A.Eo, "The Structure and properties of biriary metallic system". Vol, 1, 1959o

61. AyLmore, D.v/,^ Gregg, S.Je, & Jepson. V-'^B., J«Inst.Met., 1960, 88, 205

62c Sthapitanon-ia, P., & Margrave. J.Lo, J.Phyz.Chem. , 196?, 60. 1628.

63. Pjlling, NoB., & Bedwo^h, R.E., J.InstcMet., 1923, 2?, 529.

64. Adams, lo ^ .et_al. J .Electrochem^Soc., 1962, IO9, IO5O.

110 CHAPTER IV The reactivity of aluminium nitiade

IV ol Introduction

The development of sintering and hot-pressing techniques has enabled aluminium nitride, and the nitrides of silicon and boron, to be used more extensively as ceramics. The resistance of these nitrides to hydrolysis and oxidation is increased considerably when they are hot pressed up to temperatiires approaching 2000*^C.

These conditions may bring about structural changes in the nitrides which may compact the crystal lattice thus altering the characteristics of the material*

However, the rates of hydrolysis and oxidation would seem to depend on the intrinsic reactivity and surface available for chemical reaction. Impedance of the reactions by layers of products surrounding the remaining nitride particles may become significant. In the present chapter, production and sintering of aluminium nitride are considered in relation to changes in, phase compositionp siirface area, and crystallite, and a^regate sizes on hydro lysis..and oxidation under various experimental conditions.

The chemical reactivity of nitrides is controlled considerably by the extent to which they have been sintered during their fomation and any subsequent calcination© At present, there is more available literature on the sintering of oxides which is expected to resemble that of nitrides. The theories of sintering are well established (1-8), and the subject has recently been

.111- reviewed (9). Sintering is enhanced by compacting the powdered nitride before calcining in vacuo to prevent possible hydrolysis and oxidation (10)„ This can be observed by comparison of the present work and the data reported for the oxidation of hot pressed aluminium nitride (l6)

A prerequisite for sintering is the production of finely- divided material with a suitable particle size range. Development of sintering is limited by impurities such as the oxide impurities produced by partial nitride hydrolysis and oxidation, and particxjlarly gas-producing containments such as hydroxides and carbonateso When boron nitride is purified at higher temperatures to reduce oxide content, the increased particle size make subsequent hot pressing more difficult (14)5 but the addition of silica glass will bond the material xander these conditions (15).

Sintering is generally accelerated by low melting additives

(13), but such additions may cause serious reductions in optical and mechanical properties.

112 IVol.io Xbe hydrolysis and cYi^atlon of rtitrldea.

The resistance of powdered refractozy nitrides tc the action of*

water and aqueous acids and alkalis has been suminarieed by Samsonov (l6)a

In nitride production usually oxygen must be excluded; for it prevents

nitrogen fran reacting vrith clean metal surfaceSo Occaaionally, formation

of an initial nitride si:rface layer protects against &vy subsequent

05cygen attack, and permits nitridatiozx to proceede When the nitride

layer is destabilised by hydrolysis, the nitride ions ere replaced by

J^droaiyl ions and since one nitride is replaced by three hydroxyl ions,

the film becomes vejy weak and ruptures whilst very thlrt (l?)o At

higher temperatures, decomposition of the j^ydroxides to oxides causes

further fragmentation (l8)o For example, Ir* the nltridation of icegnesiam

between 400° and 650°, metal evaporaticT' is promoted by v/aces of water

vapour but inhibited by c^gen (l9)o

The fcnnation, hydrolysis ana oxi-dation of the ionic calcim nitride

(Ca^N^) and magnesium nitride (Mg^N^) nave been described (20)o Mere

recently it has been fouod that zinc and cadr;iun films do net nitride in

nitrogen or ammonia at temperatures beiow their melting points, and are

formed only at appreciable rates at tonperatures above 600° {^9)o Tney

are i^ydrolysed rapidly to ammotvia soluble complexes, lA{m^)^{OH)^ where

X 4 for M = Zn or Cd(i7)o Comparison of the molecular susceptibilities

of magnesium, zinc and cadmium rdtrides shows that the pciarisiiag action

of t^e metal icn decreases from magnesium to zinc to cadmium^ Nitrides in

Group III of the Periodic Table (boron, etluminium and gallium) and Group

XV (ailicon and tin) show covalent character and are more resistant to

i^drolysis and oxidation trian the nitrides cf magnesiiim and beiyllium (26)^

113 Boron nitride appears to be more chemically-reactive than

aluminium and silicon nitride. Finely divided boron nitride is hydrolysed

slowly by hot water and dissolves completely in boiling 20% sodium

hydroxide in thirty minutes. It is also observed to dissolve in acids

and alkalis al 20^C (22). By comparison, the reactions of the nitrides of

aluminium and silicon with hot water are inhibited by coatings of hydrous

alumina or silica respectively.

Hydrolysis is generally slow in mineral acids and alkalis (23, 24),

but there is complete dissolution of aluminium nitride in 30% sodium

carbonate solution at 80^, and of silicon nitride in boiling hydrofluoric

acid (25). All the nitrides oxidize at higher temperatures above 600*^.

the most resistant to oxidation being silicon nitride with respect to

temperature.

IV.lii Materials

The higher temperatures generally required for the production of

aluminium nitride (see Chapters III and V), cause sintering to the

extent that samples generally have specific surfaces of below 1 m^.g''.

and average crystallite sizes of over 2

More finely-divided aluminium nitride was obtained by ball-milling.

Thus, 5 gram batches of aluminium nitride were ball-milled for times up to 10 hours. Changes in specific surface and average crystallite size are shown in Fig. 12.

Electron micrographs showed that the original nitride consisted of single crystals and aggregates of about I -2 ^ m size, see Fig. 24a

The single crystals were fractured in the earlier stages of the milling and the fragments were incorporated into the aggregates which remained approximately the same size throughout the periods of millings, see Fig. 24.b.

114- The ohango in speolfio surface during the aiUine of A1N« I 4 —4

The change s»erage

2 4 6 8

Fi^. 12,

-. 115 - This the average crystallite size decreased rapidly at first and later slowly when

the crystallites became of sum micron size,

A closer x-ray examination of the milled materials showed that any inherent line broadening was in fact mainly due to strain introduced by milling rather than particle size (68. 69), since the average ciystaUite size was always above 0.4 ^ m.

IV. 2 The hydrolyfiifi of nhiminhim nitrirtf

The sample of aluminium nitride which had been milled for S hours

(S = 4.0 m V, average crystallite size 0.47 yvw m) was hydrolysed in water at

95^and in steam at 580-520°C and 680-640^C.

IV 2.1 The hydrolysis in water ("Wet" hydrolysis)

The sample was hydrolysed in water at 95^C for prespecified times, after which the partially hydrolysed smaple was filtered off. The residue was washed twice with SO ml portions of acetone to remove immediately most of the water remaining in contact with the nitride. This would prevent further hydrolysis and ageing (26). The last traces of acetone and water were removed by out gassing the samples at 150^jn_vacuo.on an electrical sorption babnce (26), before measur- ment of its surface area by determining the adsorption isotherm of nitrogen at

-183°C,

Portions of each sample were thermally analysed at (a) 200^C in air when physically adsorbed water was completely removed, (b) 500*^C in air when the bayerite ( c< - AJjOj SHjO) and boehmite (AI2O3H2O or ^ -AlO.OH) were almost completely dehydrated (27), and (c) lOOOO^Cor 1200°Cinair when the remaining aluminium nitride had been oxidised completely to oC -alumina; the final weight also gave the total amount of alumina formed.

116- TI^.-s ;:ha3e5 pr&7.«n: ware identified ty x-ray difrraotometry and

irirra-red spec^roscopyo The presence of retained, nitride; and bcehmite

.V..- - voveal^id by the jc-'ray diffra-^tomjifivr traces* Ho\'rtrv'er, the bayeriie

v;di jc-i'ay amorrphouo ard waF letacted together v^th boehnjite by using thr;

'•^;•J.:•: .•Cul-l tcchni-nir: thr SP 2C0 irjfra-red Jipe'^^lr-'-photoiaetftr. The

rv-.v.fLr^ of th*: x-r^xy ar^d J_nf!*a-red ftiialysis a.r«- giv^r* in Table? 21and22.

Vr.c: produGt*i cf ''-v'drolyHiJ= by v/3ie.r cofixained approxiinateay 1

rr,c »r;?'-lr; of bay^^rit''^' r.j every ^ m lfcci..le--3 cf boehmiT-r and their fonoation

"cnrL?* Tjnt r.-i-^h th-r pH conditions in the surrovr.dlng cEclutionSo It

:-i -'.poritid that at pfi val-.ifr53 gr

•jn'jrphcus >-a.(uniniUiT ydnoxidt^ whxrh will rran=foi-m at p:-i 9 to bayerit^^o

Th« taye.rire-gibb^ilE ::ransfo-nnation takes place an pH 12 at ^0-60°C (28) o

TTI^: pH of the .surrouadijig solution vras estiinated a~ being ir. the range

7-11 which is ccn.

Ir is repOT'ted also thai a highly protective film of boehmire is fonned vTheo ^a•a'T!iniuIrl metal is dipped into boiling water (33).

Tliv hour-milled 3ample of alumin' m r '"ride was Kydrolysed fcy

sfcoot dCfj at 9,^^C in water ir. 5 hours •Fxi„.l3(z)), Thereafter, hydrolysis wrj^ oongjar-etively SIOT. Th^ oonsideriil J iri reases in specific s^^rfaoe

Sj, iunng the first 5 bours cf liydrclysis (Pig.13(a)) indicate that ci7/5criljites of al--ualna hydrate m;.st split off from the nitride paziiicles bi-'fore their grOT-vt-h i s promotfji by ageingo The nvicleetion enei^gy of th^=!J^ orystallite?s is a function of the initial nitride surface available

fcr* hydrclvsie.. The h^^dto-^s-ali-iinin?. 313'stallites grew as the hydrclysix i3 conrirued and tht=re is a subsequent decrease in specif^ic aurfaoe a^^ thti'Kydrous oxidr? crystalli.tes :5o-r:r?e on the nitride parti-^les.

117 Table 21

X-ray analysis of hydrolysed aluminium nitride

milled 5 hours aluminium- hydiolysed hydrolysed hydrolysed boehmite gibbsite bayerite nitride 5 hrs. 10 hrs 20 hrs

Intensity (I)

6.01 40 6,01 80 6.01 210 6.11

3.13 30 3.13 60 3.13 60 3.16 3.11 3.19

2.71 180 2.69 60 2.68 30 2.68 30 2.69

2.47 120 2.47 3 2.45 2.45

2.37 320 2.36 50 2.36 70 2.37 80 2.35

-118- Table 22

InPra-red anal.vsi.s of hvdroJys.d alxaminitim nitrdde

5 iir:f. 10 hr-».. 20 h»-=. boe imlt-i ba erj te hydr-:?lys.; ? bylr'.''jyEi ~

cm cm U (30 (29

3500 shj Hi 3500 shp IP. 3260 .m ;»<^60 3660

3070 5h. w 3070 303y 330)

2130 vr 1250 w 1150 1149 3420

1070 s 1070 s 1070 w 1080 1063 1020

970 vT 980 w 720 w 975

720 rr 720 w 750 73^ 770-720

694

dV- _ si^Duldar

strong

b broad

m -

w - v/salr

tl9 «o V

AIM rl I i O CB O 5 o Im

••••'Vi if V. .•> The ciystallites eventually fonn an impermeable layer of hydrous oxide which prevents any further appreciable hydrolysis Fig 13 (c). This behaviour is analogous to the wet hydrolysis of calcium and magnesium nitrides and the hydration of lime (20).

The actual variations in surface area, when 1 gram of AIN is hydrolysed is shown in Fig. 13 (b). Changes is siuface area of the unchanged nitride ^ (represented by the dashed curve in Fig. 13 (b) are calculated on the basis of the reaction proceeding by inward advancement of the nitride-hydrous oxide interface (34). The surface area of the hydrous alumina (by difference) accounts for practically aU of the/ total surface area {cS. dashed curve). The corresponding average crystallite sizes of the hydrous alumina and the remaining nitride as shown in Fig. 13 (d) are 0.018 • 0.024 m and about 0.25 |fUn respectively.

The hydrolysis involves change in crystal structure from the hexagonal structure of AlN to the orthorhombic structure of boshmite and the hexagonal structure of bayerite and a considerable volume increase (0.724 of the original volume). Since the nitride changes its volume 1.724 fold when it forms hydrous alumina, hydration of x gram in a 1 gram sample of aluminium nitride would cause the proportionate volume change

(I -x) + 1.724X = (1 + 0.724 x) The proportionate change in surface = (I + 0.724 x)^^^. In general, if S and S* are the surfaces of the aluminium nitride and its partly hydrolysed product, then,

Sl^S =(I+0.724x)2'' i.c. = (1 +0.724 x)

121 Gcxpl-:t^ hy'^n'ilysis v/c-ld give a ^^urface chaiigs of (l,72if)'' l.ifJBj

ir thsre v/as no splitting cf crystallites product* Increa^a&o in the S ri^j2.'b:\r/ oP C2ystalJLite.5 car^ e=tlaiatcd 34 from the ratio .L^g

•,vhe:i*r: S-, id S are the values of the surl a'-e area of the hydrous

almniria I • 1.438* and the specific surface of the ori.ginal alijminiura iiitrade reapectiv'elys allciTance btang n^de for the change in latMce

stf.'j;:tizj:*5:- Thas, after 3 hours hydrolysis each original AIN crystal.lite i:j.-nducv::3 .TiH^500 CTy.staHites of hydrcus ozide whj.ch increases to 15^200

^rr^,r 10 Kouxoj althcugl-: therv. is little fur-ther hydirolyais. Betv/een

;) rxnO 10 >;.Tars,, increase iri suxfa'.'-- Is caused by additional hydration

vji'j ••^oinpletior. of th^ r^-.o'otai li.?ation cf the newly formed hydroas ai.'-anina;' to their r.oMoal latlicf! otrL;ctur^5.; this is cc^nterbalanced by

ageing jf the hydrcM.c al^^i.na v/hicr. becomes more Tcark'.-ii after 20 houT« vrher. thfci ovt'r.all -r>'.^tall."j + r 5.r.cr*^aK^=- is rrduced to 7*^00.

Optical and electron ipicrographshow that the hydi-^Dlysed material r.or.rsletd of lar^ge aggr^gat^?- of ever 100 size corapared v/ith the

i»niaj-'.er aggregates .-P about l-? rise of the original ndlled nitride.

Tlv3 e.slJmation of the partial nize is deBr.;ra.bed in Chapter- !!•

AfT^r hydrolycii^ for 3 hc-rrs the particle size is 100-130 ^ ir* and

tni3 is increased ir .rnngy to 120-160 ^ m in a further 3 hours. The ni5.v^rial. sinters a.fter thds period to givt larpe.aggrtgates cf i*20-.^00y*\m at 20 hours hydrolysis. Thsrss independent reault?. agree \vith surface ar+^a :jh^»-:acteri3tics of the mi-llcd material •

3.V.2.±i The hydiolysis in steam ("Etcy" 'hydrolysis)

The pyr':^l^v^i^olys:i.o of al-Hnirii-Lir. nitride was ^tpjdied at temperatures in th" range 580-520^ and 630-640*^0 r+^^pcctive^y. The ar.alysis of al'-unini;t;in nitride for Viilrou.~.n can carried cut under similar conditions

.silr.i/, 5odrxTi or pota^-i ii:: hydror^iie pellets.

- 122 - A v.-eighed airiouiit of nitride in a puroy. buat was placed ijn a horizontal fcabe f\jmac9 a!id ateani supplied at an approximately constant

rate, A blank ran was mada -tc detend.ne T.he rate of steam passing throu^ the c-ystem. This established asi 2,L oc/min. As a rasiilt of the

3t^ai3. a tTmperatu.rf- dr.:p of UX^GO^C was observed.

Any aiMonia given off by the pyro-hydrolysia v^as ooliected in a beairer in riich v^a:f placed 25 mis cf ^ boric acid and 3 d.cops of a mixed, methyl rec roicocresol green indicator* The amaznt cf ananonia evolved waft detejii- fid by titrating the condensate against O.i N hydrochlord.c acid*

O.if^ ammonia v/as formed in 10 hours at 560-320'^C and 2.ii?o in 7 hours at 680^6iiD^C. This corresponds 0.97% and Sofi^ hydrolysis r^spectivelyp

The amount of hydrolysis is low compared with iiquid-solid reaction and it woiiia •'?>-iggest among other things that a different mechanism of hydrolysis is rate-controlling.

The results sogge5.t that the ateam promotes sintering of the nitride and presents such a rapid hydnniysi.s as in the liqmd-soii.i reaction.

The sintering of the nj.trlde i- a bsLrrier to further hydrolysis and the rate or t^ydrolysis is veiy much curtailed as a resiilt.

IV^3 The oxidation of alunnini^am nitride

As AIN has application as a hi.gh temperature material^ a study has been undertaken cf (i) mechanism of reaction at these tenperatures v/ith par^i'^ular reference cry^fcaXlite size,; (ii) the change in surface properties a3 the reaction takes place. Aluziinium nitride oxidises at temperatures above 600*^0 forming aluzninium oxide in one of its crystallcgraphio forms depending on the ten^jerature at which the reaction is studied.

'123 The kinetics of the oxidation of aluminium nitiide and the effect of paiticle size on the rate of reaction was studied, using a theimograveimetric balance in the temperature range of 700^C to lOOO^C. The experimental technique is described in Chapter II

Although ihe initial mass of nitride does not appreciably affect the reaction rate (35), one-gram samples of aluminium nitride were used in the experiments for ihis weight is more convenient when interpreting the results.

One-gram samples were placed in a 10 cc porcelam crucible and suspended a lew centimetres from the thermocouple. The same conditions were employed throughout the experiments

IV.3i The oxidation reaction

Although moisture is known to increase the rate of oxidation (36.37) no attempts were made to dry the au in which the nitride was oxidised so that oxidation kinetics experimentally derived could be applied to the material when in general use.

Therefore as moistme is present in the system, ammonia will be produced according to the reaction.

2AIN + 3H2O-^Al203 +2NH3. .

As the temperature increases, the ammount of ammonia decreases and the amount of nitrogen increases according to the reaction

2NH3 + 3H2. such thai in the temperature range considered, the amount of ammonia present is very small compared with that of nitrogen. The activation energies for reaction of aluminium nitride with moist oxygen and moist nitrogen are 26.5 and 7.3 k. cal. mole'* respectively, and the rale determining step for the low activation energy for the reaction of moist nitrogen is attributed to absorption (38).

124. it was therefoie assumed that the raauireactio n taking place was

2AIN + ^2 ©2 AI2O3 + N2

IV.3.ii The rate laws of oxidation The rate laws of oxidation are classified into three main groups: (a) Logarithmic Rate Eqnations: (b) Linear Rate Equation: (c) Parabolic Rate Equation.

These rate equations are dependent on a number of factors (61) among which are temperature, oxygen pressure, elapsed time of reaction, surface prepaiaiion and pre-treatment of the system.

(a) Logarithmic Rate Equations

These equations can be mathematically expiessed as a) x=k| log(t + lQ) A

b) a = B-k2togt X

where x is some measure of the oxide formed, A and B are constants and k I and k2 are the respective rate constants and are known as a) direct logarithmic growth and b) inverse logarithmic growth respectively. A number of theories have been put forward to explain these laws based on various rate determining mechanisms such as cavity formation in the oxide film or chemisorption (62) (b) Linear Rate Equations Linear oxidation can be desciibed by

dt i.e. X = kj t + c

If a relationship isgovemed by linear oxidation, the surface reaction or phase boundary reaction is said to be rate determining.

125- (o) parabolic Rate Equations

Parabolic oxidation is a diffusion-controlled process and the amount

of oxide formed in an interval of time (t) is proportional to the square

root of t. It can be expressed as

dx k, dt = X

i.e. - k, t, X = k, t^

IV^3,iii The kiietics of the oxidation of aluminium nitride

The f^-tors which govern the kinetic laws for gas solid reactions are;

the rates of nucleation and recrystallization, the chemical reaction at

the phase boundary, and the rates of diffusion. The gas-solid reaction

initially takes place at the surface of the solid and the part played

by a surface in a chemical reaction has been discussed by G-regg (43).

G-regg gives the classical example of the decomposition of calcium

carbonate and cr nsiders the key to the c ^ntinuation of the reaction

Ga ( 0 > Ca 0 + CO^

is the surface heterDgeneity- On the surface of a solid there

are regions of pai-ticularly high potential energy where the energy

barrier opposing decomposition is lower than elsewhere, and these areas

are the regions of nucleation or active sites. In other words, the

points at which the chemical reaction can begin,

VtTien discussing the reaction of powders, it is necessary to consider

the influmce of reactant particle size and shape on the reaction rate.

By considering the assumption that a gas solid reaction may be controlled

by rate of gas diffusion through a product layer Jander ( M*) derived

the e _tion k ; = 1 - (1-F)^

v;here k :.s the 'parabolic rate constant and t is the time in which a mas^$.

of reactant is converted to a mass of product P per unit mass.

-126- Howeverj, Jander's equation did not consider that (i) the ratio of

surface area of partially oxidised crystallite to area reaction interface

progressively changes during the reaction (4^6), and (ii) the reactant

and product molar volumes are not equal. Carter (45) modified Jander's

equation to give

[i. (A-i)# + (A-i)(i-P)* = z + 2 (I-a: ^ r

v/here r is the initial radius of a particle and is the ratio of product

and vf.p^nf->^r\t molecular volumes.

Several kinetic equations have been derived and the equation v/hich

connects the kinetic parameter v/ith the experimentally determined function

is dependent on v.-hether the original powder particles are considered to be disc-like (39), c-ibic (40), spherical (41), or needle shaped (42).

From electron microscopy, the particles to a first approximation co'jld be supposed to be circular. The geometry of situation v/as limited

to 2 dimensions by the instrLiment, and it v/as assumed that the particles v/ere spherical i-ather than disc-like. The results of the thermogravimetric

study of the oxidation of aluminium nitride fitted the equation derived for spherical particles.

Kinetic ecraation

The rate of reaction v;as considered to be experimentally expressed as the amoi^nt of alurir ' •: nitride converted to alumina in time t as F

v/here F - m t - - 1 ^^r v/here m^ = mass of the ScOiple at time t

= initial mass

- Molecular weight of the product

= Molecular weight of the reactant and the value of F ^vd.ll vary from 0 (t = O) to 1,

- 127 - It is aseumed that the particles ere sphericaJ. and 30

if V is the volums ot a particle and r is the radtu£

Tf is voivjEe of -^^iildTial AIN it ar^y tine t and esauming that the

shape of the particle does not change during oxidation

then - V = VP where VF is the roliime changed tc alumina in

time

If r. is the radlug of the particle af reaidual AlW

r^ T (I-P)^

The vr-ls^e of aljnilna fo-naed V^is eqiif.I to the difference In the initial voluue and the volume cf the res-idual AIN and there is a molecular volums changa

wherr^ X is the stolchlonietriC ratio of the molecular ?ol'jces of alumina and aluminliau nitride according to the reactioi;

2 AIN - V2 0^ Ai^O^ * N^.

The total volume (V) at any tlroe t is therefore equal tc the f^um of the volume of aiiamizja formed and the volume of ti-ie residual nitrideo

:r (V = (V-V?))X + «• - VF

= V(l =• F * X F)

Tnerefore r (1 - F 30 the tota3 -;h5.ckness x of r^he layer of alumina will be

128 If the rate of diffusion is very great in relation, the rate of

reaction then is - dN dt

v/here A is the surface area of the spherical particle

A = 47rr^ r^ ^AU^I

v/here v^-j^^ is the molar volume of aluminium nitride,

dt v^^, dt 1

dt - '^l ""aw

1 - (1-FF = v^^j t/r and if diffusion is not rate controlling 1 - (1-F)^ v;ill vary linearly vath time.

But if rate of diffusion controls the reaction, the derived parabolic law is expressed as:

dx _ k dt ~ — X v/hich, v/hen integrated, gives

x^ = ak^t where x is the thickness of the product;

• 129 1 1 r (1-F + F)^ - (l-F) 3

r^ (1-F + F)* - (1-F)^ ^ =

(1-F + F)3 - (1-F)^ ^ = 2k2t

2 so a plot of Z v/ith time v/ill vary linearly if diffusion is the rate

controlling process.

Estimation of kinetic parameters

Calculation of the mass converted in time t, F;

F = m. - mo/ m ^ - 1 t ' o Mr Mr = 2M^^j v;here M^^ is the molecular weight of aluminium nitride.

-\ Mp = M the molecular v/eight of alumina ^^•2 3

Mjt = 82

Mp = 102

Mp/j^^ - 1 = 102/Q2 - 1 = 0.244.

F = m^ - m _ A m •rT^J" ~ 0.24Mn u, 24Mn

Calculation of

\ is the stoichiometric ratio ^of the molar volumes of aluminium nitxi-de and alumina- From the x-ray results of the product of oxidation, the aliamina was identified as -alumina by comparison of observed d-spacings

and the d-spacings given by the A*S.T.M. index see Table 25. Aluminium nitride is reported to convert to alumina at temperatures as lov/ as

600 C (38) where the form of adumina is possibly^-alumina.

The densi ' \es of aluminium nitride and -alumina were taken to be

3.2/ and 3-97 g.- -m respectively.

-130.- These values gave the molar volumes of aluminium nitride and oC -alumina as 27.55 and 12,57 cm^ respectively,

= 1.19. 2 Hence^ knowing /\and P^ the values of y and Z can be found. 2

The calculation of Z is particularly tedious and a computer

prDgramme in Portr^m IV for IBM 11.30 Computer has been v/ritten to

calculate these functions (See Appendix V), Graphs of percentage

conversion (Pig. 14)? y and (Figs. 17 and 19) for various times 2

at different temperatures v/ere dravm and from the slope of Z against

time the reaction rate constants (k^) v/ers found.

The determination of the activation energy for the oxidation reaction

The rate of reaction is proportional to the rate constant k. The

relationship vri.th the rate constant and the activation energy for the

process is given by the Arr+ienius equation

k = A.e . where A is the frequency factor or pre-exponential factor. —E/RT

e is sometimes termed the Boltzman factor where E is the

activation energy^ T is the temperature in degrees Kelvinp and R is the gas constant.

From this equation

Ink = InA - E/RT

. log^ok = log^Q A - 303RT

= log^O A - E4^56T

Hence a plot of log-j^Q k against VT will give a straight line of slope

E/4'.56, from v.-hich the activatio«n 13energ1 » y for the process can be calculated So*!

T5I

i 1 t

Fig. 14* The percentage conversion of aluminium nitride to a-alumina at various tenperatures^

- 132 - lAany factors contribute the initial shape of an oxidation isotherm, and these have been enumerated by Gulbransen and Andrew (48). These factors are (i) the influence of the decrease of roughness or surface area as the reaction proceeds, (ii) the influence of the heat evolved in the reaction on the rate of reaction, (iii) the effect of impurities in the oxide as the reaction begins, (iv) the change in oxide composition, (v) the influence of potential fields at the gas oxide interface due to absorbed oxygen ions according to the mechanism of Mott (49).

It has been shovm (4^) that as the reaction proceeds, that the 2 "l sample of initial surface area of 1.1 m og increases to an 2 -1 estimated 1.6 m g in a period of ifO hours. In the period studied, that is 0 to 7 hours, there is an 2 -1 expected increase in surface area of 0,1 m g so it is assumed that the effect of increase in surface area is negligible.

Prom a literature surveyp a value of A H = -I36 k.cal/niole (tO) for the heat of reaction is obtained. As the temperature maintained at + 2*^0 throu^out the experiment, this factor was not considered to affect the situation in the temperature range considered. However, this effect is apparently important at higher temperatures (35).

The estimation of any impurities in the initial oxide was not made in this study, and hence the effect of this factor cannot be considered.

It has been reported that there is a change in density from the surface oxide and internal oxide when metal pov/ders are oxidised (3l),

- 133 but in the present study the density of the oxide v/as assumed to be constant although this effect could influaice the initial oxidation isotherm,

r^pas and Kingery (52) have studied the electrical conductivity of single crystal and polyciystalline alumina in the temperature range 1400-1800^0 under various oxygen pressures. At the high pressure region, the conductivity increased slightly with pressure.

This v/as attributed to absorption of oxygen on the surface where it, according to the equation

I O2 (g) ^ 3/2 0^~ (ads). + V^^3 ^) 3 ®

If this effect is true of aluminium nitride at atmospheric pressure, the production of voids would act as nucleation sites, i.e. regions of higher potential ener^ from v;hich the reaction is able to proceed.

From the discussion above^ it is assumed the effect of the absorption of oxygen and the assumed difference in density betv/een the surface oxide with respect to internal oxide play a major part in the initial rate curve.

The types of oxidation isothem have been described (44), and a comparison of the isotherms obtained in this study shov/ that the isothemis are decelartory throughout^ that is the rate progressively decreases as the reactant is consumed- Hov/ever, there is a slight discrepancy in the continuity of the isotherms. It v/as thought that perhaps this may be due to an experimental error and a gram of kl^-^ was heated at 960^0 under the same conditions and the

13if - weight of the sample remained constant throughoutp thus obviating

the idea of experimental error. To further investigate this effect

a detailed plot of the oxidation of aluminium nitride was taken at

3J>0^C at ten minute intervals over a period of 3 hourso The results are graphed in Pigo 15* Prora this graph there is change in shape in the region A A' and this begins to occur after approximately

1 hour.

The effect could be explained by taking the points a^ b, c, d«

At the star^ of the reaction p nuclei are formed at areas of hi^ potential enei^ as previously described. These nuclei are random and the area of reactant pix)duct interface is small and hence the reaction rate is slov/. At the point b the nuclei have started to grow and with new nuclei being formed the reactant product interface has grown,, and hence the reaction is faster.

At point c the nuclei have grown to sufficient size such that they overlap and cover the surface conpletely, so the reaction begins to decelerate as further reaction results in the reactant product interface decreasing in area.

In the region of d there is a slight increase in the reaction.

This may be due to the fact that the formation of initial oxide layer takes place at faster rate than the nitrDgen, formed in the reaction, diffusing through the oxide layero The result is a build-up of pressure at the reaction interface which causes the surface to break and hence the exposed nitride acts as a nucleation point for further oxide growth.

135 4-5

Time, Kf

•P

4- ^—1—4 1 1 8 lo

Fig. 15. The percentage converamon of aluninixim nitride heated at 930*^C for 3 hours.

- 136 - Thii-3 oonceot of a breakdcv/n in the oxide l^yer is descriptive oi"

lijiear k-inetics^ and has been observed in OLher gas solid systems

(iVOy 4ij 53)0 A plot of fi.rst oro.or kijietic-.= 3^alnst time sterns in

Tact there is a change in the ord»';r of reacticrj, TrJ.^^ can be seen in

:'ag. 16 \7}iei'^' the slope :.^hsnge£ at a., a* no b' foj- the plot of Q

VLôln-at time for .960°C and 910^C rcsTêc tavî-iy. v;here - .:og Vi'".

A plot ot' log t (time) against log x (x -. percentage conver-sicn

uC aluiri.i.na.) v/a^ made (see Fig- l'3b) r.rcm which. 'i:h<: slope gives the order of reaction. From the:^-e plots it v,?j.s ai&o observed tr:at th^:: ord.er oi' reaction changed frxr-m ^ to 1 in rj\( 1?-//:^'" tomper^tijj-e regicr.o

7:hi*?i i.s due to the fact that although cj-adp.t.icn or alujfitniujii nifrid':

begins above 600'"C. th.e-ve ir not an app-'^-?:*I ar.". e amount o:' o:ri'J-e forced and thei'a is on-iy a suj^face reaction rr-».;i.-)g c.a.'-t at these temperatures.

At higher temperatures the order reaction is initially 1 changing to a i i:ntli a'Dove 9^0"^!!' the ov.-^ral i r-i-ao t ..on '•rirc'tios are paraboliCo

I'rorri the plot of y against tine (t) for various temperatures for a period of approximat'^ly -p; hoL:r> the rclati',:nj=.rdp becv/een y and t is approximately linear (see rig» -7')^ ad;nng furrhtt* e\d.drnec.- to the idea of nucleation as a sorfaoe r-Hai'.tion br-ing th:. initial rate contrclllng mechanism. This is further exempl:i.?ied by thi e fact that 2

tihe relationship Z to t is not initially- Vine^i::- i^ the lov; temperature region (see Figo 19) s and h^-ice diffusion play.-^ very little part in the Initi.al stage of The reaction^

137 T-5 0-5 I JL'C legs.

(a) A plot of first-order kinetios iTith tlfio for various teiapetaturefl* Pig. 16. (b) A plot of log t (tine) with log x ( z is ^ conversion)* - 138 - Ha.vever, as the reaction proceeds, diffusion becomes the controlling mechanism as the relationship betv/een z and t becomes linear. This is true for values of P bet^veen 0.003 and the^final readings taken in the kinetic study. So the mechanisms which occur are linear kinetics follov/ed by parabolic k:^netics follov^ed by a short region of linear kinetics and the retum to parabolic kinetics. This type of linear pcirir.lxCi ic relationship hos been encoijntered by other authors (59) and

'.i:- •*::li.:/:-.'.oy: of c-;.licon ni.i'.i'i.oe (54) t':\ri Icinctic equation used in lhi3 type of mechon.i3rn X'a

vr •:- A A V/ rz k t C

•.•.•r-.rjTv: is the v/eight incrd-r-3e

k is l.i~:c overall rate cons-tant

i:;ec:u^:":i"^: v.ould conr^ccuently not l\ clet^iled picture of the oxidation klneticr:. Tl-.e convorEO ::>f thin r.v^ch.'r-tiiyiv: (knc-r. us pp.ralinear kinetics (61)) is not to be confu.scd v-lth the above equation

T:i!?.?.a kinetic .';t;udie^: h^.ve he-jn liin.itod to 0. seven hour period in which a m^iximujn of 30 per cent conversion to .-.luirLina v/as observed. To obtain an overall picture, samples of aluminium nitride of surface area

2 -1 l.ln g v;ere heated for longer periods of ti"e r.nd as m^^.ch -"s 94 per cent conversion to ali-unina is observed in 130 hours at 1000°C« Rarabolic kinetics ' re obeyed in the initial period of 2 - 22 hours, as can be seen 2 from a plot of Z against time (t) (Pig. 18). Dtu^ing the first ho\ir interface reaction is rate controlling as can be seen from a plot of y against t (Fig. 18)• After the 22 hours, the plot of Z against t is no longer linear for values of F greater than 0,6.

- 140 - 1

1 iO So 40

Fig. 18.

A plot of ^ against tins* t« for periods up to }0 hours.

- 141 - This is probably due to the layer of oxide no longer growing in regular

fashion and the approach to linear kinetics from the plot of y against

tj suggest the reaction is mainly taking place at the reaction interfacSo

This is a relatively slow process from which the oxide layer will progiess

until it finally sinters and prevents further difl\jsion of oxygen to the

interfacec

Prom plots of Z agaicist time for different temperatures, (stse Fig<,l9)

the slopes of the straight line portions were found and these values were

taken as the reaction rates (k)o A further plot of log k against the

reciprocal of temperature in degrees K was made (see Pigo 30) and the

slope was equivalent to eAO56H where E is the activation energy and a value

of 53 k cals/nole was calculated and the equation can be expressed as:

This value ccanpares well with the oxidation of aluminium nitride in purified osygenj to form alumina (vis: 50o8t3 k cal/mole for a surface area

of OCM6 m'g (59)j and 49 k cal/nolQ (35) in the temperature range

650-1 iOO°p no surface area measurements being given)(see Table 25)0 This agreement emphasises that the main reaction taking place when aluminium nitride is heated in air is the fonnaticn of aluminao

It is concluded that the reaction follows first the fomation of alumina at nuclsation points on the surfaceo While the regions grew linear, kinetics are observed until a coherent layer ferns when parabolic kinetics are recorded, until there appears a slight break in the coherent film allowing further nucleation until the surface is recovered and parabolic kinetics are further observedo

142 Table 23

Activation energies of the oxidation of alumird.um nitride and related material s

Activation energy Fonnula Conditions Ref. k cals/mole

Al 660 - 850°C 99 12

AI2O3 sintering studies 130 - 170 59 1300 - 1900

AIN ^2 51.8 59 AU^I ^2 49 35 AIN air 53 present work

61 54

axr 68 54

Sic oxidises to 15.6 31 amorphous SiO,

Sic oxidises to 20.2 31 crlstoballite

23.9 32-

143 = I

A plot of 2° againat tioB, t» for various teoperatiiros* - 144-^ To ujiderllne this breakdown in the ooherent layer, the aotlvation

enex^ for the reaction of moist nitrogen with aliuslnluA nitride in a

temperature range of 600-800^ is reported (38) as 7«3 koal/aole.

However, a value for the enez:gy of activation for the reaction of

aliminixim nitride in dzy oxygm U reported as 24«3 keal/oole (3S), but 2 -1

the surface area semple used in tl at study was 1.7 a 6 * and hence by

oaq)ari8on the nitride powder used ^\ the present wozk would be acre

reactive above 700^0 and an activation enexgy of less than 7*3 koalAK>le'

could be expfictcd for the- rrs^iction bcV-veun the sar.ple and nitrogen- The

ionic it.dius of nit.rocr-n 1-71 -** -nd ii- is doubtful v/hcther nitrogfin 2- would diffuse ;i3 T-' ao nit\Xintr\ nouli} diffj-jc as atomii ratiicr thun ions.

The atoraic radius of nacrogen ia 0„71 '^-9an d the ionic radius of aluminium

is 0.5 30 for purely geometric reasons the aluainlura ions would diffuse

along the grain boundaries rather than t}urougJi the crystalline material

(60)1 faster thriXi the riitrogen atomse Cmsoquently, due to the assuasd

low activation energy of the nitride in the presence of nitrogen, and the

easier diffusion of aluminium ions, there is a break in the coherent oxide

surface to allow the removal of nitrogen. As the continuation of a coherent oxide layer growth is observed without a further breakdown in oxide surface, the further reraoval of nitrogen from the system would seem

to be by some diffusion process, perhaps through the fibrous oxide layer

(a).

As oxidation will be controlled by the rate of arrival of roactant at the reaction interface, diffusion of the fastest moving spaoies is

rate controlling.

. 146 • As previously discussedj, the diffusion of aluminium ions would be

faster than that of nitrogen atomso In a study of the oxidation of pure

aluminium in the temperature range 400-630°Cp the rate controlling

species v/as identified as Al"^"*" and an activation energy of 52 k.cal/mole

(60) ajid 54 k.cal/mole (64) was recorded in accordance with parabolic

kinetics. These values are in excellent agreement with the present

results^, and a grain boundary diffusion of Al*^^ through the oxide film

to react at the gas oxide interface is compatible v/ith the experimental

results obtained in this work.

The diffusion of oxygen in polycrystalline alumina has led to

activation ener^gies of I3O-I7O k.cal/mole (591^65^66) and comparison

with 53 k.Cal/mole would suggest that diffusion of oxygen ions in

alur-if^-ilin nitride is not rate controlling* This disagrees with the

i.csults of Guichon and Jacque (35)» v/ho concluded oxygen ion

diffusion to be rate controlling* This hypothesis v/ould therefore

appear to be incorrect from the present work. Hov/ever^ they showed

that there was a relationship between the rate of reaction ajid partial

pressure of oxygen in the systerrir, but limitations in technique did not

allov/ an evaluation of the order of relationship.

The results of Cooper et al (59) showed the relationship betv/een

the oxidation rate and partial pressure as

oxidation ratert. ^

The mechanism of absorbed oxygen on the surface of polycrystalline alumina

(52) which ionized according to

3 O2 (g) 3/2 0^" (ads) + V (A ) 3 e has been adapted for the surface reactions of aluminium nitride.

147 V/hen the process attains equilibrium,

a constant

The production of the positive holes at the gas oxide interface will detennine the extent of the driving gradient of Al^"*" ionsj v;hich is rate controlling from aluminium nitride through the oxide layer to the oxide-gas interface.

IVo3oiv The effect of pai^cle size on the rate of reaction

5 gram samples of aluminium nitride of original surface area 2 -1

Ook mf.go were milled in a porcelain vessel^ with a number of alumina balls of different diameters^ for periods of 2^ 5 and 10 hours. The oxidation rates of 2 hour and 10 hour milled samples were estimated as previously described at 872^5 910^, and 960°C, and compared with oxidation rates of the original samplCo

The 5 hour miJ.led sample was set aside for hydrolysis studies.

After each milling periods the material was recovered as described in Chapter II. The "surfaces areas v/ere determined as previously, by the BoEpT» procedure. From the deduced particle size, a comparison of the r^te constants for the particle sizes for a specific temperature is given in Table 24*

14B Table 24 c oTpaidson of the reaction rates of constants of milled samples at

vaiious temperatures.

T.,.EgW,. -^^J^ H.t.Co„.t»t -3-15

872 • 0 0,077 X 10"^ 0.4

2 0.258 xX 10"10"^ 2.7

10 0.436 X 10"^ 4.8

905 0 0.235 X lO'^ 0.4

2 0.61x10"-^ 2.7

10 0.67 x 10"^ 4.8

960 0 0.47 X 10"^ 0.4

2 0.89 X 10"^ 2.7

10 0.79 X 10"^ 4.8

- 149- As expected^ when increasing the surface area of the material, the

sample becomes more reactive as can be seen from Table 24 which compares

the rate of reaction with surface area. A tv/elve-fold increase in

surface area as a result of mil.ling the material for 10 hours increased

the reaction rate constant by the order of 56 times at 872°C,

As the temperature is increased^ however, the increase in reaction

rate is not so great- For example^ at 905^0 the milling of the sample

for 10 hours introduced an increase in rate constant of 28, yet at 910°C

the incrCELse is of the order of 21.

V/hen comparing the results of aluminium nitride heated in air having

been mi.lled for 2 hours and 10 hour-s respectively; at 81 2 there is only

a slight modification in the rate constant (see Fig. 21), and at 905

(see Fig. 22) and 960 estimated reaction rate v/ithin experimental error

is constantc This effect has also been observed in the oxidation of

chromium nitride in air (63).

The results suggestr, therefore5 that increasing the surface

area by a factor of 63 tends to make the sam.ple more reactivebut

any f\j3rther increase in the surface area has no appreciable effect

on the reactivity of aluminium nitride.

IV.3.v The effect of impurities on the oxidation

As one of the methods of preparing aluminium nitride studied was

the thermal decomposition of ammonium hexafluoroaluminate in gaseous

ammor-iaj, the effect of alum.inium fluoride on the oxidation of

aluminium nitride v/as investigated.

V/eighed amounts of -aluminium fluoride (fomed by decomposing ammonium hexafluorcaluminate in purified nitrogen at 750°C) were added

50 tohf.

onm'Mi

The effeot of mining on the oxidation of alualnlua nitride at 87^0.

- 151b- to 1 gram weights of aluminium nitrdde smd the fluoride present expressed as a weight percentage.

The effect of adding the fluoride is shov-Ti in Fig. 23. The rate of oxidation is remarkably increased* ' U^o2. wrt^% increases the rate of oxidation- but the 'final^ amount of decomposition observed is less

than that observed v/ith no fluori.de present. 9.3 vjtofo again increases the oxidation rate more than Uc2}^<, but after a period of approximately

1.5 hours^ the fluoiTi.de itself begins to oxidise and a weight loss is observed. A 19.8 vn^fo addition in fact resulted in a constant weight loss and hence the fluoride preferentially oxidises and can no longer be considered an impuri. tVo

Flucrides are also knov.Ti to have a catalytic effect on the oxi.dation of metals (6?).

IVo3.vi The chanRC in surface properties of aluminium nitride and

silicon r.i.tride

Separate half gram portions of aluminium and silicon nitride v/ere oxiui-sed in air at QOO^ 900^ 1000*^0, As expected^ the conversion to aluinlna takes place more rapidly as the temperature is increased.

Weight changes were measured when the sample was cooled to room temperature and percentage conversion was found for each temperature at diffei-^nt intervals of time. The products from the oxidation were identified by x-ray techniques as described in Chapter II and were idenoifi.ed as -alumina ( o( -Al^*-*^)^ and silicon dioxide (S iJ^p tridymite and ciastoballite) even in the early stages of the reaction

(see Tables 25 and 26)<, Certain samples ^vere further examined by

153 O ALN 2au QAj

t 4

Fig, 23. The effect of altminlum fluoride on the oxidation of aloDiniua nitride*

154 - the use of a Philips MdOO electron microscope (see Pigs. 24-27)«

A laj^ger amount of nitride was required to measure the change

in surface area and 5 gram samples were oxidised in air for various

timesj, at a 1000*^C« The cooled samples were outgassed in vacuo at

200°C before their specific surfaces were determined by the BcEoT,

procedure (47)*

The deduced average crystallite sizes were compared with the particle sizes ranges determined by electron microscopyo

No oxynitrides have been observed in the present study and it appears that oxynitrides are fomed only at higher temperatures (55) where the respective nitrides and oxides are mutuaJ-ly soluble, or in the case of aluminium nitride by nitridingo< -alumina in ammonia at low tanperatures (56). Fig* 28 shov/s the overall variations for aluminium nitride in specific surface^ and average crystallite size during the conversion to alumina. These are compared to the oxidation rates Fig« 28d3 changes in the number of crystallites

Fig. 28c5 and the average crystallite sizes of the individual unchanged aluminiiira nitride and the product oc -alumina Fig. 28f«

The aggregate siges,, estimated by electron microscopy are given in

Table 2? to be compared vn.th the crystallite sizes.

155 Table 2=

Aluminium nitride heated at 9Q0°C for 96 hours

3.48 w

2,68 3 2.70

2.33 vw ^ 2o55

2.4^ V/ 2.49

2.36 s 2.3? 2.38

2.OR V/ 2.09

1.83 w 1.83

1,6 w 1.60

1.33 V7 1.56 1.53

1.40 -ij 1.41 1.43

1.37 w 1.37

1.31 w lo32

lo30

s strong

V/ = weak

vi,v = very weak

156 - Table 26

Silicon nitride heated at 1000°C for 96 hours d , obs I d d a c 4.14 4.04 4..30 3.77 w 3.88 4.08 3.37 3.81 3.23 s 3.14 3.25

2o98 s 2o89 2.92 2.96 2.82 2.84

2.46 s 2.53 2o47 2A7

2.3 vw 2.32 2.34 2.37 2„29 2,17 V/ 2.16 2.17 2cl2 2c 0? 2.0? 2.03

2.91 s 1.94 1-99 1.93 1.97 lo?95 1.8? 1.87 1.74 3 1.75 1.76 1.76 1.69 1.64 lo58 WV/ lo60 1.64 1.61 1.58 lc51 WW loSl 1.46 1.50 1.52

1.33 w 1.32 1.38 1.4 1.33

d crlstoballite a d^ cristoballite

d^ tridyraite

157 Pig. 2ifa, AluainlMi nitride.

24b. Alumin*to nitride Milled 5 houra. | ^|^^*| Pig, 25b. AluninivM nitride heated 24 homrm at 1000^0,

1^ Pig 25a. AliMiiniwt nitride heated 5 hou»a at 100( Fig. 26a. Aluminium nitride heated 9G hours I'^o C

Pis. 26b. Silicon nitride

Pig.

7b. Silicon nitrid .rs at 1000 C.

/ Table 27

Variations in aggregate sizes during the conversion of AIN to ^ "^2^ at 1000*^0 in air.

Time, hours % conversion aggregate ' size ( A^mJ

0 0 1 - 2 .

5 51.3 3-5

24 67o7 3-6

96 82.7 3-7

163 85o9 4-8

162 - Fig*^ 28.: Caparison of the rate of oxidation of AlK at alOOCPc vith the change in i)8peolfio surfaoe ii) the nsmber of exystaUites iii) the average oiystallite siEe^j

- 163 - V/hen considering aluminium nitride, the variation in oxidation

rate is accompanied by a corresponding change in specific surface. The

oxidation rate is accelerated over the first 50 per cent oxidation and

becomes progressively slov;er as the reaction proceeds, see pig.

There is an initial increase in specific surface accompanied by a linear

rate in oxidation v/hich indicates that the alumina initially formed on

the surface of the nitride splits off to give smaller crystallites.

This splitting is due to the change in molar volume when converting to oC -alumina and the corresponding change in crystal lattice. A measure o. 3 of the crystallite splitting is given in P .g.28c. vriiere a plot of /S

against time is given where S* is the actual surface area. Molar volume

change is not required (57) in determining this parameter. The extent

of crystallite splitting is comparable v/ith oxidation of titanium

nitride (58), but far less than that of calcium nitride (4^0. The

Tammann temperature, v/hich is half the melting point of a compound in

'^K, are approximately 1340'^K and 1200°K for aluminiiim nitride and alumina

respectively, indicating that the sintering of ot-alumina would be more

extensive at lOOO^C. This extensive sintering of the £7<.-alumina tends to

bind the un- .cLdised nitride peirticles together. This is confirmed by

the changes in average crystallite sizes deduced from the surface area

measurements. Accordingly, the aggregate sizes indicates that the

original nitride contains mainly single crystallites, and the oxidation

results in the fonnation of aggregate s of 3 - 8^m (see Pi .5. 28) in

which the individual crystallites appear to be over 0.5yt

stages of the oxidation. This is verified from Pig. 28pv^ere the

crystallite size of alumina at 60 per cent conversion is approximately

- 164 0.3^m. Beyond 80 per cent conversion, the oxide layers sinters and

prevents the gaseous diffusion of oxygen through the oxide layer and

the process is controlled by a solid-state diffVision mechanism.

The mechanism now involved is extremely complex and depends on

the area and defect structure of the contact areas between th solid re-

actante and the product". As the reaction rate is relatively slower, the

movement of the reaction interface is very slov/. This may be due to the

fact that there is a small contact area between the alumina and aluminium

nitride at the interface brought about by the sintering of the alumina

layer.

As there is a gradual reduction in the average crystallite size of

ail^-miinium nitride and a sudden increase in the average crystallite size

of alumina after lOfo conversion, the interfacial contact between the

0( -alumina and aluminium nitride wou^d not be expected to be great, and

hence the rate of solid state diffusion and rate of reaction is very slow.

By Gontr st, silicon nitride is more resistant to oxidation as can be seen from Fig. 29. At a lOOO^C after 60 hours, 2&fo conversion to cristoballitfc is observed and the corresponding conversion to oc -alumina is 93?^. As oxidation occurs, the specific surface of silicon nitride initially decreases, as theoi.-cristoballite formed acts as a mineraliser.

The Tamraan temperature for silica is 720*^ and the specific surface is 2 -1 observed to fall from 1.7 to below 0,2 m .g v^hen one third of the silicon nitride is oxidised. The silicon nitride and silica thus tend to bond together. Consequently, the oxidation is increasingly controlled by solid state diffusion, and, as observed, the rate of oxidation is slower than in the case of aluminium nitride.

165 - t t Fig,29. Comparison of the oxidation of aluminium and silicon^n'itrldes. MbMta aoolIlB boa autatmalB 1. Bxztig G.F., Kolloidzeitschrift, 1941, 97, 281.

2. Kingery.,V/.D., "Introduction to ceramics", I96O, (New York; Wiley). r 5.,, Coble, R.L., J.Appl.Riys., I96I, ^2, 787, 793.

Li.. Coble, R.L., "Fundamental phenomena in the Material Sciences", 196^5 Vol. 1 (New York; FLenum Press).

5. Kuczynski, G.C., "Theory of solid state sintering", I96I (New Yoric; V/iley, Interscience).

6. \7bJ.tey J., '''Science of Ceramics", Proc. Br.Ceram.Soc., 1962, 1 305, London (Academic Press).

7. ibid., 1965, 3, 155.

8. Pedorchenko, I.M., cS: Skorokhod, V.V., Izv.Akad.Naiik. SSR, 1967, 58 (10), 29; Progress in inorganic mterials; 50th Anniversary Publication, Akad.Nauk.SSSR., Oct. I967.

9. Thummler, F,, & Thomma, W., Met .Mat. , (Met.Rev,), I967, 69.

10. Chiatti, P., J.Am.Ceram.Soc., 1952, 35, 123,

11. Sato, T,, J.Appl.Chem.,- 1962, 12, 553.

12. ST^rmlv, V/.n. , J.Electmohera.Soc. , I96I, 108, 1097.

13. Glasson, D.R., J.Appl.Chem., Lond., 1967, 17, 91. li*.. Hiiddlesden, S.N., "Special ceramics", Proc.Symp.Br.Ceram.Res.Assoc ., 1962 (London; Academic Press).

15. Carbor-jjidum Co., Brit.Patent No., 1,052,295.

.16. Shaffer, P.T.B., & Samsonov, G.V., "High temperature materials", 196V, Handbooks 1 & 2, (Nev/ York; Plenum).

17. Glassonj D.R,, & Jayaweera, S.A.A., "Surface phenomena of metals", Scc.Chem.Ind.Monogr. No.,28, 1967 (London; The Society).

18. Glasson, D.R,, J.Appl.Chem,, Lond., 1963, 13f HI-

19. Jayaweei^, S.A.A., Thesis, University of London, I969,

20. Glasson,D.R., & Jayav/eera, S.A.A., J .Applied,Chem., Lond., 1968, 18* 21. ibid., 1968, 18, 65.

22. Taylor^ K., Ind.Eng.Chem., 1955, 47, 2506.

- 167 - 23o GoUins, J.^ & Gerbyp R. ^ J.Metals, 1955, 2^ 612.

2U.^ Schvaiger, M.Io ^ Zavodakaya Lab-^ 1960^ 26, 1223»

25. Billey, M., Annls.Chimo, 1959, 4, 795o

26. Glasson, D.R.^ J,Appl.Chemo, 1960^ 10, 38.

27. Gregg, S.J., & V/heatley, K.H., JoChenioSoc., 1955^ 3804.

28» Oomea, de Boer, J.Ho^ & Lippens, B.C., Proc. 4th Intern. Syn^. Reactivity Solids^ 1960 (Published 196l).

29. Sato, Top J,Appl<.Chein« p 1963^ 13p 3l6o

30o White, V/.B., & Roy<, R. p Ajner.Mineral.., 1964, it9, I67O.

31. Jorgensen, P.J., et alo J.Ain.Ceram.Soc., 19599 h^s 6l3.

32. Jones, JoAo, Ph.D. Thesis, 1970.

33. Bryan, J.H., J.Soc.Chem.Ind., Lond., 1950, 62s l69»

34. Glasson, D.R., J.ApploChem,, 1958, 8, 798.

35. Guichon, G., & Jacque, L., Bull.SocoChem. France, 1963, i, 836.

36. Jorgensen, P.To, etaX. J.AmoCeram.Soc., 1961^, (6), 258.

37. Dea3., BoE., JoElectrochem.Soc., 1963, 110, (6), 527.

38. Bhat, T.R., & Khan, I.A., Indian J.Chan., I967, 1, (lO), 499.

39. Massoth, F,E., etal<. J.Hiys.Chem., 1960^ 64,= 41if.

40« Massoth, F.E., & Hensel, W.E., JoPhys.Chera., 1959, 63, 697.

41. Farrar, R.L., & Smith, H,A., J.Phys.Chem., 1955s 59, 763-

42o Massoth, F.E., & Hensel, W.E., J.HiySoChem., I96I, 65s 636.

^3. Gregg, S.J., "The Surface Cheraistiy of Solids", 1951, (Chapman & Hall)

44. Jander, "Chemistry of Solids", Galway, A.K,, I967, (Chapman & Hall).

45. Carter, R.E., J.ChemoPhys., I96I, 34^ (6), 2010.

46. Coles, N.G., etal. J.Appl.Chem., 1969, 19, 178.

47. Brunaer, S., etal. J.Am.Chem.Soc., 1938, 60, 309.

48* Gulbransen, A.E., & Andrev/, K»F., J.Electrochem.Soc., 1951, £8, 241.

168 49. ^fctt:^ N.F.J J^=.t.Mer.als^ IShJ^r, 12, 36?.

30. Hodgmanp G.D. ^ etal. "Handbook of Chemistry & Physics"p I96O5 Th^ Cheriical l^^abber Pablishirig Goo_, (Cleveland),

3I0 Flanders^ H.E.„ P.B.Rept-op 1960, I285 568.

32o Pappis^ J.,-, & Kingeiy^ V/^D.^ J.Am.Cerain.Soc. 5 19615 44.^ 459,

53. Ku'baschw/aki T Ao Hopkins. B.K, ., "Oxi.dation of metal.s and alloys", 1962:, (Butter.vorths)o

34. Horton„ R.M.^ Joi^m.CerBm.Soc. ^ 1969j. 52, (3):, 121.

55. Adams, I.A. ^ .Electrochera.Soco 5 1962j. 109, IO5O0

56, Lejus. A.M., Rev.Hsu. riSoTerr^^oRefrac. I964, I., (l)^ 53o

57^ Glasson^ D.R, & Jciya.-*ve.e;ra. S^A.A*^ JoAppl.Chera.

50. Glasson^ D.R. ^ J. Appl .Chem,Lond« ^ 1958p 798.

39- Cooper-y 0 ,F, _ela.lo HroOo S3rmpoBriteCerani.Re3. Assoc. (Ed. ^ P.Popper^ 1962. 495 (AoadeiTUX Press)o

60. G-rfigg. SoJoj Htal. J.InstcMetals- 1960, 66^,. 205.

6lfl Kofstadj P. 5 "iid.gh temperature oxidation of metals",, 1966^0 (j. Wiley & Sons).,

62. E-rans^ V^Ron "The Corrosion and oxidation of [netals'% 1960,^ (Edwa-.d ATTiold Ltd., Linden).

63. Ic Aliop 1969.') private conrnpjn-i.oationo

64. Be:::k5 A.Fo;, CorroScSci«-•'^6'?., 2^ (l)? 1"

63. Da'^l.e?, M,0.p N63 - 20999^ RepV.No^ NA^A TN D 2763pl965o

66, Kothari., N.C, J .Nucl «Mater. , 1963, l^.r (l ) ? ^3.

Bhat.5 T,R., & Khan, I.A., ILSoOoverr—-nt Res,& Develop.Rept. ^ Aug. 10th, 1969- 680 Gj.aason^ D.R. . & G-aa^mage^ R.B.p Chemy^lnd.^ 1963^ p.li:.66; Ganmags^ R.B., Thesis^ Unive.rr-ity of Exeter, 3964.

69. Gla^sson, D.R. , J,A-pDi«Chemo „ 1964. 14.^ 121.

169 CHAPl'ER Vc 'I^ernpdynaffiical_ aspects of the formation ar.d reactivity of

aluminium nitride«

V.l The formation of sJ.uminiuin r.itri.de

The reaction considered v/ere;

Al + ^N^ —^ AIN (l)

Al - NH^^ —> AIN + (2)

ikl^O^ * V2C ^ ^N^^ AIN + 3/2 Co (3)

AlF^ + NH^ —V AIN - 3HP (L)

AlCl^ + ^ AIN 3HC1 (5)

AIN ^ 3/202'-^ ^-'^^2^3 (6)

Thermodynamical data for the substances in the above reactions were obtained from the JAKAP Thermo-chemical tables (7)0 This data is given in Appendix. VIII„

Due to the .lack of thertnod;>mamical data for 0^^)^ Al in the rcactd-cn

(NH^)^ AlF^ 4- > AIN + em^V

6 m-^ +• 6HF the rcute AiF^ + NH^—» AIN -t- 3HP v/as chosen and the discrepancies intioduced by doing this will be discussed later* Also comparison is made vd.th the formation of the nitride from the chloride analogue*

The free energy of elements and their compounds cannot be measured in absolute termSg but it is possible to observe the change in thaimodynaraical properties v;hen a chemical reaction is induced. The change in standard free energy A ^ gives an indication of the extent to v;hich a reaction occurs and is related to the eq^oilibrium constant K by the equation

AG° =: ==RTlnK (i)

« 170 " For a chonical reaction^ it is possible to plot the standard free energy change per unit mass as a function of temperature in degrees

Kelvin, This plot is knovm as Ellingham Diagram. The main disadvantage of the Ellingham Diagram is that the free energy change as a function of temperature refer to standard states of the system, v/hich are not realised in actual systems. For instance^ the mutual solubility of the

solid components may increase with temperature, and the gases are generally not in the ideal state. As a result a pressure correction must be applied and this can be calculated from the Van Hoff equation

^ G_ =A&° + RT ( 3'ln a/ , . \ - 5^1" a/ ^ 4. \ (ii) T T ^ (products) X (reactants; ^ '

V/hen AG° (the standard free energy change) is zero the equilibri,ui m constant K is unity. Hence AG]^ ^ 0 would indicate that K-<^1 and

the produc^ ^ are present in lov^ concentration at equilibrium. The conditionA.G^-^^0 suggests that the reaction is feasible^ and the more negative the value of l\ G^^ the more thexmodynamically stable the product.

The condition A G^ refers to a thermodynamically .possible process. This process is such, that if there are no diffusion barriers or restrictive forces the reaction will proceed of its ovm accord. The free energy change is therefore important because if a process is thermodynamically feasible and in reality does not take placep then it is clear some restricting force is required to be overcome.

" The free energy change is related to the heat of formation ( AH) by

AG = AH - TAS (iii) vrfiere A S is the change in entropy. It is necessary to calculate the heat of formation as this indicates v/hether an endothermic or exothermic reaction has taJcen place.

171 - In the present work A G° and A H'~' were calculated from the

equations

AG° = AG , , - AG , ^ (iv) products reactants ^ ^

and A H° = AH . ^ - AH , ^ (v) " prod.ucts reactants

V,l The formation of aluminium nitride

V„ 1,i The formation from the elements

Due to the advances in the techniques oi' purifying metalSj the

formation of a compound from its elements has become increasingly

important. Fig. 30 shows the relative stabilities of various nitrides

formed from the element and nitrogen. It vn.ll be seoi that aluminium

nitride is expected to be more stable at elevated temperatures than

calcium or magnesium nitrides^ but not as stable as titanium nitride.

From Fig. 32 the free energy change for the reaction

Al A1.N (1)

is negative in the temperature region 0 - 2830°K and hence the reaction

is feasible v/ithin this temperat^jre. However, it is concluded from the

present work (see Chapter III),, that at 500°C (773*^K)p which is v/ell abov^

the Tamman temperature (330°C) for aluminiump that sinteri.ng of the metal

fijjn occurs. To overcome this barrier, the reaction can be carried out

in the vapour phase. The reaction betv/een aluminium and nitrogen is

exothermic. The reaction wn.ll occur at temperatures less than the

boiling point of aluminii-un (2723°K) as is reported (l). These workers

observed alum.iaium nitride at 1300°C (1773°K) where the calculated heat

of reaction is -78 Kcal/mole.

Above 2850'^K, (2577^C) A G° is positive and the decomposition of

. alijminium nitride to its elements is expected to begi.n at this

172 Fig. 30. The free energy of foraation of soae nitrides i

loo 3co. -70D tcoo temperature. Thi.s figure agrees with the reported values for the decomposition ten^^erature of aluminium nitride (see Table 4)*

The theimodynamic calculations agree v/ell with Mah et al (2), but disagree v/ith thos" of V/icks and Block (3), (see Fig. 31).

For the reaction M + i^2(g) ^"^^(s) operating free

energy change will be given by o RT = AG^ - ~ In P^^

The fomation of aluminium nitride by nitriding aluminium with ammonia is also considereds

Al NH^ AIN +1 H^ (la)

The change in entropy is very small and from Fig. 32 there is. very little change in the slope for this reaction. Therefore, A G^ is approximately equal to the heat of formation AH^, The reaction to a

first approximation is therefore independent of temperature. In Fig, 32

the plots for the nitridation of aluminium using nitrogen and ammonia

intersect at 450°C. As the temperature increases A G^ for reaction (l)

becomes less negative whereas A G° for reaction (la) remains approximately constant. It would therefore suggest that it is themodynamically easier

to form the nitride from ammonia at temperatures above 450*^0. This

point may allow the nitride to be prepared under the experimental

conditions described in Chapter II, substituting ammonia for nitrogen

and nitriding the aluminium film.

V.l.ii The formation from the Serpek reaction

V/hen considering the Serpek reaction to form 1 mole of aluminium

nitride

Al 0 + V2 C(s ^ ^ ^ AU^, . + , (3)

17^ " Wig, 31. A ecaiparlgon of the free energy of fonaatlon of AIN from its elaaents.

-lOJ.

-aoJ. 1

-sol

56o

- 175 - and assuming the solid ccmponents to be In the standard state, the

equilibri.um constant is given by

From Fxg,32AG° = 0 is at 1980°K lyOO^C).

At atmosphere pressure p^^ "*" ~ ^* suppose PQQ oC.

3/2 Hence = QC,^^

In K = ^ log _oc£ ^ 1-oi

Thus from the calculations for A for this reaction^ Jn is derived by equation (l).

When In K ^ O^^G^^ 0 and + o( " 1 - 0.

Consequentlyp from Fig. 13 the required root of CX is 0.68. Hence the equilibrium concentration of carbon monoxide is GOfo at 1 atms. total pressure. . From the previous work (see Chapter IIl)j.rthe results of

Frankel and Read (4) are in good agreement with this value. A.t 1900°K o * (1627 C) the carbon monoxide equiLibrlum concentration is 51?^- Therefore for the temperature range 1900-198o\ a nitrogen concentration of 32-49^ is required in the reaction. From Fig, 32 A is negative above 1980°K and the reaction i.s thermodynamically possible above this temperature at lOTrer nitrogen concentrations. The reaction is endothermic, and at

2000°K the heat of formation is of the order of 80 Kcals/mole.

The working free energy'- is given by: 3 AG = ^G° V2 RT In P^Q + ^.^T Inp ^2

176 Fig» 32* Free energy of formation of AIN fr<»i various methods of preparation.

- 177- It must be remembered that the above calculations v/ere m.ade using

ideal conditions. Howrevery as previously discussed^ side reactions

-such as

AIN + C ^ AlCN

may occur auid ideal conditions ma^not be realised at elevated

tempteratTJLreso An examination of the reaction to form the nitride from

alumijri.um carbide and nitrogen would thus sefem ptrofitable. The reaction

is proposed as '

.i-AJ^C^ + AIN -K 40 (7)

From Pig. 32 the reaction is possible at all temperatures in the

considered temperature^, but above 2100*^C aluminium carbide sublimes.

The reaction is weakly exothermic as A.H?^-JQ is -4o22 Kcals/mole.

It has been suggested (5) that aluminium carbide is initially

formed in the Serpek reaction by the reduction of alumina. The proposed

equation is

i Al^O^ + i-Al^C^ + V2 CO (8)

•and subsequent conversion to aluminium nitride is suggested by

reaction (7). Reaction (8) is thermodynamically -^favourable as CiG^ is positive in the temperature range considered (see Table 28)* The

formation of the nitride via the carbide is therefore not thermodynamically

sound. The formation of aluminijm nitride by the Serpek reaction must be by the reduction of alumina v/ith carbon in the presence of nitrogen without-any intermediate reactions occuring.

V.l.iii The formation from the aluminium halide derivatives

In the reaction of alumini.iom fluoride vath-gaseous ammonia to form

the nitride

.T,179 Table 28

i.Al^O^ + C ^ Al^C^ + V2 Co

Ten?: ioK) A ( kcal s/mol e)

0 1Z,.5.996

300 - llA-733

1000 + 81.366

1500 + 48o993

2000 + 17*438

180 the equilibrium constant is given by

% " (4a)

AG° = 0 at 150o\ from Fig. 32; a similar gaseous relationship as with

the Sexpek reaction is shown b^ equation 4a and an equilibrium concentration of Gl^o HF v.ould be expected at 1500\, However, the

reaction was experimentally observed at 960°C (1233^) and the

calculated equilibrium constants at .1200^K and 1300*^K v/ere 3.814 x lO"^

and 8.269 x lO'^-^ respectively. The concentration of HF .at 1200^ and

1300'^K assuming ideal conditions v/ere 7«15^ and l8olf/o respectively.

The reaction .takes place at 960*^C although the free energy change is

+17 Kcals/mole, aJid the conditions thermodynamically unfavourable. But

there is an appreciable partial pressure of HF. The HF is swept away

by excess ammonia driving the reaction towards nitride formation.

In practice the reactant v/as ammonium hexafluoroaluminate and the

reaction is

(NH^)^AIF^ -V 4^^H^ —^ AIN + Sm^F

At 960*^0 the ammonium fluoiude exists as its gaseous con^onents ammonia and gaseous hydrofluoric acid and the ammonium hexafluoroaluminate is completely decomposed to aluminium fluoride, ammonia, and gaseous hydrofluoric acid. The conditions are therefore the same as in equation

(4), exc^ept that aluminium fluoride may be present for reaction in the meta stable form. In this case, chemical equilibrium will be further distorted due to the presence of the hydrofluoric acid gas formed from

« 181 =. ammonium fluoride and the reverse of reaction (4) is favoured^ However

in the presence of flovjing ammonia the HF formed will be carried away

and in reaction (4) the forvvard case is very much favoured.. This is

observed experimentally and the effect of increasing the ammonia flov/

rate is to increase the amount of nitride formed per unit time until a

rate of some 50 cos per min is observed (see Fig. ?) after which the

amount of nitride formed is constant« One possible explSLnation for

this is that aliominium fluoride has the highest lattice energy of the

Group III hsilides (I3OO k.cal/raole)^ due to the nature of its chemical

bonding. The lattice energy decreases to 1120 kcal/mole for alxmiinium

iodide. The reaction is endothermic and is favoured by an open system.

By comparison the reaction betv/een aluminium chloride and

ammonia to form the nitride is thermodynamically more favourable at

temperatxires greater than 560°K where A G° for the reaction is zero

(see Fig. 32). The nitride is reported to be formed from the chloride

at temperatures in the region of a lOOO^C (6), but the adduct mono-

aramino aluminium chloride is first formed and decomposed by direct heating in ammonia. The monoammoniates are also formed from the iodidCj; bromide, and boron trifluoride but no adduct is formed with aluminium fluoride (see Chapter III).

The heat of reaction is less endotherraic for the forination of the nitride from the chloride than the fluoride. A smaller heat input is required and the reaction can be carried out best at lov/er temperatures.

V.2 The reactivity of alumi.nium nitride

The oxidation of aluminium nitride is thermodynamically considered and compared v/ith the oxidation of silicon nitride^ Due to lack of

= 182 - thennodynamic data on the hydroxides of aluminium the reaction

AIN + 3H2O Al(OH)^ + NH^

could not be considered.

V^Soi The oxidation of altunijiium and silicon nitrides

The free ener^gy change for the reaction

AIN + ^2 O2 ^ A] ^-^ +

is negative irrespective of temperature (see Fig. 34)« The oxidation

is reported to begin at tonperatures as low as 600^C (6). In the present stucSy the nitride did not appreciable oxidise until 800*^C.

The equilibrium constant is given by

\ - V - where ^ = p^^

At 1100°K Kp is 1.008 x 10^^.

The concentration of ni.trogen present in the gas phase at 1100°K at

equilibrium is therefore infenitesiinai and the reaction is irreversible.

Although the oxidation is thermodynamically favourable the boundary

conditj.ons and the percentage oxide formed is dependant on the diffusion of the Al'^"*'ions whereas for reaction (4) the formation of the products is

determined by the themodynamies of the system.

3il:icon nitride is more resistant to oxidation than aluminium ni.trltle (see Fig. 34); Cristoball.lite and tridymite are formed v/hen

silicon nitride is heated (see Table 26)0 The free energy of formation of Cristobal lite, tridymite and quartz from the elements differ by some

50 cals in the temperature range 298 •- 2000°K (3). For the reaction

Si^N^ + 3O2 2 SiO^ + 2N2

183 •.V

-low-

-600 + $00 looo {500

Pla* 3{», A o'oaparlabn of the free enevgyof f oxnation of a<»alu)Dlna and sllioa froa the respective nitridea*

- 184 - the equiJ-ittrium constant is given by

• P

^0.

= (I ^oCf

At llOO^K Kp = 2<,28 x 10^^ and hence the amount of nitrogen present in the gas at equilibrj.um is erfectively zero,

A compari.son of the thennodynamic stabilities of these nitrides vrl'ch o.xygen shov/ that per mole of nitridCj the silicon nitride is less stable J, but this is not realised in practice, although a reaction is energetically feasible^ the kinetics of the proce.ss may not be favourable as pointed out in the above examples.

185 !• Repejiko, K.N,, et al* NauchaoSb.Pr.Ukr. j, Naucha-Isaled. , Inst. Ogneuporov, 1962,

2o Mah^ A,D., et al. U.SoBur.Mines Rept.InvestNo, 5716^ I96I,

3. V/icks, C.E,5 & Block, F,E.^ U.S.Bur .Mines., Bull., 6O5, I963.

4. Tucker, A.A., & Read, HoL., Trans,Amer.Electrochem,Soc. , 1912, 22, 57.

5. Caro, N,, Z.angnew Chem., 1910, 42, 4D.

6. Renner, T., Z.anorg.Chem,, 1959 p 298 ^ 22,

7. JANAF Thennocheraical Tables, Dow Chemical Co., (New Yoik), JL9 60-65 •

« 186 - GriAI^'EH, IV' C o.r-C ludi. ng suiam ri. e 5 an d suRge s -tl on 5 for fur the r v.'O rk

Aluminium nitride is bel^ig successfoliy prepajred from therrro

d,ecompo3X^icn of ti";e amHioiLVum hexaf LuoroG.l-.imiriate in aiTimor.ia* The

re'^cti.ori is essentially betv/-*:en o:-*-aiunu.nli:!m fluoride and aznmonia and

takîs place below 1000*^00 I'hougn tr-e r-âction is îndotbennic and the thermodynajni.c ccndlticns are unfavoi/rg.bi.-e,, :he piioc^.sî cati be cpjrried

ou^. v/itho-J.t difficulty a:^.d produces matGrdal of high purityo Tha

r^ac^icn bet?,veen niT;rogen and al-.imin.v.;m is 'SKothemiic and the conditions

ara therKiodynamically favourable i,n theory^ but in pr-actice it is fcvaid

:;haT, the r-oa.ctlon doerr-: not taJce place :Satif?,fao.tor.d.l3'- even on

tfisse filns at i-7-mper'at:uree up to tiie melting point of a.l-^Td.nj-.i:r.o It

appea:-^3 that a protective layer i?- foirri-aci arid from the llte.r-dture the

'^.ffectivc .refaction is a gas ph^isr rsaetion betv-een aluminiuin vapo-j.r and o ni,tjX)gen i*equiring temperaturej?- sjxDUjna 1600 C« The Serpek reaction is

endothemdc and takes pla:^e readidy at about the same temperatui^but

XL 2 3 difficiilty to obtairi proiuL^-3 cf high p-^rlxyo

Trius it seems triat :he preparation from fluoidde and ammonia has certioin techni'?al adw/itagss ove,-r other- processes*

The work, has shown that even In a fjz-:ely div.idsd formg aluminium nitricia had reasor/able i-^isiF.tance zo oxidation at high r-emperatures.

There do^-s not seem to be any obstacles to making sinter-ed materlai.ep althov^b this v/as not attempted .m the prer^.^nt \vorko The presence of fLuorj.de in small amo\int3 might ac'ual-ly assi.c.t in the process,

T"ne reactiv'lty of ihe nitride is determined by the parxicle and cryEtalli.te sizes and the available sur-face* The nitr^ide is observed to hydrolyse mor-e in liquid water than i.::- steam. This may be a '/alia

7 po?Ln;-. when usi.ng i/he r'abricat^id ina'jei'i>jJL at. elevafced t;mperatiires in

mci.s-: aunGspher-e3„ The oxidatlcn kineticr. of aliiiranioiTi nitride *ir«

ini^ialiy linea-r chejiging ^:o para.bcliCf, and are controlled by aluminj.ura

ior. di,Cf>^3io2i thix-ugji the o.-ild-^ ].>?^v'er'o is coxnrraDn v/ith chrcmi^ira

r:::,tride^ a br-eak dov/ri ir: the p?.rabolic k:Lried.c--^ is obse.t"vedo This is

possibly due to a pr^sssu.re build i;.p of n;?--,rogen in the void.- of the

reacTion .inte rf -^.oe ^

Aluitinium r-it'.ride.u hcwev5:j'y is inorc; reactivs than s^.iiccn nitri-dej

bv, it is oi'gge^jtc-d j'-^-rjTn a comparlsi-Gr. of t.'ie mechanical prcpei'ties tt'.a.t

al\^T:ijvi.um rli^•:dde has defi.nire po^^sible use rid a ceranile riaierialc

Hov/ever. it appear^s tnac addiLii.ons to Lhe r.itride mjsi be msde beforc-

the cptinroin sintex'l.ng condition?, ai:^ rtiali.sedc Tne erfect of rhese

additives on the reaotitrity o^' ^litr^de rnigVtt, prcvo. a usefijj. sti>'dy.

The ^C'v; density or |^-ali.nnijii-'^. fluoride which has been

confinned by several density mea.^L-r-iinrnt^: Lr.. accordance vritti the

tetr'ajgonal cell suggi^strd xn the pre--s3nt worKj ponea a problem jn

.•^i.rjolurtil chemistry v/ti.ich rtso^uires fi-irther inves-:Igationo Likewiseg

i,he inability oi' either the oCcr ^"alL::crd.rdjm .fluoride to fc rm cornpo_jids

vri.tri iiirmonza. or \vater_,, althoug}! the latter are kncv/n "^.o exist

as AJ-Pj^JH^O requires i\;r^her inv!^s ti gB.tior-«

The fonnation of other nitrides by the fluordde route would seem tc

ofrer 3i.Tdl.ar advarxtages as ir. the caee of al'-jmini-iuit. In p.articijlar_„

anniori/ni f^\;osilicateo which is readily obtai-ned in a pure f'cnn and v/hich

vclatises ooffipleteiy on heating in the forin o.:' silicon tetrafltjcride« ammcinia and gaseous hydroi'j.uori.o acid rnight be v>:peoted tc form silicon nitride at about the same temper-aturer ann this vr;yjl6. offe::-- an alternative

ix-.vte to this material-

135 APPENDIX I

The preparations of ammonium hexafluoroaluminate and ajnmonium t e t raf luo ro a 1 umin a t e.

Condumetric study of the reaction betv/een aluminium fluoride and ammonium fluoride.

189 « The preparation of ammonium hexafluoroaluminate

Dissolve aluminium foil (99o999?2)(^Og) in h-C^o hydrofluoiic acid

(250 mis). Filter the thick grey saturated solutions. Aglommerates of aluminium fluoride trihydrate ( oC - AlF^ ^^2*^^ separate out and these were immediately redissolved in distilled water. IN ammonium fluoride solution is added until a TA^ite precipitate is formedo The precipitate was dried under vacuum over potassium hydroxide pellets.

The product was analysed as amnonium hexafluoroalurainate v/ith no evidence for the formation of ammonium tetrafluoroaluminate. The aluminium fluoride-ammonium fluoride-water system v/as further studied condumetrically.

The preparation of ammonium tetrafluoroaluminate

To prepare fluoboric acid 90 mis of 40^0 hydrofluoric acid were added to 4O grams of boric acid AcR with stirring until the boric acid crystals were completely dissolved. To the solution v;as added the stoichiometric proportions of aluminium hydroxide and ammonia solution.

The mixture was heated at 75°C for 1 hour and left to cool overnight.

Crystals were observed in the presence of a white residue. The crystals were separated and the aluminium hydroxide impurities removed by redissolving the crystals with the entrained hydroxide in v/atero The hydroxide was separated by filtering and the filtrate v/as left to reoxystallize. The resulting crystalline paste was identified as ammonium tetrafluoroalurainate,

Condumetric study of the reaction between aluminium fluoride and ammonium fluoride

100 mis of U'i aluminium fluoride, prepared as previously described, was placed in a 400 ml plastic beaker. The beaker v;as supported in a

" 190 - water bath thermostatically maintained at 23*^C. The condumetric cell

consisted of two small platinum plates mounted on thin glass capillary

tubingj v;hich v/ere kept at a standard distance apart by fixing in

circular polythene blocko The connection between the bridge and the

p].atinum electn:>des v;as made across a mercury bri.dge* The dip cell

was placed in the aluminium fluoride solution and a conductivity

reading taken« 5 aliquots of l.N Iffl^P were added to the solution

from a burette ^ the solution being constantly stirred. Readings were

taken after each aliquot was added and a graph of amount of ammonium

fluoride added against the resultant conductance of the solution was

drawn (see Fig. l). Prom Figo 1 a plateau in the curve corresponding

to a mole ratio of alumini'jm fluoride to ammonium fluoride of 1 to 1

is noted (point A)^ and is therefore probably due to the precipitation

of ammonium tetrafluoroaluminate although x-ray analysis did not show any formation of this phase. At point ammonium hexafluoroaluminate

starijs to precipitatec No observation of a pentafluoaJ-uminate was recorded r, as has been noted ij\ the corresponding potassium fluoride- aluminium fluoride (l) sind gallium fluoride-ammonium fluoride (2) systemso

191 t

3 U,

iOO 3oO 400

1.92 1. Coxp Bo, & Shaipe, A.Gc^ JoChem.Soc., 195i*-p 179Sp

2. Brer/er, P.Ho, Carton, Goo & Goodgame, D.H.L,, J,Inorg«I^l*Cheip.. J-959s is 560

'195' APPETOIX II

Ifethods of GhemlcfiuL AnalyaiSi Accirrate weighing technique using a microbalance

A small nickel crucible -was heated over a mekker burner and was

adjusted at intervals so that all the crucible came into contact with

the hottest part of the flamep which was approximately 1000*^0* After

10 minutes the crucible v/as transferred with nickel tongs to a

dessicator. The dessicator v/as placed in the balance room and allov/ed

to cool to room temperature in 30 minutes o The crucible was placed on

the balance using plastic tipped tv/eezers and left for 10 minutes to

redioce buoyancy effects to a minimum. The weight was recorded and the

process repeated until a constant weight was observed. At this juncture,

the specimen for analysis was introduced into the crucible and hence the

weight of specimen was found.

Deteiroination of ammonia in ammonium hexafluoroaluroinate

The estimation of ainmonia was completed using a Kjeldaiil apparatus.

The reagents used in the technique were 4C?S sodium hydroxide, 2?5 boric

acid5 O.IN sulphuric acido

An accurately weighed milligram amount of ammonium hexafluoro•

aluminate (5Qing) was dissolved in distilled water and made up to 100 ml

in a volumetric flask.

5 ml of the solution was pipetted into the distillation unit and

washed through with 5 mis (2 x 2«5) of distilled water. 5 nds of k-Ofo

sodium hydroxide was added and steam introduced into the distillation chamber. The distillate was collected in 10 mis of 25b boric acid with k drops of the mixed bromo-cresol green/methyl red indicator and titrated against /lOO sulphuric acido

195 The percentage ammonia was determined from the equation belows

5 X normality = Titer (T) X Normality (0,0l),

Noiroality = T x 0,01

Cone, = T X 0.01 X 17.01 g/l

fo =: T X 0.01 X 17.01

5 X 20 Y/

where V/ = weight of ammonium salt dissolved in 50 ml.s,

Ammoriium sulphate v/as used as a standajnd in the technique.

Determination of the nitrogen content in aluminiuin nitride

The specimen to be analysed was placed in a 6 inch side-aim pyrex

test tube, A fev/ turnings of fine copper tubing with water passing

through were placed around the neck of the test tube to cool it,

Pctassi\im hydroxide pellets were placed on top of the specimen.

The tube was surrounded by an open ended protective glass cylinder.

When heated to avoid vigorous splashing of the molten hydroxide, a pyrex

glass stopper circular in form, was mounted a few millimetres from the

top of the pellets. A trap was placed before the test tube. Prior to

this was placed a dreschel bottle containing distilled water. Immediately

after the test tube was placed a quickfit trap. This trap was connected

to a sintered glass inlet which was lowered into a 500 ml conical flask.

Preparation of mixed, indicator

0,1 grams of bromocresol green and methyl red were carefully v/eighed out and respectively dissolved in tvro 100 ml portions of 95?^ ethanol.

The solutions were mixed in a 5 to 1 ratio of broraocresol green to methyl red.

196 Method

0«1 - 0.4 grains of nitride were accurately weighed and placed in the side-arm test tube, 10 grams of A.R sodium l^droxide pellets were placed on top of the nitride* 100 mis of boric acid and 1 ml of mixed indicator were placed in the trap prior to the teat tube^ to ensure that any feed back of the ammonia woiild be accounted for. A similar portion of reagents were added to the conical flask. Argon (B*OoCo) was passed through the system at a rate of 60-70 bubbles a minute for 3-5 minutes to expel the air in the syst^i. The solids in the test tube were gently heated with a mekker burner placed under the test tube. Any liquid that condensed at the neck of the tube was ronoved with a small bunsen flame. The ammoniacal liquid v/as carried into the quickfit trapp where it condensed. V/hen all the Hquid had condensedj the trap was gently v;armed and the ammonia collected in the 2^ boric acid solution in the conical flasko The resulting solution was titrated against O.IN sulphuric acid and the nitrogen content deteimined in the noimal manner. Dsteimnation of fluorine

The fact that aluminium interferes in the recovery of fluoride is

well knowno However^ when the aluminium ion to fluoride ion ratio is

100, no interference is observed using the V/illaixi-Winter distillation

procedure, (l) V/hen this ratio is increased to 500 there is a 5 to 10??

negative bias (2). On the basis of wt ratio a 4:1 ratio is tolerable (3).

The presence of these two elements together will also interfere with the recovery of aluminium. Even small amounts of fluoride intex^fere in the detemdnation of aluminium colorimetrically and the formation of the AlFg ion hinders the estimation of aluminium by flame photometry (5 ). A spectroscopic method has been reported for the determination

of aluminiiim in the presence of fluoride whereby the addition of boric

acid stabilises the fluoride by forming the BF^ ion. However, only 47

to 19fo recovery is reported (6),

For the determination of the components in the same compound,

methods have been suggested such as wide line nuclear magnetic

resonance (7), and electron spectroscopy (8),

Determination of fluoride in ammonium hexafluoroaluminate

From the above methods, for aluminium present in aramonitim hexa•

fluoroaluminate the V/illard-V/inter method adopted for the analysis of

fluoride ions, using potassium cryolite as a standard. The method is

based on the removal of fluoride by steam distillation, and subsequent

titration against thorium nitrate solution using an alizeirln complex

Standardisation of the thorium nitrate solution

2,211 grams of sodium fluoride v/ere dissolved in distilled water

and made up to a litre in a volumetric flask. The buffer solution v/as

adjusted to pH 3i> using ^/lO sodium V\ydroxide. 10 ml of the sodium

fluoride solution was added to 25 mis of distilled water, 10 drops of

indicator were slowly added, 10 mis of absolute alcohol were added,

generating a pink colouration of the solution. This pink colour v/as

dischai^ged by adding one or two drops of deci-norTnal hydrochloric acid.

Pijially, 1 ml of buffer solution adjusted to pH 3 was added, and the

solution titrated against thorium nitrate solution using a blank

titration of distilled water.

Test Titration (T) - Blank Titration (B) = 10 X 0.053

1 ml of thorium nitrate solution = 10 x 0.053

(T - B)

= 198 - Method

The distillation was carried out using a quickfit micro-apparatus. An accurately weighed micro-quantity of the complex was placed in a three-necked pear shaped flask. 10 ml and 5 ml of 70jS phosphoric acid and perchloric acid respectively were slowly pipetted into the flask^ excess glass wool was added and the flask placed in a heating mantle. The temperature was raised until a 100*^0 5 at which the quantity of water present distilled over© After a few minutes, the tenperature began to rise again and was maintained at a 140-150*^0 by running in distilled water from the dropping flask as required. 50-75 mis of distillate for 50 milligrams of solid were collected in approximately 2 hours.

The distillate was made up to a 100 mis in a volumetric flask,

25 mis were taken and the fluoride content of ammonxuin hexafluoroaluminate

found by titrating against thorium nitrate colution.

The chemical analysis of aluminium fluoride

The determination of fluoride ions using the V/iHard-Winter

distillation technique, was found to be unsuccessful v/ith and

aluminium fluoride. Aluminium has been determined in the present study

by decomposition in concentrated hydrochloric acid and subsequent

estimation as aluminium oxinate.

One method is to Aise the sample with alkali carbonate silica

mixture in fixed proportions, whereby fluoride is converted to the alkali

metal fluoride (74) •

The fluoride can be subsequently determined by passing the solution

through an ion exchange column to form hydrofluoric acid. As there will

be alkali carbonates and alkali silicates present the fomation of carbon dioxide and silicic acid is expected, and hence the effluent is likely

« 199 « to contain hydrofluosilicic acid. Calcium chloride can be added to

convert this to hydrochloric acid which is titrated hot against sodium

hydroxide using a standard indicatoro The operation technique is time

consuming^ varLedp and tediotiSo The results reported using this

technique are lowo

A method which Is similar in principle but less varied in

technique, is described by Bognor and Nagy (9). This method was used

to deteimine fluoride in aluminium fluorideo

Preparation of reagents used.

Potassium sodium carbonate

A.R grade sodium and potassium crabonate in the stoichiometric

proportions were blended together in a ball mill for several hours.

Silica powder

Finely divided silica powder was roasted in a furnace to remove

any water and cooled to room temperatvire and kept in a dessicator.

1% lead chloride solution

5 grams of lead chloride were accurately weighed out and dissolved

by gently heating in distilled water in a 400 ml conical flask. The

solution was cooledj transferred with washings to a 500 ml volumetric

flaskp and made up to the marie.

Saturated lead chloride solution

The solubility per 100 ml of water of lead chloride is 1.49 grams.

An amount greater than this figure was dissolved in a 100 ml of distilled water to give a saturated lead chloxide solution.

/lO mercuric nitrate

50 grams of mercury (99.98^ pure) were weighed out in a conical flask. 125 mis of distilled water were added and the solution gently

- 200 - heated over a mekker burner in a fume cupboards A few drops of

concentrated nitric acid were intemittently added carefully, until the

mercujry had dissolved. The solution v/as boiled to drive of*f the nitrous

fXimeSp cooled and made up to 500 mis in a voliametric flask, 50 mis of

the mercuric nitrate solution were diluted to 500 mis to give an

approximate ^AO solution*,

OmlSi erioglaucine

0,1 grams of erioglaucine were dissolved in distilled water and made up to the mark in a 100 ml volumetric flask o

25 mis of ^/lO ammonium thiocyanate were diluted to 150-200 ml with distilled water and 10 ml of the dilute nitric acid and 2 nil of the iron alum solution were added. The solution was titrated against the meinuric nitrate solution^ until the end point of the red colour of ferric thiocyanate just disappears^ leaving the solution water white.

The noimality of the mercuric nitrate solution was determined as

0,09275 N.

Method

0.1 grams of o< -aluminium fluoride v/ere accurately weighed using the micro-weighing technique. The fluoride v/as thoroughly mixed with 0.3 grams of roasted silica powder and 1.5 grams of potassium sodium carbonate and slowly fused in a platinum crucible at 700*^0. After 15 minutes the fusion mixture was cooled until the dispersed melt v/as nearly solid and then the crucible was placed in cold water. The melt was trauisferred by inverting the crucible and gently tapping the bottom until the solid fell into a 200 ml beaker containing 50 ml of hot water. Any remaining solid lumps were removed with a rubber policeman and a few mis of hot water were added to the crucible to ensure ccmplete removal of the melt. The slurry vras left to stand for 2 hours©

201 The suspension was filtered into a 250 ml volumetric flask and

the filtrate made up to the maric^ 50 ml of the filtrate were neutralised

in a 200 ml beaker with hydrochloric acid until red with methyl orange

indicator. The neutral solution was heated to 70°C on a water bathj,

and 50 ml of 1% lead chloride solution were added with stirring. The

solution was re-heated to 70*^C. This solution which now contained a

precipitate was neutralised with 0o2N sodium hydroxide solution until

a yellow colour just appears. The solution was allowed to stand for

22*. hours o

The precipitate was collected on a G-3 sintered glass filter and washed three times with 10 ml of saturated lead chloride solution, and twice with 10 ml of 50^ ethanol. The precipitate was then dissolved in

5 ml of hot 4.0 N sodium hydroxide solution. The solution was cooled and

10 ml; of 1.84 s.g. sulphuric acid were carefVilly added. 1 drop of potassium ferricyanide and 0.3 ml of 0.1% erioglaucine indicator were added and the cold solution was titrated carefully with the 0.09275 N mercuric nitrate solution until the end point p due to the colour change from green-yellow to carnation redp was established. The last few drops are added slowly as the colour change is slow. Throughout the operation undue dilution was avoided.

Determination of aluminium content

A solution containing a known weight of the particular compound was made up to 250 mis. in a volumetric flask. 25 mis of distilled water were added to 5 nils of the above solution. The solution was heated to

60*^0 over a bunsen flame and 36 mis of a 2% solution of 8-hydroxy- quirxoline was added. To coraplete the precipitation of the aluminium presentp approximately 4 grams of ammonium acetate dissolved in a little

202 water was added. The solution was left to cool and a yellow flocculant

precipitate was observed^

The precipitate was filtered through a 50 ml Gl*. filter beaker and

dried at 120°C overnight. As the beaker was weighed before and after

filteilngp the weight of altuninium oxinate isknovm vid hence the weight

of aluminium can be found from the fact that 1 nig of aluminixim oxalate

contains 0*0587 mg of ailuminiumo Hence the percentage aluminium in

the hexaXluoroaluminate is given bys

0.0587 X . IQOc

where x = -jveight of oxinate precipitate

W = original v;eight of ammonium hexafluoroaluminate,

The standard for the determination v/as potash alum.

203 Willardp HoHo , and Winters^ O^Boj IndoEng.Chem.Anal.Ed. , 1933p 1P 7.

2. Wade^, MoAo p Yamamarap S.S.,, AnaloChem., 1965x, JZP 1276,

3. Grimaldig F.Sog et al. Anal.Chem., 1955s 918.

4. Murtonp F.R.C.p Inst^SupoSanit. ^ 19k9o 12p 728o

5o Eschelmanns HoC.p et al. Anal.Chem.^ 1959p 31^ 183.

6. Kurtzp UT.j, et al. Appl.p Spectroscc^ 1968p 22^ (4)p 283.

7. Ferrenp W,?.^ and Shane^ Nop Anal.Chem.p 1967p 32P 196.

8o 0*Neillp P;p private coranrunication.

9<. Bognorp J., and Nagyp L.^ Koliaszati Lapokp 1958p 21? 338.

20k. APPENDIX I II

Computer program (NGITO) in Fortr^ IV for the IBM 1130

Estimation of ciystallographic parameters«

205 r ^ —. II - < - II — • - 11

I 1

' • • — — ^ X, -T „.j _Ji; • - r - i It 1- o

V- -• —. V ' -J ' - ••—*;( •... 11. <: 'i • •-T;-']'^- ;m-- t|'-^— -•

r* p C-' •-. •'' ''' r C: II :. c • -•: , C :t >; f

- 205 ^ Computer program (POEH) in Fortran IV for I.B.M. 1130 - Estimation of surface areas.

208 LOG •:>oi\f\ conn

V? 05 // FOP

r-=WFlG'-T f':ITyOr:F'. ABSOPRFD. W = '.'/FIGH' 0- S A' P L " . A T = A T V C c p -H - R I C -^FSS'J'^f^, '^ = pR"S£'wKr AD, CiG^WF IGHT OF ^Î'^ÔGFK ARSOt^°FD PF=? G'Â^' '^c' CAV->Lc 00= A Ti ;D AT I ov VArifMiR D",P55MC'F'

o y A\-D Y AND ALSO OF J-'^^UT DATA CM

T:-r -:-^LLÂi^G nAr^f-^, yv;/ AN:: YV-I.\ IN ^HAT CK.":^^ II\ FCP^Â^ 2F8.C THl^'iD CAT; A- IV-I ^. •,.f r> \r^ V Ap T<\-*?vA T FIG,2 Ar D rl2»^ T;--P,\ -VTAD G A^ " r. " p A j "> CAÔ F?f.'»'-'AT F12.5 A.'.:D FiO,2 -•-^'r-r CAP";S C"\S'"Ttrr' A SFT '-r ^ I^ AL CA::r -'WST y'- vL'>'<-< APPENDIX V

Computer program (NIDKINETIC) in Fortran IV for I.B.M. 1130

Estimation of kinetic parameters.

213 PAGE 2 NICKINETIC PROGRAM C OXIDATION OF ALN AT lOlOC UNMILLED DIMENSION AN(50) NREAD=2 NWRIT=3 WRITE(NWRITol07) 107 F0RMAT(lHl,3Xf 'X» t 8X ,' Y • tSX , • A S lOX , • D ' • 13X , < 2 • 113X» • R • • HX • • G S 12 IXt 'O' •l^Xf •/) READ(NREAD»95)N READ(NREAD»96)W READ(NREAD.97MAN( I) •I«ltM .. --r.:.-..-.:.- DO 10 Iol,N PC(AN(I))/(0,2439*W) Fol-P CALL CUBRT(F9X) Yol-X A=SORT(F) Do0.5»((1-A)**2) SBP*0O1^ EoF+S CALL CUBRT(E»B) Z°(B-X)*^»2 . T=SQRT(F+S) * RoO«5»((T-A)*#2) ^ G=AL0G<1«/F) Ji| . .OoALOG(P/F) W Vo(0.5*(1-(F#*2)/(F**2))) I WRITE(NWRITt9fl )X»YtAfD»2»t?tG»0»V ' 10 CONTINUE 95 FORMAT*12) 96 F0RMAT(F6«4) 97 F0RMAT(13F6t^) 98 F0RMAT(3(F6.4»3X)t3(^9.7t5X)•F6.A•5X,F9•7»5X,F12.101 CALL EXIT END FEATURES SUPPORTED ONE WORD INTEGERS IOCS CORE REQUIREMENTS FOR COMMON 0 VARIABLES U2 PROGRAM 306 END OF COMPILATION // XEO Reprint - The formation and reactivity of nitridesp Part III.

Boron, aluminiiim and silicon nitrides^ JoAppl.Chem. p 1969p Ig.^ 178.

215 178 Coles et al.: Formation and Reactivity of Nitrides. III. FORMATION AND REACTIVITY OF NITRIDES m.* BORON, ALUMINIUM AND SILICON NITRIDES

By N. G. COLES, D. R. GLASSON and S. A. A. JAVAWEERA

The reactivities of boron, aluminium and silicon nitrides have been compared. Samples of these nitrides have been converted to oxides by being calcined in air. Changes in phase composition, surface area, crystallite and aggregate sizes have been correlated with oxidation time and temperature. Crystallites of alumina. a-AliOj, split off from the remaining aluminium nitride before they sinter and inhibit further oxidation. The diboron trioxide, BjOj, and silica, SiOa (a-cristobalite), immediately act as mincraliscrs for the remaining boron and silicon nitrides, and progressively retard the oxidations.

Introduction vacuo before their specific surfaces were determined by The formation, hydrolysis and o.xidation of the ionic B.E.T. procedure*^ from nitrogen isotherms recorded at calcium and magnesium nitrides, CaaNj and MgiNj, have -183° on an electrical sorption balance.*^ '* The deduced been described in Pari II.* More recently, the authors have average crystallite sizes (equivalent spherical diameters) were found that zinc and cadmium films do not nitride in nitrogen compared with particle size ranges determined by optical or ammonia at temperatures below their m.p., 420° and 320" or electron microscopy. respectively. The nitrides, ZnsNi and CdsNi, are formed only at appreciable rates at temperatures above 600'. They Phase composition identification arc hydrolysed rapidly to ammonia-soluble complexes, Samples were examined for phase composition and crys- MCNHaMOH):, where < 4 for M = Zn or Cd.^ Com• tallinity using an A^-ray powder camera and a Solus-Schall parison of the molecular susceptibilities of Mg, Zn and Cd ^-ray diffractometer with Geiger counter and Panax rate- nitrides shows that the polarising action of the metal ion meter. Certain samples were further examined by optical and decreases from Mg to Zn to Cd. Nitrides in Group IH (B, Al, electron microscopes (Philips EM-100). Ga) and Group IV (Si, Sn) show covalent character and are more resistant to hydrolysis and oxidation.^ In the present paper, the reactivities of the covalent nitrides of B, Al and Results Si are compared with one another. Fig. I (a), (b) and (e) shows the overall variations in Thermodynamics of nitride formation and the relation specific surface, 5, and average crystallite size during the between bonding and crystal structure have been discussed conversion of aluminium nitride to alumina at 1000** in air. in Pan 1.^ Boron nitride is more chemically reactive than These are compared with oxidation rates Fig. 1 (d), changes nitrides of Al and Si.* Finely divided BN is hydrolysed in the number of crystallites Fig. 1 (c), and average crystallite slowly by hot water and dissolves completely in boiling 20% sizes of the individual unchanged AIN and its oxidation NaOH within 30 min. Dissolution is perceptible also at 20° product, a-AliOa Fig. 1 (f). Corresponding variations in the in acids and alkalis.' Reactions between aluminium nitride aggregate sizes arc summarised in Table I. or silicon nitride and hot water are inhibited by coatings of hydrated alumina or silica on the outside of the material.

Hydrolysis is generally slow in mineral acids and alkalis,*'^ —^ but there is complete dissolution of aluminium nitride in 30% NajCOj at 80° and of silicon nitride in boiling HF.« All of 9 V these nitrides are oxidised in air at higher temperatures. Boron nitride powder oxidises appreciably above 800°,^-'^''° y V the rate der>ending substantially on the preliminary cal• I- cination temperature.*' Nitrides of aluminium and silicon 1 OJ . } 1 t 1 I oxidise at temperatures above 600° and 800" respectively, ... ' ' ,,, < lllfnl and again oxidation rates depend mainly on the intrinsic ' ' innJ ] - ^ ^ reactivity of the material and the available surface at which - / - ' oxidation can occur.^ Changes in phase composition, sur• \ r face area and crystallite and aggregate sizes are now correlated r with sintering and oxidation conditions for the above nitrides. \ - Experimental Procedure \J\ Separate portions of powdered nitrides of boron, alu• 1 1 minium and silicon (Alfa Inorganics Inc.) were calcined in air CCfJ'/ERSION.% CON\.'ERSrOf4.% for various times at fixed temperatures. Oxidation rates were Fig. I. Calcination of aluminium nitride in air at IOOO''c estimated from weight changes of the samples during cal• In (b), broken cur\'e represents actual surface area {$') for an cination.^ The cooled products were outgassed at 200° in initial one-gramme sample of aluminium nitride

•Part II: /. appl. Chem., Lond., 1968, 18, 77 J. appl. Chem., 1969, Vol. 19, June Coles et al.: Formation am/ Reactivity of Nitrides. III. 179

TABLE 1 \'arialions in agt^regate sizes during the conversion of AIN lo a-AI^O, at 1000 t in air

Time, h Conversion, % Range of aggregate size,

0 0 1—2 5 51 3 3—5 24 67-7 3—6 96 82-7 3—7 168 85-9 4—8

The samples of boron nitride and silicon nitride had specific surfaces, S, = 11-5 and 1 -7 g '; average crystallite sizes, 0-23 and 11 pm respectively. They oxidised in air at 800" and 1000 1200 ; rates are shown in Fig. 2. where they are compared with those for aluminium nitride at 900—1100 . Electron micrographs of the nitrides and their oxidation products arc prcscnled in Figs 3 and 4.

Discussion 0 20 Oxidation of aluminium nitride TiME.h Fig. 2. Calcination of boron, silicon am! aluminium niirithw in air at Aluminium nitride, AIN. is converted to a-AljO^ at 1000 tiijfereni lemperaiures in air. A'-ray powder photographs and diffractometer traces (a> tx>ron nitride at 800 c give no indications of any oxynitrides being formed at

(a) ( b) ( c ):

(d) ( c ) ( f ) Fig. 3. Electron micrographs of boron nitride calcined in air at 800 c (a) and (b) after 24 h, (c) 48 h. (d) 96 h, and (e) and (f) 144 h

J. appl. ( hem.. 1969, \ ol. 19. June IHO Coles et al.: formation ami Reactivity of Nitriiles. III.

(c)

f*ig. 4. Llectron micrographs of silicon nitride calcinetl in air at I200"r (a) original sample, (b) after 5 h and (c) after 35 h slower especially after about SO"., con\ersion. These \aria- apparently sullicient to cause a limited amount of crystallite lions in rate are accompanied by corresponding increases and splitting. In this instance. (.V 5)^ directly represents the in• decreases in specific surface. 5, in Fig. 1 (a) and (b). and in creases in the numb>er of crystallites as oxidation proceeds. actual surface area. S . for an initial I g-sample of AIN illus• Fig. I (c). no allowance being required for molecular volume trated by the broken-lined cur\e in Fig. 1 (b». C onsequently, changes.''' The maximum increases of less than twenty-fold the average crystallite size of the material at first decreases are comparable with thi>se found for the oxidation of TiN- and later mcreases, Fig. 1 (c). dcscribed more fully in the next paper. They are much Several factors may contribute to the detailed shape of the smaller than the increases during the oxidatitm and hy• initial rate curve of an oxidation isotherm.' ^ e.g. decreases in drolysis of C ajN>. vi/. 5 y 10"' and 10'^ respeciively.'-^ surface heterogeneity as the reaction prtKeeds. changes in The m.p. of AIN (> 2400 ) and Al.Oj (2050 ) give Tam- specific surface or in local surface temperature due to heat of mann temperatures (half m.p. in K) of > 13.16 K. and reaction, solubility effects, impurity concentrations, possible 1160 K, indicating that sintering of alumina should be much changes in oxide composition and electrical double layer more extensive than that of aluminium nitride at 1000 . In efiects. In accordance uilh the oxidation of coarser samples the latter stages of the oxidation, the alumina appears to act of aluminium nitride,"' a specific amount of oxide must be as a mineraliser for the remaining aluminium nitride par• formed (depending on the sf^ecific surface of the sample) ticles, inhibiting their further oxidation, cf Fig. 1 (d). and before a coherent alumina layer can he produced. Mean• moulding together the material. Changes in the average while, the free nitride surfaces remain exposed to the gas crystallite si/e of the aluminium nitride (assuming no ap• phase, so that the kinetics approach linearity. When there is preciable sintering) and the a-AI.O.^ are deduced from the sutTicient oxide of rational crystallite-si/c composition, it surface-area data and shown in Fig. I (f). These confirm the sinters lo form surface films through which normal gaseous ultimate sintering of the alumina, and the larger crystallite diffusion cannot easily occur. The reaction becomes con• sizes given during the first half of the oxidation (above the trolled by solid-state diffusion, with the kinetics becoming broken-line) are caused probably by some of the newly-formed parabolic and the surface area decreasing as observed after alumina not being detached from the nitride surface. about 50",, conversion in Fig. I (a), (b) and (d). Parabolic .Accordingly, the aggregate sizes of the materials (Table I) kinetics are characteristic also when the oxidation of alu• indicate that the original nitride consists mainly of single minium produces better crystallised aluminas.'" crystallites. The alumina produced tends to promote for• The increases in S (and decreases in average crystallite mation of aggregates, mainly of 3 — 8 \im sizes, in which the size) during the acceleratory and approximately linear stages individual crystallites appear to be over 0 5 ixm in the later of the oxidation. Fig. I (a), (b) and (d), indicate that the stages of the oxidation as also indicated in Fig. 1 (f). Similarly, alumina initially formed on the surface of the nitride splits off 86°„ oxidation of aluminium nitride in 14 h at 1100 . Fig. to give smaller crystallites. Any additional spalling at the 2(d). gives alumina crystallites of 0-5—1 nm size, sintering nitride oxide interface when the samples were cooled for al the higher temperature being restricted by the shorter surface area determination was negligible by comparison, oxidation time. since the reheated samples proceeded to give oxidation rates similar to those of samples which had been continuously Oxidation of nitrides of boron and silicon heated. Thus, the extent of crystallite splitting depends The boron nitride and silicon nitride oxidise at 800 and generally on differences in molecular volume and type of 1200 respectively, giving diboron trioxide, BiOj, and silicon crystal lattice compared with the original nitride (cf. Pilling- dioxide, SiO, (a-cristobalite). even in the early stages. In Bedworth rule for oxidised metals'"), and also on the rate contrast to the behaviour of aluminium nitride on oxidation, of oxide sintering as discussed in Part I.-* Although the con• the specific surfaces of the materials initially decrease rapidly version of AIN to a-Al.O.i involves practically no fractional as the boric oxide (m.p. ^ 450 ) and the silica (m.p. 1710 ) act volume cfiange,"' nevertheless the crystal lattice change is as mineralisers. Although the silica does not melt, it is v^ell

J. appl. C hem., 1969, Vol. 19, June Coles et al.: Formation and Reactivity of Nitrides. III. 181

above its Tammann temperature (720°) and the specific silicon nitride particles. Fig. 4 (a), also form aggregates with surface, 5, falls from 1-7 to below 0-3 m^g-' when one third rounded edges when only about 20% of the nitride has been of the silicon nitride has been oxidised. The products tend to converted 10 silica after 5 h calcination al 1200" in air as in bond together and shrink, cf. bonding and hot pressing of Fig. 4(b). Further calcination (35 h) produces larger aggre• boron nitride with silica glass.^° Consequently, the rates gates as in Fig. 4 (c). decrease considerably for both nitrides as their oxidations be• come increasingly controlled by liquid- or solid-state diffu• Acknowledgment sion, especially the latter, cf. Fig. 2 (a) and (b). The original boron nitride has a flaky texture with rod- The authors thank Mrs. M. A. Sheppard for her assistance shaped and hexagonal plate-like particles. About 20% of the in the analytical work; the University of London, Imperial Chemical Industries Ltd., and the Science Research Council BN is converted to B2O3 after 24 h calcination at 800" in air. Fig. 2 (a), while the hexagonal plates become rounded and for grants for apparatus and a S.R.C. Research Technician- tend to form aggregates as in the electron micrographs in ship (for M.A.S.); the College Governors for a Research Fig. 3 (a) and (b). Further calcination continues this aggre• Assistantship (for N.G.C.). gation, cf. Fig. 3 (c) at 48 h, and after 96 h the rod-shaped John Graymore Chemistry Laboratories, particles become distorted by the newly-formed B2O3, cf. College of Technology, Fig. 3 (d). When over 80% of the BN has been oxidised after Plymouth . - 144 h, there is sufficient B2O3 to crystallise out and change the cf. aiso S.. A.^ A. Jayaweera, appearance of the aggregates as in Fig. 3 (e) and (f). The ,Ph.D. thesis (London).

References ' Glasson, D. R., & Jayavveera, S. A. A., J. appl. Cbem., Loud., " Podszus, E., Z. aiiorg. Chem., 1917, 30, 156 1968, 18, 77 '2 Brunauer, S., Emmett, P. H., & Teller, E., 7. Am. chem. Soc, 2 Glasson, D. R., & Jayawecra, S. A. A., 'Surface phenomena of 1938, 60. 309 metals'. Soc. chem. Ind. Monogr., 1968, No. 28, p. 353 (Lon• Gregg, S. J., J. chem. Soc, 1946, p. 561 don: The Society) 3 Glasson, D. R., & Jayaweera, S. A. A., J. appl. Chem., Lond., Sartorius-Werke, 'Eleclrono-vacuum balances', 1963 (Got- 1968, 18, 65 tingen: Sartorius-Werke, A.-G.) * Samsonov, G. V., 'High temperature materials", 1964, Hand• " Gulbranscn, E. A., & Andrew K. F., J. electrochem. Sac, 1951, book 2, pp. 235, 266 (New York: Plenum) 98.241 ' Taylor, K., Ind. Etigng C/iem., 1955, 47, 2506 Cooper. C. F., George, C. M., & Hopkins, S. W. J., 'Special « Renner, T., Z. atiorg. Chem., 1959, 257, 127 ceramics', Proc. Symp. Br. ceram. Res. Ass., 1962, p. 49 ' Collins. J., & Cerby, R., J. Metals, N. Y., 1955, 7, 612 « Billey, M., Annls Chim., 1959, 4, 795 (London: Academic Press) ' Zagyanskiy, I. L.,&Samsonov.G.\.,Zh.prJkl.Khim., 1952,25,557 " Sleppy. W. C, J. electrochem. Soc, 1961, 108, 1097 Samsonov. G. V., Markovskiy, L. Ya., Zhigach, A. F., & '» P'l^'ne, N. B.. & Bedworth, R. E., J. Inst. Metals, 1923, 29. Valyashko, G. M., 'Bor, ego socdinenya i splavy', 1960 (Kiev: Akad. Nauk Ukr. SSR.); USAEC translation, 1962, No. " Glasson, D. R., J. appl. Chem., Lond., 1958. 8, 798 5032,(0, 209 " Carborundum Co., B.P. 1.052.295

J. appl. Chem., 1969, Vol. 19, June

c Kiermoohemlcal Data

220 « • ral. moir' dm- f -tK'- HOL- WT. - U;.3S1 T. 'K. S* ALUMINim THICHLOHIDE (AlCl^) C CRYSTAL)

- 100.?99 159.JOM IMF IN I Tt C .uuo .CUO 1 167.78'. 31S.71.P - -ICQ.so + O.ZO kcol. sole 100 11 .<^u9 7.syi ft ! Til - I'fl.OTp 116.i9? 171.iy7 700 19.1 17 ie.?07 ?•> t<17 7,03^ - iisp.oi: ISO.616 110.TOO ;Q& LiO .(too - -166.58 *• O.ZO kcol - cole ?• - 25.45 + O.Ki cnl. dcg-'^ cclo'^ f 238.15 ?oo 71 .9T? 74.^0''. ?h ii^O .CI - 16S.^73 110.bOl 1C0,6?7 7fl.071 .44 kcol. BOlC -co ?3.1 11 71.ex. 7,70'. '" Vir.ft'lp ^dp *y* "70 hi"? - *l(jT.ftOs" "IJB'.CO*- (to dloer) - 28.0 * O-S Iccal- cole 48.A70 (to dicer) - l460)'K. a 298.15 71».190 7,li9 - ir7.i9? 137.936 700 7i.a70 4&. 79;> ;? 9*1 9.694 - 166,*37 177.77? 30.7 '» ?i.7«.7 600 It 097 - I66.0ft5 171.6B9 115.171 78,710 900 76.T17 ; 'i 7«(? U.9*.9 - 1^S,A9*. Heat of PorcJtlon. 7'..11B 1000 ?T.yoo ie 17.6-^ - 1^7.420 110.1'.? J. p. Coughlln, Phyo. Chen. 62, 419 (19Se) censured the heOl of oolutlon of cryo'-alllne ar.hydro'Jfl 10A.BR& :o.9ie 1 100 77.717 SB.817 CO 31 1 ^0.31'i - l^''.755 l.T 4.360 a hydrochloric odd nolutlon. Daaed on tJic dote, £H 99.?«? alualnuc chloride ond aluolnun ot 305.15 K r 258.15 i:co 77,4.00 M . 191 '•I 9^)1. 23.087 - 156.n7t J8.0fl3 9-).7M 11.761 I'OO 77.b50 b > - l6^.;79 - -51.67 • 0.14 kcal. aole"^ for the reaction Al(c) * 3(HC1-12.731 H-0){1) - AlCl,(c) 88.77? n.779 IfaCO 77.667 rs.t)9 4T> •on ?e.59»i - 16*.,67*. •nic heata of so:-Jtlon e?.a39 17.060 ,'oUe of £H' 293.1S AlCljtc) eolculoted to be -166.56 + 0-20 kcal- nole 1^00 77.7t.C ',7.3bl fct .639 U.367 - 163.9I!.? of AlCl,(c) reported by the prevloua InvoHlseiorB arc Hated as followsi 170 77,600 t7 .3C3 - 1*1?.r*.* 77.61'. 10 Concentration of Sol-Jtla.T noo '•T.eai • loe J6.9?Q - 167.5?e 77.113 o.TTO Kane of TnvoBtlpntor Heat of Solution BS.BU 1900 77.97S 7?.'.?t SO •3^9 19.710 - 161,e:r ft.II? ooloo of HjC/cole AlCljU; 61.116 kcal. ROlo'^ :.91ft 11 • IM '•7.?>n - 1^1.^.7 6 7.051' 1000 78.UOO 1 7b.17? ^? .7ir. ••^.312 - 160.lie 16.ne 6> 116 Ttioaeen (l) -76.5 + 0.3 (la'C.) 1250 Roth and Buchncr (2) -78.09 + 0-27 (20'C.) 2500-4730 Roch and Borgcr (3) -79.45 (ao'C) 4000-9500

(1) J. Thoaaen, "Theraoehenlache Untcrouchuneen," Borth, Lelptlg, 1882-1686. (2) W. A. Roth and A. Buchner. 2- Ele'rtrochca. 40, Ifo. 2. 8? (1934). (3) W. A. Roth and E- SBreer, 2. Elelttrochea. 44, flo. 8, S40 (1938).

Due to lack of appropriate aiKlllary data, theoe heata of aolutlon were not uoed to cBlculflte £^ • for AlCljCc). The heata of formation (20"C.) for AlClj(c) were reported to be -167 and -107.5 j 0.4 kcol. cole -* ty V. Kleca r B.^d E. Tankc, Z. anorg. allgca. Chca. 207, 166 (1932) and H. Slenonoen, 2- Elcktrochco. 55, Ho. 4, 337 (1951), respectively. They were obtained by nolutlon celorlnctry and not uoed for nloller reason-

Heat Cacaelty and Entropy.

The lov temperamrc fteot copoclty, IS'-ZZQ'K-, »n3w Chenieol Coapany, "private coaaunlention, 1980, reopectlvely. The two oeta of data were joined oaoothly o: 299'K. by a grophlcol aethod. Above 465.6'K. the voluca were eatlcBted by (r.rnphlcsl extrnpola* lor.. Sjgo le reported by p. I. Oettlng, prlvotc coccunlcntlon, Septecber 10, 19G2, baseo on the data dcterolned by •'. E- Hatton, a. C Slr.v.e and D. R. Stull, loc. c:t-, unlng S*g (extrop.) - 0-094 cai. deg.'* Bole"^ The high :e=reraiure neat cat^bcltleo were nloo reportvl Ly W. Platr.er, Z- onor^. Cheo- 200, 332 (1931) which were not -.inei.

WelLlnK Lata-

and Mere reported to be 4es.G'K. ar.d ft.5 Itcol. oole" reapettlvely.by W. Plochcr, Im*. c!: TTie value '^f fiH* adopted waa detenr.lned ly ft. A. KclAnald, lor- clt.

Heal and Tenperature of Subl _l cat ion.

waa calculated froo the vapor [.rcBHure data by trio aeeond law oethod. The adopted value In the 299.15 dveroe-! of alx aH a 298 15 ^"^""o derived froo oln vopor preooure drteroinatlona. Por detalla aee Al,Clg(e) table. T woa oollnflled ao the tenperaturc at wnlcn the free energy rh(tn(i;e of the reaollon 2AlCI.(r) - Al2Clg(g) epproii'-.hen zero-

Dao. 31, IBeOl Jun* 30, lOOli Juna 30, lOQSi Kar. 31. 1984 AlCl f ^•1. infti'' 'i r,. ' - hrai. IUOIP Aii; l»g Kp T. 'k. ALUKlinjK -Tlll'J.UOfilUi; (AJP. )

_ tSf.. s 1 '• lN^ KITE 0 .000 lOO l'.( IN J1 f 7Ta - IS (. *',S IS I .bt){> TbB. 132 / • - : I- kcnl- rolp ,•^ 1 .'•••u Its./n* 377,291 0 \. 1 ) .Kt.i 1 .s"» - - 'r ro.r 1'.1 "*' i 1• .ll 1 .j:: ^ . H. -J', 0 /••a.bie . -J ••" - - • O.KC Ural, calf 1 _ jia .'M» ("•ti. '^01 .'-.^ '« »/ 1 I.B^ 1 .0^ ' - 1" tV.. 7J.5 . • i- ' 11..f - - Ifil .716 <'.7. 70 )J6. 1 »•* ti./. 636 /• IH. I I/ l**/ - - 'i • •. - h J?t . Ifc * 1 Ji-,.6'.B 1.. 1 •v.fl'.Q ; T-.T.*,::J 1.1 •!,<• •-iff.'-i uf ixo Irdi jcrJcTJl iier oi-rs',rJi tuna • I'lt-y ore ^9. v3% r.' CM' 'J J • _ ? . .».s ' - .;" "I Bt.. r36 .1. J1 - r ..'.-*' :^ •.. L •.:.r:l, ;.jilt.-.:,J L'.; 4 .if -t=r, .3: - , Pre i ir it.:)r^ iLjorl JLTJ, 1 Jy'.j '.yi-l. cr.l "TTTu JO •> 7. 7).*.T» 11 • '•••'t JS6.US"Q 307 .".e7b 4. 1 1 - - Ti./'.Vr. ,.'M-I _. [\)

.•F»U.^B'J b7.!,53 I'.u in 0 Li-t : ii: 1ft.71.0 - bl .638 13- ?0 : 'JO ^, • ^ J • 1 . AlU 7 ) .767 - rc:o; :rl La- cc'.^td, rr«5 tncilr fq..llltrlurj c-r.;,1.oni!j for tho rtacHon S/i AlF^tc) * M,?!?) - 771.378 <-?.3e>2 M; 1. a 0 - - ,;}. ;-.r, la.ccJ a ovica-. ,f or^an ihroish o -3tcr l-thlcr Oi.il thrri thi-oi-eh the SIF, n • >U 38.6)0 ." - »<•• 1 IB 31 - '• - - ; .->• 1-. _ 2i<).3!>6 J 36 »>. 177 31 .^bt. - . • 3b< iS'* 3i.. - 1^^. 3B0 - 7i3.3»JB 37.S74 i9 - )S3.8u6 - ?i.7.-?7 iuib>>6 7^1.la* 77.7B7 ?7.. ••a."ISO 34. •I'.A - 153,?J? - »S?.b78 23i,7?* 2>.757 c^c J7.3C0 61 jhfr -J .7hl • - Tno tc-frc-O'-'-rp ..i.L..*K.) licai ;otoclly, C^, wao cecEjrcd ty C 3. Kir., ;, J. Aa. Cher.. Jc:- 5, 2:Dfl .»30-:iCD'Ji.) -30 iJotcmlnirJ oy C J. C'Erlcr. crjd K. K hcUey. J. An- Ch.rr Sec- -! 22Q.9O0 73.925 tLOlC). Tr.p hcnt eo^cc;'.^ t2 &U•a7b -b.OOh 3<»i.q?s - ?100 torrcc-.cd by w. B. Pram*. J. Pnyo. Cr.c=. Gf;. lUl (IE! -7.777 2?'..1U4 22.762 ^iClS i:S5?). Thlo coto Jri 1). : ?3o ?7.Bsa /. 1 f. 1 .Q7B - - 3iW,45J 21B.339 20.766 ne lot. icrtperaturo at r:'3.1'"t. Tho oLove HOO'K. woo exiropola'.cJ. ?300 6". ft. J (• ;^ •Q<>0 - liOOl H33 joined erj;-:.L(Oi: > 13 - 212.607 10.360 bC S3.411 - 144.831 - hoo toifcn frcn ii. 3- K'.f£, 10(. cli <1C£. ia...'S7 6' .311 - - Trpn;iltlon CatJi.

7, - 7;o*K. anJ fi.';! - ICO fol. aole'* frcn v. 0. PranH [loc. clt.]. *i

icfli of Siibllyaiii-^.

Thf acloclcJ cnir.3:ry of tubllnailon, a:?* jns.is* obtained ty avpra£lii£ IH8 3rd lah iJ{" j^^ ^^ VBIUPD froB fourtoen oeia of yajor trctci.irc uaio oc reported in nlno different inv^ot icmieni. The aor.j-pMan <.3B cade iMt only AlP^ rarc^er cor.trltjttjd to liic rc.-:oi-rfd vapor preeoure. Thecc at* value* are cu-r-jrliea oa follo-si

No- of IIB-Se Ko. of nar.ge 259.IJ McaB-jrc=cnia riEOl. r.ole* Reference Keaourer.cnt kcfll- eol' Pefr.-er

7:.j'.» 0 991-1101 71.791 t COS ijsT-iSrt OMO n 939-1102 7J .ICC I O.Ofl lA'-.-lFC I!.TO! 0.3* e 9G0-1O3S 71.207 I O.KO 9 93i-I031 71. OS*; * 0.09 10 10C1-1114 71.15G * o.ce ••coeo 0.22 7 71.05* O.CT I:J:-I:I)O 7:.6ii 0.0^ 0 9*3-1067 71.02G •

J. KaryonklnKaryankln,. :.. rr-yafr.ys .. CheaChra.. iUS.m) U, srfl (Iiii9). 0. Huff cm LrOcufhfr, nnorj. alien, cnen. 376 ( 18J4). w. Pltrien, Jc-clinc HorMfcuiJi dcr Anorgnii. Piilnlo. SEB, iSp (:9J3) f. .iroDO. J. CBrrholl, P. J. C Kcni. «iid P. L. Le»l. DIBC- Pereiiay Soe. *, EOC (15*8). • - P. -itt, r',^::o, 0«forJ Univ.. ilyr-S) Bi> r.'t«rf:J by Krajse, ei al. (ref. 0- /.. «. fTvreiv. J. V. rj;t.or3l.£i)n. *- H- Hrr-ryonov. anJ Ye. [,. Oeraotcov. Znur. fJoorft. fJiln. *. II. P. hrai^p, .'r., A. C Vuior. fliij T. p. K.URIBO, Hat]. Pur. i:tJ3., Pmllrlnori Rrpgrl 7M,.6, ) January I?63. L>. L. lUtJei!*.

b. L. KLUtoiiErarJ, Aercnutronlc, Ilehroi-t Prnrh Calif., private fi—--.ml cat Ion, July 10, llfil-

n. p. Poi-ier. E. C. Zeller, J. Cn*o. Pi.yoleB ii, 856 (1960) have rcrorled 1 lo » of Al^Pj "t atoot lOOO'K. A. IhjclUer, Arthur 0. little. Inc.. rrofireap nrjAjrt No- i, 1 Auaual to 10 SeptceHer 19C2, Conlmet 3A.)O-OSO-ORD-SS hiio rerortej a neat of dlcerlioilon in aRrrccent i.tiii Porter and teller. R. ?• Krauae, "t ftl. (loe. tit.) have c?iin«ieJ • correeiion for the iilc^-riratioii of AlP^. Tlie neat of ajbllMtlon, «l* Q. corrected for dleerl=atlon kno founJ 19 be atout 10.9 kcal. raie'^ by Nrngse. et al. ThLa neat of eubllRailon was calculated to be 73.0 • 1 kCOl I rjli> * at ZC.I.l! • rter ari'lllng a correriwrt for the dlfrerenro in ine JAUAP and l(.D.3. tre- tntrgj functlona.

Ti-ricrnluie of ou! 1 IfJilcn, 1 t-ao eolrulated. AIF, D«c. 31. 19S0I Sept. 10. 1963 'ill mnt^"' Air T. 'K. S* '•*»« K p ALUHIUUH HimiDE (Airi) (CRVSTAL) 0 - *O.SS • 74.785 - 74,7^1 100 1.366 9.ino .B97 - 75.?t,l - 7J.187 119,942 :c& .195 7,2**l - 71.701 - 70,97V 77,518 '•.S16 • 0^^ - 7J.6UW - fla.;95 lw.279 )00 <..e&i .013 - TC.dvi. ^rn" -''-e ^ 0.3 kcDl. BOIC" 7,15^ - 68.149 49,935 f 296.15 •76.0 t O.i keol. oole' SCO - 76.U9 36,080 i.716 1.737 - 76,2Jfc - 63.5u3 27.756 6C0 ::.t<.e ^.^71 2.747 7w - 74.2w7 - 5-.96: 2:.204 7.?4i 3.816 Ouw - :6.18a - la.i.'J 18.24U >. 177 o.o;'o *-.*l?6 - 7t.l66 - 1^.857 11.267 a. 700 - 76.lib ll.tSi :t.7i3 - ij.3i: 12.911 1.772 - 76.611 - 5J,634 11.065 Heot of Pora..iion. • • wt) ::.7tg I7.esi 8.19*. • • wC ::.93t • 78.177 - i7.B31 0. 104 10.QO? •J.J7* T))c oelocccd heat of fornatlon lo Che avcroge of two independent ealorlcetrlc dotemlnot ions. The heat of :soo ::.Q7i - 76.497 B.203 • V.76» foroocIoTi reportefi to bo -76.5 t O-Z kcol. nolc'^ ond -75.5 t 0.4 kcal. oolc*^. THo foi-mer value -os re• ::.yv: - 78.417 - 42.26- 7.104 uco :-.7:: i:.i77 il.94Q - 76.339 - 39.*sr ported by C A. fJeugetauer end J. L. Karerovo, 2. Anorg. Allgcn. Chen. g;90, 8? (1957). The later va^ue was re• :i.^?3 ?:.3K ::.77t 6.163 i 3. Kw - 70.262 - 36,:w9 1. )4fl ported by fi. 0. Kah, E. 0. Sing. w. Vellcr, and A. v. Chrlntenoen, U- S. Bureau of Mlnco flepopt of ;r.veot,*.- IttOO 13.34S eatlono 5716 (1951). :7co - 78.186 - 33.9iU 4.636 ::,5oo ?3.C30 15.132 :flcc - 78.110 - 31.178 4.0CB .'3.717 10.733 - 70.W33" - 28.4;j J.450 :coc J4.367 U.<)36 Vapor preoflure ceaauresento agree with the aeleeted heat of foroatlon. Par Inntancc 298.le " :oco - 77.917 - 21.664 2.912 kcal. cole'^ for AirJ(c) vaa colculotod fron the heat for the reaction 2AlII(cl - EAICE.) * "^(e) er.l -.r.e rea-. w.m - 77.881 - rr.9:» 2.5U4 of Bufcllciatlon, 78.c '-tea;, aole"^, for Ai(c). Thla heat of reaction wae obtained froa a tnlrd la> coLcula:icr. is.ass 2v.IbQ rio.i - 77.804 - 20,169 i:.L:i ?t.l3S 2*090 ualng JAKAP vnluca for the free cnorey funetlona and toralon cffuolon preoouren neaourefl by D. L. yi'.^er.trar.e i:.i35 - 77,7:7 - :7,4;s 1.731 26.677 16.77t 22:772 - 77,640 - 14.687 1.396 .and L. P. Thcard, Aeronutro.Tic Technical Report U-1497 (1961). Vopor preoourc •caourcnontfl with a el.-rcralflnce :'.cc :7.199 l3,QQa - 77.i7w :2.:6s - ::.9i; i.oea in a vncuun oyotcn ty L. H- Drc£er, V. v. Dadape, and J. L. Kflrgrave, J. Phya. Cnen. 66, 15S6 tlSEZ) agree i-i:--. ;7.eo9 2>.?02 - 77,*91 s.:i8 .006 the aelectcd fiHj ^se 1*=' recalculated with the aubllootlon coefficient [ tt-2.Z K 10"^) reported ty I': ::, 19! ?e.l67 le.ooa .^20 - :7.4i:r 6.49w .141 ..XS.OAl •:•!&}?... r 3.763 Hlldcnlirond and Thcord, osac of the Knudocn coll ocflBurcmcntD by M. Hoch and D. '•'hltc, "The Voporlrailcr. sf Bcror. I :3.76i .'..xiaii.. i 250C ;;.23: .a. a19 - U7.6W7 "V6Tf" .040 Nitride and Alininun Kltrlde," ASTIA Unclooalflcd Report 142616, October 29, 1S5G, agree with the selected heat 1000 :0.Q15 JO.0B2 - 147,127 i.9ca - .-45 11.136 - of fomotion. 31.301 - 147,238 •&I6 02 Earlier dotenainatlona of the heat of fortrmtlon which apparently are in error are tfUTTsnarlsed cy C- A. IiQUgebauer and J. L. Kargrovc (loc. clt.) and by L. H. Drcgcr ct al. (loc. clt.). I

Hoai Capaelly and Entrofv.

The heat cepaclty ar.d entropy were reported by A. 0. Kah et al. (loc cU.). T^iev acaoured perature (51-2S8.15'.) ar.d^hlgh tenperature (239.IS.lflOO'K) heat capacUlea and extrap;iated the : ca- :o:ac:: froD 0 to 51 K uams tr.e T' law. A s^nooth extrapolation of the heal fa,.aclt^ .aa rj>ae Cron laoc* - The heat content of Al'Kc) waa recently detorclned froa JOG to IZOO'K by R. rera^l, -Heat Conterta c- Subatancea at Klgn Terpcraturea," M. s. ITiealo, Unlveralty of viaconoin (19^1), The enthalplea repor'e: Kezakl are atout 1« greater than thoae of Kah ot ol,

DeconpoBltlon Datfl.

P. 0. :chU..: L:.': -.UllDaa. Bull. A,n. Ihya. :;oc. II. 4, 15. MS?.) puuioo mo vaporiro". with tho ^Bnn nv^r.,rr.r.o'.,r and detected only tha eaaeoua eperl.,. Al nn-i Tlu- ,.n.erMm-.. ot wnic AllKc) one AI(^;) ^..re e-^ua], 2788.9'K, woa token aa th« t..r,i,..ror.ur... or de.-or:"..riito.

Dec. 51, 19601 Dec. 51, 1961( Dec. 51, ral. itii>li' ili'll —- <• * AH; T. "K. ;].iiK;ini« OXIL-E { ALCHA AigOj) KOL. WT. 101.960

•'17 .bib |fjF im T£ 0 JO M 1 MI It - inl,/.•>'. - B^7.;0• JOS • III. . * I' - • loii.p i.? I .sJt.7 • . .f '. ' • 1 1 I. * - 1 .•..' - b > ' > . J. l> i - • tfi. -7b /'7.t2i

- ( TT.'.kO 27!!.llf IB.'*'*') ;/..*") 1 ; •.. - i.jy.t(f t rj.(>id ?^2. 379 - 12.1 M col . •!• - •40U.-1 * Kcol . nol< It*. 1 V. 1 .• •'2 jB-lS - suk. . f, 7S - I'-'i.M? iOO !>? I - - • r" I ^- * H CH_ - CtJ.iO * 0.55 kcol. noli •.^ - i^., . I', i. - ^-iS. 3B'J W.i'.'. no »;-, . • >1 - ^. ;i ,i«JH - • fi 7 . Vi.' w I'-B.')/^ uO.«81 «.: 11 900 1 - 7 .'^ - l-i't.aft'i - (I'D .'.<>; - ej.97> QOD ." ' k 1 1 - ] noC ?-.fl I*. . )4 iH.fii.1. - - .*2''. li^l 117. .»Q^ ;!e8*- of I^orcailon. 1 130 V.l /i ^ftl /!.-<.<. - 40''.l81 - - t.y3.o2' 100.^r27 St.360 1?00 »r 7i» - Tnc value of i'lj. derived fron tr.e direct concuotlon of pure nl^jnlnua In oxygen woa tohun froa A. D. Kan, ,"•0 ^7,7tS - '.C3.'. »7 3'!i ,f>ao I ^00 * 1 .0»2 f>.no - 1- ;o ^J. 3 1 1 •o; - l.lJ'.rtlO - 2oi.flfta I. rr.iB. Cnon. 51, 1572 (1957). Other values for obtfllned In Liie onne woy oroi -559.04 * .24 ^ctl. - i«2.'.')l c-l.bfll : S02 S-*. !>>.<) 3; - -oH/rted by P- E. Jnydcr and H. Zillz, J- An. Chca. Soc 67. SBJ (1945), • 400.-1• * -' i kcol. mole'' rejior'.ea Ly 38. J] 7 LA.13 »; .^2C '.'I 17.-81 - 111 - 279. J3<. C- £. Hollcy, Jr.. ond E. J. Hubcr. Jr., J. Ara. Cc.en. Soc. Ji, 55:.* 113::); onJ ; " kfo.. rcro::ci -i.S -.^•.38^ - 1.') •> 270.612 .11.. 78B 17CC - Lv A. Scnneider ana Q. Ootlo-.^, Z- or.iVK- J- allt^ca. CJica- ZT?. 41 (1954). 1 floo M. J?>* > • 117 - iOl.1»» - 2^2. »1 1 3!.763 ^3. 11ft 1 e - ...ij .".I ^ - 2bb.25'. .?". 1 - huj .n7 .«i 71.7.blU 27.:i>7 ?0O-' 3>.J-0 \fi 716 ?y. i 7*. - - 'oo.i?! 2'-. 077 ?100 13.??9 01.0 71.0.CI 1 Heat Capfttlty and EnlroiiVi 2700 - JOfl.956 - 2>2.'.?7 ^ » , ina - 10R,i7b - I?!..972 21.•'67 The ncDi capacity aeasurcscnts reported by 0. T. PurukOkO, ~. B- Douglas, R. E. McCoskey, and D. C. CimlngOi ••V3Vfffl6' "-'i67',T7Ci"" '?l7".ii6" '"I'o.-'QC - 307.]7? 19.31.3 Us' to 1200'K.J, J. fioaearcfj Notl. Eur. Standarca 57, 67 (1956), were enployod In trtlo tabic. Low tcnpcreture 2S0O 7?.2^6 . V)S 06, w^? - ?0O.B3'- oeosiircnenta were also aade by ?. Slcon and R. C- Swain (30-2aO*K.), Z. Phyolk. Chen. 38B. 189 tl9iS); £. C. 'C.)72 ?02.lii4 n.ocg ?600 >'>.31(l TJ.*27 .^61 - 396.5S0 - Kerr, H. L. Johnston, find H. C. Holletl (20* to 2S5'K.), J. Ao. Chen. Soc 72, 47*0 (l95p); J. w. Edwards and 7i.''26 i - 7 i.bjt - J9b.01i IQ&.BOe 1^.77b - ^36.17^ - a. L. KlnsBton (53-2Sl'K.), TronB. Paraday Soc 53, 131J-22 [1962); E. H. Rodlslno ond K. 2. Gor.cl'akll, {100- ?800 70.1Qb -9 .*«7 n,?n 164.I**' - 1?.0M ?500 1:. .<44iO 77.^.^.8 .Q .^^0 - b-^htin - Pl.tiflfl 900'K.), Zhur. Plz. Khlm. 52. 1653-62 ;1958); B. E. Walker, J. A. Grand, and R. H. Miller (aOO-900'K.), j. Phya. 1000 >•>.:-(> 7»). 5*6 %0 .••na - •>^^..2^^ Ii9.u7i> 1 1.^88 - Chen- oO, 251-J (1956); B. Dfthoon, E. 3- Hrockett, and T. E. Erockeit (7O0-1400'K.). j. Pnya. Chen. 67. iSfiJ - •>>3.]3> 11.6.sni. ly. 131. ^100 lb. i*c 7 (lW4). All of the ftfcove low tcEperatupe aota 0. IM 32DO 'S,S30 ^ } - ^32.0?a - 1*1.. 13!) ^1.»32 • 121.718 a.oM 3^0r s • , •>; 7 - iao.ooe are in ^ood flgrococnt wltn Purukowa'a work- 03.U-? - i?«.-'»7 120.»1B 7 .029 •.ft.;.?:' 3 50C .0? J - Jft.992 — The neat copacltlca above :2C0*K. . 1 ZOO-.SOO'K.) were t:iken fron the cninolpy noonnrencnto of P- B. Kor.tor, L. 3. U:areva, V. V. Ka'ndyba, and E. H. Poalchov, Ukr. Plz. 2n. 7, 205-10 (1962). Thn heat capoclty values above 2500*K. wore extrapolated. Hljh :enpepoture meaaurenento were alao r.adc by the following inveatlEynora: V. Ya. ChcWiovakol (5OO-20O0"K.). Inih- Plz. Zn., Akod. Houk. Beloruaak SSR 5, 62-5 (1962); A- Pi.-r.-ler and H. Olctve CllOO-2iOO*K.), Conpt. Rend- 2bi^, 4255-95 (1962); C. H. Snoxote and B. P. Naylor (500-1800'h'.), J. Arc. Cheo. Soc. 67, 72 (1945) and H. L Johnaton and M. Hoch (1000-20DO*K.), J. Phyo. Chco. 65. 1184-5 (l?61); onO V. A. Xtri:iln, A. B- SnoldUn, eno V. Vfl. C.iekhovakll (500-2000"X.), Doklody Akod- Wcuk. ^SUlt (_35, 125-6 (1960). Kuaerlcal values were not available frjo KlrlUin, et al., but ampnicol voluca wore in cloae nsroeocnt wiin an extrapolation of PurukOMO'a dote. Tnc entropy at 298.15 woa rcpartod by T. Purukawa, ot al., loc. clt-. ualng -1 0-0105 cat. deg.'^ oole

Keltln>; Dnta.

The cieltlns data vicre ootainea froc. tne meaaurenicnts of P. B. Kantor, L- 3- Lozoreva. V. V. Komlyfo, and E- M. Foolchov. IOC. clt. S. J. Sffinelder "Conpllatlon of the Keltlng Polnla of Uie Heuil Otldca," ::BS Monograph 68, p. 6, Oct- 10, 1955, given a review of the neltlng poinie that range fron 2267 to 2545*K.

nni*. 11. 19501 Sent. 50, 1961J Mar. 51. 1964 Al .0-, •r«l. intilp*'rfrn.-' l.<-.l. tllolf-'- T, 'K. AM: CAHBOH (C) 0 *000 .000 (RSPEREHCB STATE - ORAPHITB) INFINITE • '52 .000 KOL. WT. - 12.011 100 .395 • 000 • 300 .210 <:.591 .236 200 1*202 .770 .000 .000 .000 1.570 ,160 298 2.03B 1.359 • 000 • 000 • 000 1.359 .000 • OOO • 000 .0C9 300 2.014 1.372 1,319 .004 TO 2.ail 2.075 . :>co .000 • 090 - 0 1,450 • 219 .000 '^f 298.15 500 3.496 2.7B4 .033 .090 1.646 .169 .000 .000 • 000 298.15 " i70-89 • 0.5 kcal. Bole"^ 600 4.038 3.471 1,095 ^298.15 - deg.-l oole' .947 • 000 700 4,4.4? 4,126 • 300 .003 2.166 1.372 .OCO eoo 4.739 .000 ,900 4,7fc0 2,449 1.831 900 4.970 1.311 .000 • 003 .000 2,736 2,318 .000 1000 9.149 5,044 • 000 .OCO 3.320 2.9<4 Heat or Pomatlon .000 *000 .000 1100 5.304 6.347 3.300 3,347 .000 Zero by definition. 1200 1.430 6.809 3.173 .000 • 000 3.963 .030 1300 1,127 7.248 3.839 .000 • 000 4,432 .000 .000 UQO 1.605 7.661 4.09a • 000 4,998 .003 1100 1.669 6,010 .000 .330 4.348 1.552 .000 .000 .COO Hent Capacity and Extrapolation I 600 1.7J1 8,417 4.591 6,122 .000 1700 5.765 3.765 4,027 .000 .909 6.696 • 000 The low tcapBrature Cp ceaaopesenta of P. H* Xeeaoe and H. Pearlcan (1* to 4"K. and 10' to 20*K.), Phya. 1800 5,803 9,096 5.055 .000 • 900 7.275 .003 1900 1.936 0.411 5.276 • 000 .000 Rev. 99, 1119 (1955), and of W- DcSorbo and 0. B. Hlchole (1* to 20"K.}, Tha Phya. and Chea. of Sollda 6.'352 7.617 .000 2000 1.861 9.711 1.490 .000 • 300 9.442 .000 (1958), were joined aooothlr with the Cp oeaauretaenta of W. DeSorbo and V. V. T^ler (13* to SOO'KO, J. Chea. .000 .000 2100 5.B91 9.999 5,69B Phya. 21, 1660 (1953). Cp values above 300*K Mere taken froo National Bureau of Standarda Heporc 6926. "Pra- 9.029 .000 2200 5.914 10.272 .003 .900 5,900 9.620 .000 llDlnary Report on the "nierDodynBOlc Propertlea of Selected Llght-glenent coapounda", July, I96o. Heat eapacltj 2300 1.936 10.136 • 000 .030 6.091 10.212 .000 2-00 5.916 10.789 .000 .900 valuea above lOOO'K were ed^ustad to give anooth resulta. Above 4000*K> the Cp valuea are eatlcated. 6,286 10.807 .000 2100 5,974 11.032 ,000 .000 6.471 11.403 .000 .000 .000 Sjg and Hjs were calculated to be 0.00265 cel. deg."^ nole"^ ond 0.03982 cal. oole"^ reepoctlvely fpoa 2500 5,992 11.267 6.651 12.002 anootb Cp values ualng Veddle'a rule. 2700 b.009 • 030 .000 11.493 6.826 12.602 .000 2600 • OCO ,000 b.:26 11.7U 6,997 13.203 .000 7900 • 000 .000 6.042 11.974 7,163 13,907 .300 3000 .003 .000 6.017 12.129 7,325 14.412 • 030 • OOO • 000 .380 3100 0.073 12.328 7.483 11.019 .030 .000 3200 6.oaa 12.521 7.639 .030 11,626 .030 .000 3300 6.103 12.708 7.788 • .000 16,236 .000 .000 3400 6.119 12,991 7,936 .000 16.847 .000 .000 3100 6,134 13.368 B,OBO .c:o 17,460 >000 • 000 • 000 -3600 6,150 13,241 8.221 18.074 .003 3 730 6,161 13.410 fl.359 • 000 • 030 16.69c .030 3eno 6,191 13.575 .000 .0C9 8.494 19,307 .OCO 3900 6,197 13,736 .300 .::o 8.626 19.926 .000 4000 6,213 13.893 .000 .003 8.716 20.146 • 000 .000 • 000 4 100 6,230 14,046 8.893 21.169 4200 6.247 .000 .000 14.197 9.009 21.792 • 003 4300 6.264 • 000 .000 14,344 9.130 22.418 .003 44O0 6.291 • uUO 14,488 9.250 2J,C41 .3C0 6,299 • 003 .030 4100 14.629 9.368 23.074 • C03 • 003 .003 • CO 4600 6,317 14.760 9.464 2^,305 4700 6,331 14.904 *:oo .030 9.198 24,937 .v-;o 4800 6.314 11.036 • 000 .000 9.710 25.172 •.003 4900 6.373 15.169 • coo • 003 9,820 26.2CS .JC3 1000 6^392 11.296 .003 .000 9.92B 26.846 .033 • CC3 • 000 .COO 1100 6.412 11.424 10.031 27.487 • 000 1200 6,432 15.549 10.140 • 000 • 000 28.129 .033 1300 6.412 15,672 10.243 .090 .303 28,773 .003 1400 6.473 11.793 10,341 .000 .000 29.419 • 000 5500 6.494 15.912 10.445 • 000 • 000 30.068 .000 • 000 .300 1600 6.116 16.029 10.54J 30,718 5 700 6.138 • 000 .000 16.144 10.64 1 '1.371 • 000 5800 6.560 16,218 I0.7J7 .000 .000 .033 32.0^6 • 000 5900 6.183 16,371 10.831 • 000 • 000 6000 32,693 • 003 .000 6,606 16.4B1 10.924 33.34,: .033 .000 .OCO • 000

Morch 31, 19C1 •r* T. 'K. M*-ii*,„ AM; 1 CAflBON .-0:.-OXIDH (CO) (IDEAL OA::) 0 .000 KOL. iTT. - 29.011 .000 7.072 - 27.200 100 • 77.700 rNFlNITE 6.»16 10.614 13.401 I.379 - 26.876 - 78.741 67.809 ^ m. >A.*35..,.47 6ft1 - 76.599 »7.fl4 .600" 7l-.'4TT • ••JJ:SSI 300 6.96) *7.?57 47.?14 • OM 76.414 - 17.673 73.910 ^'f 298.15 • -2S'*155 + 0-62 keal. nole"^ 400 7.013 49.765 47.4Ra .711 76*318 - 14.975 19.109 500 7.171 50.841 48,006 1.417 26*706 - 37.144 16.735 around State Configuration =298.15 - : 0-01 The apoctroacoplc constanta listed abovo ara for the natur• 30.788 99.707 3400 8,940 66.467 98.S61 25*927 6.206 - 30*988 - 05.609 ally occurriT^g isotopic conpositlon given by D> Stroslngor, J. M. Hollander and 0> T. Seaborgr Rev. Hod. Phya. 3500 8.961 66.74A 90.083 26.822 - 6*145 31.10? 97.509 6*008 30, 585 (1958). 3600 8,973 66.999 59.799 27*710 91.300 99**00 6.034 3700 8.984 67.245 50.911 - - 28.617 31.608 101.286 The diaaociatlon energy had been aelected by L. Brewer and A* W. Searcy, Ann. Rev. Phye. Cheo- 7, 259 (1359) 3800 8.994 67.485 99.717 5.982 20.916 - 31.S16 - 103.16* 3«00 0*004 ^7.718 90.019 5,093 Belior at al uaed o lower value for tha dlasociatlon energy in their calculfltlona. However, their au=atlon» 30.416 - 37.031 - 105.030 4000 9iOI4 07.046 60.117 - 9.886 convargo rapidly and thlo introducea no aenalble error the fimctlono. 31.316 17.7*7 * 106.008 9.841 4100 9,024 68.169 00.311 37.218 *700 37.*6* 108*77* 5.798 9.033 60.387 60.901 33.121 - - 37*684 110.630 5.756 4300 9,047 60.599 60*687 34.075 - - 37.906 112*403 5.717 4400 9.011 68*807 60*869 34*930 33*130 - 114.339 5*079 4 500 9*059 60.011 61.047 35.635 33*316 - 116.177 5.64? 4600 0i06S 69*?l0 61.273 36.7*1 33.904 118*012 9.607 4 700 9.076 60.409 61.395 37.649 - - 33.014 119.649 3.573 4800 9.084 69.906 61.964 38,557 34.046 - 121.672 9*540 4900 9.097 69.784 61.729 30.465 • 34.260 - 123.497 5.508 5000 9.100 60.967 61.892 40.379 - 34.516 - 125.315 5.477 SlOO 0.107 70.148 62.092 41.285 0.119 - 34.755 - 127.192 9.4*6 5 700 70.379 67*710 47.196 3**909 178*041 9*410 1300 0.173 70.498 67*369 43,108 39.737 - 130.7*1 9*991 5400 9.130 70.680 67.517 *4*02I 35**80 - 132.94? 9.964 »900 0.138 70.836 A2.667 44,93» 95.727 - 134.336 9*338 ifiOO 9.143 71.001 67.8)4 49*849 39.07* 116.1?9 5700 9.133 71.103 A7.099 - - 3.3)2 46.763 36.273 137.019 3800 9*160 71.322 63*102 9*268 47.670 • 96.*76 •- 139.008 9*?64 5000 0*167 71,479 63.742 48.995 36.730 141.473 9.740 6000 9.175 7I.63J 63.981 40.513 - - - 36.989 - 141.749 3.216

Karch 51, IQOI CO • —

•'• f Krai, moir " T. 'k. >/T II'-11%, Alt; At; Hydrottn (H,) (Id«aj 0*1 - Rar«r«nc« 3Ut«) Nol. n. 2.016 • .pj. ti;;.... .ccc .cfg •..»)) >. in 7 17. .1'> - i.,'f>i .bio' ^OCO 6.51^ 31. .a:o Qround St«t« Conriguratlon • 0.0 B *29C.15 " ^^-^ * 0*01 cil. dog.-^ .ol*-^ . 3/.'.7i .'. 1 .>6 .CCP .03C • 03C :. 3-. J 1. 1 'j 3 ,,1 - .3. J 7 . [. t 7 ,/ JJ. ?i •> '.il- '. •" .3L3 *3t: 7, 11.M ' 1, **f) •Ji-.t'-J .3^0 4405.3 ca. •*•" 7. * I'J 'SI, 7 (> 3*.. 'to ...'^1,4 .: ; .333 (^- 2 :.;. -1 7.i:: fi.670 .030 .000 .000 B. - 60.848 ca -1 3.0664 CI r. - 0.7417 A .i': 7. ' > <.l*1 ^,l.Ot .0"*:' • OhO 0(a 7,1.7. * 1,t." 36. lie 7,1*.8 .033 .OwC --,*." 7.t . 1.... ie7 3t.'.<.3 7.9 i; .[?.•'-' .PC .3 30 7.7, J . 7:6 Ji.'»37 4.66^ .003 .3 3C ".S.^l 7 37.11H 9.^1,6 .0;.- .c:3 .COO Htit C«p«eltlcs and Entropy - ." 7.:;^i ^7,675 1.'..13 .ccc .c:o 8.-1* ti,. li J 11. .30 .03; .cc; .o:c H. V. voolley, R. B. Scott and p. Brickvtdde. J. Riiiarch Kit. Bur. standirOs 41, 379 (1949), ealculttcd .". -• fl.l. i 5rft ll.Vib . 3i.r .C33 0. .: e. r-j i.!>.:„i. 33.67** \i,b'jl . .300 th« th«r«adynulc functlont by • «cthod of direct tvuMtlon for narsal (75^ ortho ind 25< para) ualng apvc- troicoplc eonitinti darivcd froa an aoAlysls of U. V. band spectra. ITiest conatanta ars aora prtftrtblt for ui« . 1:. W.^7^ 1 J.«.7i . - -' 3 .OLO .coo 9. 'VI 3 ?. 1<.,1 7 . .or: .030 In a aujsatlon atthod than thoia obtained by Q. Karzbtrs, Can. J. Raa. A2S. 144 (1950) fro* tht acaiurtd quad- r •,; . i-fc. if.ici li.i*'- . 3 .Ow- .030 rupola transitions In ths ground atata wnich accurataly daacrlbe the loxtr vibrational levels only- Jn any casa <.b, t, 7 lv.()6J 1!>.-.'J .3, 3 .31. .030 «;.47i, r-fc lb.Si.lj .03 3 «coo the dlffarancs in tha Punctlona rtsultlng froa tha tvo aets of data art Itss than 0-21. .t.: B.a:"* -.7,^13 n.vtb . JCJ • CLO .oco Sine* tha entropUs of Woollsy at al. contain a contribution froa nuclear apln, a corractlon of -fUn4 via 1.7, '.:.66: lP.'..Ti .OT .OOC .ceo applied. Rowavar, tha entropy due to tha alKlns of ortho and para hydrogen which la a constqusnca of nuclear I r.. S.7t7 ..7.6I'' '..'.Vli iv.i.4d • 3 .oco .000 . ^ -; R. 3: <.ti.l6c> i::.3..t : .033 .ceo spin la included in the total entropy alnce this resulta in eorraet aqulllbrlua consUnts Used upon third law IS "J i.U.i-t'- :i.;:: .. '3 .C-- W .030 calculations. Dlffarencea In tha values of Rand vsre found to have a negligible effect upon the fu.-:ctlons. CM .. t.yii ..e.7!:ti .33J .0^0 aiallar calculatlona with a different aethod of eatlaatlng the higher rotational levels by K. L. Johnston, ; - ^ 1.1.«55 if2.9V; . - . .03: .000 9.. 12 '.'i.3r ..c. 77 23.H'n . ;' .J". .0:0 L. 0. Savedoff, and J. Balsar, Technical Report Ko. 2, Project R.p-316, Ohio state unlv. (19*9), result In .-.1. • I ... ,i VI. :-.7'

- 11.. . 1 . 'i 1. ! 1 7 • .C.3 ' i. j; " ">. t y 3 3;...53 .c.;c 1 . '.: 1. 3-. l'*^ - ••- '*.7c; t^,.;6 31,1,J 1. L. i.;.,.'>3 Ji.. > -i ' 5.. I .. . .c:c •(, ( -'y . *•:. r 1. b >. , 71. < ^' .i , .0:0 - -.; • ^.^l'• ul., , 11. ' 7, /. ', *Cw3 '-.Til ; J. • rj t*'. 77 IH.ttii', . .. U'. .uuo ' J.. i 1 . . .u.O .c:.3 'i.? - r3.i. . 3;(. 1. .Q**) .1. '. .OCO • o-.D •J. . . '(,''••' •.1 ,; .CC3 •).t • *.!>. 7:'v 4i .'.l.V .000 .« 1 •. l.t.^: ' J , n 7 .OCL 1.6.: .6 b*>. inn . L J .3JL

*5.il3 *5.7(13 , - - .C3l - ^ 1 1,6. *6.7.i I ..., .cr,: .OOC 1'.. ' *.ft7'J '.t.i,*! *7,7«1 .r... .tt: .300 - • 1",U67 i,6.!iU2 *e.7H» ,f • ore lO.K'J *.6.7il *9,7V6 .ooc .oco .000

lurch 31, 1961 CIH

r loir' Ir^. — r -hral. mi)Ie' - —N T. 'K. -R K iiYiiit'i'iEH ciii.tinciF (iiri) KOL. WT. - 36.46b

0 .Ouu ouo iNFINIIC 2.315 _ 2 / . '.11 9 ••.'.or* I^F lr.r TE i:3 6.950 17 .041 S0.ft»5 I .)79 - 22.061 - ?;,?»9 *9.759 4S.7B2 7^.515 '4.524 200 6.961 (.1 .665 - 22. J79 - ;itaie CtttfIffuraMcr. - -22.019 * O.n kral. r^le" 6.964 44 6*5 44.^45 22. '63 J70 .6.696 - - • 0.0*^ kcal. Bole no 6.964 44 6B8 44.A46 . ".13 ?2.0t4 7:.787 16.996 691 72,129 A.9T3 46 44.019 . - - .'1,012 12.573 I.^vln en-l Quantun Wwipnta ):o 7.CU4 1.8 252 1 .<.:? - 72.?i7 - /.».224 10.151 40.0)4 6 = 0 7,069 49 5)4 7. 112 - 22.7an - 73.420 6.533 0 ] 700 7.167 50 6)0 4A.SQ7 ?. J2) - 22. 16ft - ? t.602 7. 36B a:o 7.289 51 595 47.163 1.545 - 22.440 - 23.774 5.494 u/pX^ - S2.06 cc."* 7.4?3 52 k61 47*704 <^.^91 - 22.505 - ^3.W36 5.BI2 1030 7.5&9 »3 250 4e,??c 5.^1J • 27.552 - 24.09) 9.265 11.. c-.. a . - 0.1257 cR."* r_ - l.L'MC a 7.693 53 977 49.711 5,793 _ 72.611 24.24) 4.316 1 i;o - I'"St Porrjitrn. 1230 7.B1Q 54 652 49,17B 6.5-9 - 22.652 - 2».390 4.442 1 J30 7.936 55 26) '.<).ft24 7. 35% - 22.660 - 24.534 4.124 ?hp celected valte, Roaainl'e r:;« calsrlr.e-.rle KeaBureKcnt (l) of the dirort rcr.binDtlon of ifje elorenia. > B.04] S5 675 50.049 9. l55 22.718 24.675 uoo - - 3.Si? 033Bnf..,lly me aB=e as that In the revlseJ ver:ilon (2) of Clreulor £00. JAlIftP cnalyccs of the r,3ro recent eeaoire- 1503 6.U1 S6 4)1 ^0.4Sfr a.''',5 77. 74« 2-<.Bl} 3.619 - - •••nto ore BJaisarlsed boloti unlle tf.e earlier ecasurer;'nta Have been rovle-ed by Roaolnl (l). 1600 8.229 56 961 50.947 9. 7R3 - 27.769 - 24.950 3.408 Qate Metnod ?=9.15, Deferences 1700 B.310 S7 46) M.221 10.610 22.790 25*086 3.229 - - (keal. PDle'M IBOO 8.382 57 940 51.'.R1 11.445 - 27.609 - 75*221 3.067 1030 6.449 58 395 51.9/8 l7.2flT - 22.826 - 75.353 7.916 Tews^n, fiEhroce 19Gi -c=;jr'.fl;n of HCl, HjiÔ, and :;o_ by •22-1* • 0.12 2.i,*,5.6,7.9.9,10 2000 8.509 58 630 52.262 13.135 - 77.B43 • 25.406 i.785 B::.tlc.i cBloncetry Lacrier, ct al. 1343-S2 Catalytic caitlnailcn in flow calorlrêler -22.10 * 0.12 11,12 2100 B.564 59 246 52.565 13.^68 - 22.859 - 25.616 7.666 Roth, Hicnter lGi4 Iireei CBttlnatlcn m tj«b calorlaeier -21.50 * 0.05 2230 S.614 59 646 52.997 14,947 - 22,875 - 25.750 2.558 li 7)C0 8.660 60 030 53.199 15.711 - 22.691 - 25.B80 2.459 von '.artenkerB, Kanlach 193? Direct CKbir.atlon in flo- calorlineter -21.90 • 0.01 14 2^30 8.70) 60 399 53.491 16.579 22.9J6 26.007 2. 368 Roaalnl 1952 Direct csiblnatlon in flou calorlaeter -22.00i * 0.012 - - 71 2S30 8.747 60 745 5).7TS 17.451 • 22.924 - 26.137 2.269 lQ22'6i tr\ rr» f-cf. and A3l fro* Etattatleal 1 =a:nanlc* •??.02 O.Oi 2600 6.778 61 099 54.050 16.327 - 22.940 - 26.266 2.236 Leala 1606 £=-::itrla for reaction HCKg) • 15,IB,17.18,19, 20 CO 2700 B.B12 61 *31 54,317 19.207 22.056 26*394 2.1)6 - - 1/* 3J;B) - 1/2 HÔlg) t l/Z Cl,lg) -22.;o 0.«4 02 ?B00 B.844 61 T5? 54,577 20.090 - 22.977 - 26*521 2,070 21 2O30 6.674 62 06) 54.BIO 20,975 22.99T ?6.647 2.008 W - - Tiie direct coeblnatlcn veluea of Sot.i-Rle.-.ter (li) and von Vartenterg - Kanlsch (J4) are 0-71 leaa negative irjn that 3030 6.902 62 364 55.076 21.864 23.018 26.773 1.950 - - Of RaeBlnl; nowever, all of the other eet.ioda favor the aore negative value, "nie Roth - Rlchter valut aay te affected by 3100 6.928 62 656 55.316 22.756 - 23.040 - 26*897 1.696 errora In tne •easureient of --ne extent of reaction by HCl tliritun (9,22). .ince a set of cjiperlienta taaeJ cn detentiinatien J200 B.953 62 940 55.549 23.65U 23.C64 27.021 1.945 - - of the arsDunt of Hg gave a value of -ZZ.Zl KEBI. «ole'^. 3330 a.976 63 216 55.778 24.546 - 23.090 - 27*144 1. 798 3400 fl.999 63 464 56.000 ^5.445 23.116 27.266 1.753 Roaelnl'e value la conflmed t> B variety of independent nethoda. The aolutlcn celoriaetry (3). incup/i it la releted 3500 9.02U 63 745 56.216 26.346 - 23.145 - 7 7.3B7 1. 710 - ttirouEii a coxplea reaction acnese, la taaes cn ereclea wfilcfi ire no- quite well kno-n. E.«.f. eeasureMnts (IS, 1(1,17.19, 3630 9.041 64 000 56.411 27.249 23.175 27.509 1.670 IJ.CO) give ap* 2gg_,2 - -22.Jii; aea.clr.c an un.-erta'niy of 1.0 BW. m E*. thlo leads to aH^ - -22.02 • 0.01 - - f ?t9.15 3 700 9.C61 64 24B 56.A3B 26.154 23.207 27.629 1.632 when ccablned with the atatlatlcal entr.-ples ~Th e equilibria of- Lewi- s (G25-£9r*K'— l give nX,- .20 . 0.44 {aeeond 0,079 64 490 29.061 - 73.240 - 27.7*9 1 .506 f 291.16 • 3S0O 56.^42 • law) and -22.10 * 0.04 (minJ lek). 3Q30 9.09B 64 726 57,041 29,970 73*276 - 27,066 1.562 - - 1. P. D. Roaelnl, J. Res. K.B.S. .191?). AOOO 9.115 64 056 57.236 30.881 73*31) 27.901 1.579 - - 2. D- 0- vagaan, private coanuTilca11.-.-,, xatianal rureeu of Ctandarda. June 26 fc i. U. H. Jonnaon, J. B. Antroae, J. Ses. .'i.P.S. ^:A, 42/ (1663). *100 9.13? 65 162 57,427 31.793 23,191 - 29.101 1.498 J. R. F-eknian, P. D. Roaaint, IMJ. , J, S-JT ilalT). *?00 Q.t«B 65 402 57,61* 32,707 - 73.392 - 26*216 1.468 • . H. Jonnaon. 3. Sun-ner, Acta ilfanj. 17, 1917 (i9fli). 4)00 9,164 65 617 57.798 33*62) - 23.433 - 76.329 1.440 K. Kanaaon, S. Cunner. Ibid.. 1 Tri «196.M. 4400 9.160 65 828 57.978 34.540 - 23.476 - 28.441 1.413 w. 0. Oood, J- L. Laclna, J. FTPCCJIIJLtl. J- *»• Chcas. Iloc. 6: 59B9 (1050). 4500 9.195 66 035 58.155 35.459 23.521 28.559 1.387 C. E. Vanderiee, J. A. Shanaon. J- rh>a. t.'r.e!'. 67, 2i>09 (l'J6J). - - C. E- Vandenee. J. D. Kuiirr. IMd., lltfiyT. , S. R. Ounn. L. 0. Crcen. J. I'net. D-.f. Data fi. IflO (iWl). • 4630 9.21U 66 2)7 58.328 36.379 - 23.566 - 28.667 1.362 J. fl. Ueher. J. J. KcSlnley. or.j.. L- KU-.-iel, 0. Kelaon. J. D. Park, J. A*. Che«. roc. 71. uai tll^'-'). 4700 9.224 66 *35 56*609 37.301 - 23.612 - 28.775 1.338 J. R. Lacncr, R. E. ieruty, J. ?. [ar,^, itld-. 5292 ( 1932). 4800 9.236 66 620 58.666 39.2?4 - 23.660 - 28.685 1,315 w. A. fi3(.h, H. RUhVer. phjsU. C-.;=. i^V, m ilSi*). 4930 0.252 66 620 56.flll 39. U8 23.708 • 2B.993 1.29) H. V. Warienberg, K. Hanlocn, iriJ., Au".7Tti il9i:)j A16*, 1*4 (1934). R. 0. Batea, V. B. Bauer, J. He*. S-.PTTT"^. :fll llSSlTI 5000 9.265 67 007 50.00? 40.074 - 23.757 29.102 1.272 - - H. 3. Harnea, T. R- Pa»lon, J. fija. Jhra. 531 tlVJl). _ J. 3. Aoton, P. L. Olttler, J. Ar-.. :.1e2. jif. 77. 317i (1955). 5100 9. 2 70 67 .191 59.]51 *1.001 23*807 29.206 1.252 R. H. Qerke, Ibid.. 44. 1664 tH-::i> 41.913 *200 9.291 67 371 5«.'<06 - 23*658 - 29*313 1.232 N. Kaeeyaaa, H. Yacauito, Z. Qka. Pr.'.*. :rp. AcaJ (Japan) 3, 41 (l927)i roc ChcBi. Ind. Japan 7<), C'9 llP20)j 9300 9.304 67 546 59.461 42.859 - 7 <*910 - 29.416 1.213 fro« CheB. Aba. 21. £3* (l?2?l. 5 400 9.310 67 .722 59.A13 *).790 - 73.96? - 29.921 1.195 :•. .-. Ojpia, 0. 37 HUie. D. J. 0. Ives, Trsna. Paraday Coe. 59, l87t (1963). 5500 9.320 67 .693 50-762 "•4*723 24.015 29.622 . 1.177 J. K. l-cwla. J. AB. Chea. Soc :a, 1?;^'." iiM6). - - u. A. Roih. 2. Klektroene*. S5,"T0I il3*4). • 5600 0.341 68 i061 59.908 *5.556 _ 24*068 - 20.724 1.160 5 700 9.353 68 .227 60*053 46.591 74*123 29.0Z6 1,144 Heat Caratlty and Entropy. 5 800 9.365 68 >390 60.199 »7.927 - 24.177 - 29.92B 1.138 5900 9.376 66 .550 00.335 48.464 - 24.293 - 30.027 1.112 - - Spectroaeople conatanta for HCl" and HCl^' -ere aelerieii froia the work of E. K. riylor. n. Tldweii. -j. Elektrocne*. «000 9.366 66 .707 B0.47* 49.402 24.769 30.121 1.097 - - 6*. 717 (1960) and C. Haaualer, P. Barchewiti. Co«pt. renij. 2i6. iO*0 (195B). The valuea were adjuated to 76.53* HCl^*.

Dee. 31, 1960| K»r. 31, 1361| Sept. 30. 196* — r*l, mnir drc,

T. 'K. -a*-ii-m AM; 1 "R Kf HTOROnUJ VI tjdltllV (HP)

0 • UOO . jja if.r tN rIr - /.nss •.4. 7'J(J »4. 'HH too 6.967 1 .1-1 b ;. T ^0 1. 'no '.4.04'J l*. 1. 342 • .9^7 . . I . f. , > 0 t 4 . 7 '1S » "i. 1 7 1.17 7 79a" 4"' 4 d 1 • • '1 .I'll '.4. nry'. - f • . « M 4 /. n '^s Jroujiii r.: .lo (.".-iil'lr.-riJt'.'in * X. • . . • • > <> 1 . • ItJ ."A ^ 64.1,J - 4 f.S77 'f J 4U0 - ;.' <.' • 4.C1. ' S. 7 •, b SOO 4' • 1.1 1 .h '• .1'.? 'I- 2..J.:; 10 r . ,1*1 . ' 1 Ci ..'. •' /. I 4 •4.'.' , t, .J 700 7.,. ^ • 4' . .-.0 4 . • f • *•. ^J.S7, <]00 .1 •? —>w >.S ^s. 1. •• *••. 900 . ?. (1 . .* '"i '../II fcS.,» .4 - • •. 1«.• iro' i !• • . • < j «"••,•. •J 4 61,7^9 I<.,4^t> ••••.'•''•i". 1: •••1' 01,; ,.oir.j-i 'rtL'ii'i.iE;

1 130 1- 1 .•94 .••••,> '1 • , ' l.'.-- s^. »''7 1 ».1'3 1 ?00 T.i.v7 . J. . iiij'^ '.•..4*.? - •'. »'I I '"fi 7.5-4 l . »/l . f. .. -1 ft.T . 1 4 ,j'O'- ts.s 'C * . . 4<4 h 11. 1400 7 . t.. 6 .'•I.'' •>. 11.1 '.H9*, '.s.<, ,s - ^'.S17 n. '>n2 I -lOr 1, 7 , k . - - V -'.114 rl .' ' ^ . S 7q - S. 1 f * *.691

I'l.jn ».tJ JL .^1 9.i.17 •'. *: I ' s. ••49 ' *. .f. 1 2 9. 131 1700 7.o-;i t \ • StSS » r.077 I*J.771 61.B17 • •^,69^ 8.172 1 POO '.V -7 , _ 1 d 11 .o:s tS.'M 7-3 (Jj p. 1 -1 . ^»7 I. ^ .174 l?.^7h - •.6.82v 7. 3i.l 5,. - Sj. vfJS ca. r. - 0. JlCe A 7133 .&5S 4 J. jqt ii...4l S' . "0 - '••.."60 6.9*a 7700 - * .,•10 .y.4U4 .l..7^P WT - sn.99; 1. ^44 ?»on Ill .-11 41.0^4 -1.09' , 184 - •^.i3j 6. ISO ?-00 * •: . 7v> ^ J . T.S IS.mi f.'>.?4y - »^.9M 6. .*9T 213n F:.4,2 • T • 137 U .£./ f 16,-"TS 6f|.?9* '••.991 ••.esi .4joi of Forrx'-lon. 7eoc i3.-'»l 4fta .'.92 17.r.21 66.»11 - 17,J17 1.611 2 700 B,5-U ^7,700 St. .649 ;8.47J ''.•<.4>. * - «i'>.U4l 5,4?S The heat of^forootion la a rov-ed valuc^ :flaed on la) ihe ccooun-ncnt or = jiS.i . 0-3 kcol 2800 8.534 .1^2 S1.100 19.320 6 >.4t9 - 67. ^'Sl S.7'4 :.t..a and Barrow". (b) the n«r.o colorlr.etrlc rolue of ^H'^ ^^^^^ . .s..« > 0.1 kcol. r.ol^^ fr.n ..n V.:!, nbcr. 2900 ?.C^S 1L .447 .'J. 19 J 6t.113 - iT.uSJ 1.->S 8.t64 6^7 SI,^79 2i.3i4 .S67 - 67.U5 ".SBS onJ ocu-^t=o , and (c) the SIO,, H? ocnene given ty Peder, Hubbard. Uiae, and Karsrovc'. Thc.ie loi ?ad roopec:lv>.-ly MOO a.'-i «> 1 .nio "'f ?^.15 • -^^-^ t ^-^-r^-l^-^^ r ond -6^.e2 * J.12 Kcal. Mle'^ Hc03urcr....nLD Involvi,!.; HF In'iV.e jri.922 66.£20 - 17.172 4.712 1200 9, 7 J> I '1 ^2.794 60.07 3 - 67.1J7 -.^81 vl;l:i::y a:" -0= tonj.oraL-jre'''"_i.^.:-e no: conrldereJ tecBLse of ihc unLorifilnty '.n tho 13U0 S. 7cib non-ldcoUly ror.-oi-; :ons . •»sS ^>.h^9 6t.72-* - 6?.110 .3 4.447 :o aoaoclOLlon of tho vo:cr :Jf -i non- 3400 P, r -J 'j 7-,0 '.2.S79 ll-.y p»rroc'.lonfl** Di-plleO to li.e .iaio of Ar:r:.-!-cr.^ end •'j.-i/ i'i.s4n 6*-. T91 - ^7.163 4.317 3100 ft,a<9 *• • „4* S7, 71*0 »'S.4j') 6^.^ 'f - •'7.171 4. 104 g - mui. , f on: irTilr-i; the /alue .iolertoi.

3600 fl.e:>7 : Jt S* .cqs f>^.39i - S7.160 4.37B T. T- Arcatronc, llatloiial P.ir'':«u of .i'.aiiUcr.;tt. prlvttc carjiunlfoi ion. t[i>venber. 13C5. WOO 1].9B4 r 1 ; )7 *. l»6 ^•7.701 ^•'.9« 7 - 67.187 1.969 1B0D 3. Ji 0 ••J :7> S J.iql J. w. c. J-Jhno and n. ?. r.irrt>..-, Pi-oc. H^y- Soc A2:'l, Syi (J SS?). 67.0J3 - 67.19? ?.664 39C0 a,>34. f-! r,7.vS7 - ^7.1«8 *.761 H. von WartcnUfrr. and H- r.fr:ijt:a, iinori- alljen. Chen. Sort, Cf- (iy32). 4000 B.->98 f 1 7 J3 - 764 /V,977 6 /. 1 2 - .^7,7-w 3.471 H. H. PodcP. W. :J. HubtarJ, o- Wlr.v, o.ld J- L. Har^rave. J. ihja. Chen- 114.-; J J-.553). 4 100 &• v&J "1 >4 bI.Q49 JO.774 3. T- AmatronK onj H. S. Jonatip. J- H.-afOrch f^B-.S. 'iS (l.'PO). 67,18- - ^T.^J2 3.582 4700 «• JJ2 M on S4. pO M.671 67.243 - f^7.201 1.497 0. Ruff Slid W. V.cnzel, Z. Onar,;. all/.en. Cnoa- 196, 575 (iVil). 4 100 9. J^3 f 1. 14. 108 J?.574 67.3J,' - 57.199 ^.411 4 400 9.V-) ^7. 1J91 S-.4«7 )l.47H 67.iftS - 17.197 u. 7. Arratrons, In "Exferircntal TlierroctKinistry. ' Vol- II, H. A. .'klnncr ^.319 K.t; l4>i-, In* t'T'oclcnc t> 4 500 9. J63 67. 2*4 S4,«S4 )4.1B1 G7.«.29 - 47.194 ?.26» Publl3.^,ero, Inc., Nev. York. 1962, p. HZ.

460O 9. J91 f, ?. 4.J4 •S.79.' S4.q/2 67.414 - 67.186 ?.:9: V. Mtfdveiiev, .;r:urnfl: XirI Klilr.il ^. )-J33-1405 tl%A). 4700 9.1 JO '>2. S4 .Qtt r J6.199 67, s^; - f.7.179 J. 174 4600 9.117 *2. da 1 SS. 140 J7.1U ^7.^7B - .•7.169 3.;59 490O 9. 1 lb *• ^69 SI,109 tfl.021 67,h97 - 67.158 7.90S 1000 9.111 .* 214 SS.4'.6 6 7.767 - 67.149 2.9 35 Coi-ncli\ and iintropy. ia.Q"*/ 1100 9, 16a ? ». - »s •••J.IS71 tq,p4« fr7,?T0 - 67.136 7,877 1200 9. 1P4 A'. M 1 Sl,77^ The apectrojcoplc co.^3ta^:3 are tno.-e f-.lven In S'aiionol Bîrcou of Îiniulorda Report diCd. 16 nîiO). b-med 4w.77U 67,911 - 57.120 2.671 5300 V, 199 .^». 7oe 11.0^2 -1.69J the precise ctudiea of Kami, Tinman 67.981 - 67.102 7.767 CPlaolon IJe, Ball, and Acqulaia, J. Cliem. Tityg. M, 420 (1^6:). 1«00 9.21% J '. •.fr 1 S6^n70 42.61U 63.^-61 - 57.069 2.711 Monoiircnento of Uio rstatlonal abaovi-l ion 1 Inra in the fo 5100 9.229 ^". 1 JO S6.71S Infrared, W. tl. JtollinrhlIrfi.'J. Oia, 4J.m? 68.137 - 6 7.U69 2.66S .S.v. An. (I9fi4), coiifli-a tho onlaslon stud'.co. 1600 9.244 64. 56.^18 44.4Se 68.715 - 57.U49 2.617 1700 9.218 64. 460 46.490 4i.-»ni 68.79S - 67.U25 2.170 leoo 9.272 n4. 6J1 S6,A»7 «6,twe fta. •«7i ^7.0U4 2.175 5900 9.206 64. rao S6.7T4 47,?»6 6e.4S7 - 61.981 2.491 6000 0.299 A4 . 9»ft S6.O0H 48.165 68.54 I - 66.9*6 2.410

LJCC. 31, IGtJOj Hor- 31, l!i6l; Dec. 31, 1963 FH TBI. mola'Mrj." 'kcal. mole'

T. 'K. c; S* -

600 7.106 50.689 47.1*3 2.129 .000 .000 .000 700 7.350 91.606 47.731 2.891 • 000 .000 .000 800 7.912 52.796 48.303 9.996 .000 .000 .000 900 7.670 53.69? 46.653 4.355 • 000 .000 .000 CO, - 2357.55 cn."^ 60, «o - 1*.059 co.-^ 1000 7.815 9*.507 49.378 9.129 .000 .000 .000 0^ - [6.1 X 10*® + 0.5 X lO'^Ico."^

1100 7.945 59.298 49.679 9.917 .000 .000 .000 - 1.99825. CO. ^ - 0.01791 + 0.0001 co."^ <^ - 2 1700 8*061 55.955 90.397 6.718 .000 .000 ,000 1300 6.162 56.60* 90.813 7.5?0 .000 .000 • 000 1400 8.212 57.71? 91.248 6.350 .000 .000 .000 1500 8*330 97.784 91.609 9*170 _.000 .000 • 000

1600 6.308 58.324 92.089 10.019 .000 .000 .000 Heat Capacity and HntPopy 1700 8.498 98.639 52.448 10.698 .000 .000 .000 1800 8.912 90.370 97.8)6 11.707 .000 .000 ,000 B. p. Stolchoff. Con. J. Phyo. 32, 630 (1994). datenained the apectroacople conatanto of n^Sr^^ b7 eoa- 1900 6.990 90.78? 93.171 12.9AO .000 *000 .000 blnlng hlo aaaaured rototlonal apeetro with tho reoulta of band opoctra ^iven tn the lltarature. iTioae constants 2000 8.601 AO«22? 99*913 13*418 .000 • 000 .000 have been correctdd to apply to the naturally occurring iaotoplo coapoaitlon Hated by D. Stroaln^Br, J. H. 2100 8.638 60.6*7 93.842 14.280 • 000 .000 .000 Hollander and 0. T. Scnborg, Rev. Kod. Phys., 30. 585 (1958). 2200 8.672 61.049 54.160 19.1*6 • 000 • 000 • 000 2300 8.703 61.431 94.4A8 16.019 .000 • 000 • 000 2400 8.731 61.802 9*.766 16.886 • 000 .000 • 000 L. Qlact, J. Bolsor and H. I- Johnaton, Ohio State univ. Res. Pound. ProJ. 318, Report Ko. 9, 1953, cal• 2500 8.796 62.199 95.099 17.761 • 000 .000 • 000 culated tho runctlons for N^^A* by a direct oussatlon using apectroacoplc data given by Q. Kertberg, "Diatonic

2600 8.779 62.503 99.339 18*638 • 000 • 000 • 000 Noleculea". D* Von Hoatrond Co., Kn Tork, 1950. Itie entropies were chonaed by -lUn9 to remove the effects of 2700 8.800 62.839 99.606 10.917 .000 .000 • 000 nuclear spin included by Olatt. Belser, and Johnston, and by 0*012 for the difference in apeetroocoplo consUnts. 2800 8.820 63.199 99*670 20.398 .000 .000 • 000 2000 8.838 63.469 96.127 21*280 • 000 .000 • 000 J. A. oorr and s. Oratch, Trona. Ao. Soc Kech. Engrs.. 72, 741 (19S0), calculated a set of functions by a 3000 8.899 63.769 96.376 22.169 .000 .000 .000 direct Bu=3ation over the sround atate levels only. Asreeeent with tha functions of Olatt, Belter, and Johnston . 8.671 3100 64.059 96.619 23.091 .000 .000 •000 is within 0*11t* 3 700 8.886 64.337 96.896 23.930 .000 ' .000 .000 3300 8.900 6*.611 . 97.nfl7 2*.B?0 .000 .000 .000 See nltrosen conatoole sheet for details concerning the dlesoclatlan energy. 8.914 3400 6**677 97.91? 29.710 .000 .000 .000 3900 8*927 65.139 97.932 26.611 .000 .000 • 000

3600 8.930 65.367 97.7*7 27,905 .000 .000 • 000 3700 8.990 65.632 97*997 28.399 • 000 .000 •000 3800 8*962 65.871 98.162 29*205 .000 .000 .000 3900 8.972 66*10* 58.9A2 30.191 .000 .000 - • 000 4000 8.963 66.331 98.459 31.0BQ *ooo .000 .000 4100 8.903 66.553 98.791 91.988 .000 •000 • 000 4200 0.002 66.770 98.0*0 32.088 .000 .000 .000 4100 9.012 66.98? 59.12* 33.788 .000 • 000 ,000 4*00 9.021 67.160 59*309 3**690 • 000 •000 •000 • 500 0*030 67«992 9Q.4R2 99*50) .000 *000 .000 4600 0.030 67.991 99.697 96.406 .000 .000 •000 4700 0.040 67.769 90.627 37**00 *000 .000 • 000 4800 0.097 67.976 99*099 98*306 .000 • 000 .000 4900 0*060 68.167 60*160 39.212 • 000 • 000 • 000 3000 0.074 68.3*6 60.972 40.110 • 000 .000 .000

3100 0*063 68*929 60**61 41.027 • 000 *000 •000 9200 9.091 68«10? 60*637 •1.939 • 000 • 000 •000 3300 9*100 68*075 60.701 42.8*5 .000 • 000 •000 5*00 9.109 69.0*9 60*0*2 49.799 .000 • 000 • 000 »»00 9.118 60.213 61.0Q1 4**6A7 *000 *000 • 000

3600 9,127 69.377 61*710 49.979 *000 • 000 •000 9 TOO 0.136 A0.93Q 61.902 46**9? •000 • 000 •000 9600 0.149 60*690 A1.924 *7.«0A .000 .000 .000 9000 0.199 69*69* 61.OA* 48.321 •000 • 000 •000 6000 0.163 70*000 61*803 49.217 .000 ' .000 • 000

Karch 31* 1981 H3N

• cel. tnelf!* dfR. •- f AK; (IDEAL 0A3) rOL. WT. - 17,032 T, 'K. S' -(K'-H"„,) n'-ir„ 1 AM;

INFINITt 0 .000 .000 INFIM TC 2.391. 9.362 - 9,362 iiH* - -9.362 kcal. cole" {' 298.IS " " "^"'^ 17,930 100 - 7,949 37.169 53.177 1.599 - 10.C52 - 6.203 200 8,020 42,709 46.719 .803 - 6.195 - 45.967 cel. deg.*^ colo"^ Point Qroup C ^298.15 'TVS"' \m- 5v Vibrational Levels and Kultlpllcltlea - 3.923 3.858 300 « B.36<< 46.019 45,967 .016 11,050 .601 400 9.000 48.511 46.303 ,883 - 11.372 - 1.467 500 9.715 50.596 46.95B 1.819 - 12.037 1.114 - .487 5506 (1) 3577 (2) _ 1,378 600 10,t37 52,431 47.720 2.627 12.435 3.763 - 6.314 :.e>* 1021.5 (1) 1691 (2) 7C0 11.133 54,093 46.314 3.905 12.773 55,624 5,053 - 13.056 9.289 - 2.537 600 11.60* 49,306 - • 12.41,1 30,090 6.265 13.291 12.097 2.9J: 11.717 35.13b 5.022 60.102 31.527 13.663 36.020 - 5.072 2500' 17.810 .'72.713 - KHj (e) at Ita boiling point (239.6a*K.). 5.116 17,943 73,41* 60.600 33,315 11,603 60.890 - Their value coaparad to Sjjg^gg. interpolated froa thla table by the oethod of Lagrsnglsn curvilinear in• _ b3.762 5,160 2700 16.063 7*.093 61.068 35,113 13.3*2 66.613 - 5.199 terpolation, w. J. Taylor, J. Reaearch Katl- Bur- Standarda 35, 151 (1945), la tabuloted below- 2BCC IB.173 7*.732 61.564 36.927 13.480 - 69,476 - 5.236 290C IB.274 75.392 62.030 38.750 13.413 - - 5.269 S in cel. deg- ' sole H 3000 lB.3b7 76.013 62,406 40,582 - 13.351 72,330 * Third Law RRKO approx. to I 75,184 T'K. 5,300 3100 16.452 76,617 52.932 42,423 13.265 - 78.037 3,329 3200 18.530 77,20* 63.369 **.272 13.220 - 80.891 - 5.357 44-13 44.170 3300 1B.6C3 77,775 63.797 46.129 • 13.156 239.66 47,992 13.091 63.73b - 5.382 45.907 34 00 18.669 76.331 64.216 - - 298.15 45.94 3500 18,731 7B,B73 64,62 7 49,662 - 13.030 86.563 5.406 W. 3. Benedict, E. K. Plyler and E Tldwell, J. Rcecarch Natl. Bur. standards 61_, 123 (1958); j. Chea. _ 3.429 3600 18.789 79.403 65.030 51.738 12.970 69.431 - 32 (1950), In an enalyala of the vibration-rotation bands of IIHj 3700 18.642 79.917 63,426 53.620 - 12,913 92.273 - 3.430 Phya. 29, 829 (195a)| and J. Chca. Phya 3800 IB.891 B0,4?l 63.B14 55.307 12,656 95,119 3.470 coneider HH^ as being a pyraaidal eolecule with aycoaetry C^^i Ita rotational atrueture Is tnat of a aycaetrlc - - 5.4C9 .3 390C ie.93f 80.912 66.194 57.398 12.804 97.936 - 5.507 4C0C 16.980 81.192 66.368 59.29* - 12,15* 100.796 top. _ 9,324 Vj la the norcal vibration of tne deforcfltton parallel typo wherein the nitrogen aton spproachea and re• 4100 19.021 61.661 66.936 61.19* 12.706 103,635 12.662 106.473 3.340 4200 19,038 62.320 67,297 63.098 cedes froQ the plane of tha tnreo nyorogen aCoao. Since the pyrsald la conparat1vcly flat me potential barrier - 12,622 109,308 - 5.335 4300 19,093 62.769 67.631 65.006 66.917 - 12.58* 112.1*3 - 3.370 to the inveralon of nitrogen la low- Each atato la characterized by the vibrational and rotational quantua 4400 19,126 63.208 68.000 • 114.97* - 5.584 4^00 19.137 63.630 66.343 68.631 - 12.551 - nuabera ea well aa by the aycaetry nunber (fl*) with rcapect to the Inveralon plane. 12.519 117.812 5.997 4600 19.167 84.060 68.680 70,748 - Attcapta have been aad« to eatlcste the correction due to inveralon doubling. See. R. p. Rsnntng, J. Chea. 12.492 12C.b47 3.610 4700 19,214 fl'.,*7J 69.01 I 72.666 - 123.478 - 3.622 Phya. 3, 136 (1935)| r.. 5. Plticr, J. Cheo. Pnya. 2* 2-'* (IWD), ond C- C- Stephenoor. aii.l H. 0. HcMJion, J. An- bSCO 19,24C 64,977 69,338 7*.391 12,466 - 3,633 4900 19.264 83.274 69.659 76.316 12.448 U6.3U Chea. Soc< 61^, 437 ( 1959). In thlo case there are aycaoirlcol double Dln'ce In tlir i>.>tt^.t tal energy. The cor• 78.44* 12.431 129,137 - 5.644 3000 19,267 85.664 69.973 - - - rection Ja aflde by doubling tne energy levola halow the lop of the potential barrlrr; thoae levola above the •_ 12.419 131.973 5.633 »1C0 19.109 - B6.0*6 70.266 80.373 barrier are shifted upward. The auesatlon of thaae levels for glvee Rln^ greatrr nntropy than for the 134,802 3. (,63 32C0 19.330 ab.*2l 70.393 62.305 12.410 137,617 - 1.673 Elnstaln functions where singly degenarate vibrational energy Icvele are eoployod. t3C0 19.349 a6.7B9 70.893 64.239 12.404 - - 3.6S3 J40C 19.368 87.131 71. 193 86.173 12.403 140.464 - 143.293 - 5.694 nic rotational correction la osda by giving cT a value of C. since, if tlir lnvrr»li.»n laWea place, then 3300 19.383 87,307 71 .486 88.113 - 12.405 - each of the two poeltlona of tn« colecule are equivalent, giving nin^ leas rotational entropy tnan wnen coapared • _ 12,412 146.173 3.702 S600 19,402 87,636 71.776 90.092 - 140.«5e 3.111 to tna RHKO approxloatlon with O*- 3- 9700 19,*ie 88.21,0 72.061 91,993 - 12.421 - 3890 19,43 3 00.336 72,i4/ 93,936 12,416 131.767 9.719 - 12.434 - 3.7i» Blnataln functions are employed for the Vj, Vj. fundsaentsla, which impl H-B t\>y vvbratlon-rotatton 3900 19,447 6S.Bro 72.619 93.aao 134.620 89.197 72.693 97,825 - 12.479 157.449 - 3. M3 ftOOO 19.461 - - interaction. But, for Vj intersctlon le leplled first by asnkialng Inversion, then •loiiM tn^ O" snd the levels, end tnen euaBing. However, theaw corrections are eelf cenowltng and approximate tnct HBHO. •arch 31. 1081 • C4l. molr^'dfa.''- — kr«l. niota' (Reference SUte - Ideal Oae) Kol. )ft. - 32.00 T.-K. •IIU.)/T Oxygen, Diatoaie (O2)

2.675. .000 .000 .000 0 .000 .000 IWFTMJTr...-. 55^705 * 1.11) .000 **';6od .000 100*'"* "A;998"" 'vr.'lov .665 .000 700 6.961 40.A43 .000 .000 46.216 .000 798 7.070 40.on4 .000 .000 ,000 D* - 117.977 f 0.05 Ucal. "ole 49.004 0 ,000 .000 .000 300 7.023 40.047 49.00* .nil .000 .000 Ground State Configuration ^J' S'ga.is - *9'<» i 0-01 cel. deg.-^ aole"^ 400 7,106 91.091 49.787 .774 ,000 ,000 .000 900 7.431 57.7?? 40.81? 1.4S5 .000

.210 .000 ,000 .000 600 7.670 94.096 50.41* 7 .988 .000 ,000 .000 700 7.883 55.797 51 .Qpa 7 9.788 ,000 .000 .000 800 8.063 56.361 51.679 0- - 2 4.600 .000 .000 .000 000 B.212 57.370 97.209 COe - "80-Z« .477 iOOO .000 .000 1000 8.936 98.19? 97.769 5 - 0*0158 CB."^ r^ - 1.2074 A 6,266 .000 .000 .000 1100 R,410 56.901 51.709 .114 .000 .000 1700 8.527 59.779 91,80) 7 .000 .000 .000 1300 0,604 60.415 54.7n3 7.971 .000 .000 .000 1*00 8,674 61.055 54.744 8.615 .000 .000 1900 8,738 61.656 5^.1«9 9.70ft .000 .000 Heat Capacity and Entropy 10.5R1 .000 ,000 .000 1600 8,800 67.72? 5 5 . 60 " H. V. ¥oolley. J. Roaearch, Kat. Bur. Standards 40, 16i (1948), calculated the functions by a direct auB> 11.465 .000 .000 .000 1700 8.858 67.757 56.013 12.194 .000 ,000 .000 1800 8.916 63.265 96.401 cation to 5000'K. lYle spectroscopic conatanta used are tha SSBS sa those listed by 0. Hertberg, "DlaUwlc 63.740 56.776 13.749 .000 ,000 .000 1900 8.973 Molecules", D. Van Boatrand Co., 1950. except for differs by 2^. TTiis difference has a neglisible 57.116 .000 ,000 .000 which 2000 9.029 64.210 14.1*0 effect upon the theraodynanic functions. Ranan Qaasureoenta of rotation-vibration levels by A. Uaber and B. 97.403 19.054 .000 ,000 .000 2100 0.084 64.697 A. HcOlnnls, J. Kolec* Spect. 195 (19£0)t support the constants selected by Horsberg which were changed to 15.966 .000 .000 .000 7200 0.139 65.076' 57.919 58*1 16.68? .000 .000 .000 apply to the naturally occurring iaotopie coapoaitlon given by D. Stroalnger, J. N> Hollander, and T. Seaborg, 2 300 9.19* 65.483 *3 17.804 .000 .000 .000 2*00 9.246 65.876 5n.*57 Rov. Hod. Phys. 30. S8b (1958). These are listed above. 18,732 • 000 .000 .000 2900 9.301 66.794 SB.762 V\9 entropies listed by woolley were reduced by 0.0065 cal. deg."^ nole"^, elnco this enount was sdded by 19.664 .000 .000 .000 7600 9.354 A6.670 59.057 70.60? .000 .000 .000 2700 9.405 66.974 59.344 Voolley to account for the difference in aymetry nuaber between hoao and hetero-iaotopic colecules. Thla 9.439 67.317 99-A22 21,9*9 .000 .000 .000 2000 correction Is tsken care of when isotope olxlns entropy Is neglected, V. ?• Olsuque and R. Overatraet, j. la. 72,493 .000 .000 .000 7900 0.903 67.690 50.803 23.446 .000 .000 .000 3000 9.991 67.971 60.197 Chen. Soe. 54, 1751 (1932J.

24.*03 .000 .000 *000 See oxygen sheet for detalla concerning the dissociation energy. 3100 9,996 68.287 60*419 DonatoBlc 25,365 .000 .000 *000 3700 9.640 68.59? 60*AA9 76.331 .000 .000 .000 3300 9.68? 68,889 60*910 .302 .000 .000 .000 3400 9.723 69.179 61.149 77 28.276 .000 .000 .000 3900 9.702 69.461 61.«A3 29.254 .000 .000 .000 3600 0.799' "69.737 6l.AU 30,216 .000 .000 • 000 3700 0.035 ' 70.00A dl>n34 67.093 31.271 .000 .000 .000 3800 9,660 70.769 ,67*267 32.209 .000 *000 .000 3900 9,901 ' 70.975 67.476 33.201 .000 .000 .000 4000 , 9.932 70.776 34.196 .000 .000 4100 C.951 71 .027 67.6fl2 .000 .000 71.767 35,193 .000 .000 »?00 0.988 67>nq3 71 38.103 .000 .000 .000 10.019 .498 AI.08I 4 300 .000 .000 10.039 71.778 63.775 37.196 .000 4400 *000 71.954 .4A9 38,201 .000 .000 4 900 10.067 A3

.A57 39.20s ,000 .000 .000 4 600 10.084 77.176 A3 63.836 40.218 ,000 .000 *000 4700 10.104 72.391 64.016 41.279 .000 .000 .000 4800 10.123 77.606 64.104 47.247 ,000 .000 .000 4 000 10.140 7Z.8U 64 4J.297 .000 .000 .000 9000 10.146 71.010 .368

4*.27* ,000 .000 .000 5100 10.17? 73.27) A4>540 45.29? ,000 .000 .000 9700 10.187 73.416 64,708 *6 .000 .000 ' .000 5300 10.200 71.611 A4.S75 ,11t ,000 .000 .000 5400 10.713 73*803 65.03? 47.337 ,000 .000 .000 5500 10.225 73.991 65.109 48.353 .000 10.237 74.179 69.350 49,377 .000 .000 9600 .000 .000 10.247 74,356 65.9)4 50,401 .000 9 700 .000 ,000 10,758 74.535 A4.6A8 51,476 ,000 5800 ,000 74.710 69.870 57.457 ,000 .000 9900 10.267 ,000 74.881 93.479 .000 .000 6000 10.276 69.070

KOrch 51, 1961 4 I • I. taolr''Art. -keal. T.*K. s* -(K-.ii; ,)/T H'-ll*„ AF; raiSlLICOH TETOANlTniDS (Sl^H^) (CryalBl)

0 100 Kol. Vt- - 140.30 200 119.469 296 27*800 27.600 ,000 -179,290 dole * 112.699 100 25.910 77.948 22.800 .044 -179,759 •194.647 79.97* 22.8 CBl. des -1 c.olc-1 400 26.270 30.140 23.769 2.590 -179.674 •146.979 60.329 900 2W.630 36.796 29.666 9,295 -179,98? •136.018 47.207 600 31.000 41.685 27,991 6.276 -160.146 •129.607 97.85: 700 3).)50 46.640 10,770 11,494 -180*152 •121.161 90,80* 800 95.700 91.247 32.564 16,966 -179.992 -112.754 75.345 Real of Porcotlon. OH voB fouml In K. K- KcUey, C- S- 900 38.100 99.591 31>,B83 18.677 -179,661 •104.97b f 298.15 20.989 1000 40.400 59.729 37.16? 27,963 -179,160 - 96.03? Bur. Hlnco Bull. 40^ (1957), 17.4)5 HOC 42,400 63,671 39,394 26,705 -178.490 - 87.798 1200 44,200 67,439 41,575 31,036 -177,673 - 79,545 14.486 Heat CPfBclty and Entropy. Cp wo taken froa K. K- Kellcy, \j. s- 71,032 49.704 39.926 -176,731 - 71,409 i:.0p4 1300 49.600 Bur. HlncD Bull. 584 (19E0). Cp valuee atcvt 90O'K were CBtj- 1400 47.000 74.463 65,760 40,156 -175,661 - 59.3*1 9.886 190C 48,200 77.766 47,802 44.916 -174,576 - 99,360 e.C66 natoa- Sjgg^jj waa token fpoo K- Kelley, U- 3- Bur. Klneo

6.461 Bull. 407 (1937). R. pehlho ond j. Elliot, Trono. «Btollur£',cal 1600 49.400 80,899 49.77) 49.746 -179.271 - 47,490 9,099 1700 90.300 63.916 51,693 94,702 -2C6.245 - 99.3C3 Soc. AIKE 215, 761 (l959) calculaiau different valuea of Cp. 3.971 1600 91.100 86,616 53.964 59.653 -206.7C9. - 29.414 2.255 1900 91,000 89.596 55.388 64,999 -209,108 - 19.607 1,060 2000 92.400 92,271 57,166 70,210 -209,450 - 9.861 SubllE^fltlon Data. vas foimd In L. Brewer. L. Broaley, p. ciUea, and IJ. Lofgrcn, Natl. Kuclear Bicpgj- Scrlea. rv-lSB, TTie Cr-.e^lntry 52.900 ..55.???.. 79^475 ^.504 60.989 '"iot'fSb ->00.006 and Ketallurgy of Hlocellaneoua Katerlolo, ThepciodjTQclca, '.SlC- 1.789 2300 59.600 99.686 62.236 66.132 -198.235 IB,799 2.966 2400 9!.BOO 101.972 63.866 91.503 -196.44) 78.175 3.27B 2500 99,903 104*170 65.419 96.668 -194,647 37.499

46.740 9.929 2600 56,003 106,286 66.947 102,263 -192,643 68.442 107,663 -191.098 5t,9:5 4,527 1- Z70O 54,000 108,324 65,045 5.C77 2800 94.000 110i2B6 69.901 113.063 -189.237 I 71,327 -1 ,440 74,090 9.589 29C0 94.000 112,193 118,489 (17 72,719 129.683 -169,647 83,062 30C0 94,000 114.014 6.092

Dccopber 31, 1960. • ral. m

- 216.311 - 216.311 INFINITE 0 .000 .000 INFINITE 1.651 - 212.933 465*3*7 100 1.720 7.381 17.415 l.lOl - 2161938 - 217.309 - 209.768 778.170 200 7.620 6.319 10.889 • 414 .000 - 217.100 - 704.13V 1*9.917 298 10.634 10.000 10.000 Kol. Ut. - 60.09 - 217.102 - 704.410 1*8.93* 300 10.6BO 10.066 10(000 .020 OH 21 7.5 «• 0.5 kcal. oole 1.700 - 217,541 - 700.090 109.319 f 298.15 400 12.910 13.447 10(*47 - 217.464 - 195.734 85.511 500 14.240 16.47? ll^315 7.558 1 oole-^ - 2l7.1lf9 - 191.401 69.Tl* 600 11.390 19.17? 12.417 4.041 - 141.5 f 1.1 kcol. cole'^ - 167.100 56.412 'o 298.15 700 16.410 71.62? 13.177 5.A12 - 217.066 - 192.816 49.946 SOO 17.360 73.976 14.771 7.371 - 216.797 7^ - 84fl'K 930 16.160 ?6.?0i 11.STL 9.293 - Jli.Jii • - na.'62 5 *3.374 - 174,413 1900 16.310 27.914 16.996 iC.gie - 216.080 38.125

- 211.9U6 - 170.299 33.83* 1100 16.510 29.481 18.060 17.563 1883'K 30*261 1)00 16.7*0 10.030 19.0TS U.27T - 715.728 - 166.161 11.911 ' 162.038 77,240 1300 16.030 3?.777 70.018 - 211.5*3 17.614 - 215,110 - 157.929 2**613 £H^ 1883 * ^'^^^ UOO 17,130 31.139 20.958 19.337 - 211.147 - 113.835 22**1) 1500 17.320 34.777 71.816

- 214.934 - 1*9.713 20.45* lACO 17.110 31.811 22.677 21.078 - 1*1,178 18.7U 1700 17.710 )6.919 71.484 22.830 - 226*611 IT.096 S. Wlae J. 24,219 24.620 - 226.512 - 140.808 -me value token was reported by W. D. Good. J. Phys. Chem. 60. 380 (1952). 3 1900.. *-"226;j4r* *"-• VsV.Vii" ""l5'',6V9 Heat of Porestlon. 1 1900 18.(f60 36.9w9 ""2'i.'004 ' Jo'. »V9' m J. - 225.941 - 131.311 14.349 Feder, and W. II. Hubbard reported a value of fiH" ggg^jj - -217.75 t 0.3* kcal. nole 2000 18.200 39.039 75.723 28.23? I. Kargrave, H. H. coo neaeurod by fluorine boab colorlnetry in both caecs. 13,174 Phya. Chen G6, 381 (19G2). en' 18.390 40.731 76.417 30.061 - 275.53C - 126.191 •f 298.15 21C0 12.107 18.500 •41.190 27.087 31.906 - 221*310 - 121.883 By oxygen bonb calorlmetry. Huzphrey and King, J. Ao. Chen. Soc. u_, 2041 (l952) determined e value of 2 20C 11*135 2300 18.600 42.414 27.716 33.761 - 224.084 - 117.191 - 112.199 10,241 2*00 18,700 43.208 . 28.364 35.626 • 224.654 .209.9 kcal. cole'^. - 107.6*4 9.427 2100 18,710 43,973 28.973 37,499 - 224.322

- 225.990 - 103.191 6.67* 2600 18.760 44*709 29.164 39.3T6 - 223.662 - 98.512 7,977 Q. KL.ng, U. S. 2700 18.800 41.418 30.118 41.255 Hept Capacity end Entropy. Low temperature heat cepacltleo were taken fron K. K. Kelley end • 223.338 - 93,924 7.331 7800 18.800 46.101 10.606 43.131 . Bureau of filnes - 223.019 - 80.307 6.730 2C30 19.800 46.761 11.239 41.015 Bureau of Hlnea Bull. 592, 1961. High tenperature heot eapocltleo were fron K. K. Kelley, U- - 8**701 6.170 18.800 47.399 31 .767 . 46.891 - 222.705 3000 Bull. SB4, 1960.

^298 15 "^^ calculated froa the low tenporature heet capacltiea.

Troneltlon Data. and flH^ fron K. K. Kelley. Bull. 384.

Hcltmp; Date. T ond OH reported by Koaeanan and Pttzor, J. An. Chen. Soc, 65. 2346 (1941)

J. Chen. Phys. 23, 215 (l95S) reported va^or pressure ista of Subllcntlon Date. Porter, Chupka, and Inghran, A table of the functlone of crlatoEal'.ie was calculezed and Sl02(g) over S102(c) In the forci of crlatobal 1 te. ^ «8 detemined using the third law cethod. -me average of the reaulta was MO. 3 «al. nole-. Using i waa detcmincd using tho third law eel " 2S9.15 _ ^_ ,

Dec. 31, 19001 Dec 31, 1962 J\Cr (Free energy of formation of reactions considered on Paget70)

Reaction 2 3 4 5 6

0 4^3.152 +96^722 +36^809 -123.852

298 -(;'4.629 >71.269 +78.518 +17.653 -120.444

ADO +660699 +71.366 +10o936 -119.171

600 +57.766 +58.125 - 2.O69 -116.733

800 "65ol76 +48»936 +44.811 »14.345 -114.354

:.ooo -65.562 +AOo226 +31-696 -27.299 -112.017

1200 -65o682 +3I.6Zf4 +I8.707 -39.560 -109.717

moo -650862 +23.259 + 5.980 -51.615 -107.452

1600 -66.077 +14-.801 - 6.616 -63.473 -105.227

1800 -66.319 + 6.555 -19.044 -75.120

2000 -66.573 - 1.634 -31.309 -86.693

2200 -66.825 - 9.715 -43.412

2400 -67.107 -17.710 -55.383

235. AH (Heat of fonnation of reactions considered on f^elTO)

Reaction 2 3 4 5 6

0 -65o433 +83.152 +96.722 +36.739 -123.952

298 -64»960 ^.575 +98.640 +37.431 -124.200

400 -64.577 +84.652 +980715 +37o087 -124.129

60C -63.772 +84.40.7 +98.427 +36.547 -123.945

800 -63.110 +34.008 +97^592 +35.635 -12. 779

1000 -650174 +83.449 +96.851 +34.560 -123.600

1200 -64.752 +82.822 -35.903 +33.366 -12;.415

1400 -64.451 +82.107 -r94«768 +32.069 -123.171

1600 -64.236 +81.324 +93.473 +30.703 -123.374

1800 -64.086 +80.486 +92.071 +29.289

2000 -63.983 +79.599 +90o571 +270838

2200 -63.908 +780673 +83.976

2400 -63c853 -^77.709 +870241

23.