The Reactions of Lithium with Nitrogen and Water Vapour By
The Reactions Of Lithium With Nitrogen
And Water Vapour
by
Wayne Ronald Irvine
A Thesis Submitted In Partial Fulfillment
' Of The Requirements For The Degree Of
Master Of Science
in the Department of
Mining and Metallurgy
We accept'this thesis as conforming to the standard required from candidates for the
degree of Master Of Science
Members of the Department of Mining and Metallurgy
The University Of British Columbia
April, 1961 In presenting this thesis in partial fulfilment of the requirements for an advanced degree at the University of British Columbia, I agree that the Library shall make it freely available for reference and study. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the Head of my Department or by his representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission.
Department of Mining and Metallurgy, The University of British Columbia, Vancouver $, Canada.
Date May 3rd, 196l ABSTRACT
The reactions of lithium disks with dry and moist nitrogen and with water-vapour were investigated at temperatures from 22 to 70 degrees Centigrade with the use of a thermal balance.
The reaction in nitrogen commenced with nucleation of lithium nitride at corners and edges of the sample and the reaction proceeded by lateral growth of these nuclei through the specimen. In moist gas, this reaction was accompanied by the simultaneous formation of lithium hydroxide at the plane surface of the specimen.
Based on visual observations of the samples during the reaction, a model describing the geometry of nucleus formation was constructed and was used to calculate growth velocities from the reaction curves obtained with the thermal balance.The dependence of growth velocity on temperature, nitrogen partial pressure, and the moisture content of the reaction gas was investigated.
The reaction with water-vapour was observed to proceed in three distinct stages.The results have been explained in terms of a model involving recrystallization and hydration of an initially coherent lithium hydroxide film.. ii'
ACKNOWLEDGEMENTS
The author is grateful for financial aid in the form of a Fellowship provided by the Foote Mineral Company„.
The supervision of Dr. J.A.»Lund and the technical assistance of Mr, R.. Go Butters, who constructed the recording balance, are gratefully acknowledged.
The author is indebted to Mrs1. Margaret Armstrong for her many helpful discussions.. Ill»
TABLE OF CONTENTS . Page
I a U\[ X RO D U O i. ION ooo«o«»oooooe«oeooe«oo"ooeooooooaoaoooo- 1 A* General Considerations * . o. , ...... « . . . <>. . .. I
Bw Previous Work with Lithium ....,..„...... „, 3
Co. Scope of the Investigation. „„„.„..„ . .. „ .0 » . . . 4 II. EXPERIMENTAL' PROCEDURE A.. Design of Thermal « Balanco © 6 • o eoo oan odo oAuxiliar o o o o o a oy o oo o o -o a a o
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C„. Procedure OOOOOOOOOO oo O © OO OO O OO O O O O .« O OOOO o o O 0 III, RESULTS FOR REACTIONS WITH DRY AND MOIST NITROGEN.. . 10i A'«. Reaction with Dry Nitrogen ...... '10-
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20 . Discussion of Results for the Reaction in Dry Nitrogen ...... 13 B. Reactions with Moist Nitrogen ...... 14 1.,-Effect of Reaction Temperature ...... • 1U • 2. The Effect of the Moisture Content of the Reaction
3o Effect of Partial Pressure', of Nitrogen .0 0 1-5 C Analysis of the Results Obtained Using
^iO.l St N 11 r O 1*1 000000 »ooooooooooeooooooo«OOoo 1^ 1... Analysis' of Results for Run in which Surface Nucleation was Abs,ent ...... 22 2. Analysis of Results for Ruin in which. Surface Nucleation was Present ."...... 24
D 9 DXSCUSSlOn 0.f R© SU.1 *t> S • ooooooo-oooooooooooooooo*' 0 I... Factors Influencing Nucleation Rate ...... 30 . 2„ Factors Influencing Growth' Rate <, ...... 31
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F 9 G OT^C 1U. S 10 IT S ooooooeoooocooooooooooooooooooooo 3 7 IV. REACTION! WITH WATER VAPOUR ...... 33 A. Reaction with-Dry and Moist Oxygen ...... 3'$ B„. Reaction with Water Vapour ...... 3$ •I.-General Characteristics of the Reaction....' 3$ 2. Comparison of Oxygen, Argon, and Helium as ' Carrier Gases; ...... 43 3:« Effect of Temperature ...... 43 4. Effect of Partial Pressure of
Welt©!*- VcH-pOU.!** ooooooo'oo 0000 oooo©ooooot> ©©000 A* C „ Discussion of Results...... 46 1, General Considerations ...... 46 2. The Effect of Partial Pressure of Water , in the Reaction Gas ...... 4$ 3 , Suggested Mechanism ...... 48"
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COridltlOn 000'©0000ft»00©00©0©»©0©0©»»0 0©0©0 iv. TABLE OF CONTENTS ( continued ).
page
2. Error in Temperature Measurement Due to Liberated Reaction Heat...... $2. 3. Zero 4. Errors due to Transport of Water Molecules to the Lithium-Hydroxide: Gas Interfere ... 53 E <> Conclu.sxoris • ©©©o©»»»©o©©©©i>«o V" 0* BIBL 10 GRAPH IT ooocoo°»*oooeo©o<»©«o«o90oao*o«<>*o<»««oo 55 56 V" X c* A.P PEN D I G E S 0000000© o»» ©©•••*»e©ooo»©oo©o»0o©»aoo ©• © • A,Appendix 1 ( Results for Reactions with Bo Appendix 11 ( Results for Reactions with Wcl t 6 IT" VS. POUT ) OOOOOOOGOOeOOOOOOOOOOOGOOVO'OO"* 66 V/. LIST OF FIGURES NO. Page 1. Schematic Drawing of Experimental Apparatus ...... 6 2 „ Photograph o f the Apparatus ...... 9 3-o Reaction Curve for a Rectangular Specimen Heated in Dry Nitrogen at 110°C 11 4.. Specimen Reacted in Dry Nitrogen at 110°C ...... 12 5» Specimen for which Reaction was Initiated in Moist Gas and then Continued in Dry Gas ...... 12 6. Specimen Reacted in Moist Nitrogen at 40°C 12 7«. Reaction Curves for Samples Reacted in Moist Nitrogen at Various Temperatures ...... 16 8. Reaction Curves for Three Samples Reacted in Moist 9o Reaction Curves for Samples Reacted at 40°C in Gases of Different Compositions ...... 1$ 10. Schematic Representation of Arrangement of Lithium Nitride During a Reaction ...... 19 11.. Graph of" Incremental Reaction Rate vs. Reaction Time for Samples Reacted at 45°C ...... 21 12. Graph Showing the Dependence of Interface Velocities on the Reaction Temperature ...... 23 13. Arrhenius Plots for Interface Velocities ...... 25 14. Hypothetical Arrangement of Lithium Nitride for a .Sample Reacted in Moist Nitrogen ...... 27 15. Dependence of Reaction Velocities at 45°C on Partial Pressures of Nitrogen and Water Vapour ...... 28 16. Effect of Nitrogen Partial Pressure on Reaction 17r Reaction Curves for Samples Reacted in Moist Oxygen at Various Temperatures ...... 39 18. Reaction Curves Obtained at 3 5°C in Moist Oxygen , Argon and Helium ...... 40 vie ' LIST OF FIGURES ( CONTINUED ) NO'. Page 19. Changes in Surface Appearance of Specimens in Relation to a Reaction Curve ...... 42 20.. Arrheniu:s Plots for Reaction Rate Constants ...... 44 21„ Dependence of Reaction Rate Constants on Partial Pressure of Water Vapour at 3 5°C ...... 45 Vllo LIST OE TABLES. NO.. Page APPENDIX 1 . lo Reaction Rates in. Dry Nitrogen at 110°C . „.„„..„„... 56 20 Reaction Rates in Moist Nitrogen at Various 1?G ffip6 IT S. t Q S oooooooooo«oo»oooooooooo»eo*ooo»o»oooo*o 57 3o Analysis, of Results of Runs in Moist Nitrogen ...„.„ 59 4. Effect of Nitrogen Partial Pressure on Reaction VQ lOClty cit A*5 G OOOOOOOOOOOOOOOUOOOOOOOOOOOOOOGOOOO 6 0 5» Effect of Water Partial Pressure on . ' Reaction Velocity at 45°C 000000000000000.00.0000000 60 6. Effect of Temperature and Gas Composition on Nucleat IO IT Rclt© 00000000000000000000 0000 oc 00 e o o • o * 00 6l 7. Relative Reaction Rates of Circular and Rectangular Sp 6 C 11716 3T S oooooooooooo»oocoooooooooocooooooo 000 00000 62 80 X-ray Diffraction Data for Specimens Reacted in Moist N 11T* O ^ 61"l St 5 G 0000000 0000000 oooooooooooooeoo*o«©»o ^3 9» Reaction Rates Occuring in Dry Nitrogen after Initiating the Run in Moist Nitrogen ...... 64 10o Analysis of Results for Runs Carried out in Dry Nitrogen after Initiating the Run in Moist Nitrogen .O.o„.ooo 65 APPENDIX 11 lo Weight Increases of Lithium Disks Reacted in Moist Oxygen at Various Temperatures ..... o o o...... ». 66 20 Summary of Results for Reactions in Moist Oxygen „„. 68 3. Weight Increases of Lithium Disks Reacted with Moist Helium at Various Temperatures .... . 0 ...... 0. 69 4. Effect of Water Partial Pressure on Reaction Rates.. 70 5. X-ray Diffraction Data for Specimens Reacted with WcX "tf © JT* Vcl pOU.37 oooooooooooo€.ooou«ooooooo#ooooooo»ooooO THE REACTIONS OF LITHIUM; WITH NITROGEN AND WATER V/APOUR I INTRODUCTIONS A. GENERAL C:ONSIDERA.TIQNS The reaction between a metal and a gas begins at the metal-gas interface and usually the reaction product forms an intermediate layer between the metal and the gas. The reaction may be regarded as involving a series of consecutive steps including, for example: 1. Transport of gas molecules to the reaction layer-gas interface. 2. Adsorption at the interface. 3. Diffusion of one or both of the reacting species across the reaction layer. 4. Chemical reaction to cause increased thickening of the reaction layer. Depending on the individual case, other steps would have to be added to the list above. Quite generally, however, the overall rate of a reaction which proceeds by several successive steps is determined by the rate of the slowest step and the determination of the rate-controlling step is one of the primary objectives of any investigation dealing with the oxidation of metals. Under normal conditions steps 1 and 4 above generally occur rapidly,and commonly the rate of adsorption or diffusion determines the overall rate of the reaction. 2.. The rate-controlling step, which applies under one set of conditions need not apply under another. For example, at low partial pressures of the reaction gas it is probable that the overall rate of the reaction is determined by the rate of transport of gas molecules to the specimen. The overall rate would be pressure dependent. At higher pressures, the surface might be completely covered by gas molecules and diffusion across the reaction layer would be rate-controlling and, moreover, the reaction rate would be pressure-independent, Even under a constant set of external conditions, reaction rates may change in response to physical changes .in the nature of the reaction layer. In this connection metals may be grouped into two classes according to whether the ratio of the volume of the reaction product to the volume of metal consumed in creating it is less than or greater than unity.. (1) In the former case the film is likely to be in a state of tension and might easily develop a network of cracks which extend almost but not entirely to the metal surface. The rate of oxidation is then controlled by the diffusion of the reactants through a thin continuous layer next to the metal. The outer portions of the layer are broken-up by cracks and the reaction rate is not influenced by the thickness of the layer and hence is constant with time. In the case of a metal for which the volume ratio is greater than unity, the film is in a state of lateral compression. According to Evans (2):,mechanical breakdown should assume the form of blistering when the adhesion of the layer to the metal surface is weak and of shear-cracking when adhesion is strong and cohesion is weak. In either case, failure of the film should lead to discontinuities in the reaction rate. Recrystallization is another mechanism through which a reaction layer might develop a network of cracks or flaws (3). In this connection it is considered that sufficient strain energy is' built up • in the reaction layer to provide a driving force for recrystallization. B. PREVIOUS WORK WITH LITHIUM The reaction of lithium with water vapour has been studied previously by Deal and Svee (4) but at higher temperatures and partial pressures of water than those employed in the present investigation. The reaction times employed did not exceed 2 hours and the reaction was found to proceed according to a logarithmic rate law. The rate constant was found to be independent of the water vapour pressure over a range 22-55 nun Hg. No lower limit to the pressure-independent region was observed since the lowest pressure employed was 22 mm Hg. The energy of activation for the reaction was 6.2 to 5.5 cal / mole depending on the water vapour pressure. It is reported (5) that lithium does not react with oxygen below l00°C,but that at higher temperatures it reacts rapidly. However, Yamaguti (6), employing an electron diffraction method, examined the surface products which formed on a fresh lithium surface after exposure to room air for 5 minutes and reported observing, mixed crystals of lithium hydroxide ( LiOff ) and lithium oxide (Li2 0) .. Belyaev et al, (7) studied the reaction of'lithium with moist air using a gravimetric method. They report that, for humidities greater than $0 percent the reaction products were lithium"hydroxide and carbonate. At lower moisture levels lithium nitride formed. A drop in the reaction rate was reported to occur at temperatures above 3 5 degrees Centigrade. The reaction of lithium with dry nitrogen between -50 and +'23'degrees Centigrade was studied by Frankenburger (9) who followed the reaction by measuring the drop In nitrogen •pressure in a closed system. The results suggested that the overall reaction rate from -50 to 4 5°C was controlled by the speed of the reaction (ie. the speed of actual chemical combination between lithium and'nitrogen atoms) but that from 5 to 23°C the rate was controlled by diffusion of nitrogen molecules through a porous lithium nitride layer which had formed uniformly over the surface of the specimen. C. SCOPE OF THE PRESENT INVESTIGATION The primary object of this investigation was to study the nature of the corrosion of lithium by certain gaseous atmospheres. It was originally intended to extend this study to lithium alloys,"tut the experiments with the pure metal proved to be sufficiently demanding in themselves. II EXPERIMENTAL: PROCEDURE A. DESIGN OF THERMAL BALANCE AND AUXILIARY APPARATUS j The reactions were followed by measuring the increase in weight of a sample during the course of the reaction. The apparatus used is shown diagramatically in Figure 1. The specimen was contained in an aluminum basket lined with platinum gauze which'was suspended inside a glass reaction vessel by means of a chain-attached to the balance arm. The reaction vessel was immersed in a constant temperature bath. The reaction' gas was preheated in a copper spiral before entering the reaction vessel. The temperature was measured with,a thermocouple and controlled to within X0.2 C using a mercury thermoregulator positioned in the oil bath. A stirrer was used to ensure uniformity of temperature within the bath. Cylinder gases were employed for all the reactions studied. For reactions, involving nitrogen, the gas was passed over copper chips at 400°C to remove oxygen. Whenever required, the gases were dried in a column of molecular sieves. For reactions involving the use of moist gases, the moisture content was controlled by bubbling the gases through a water tower and then through bubble towers containing ice water or saturated salt solutions maintained at 206C. The solutions used and the corresponding equilibrium! water partial pressures were; lithium chloride solution ( 2.6 mm Hg), ice water (4.6 mm Hg), potassium thiocyanate solution( 8.2 mm Hg) and ammonium chloride solution (12.6 mm Hg), Balance Dry Box Gas Inlet emperature Regulator Spiral Immersion Heaters Figure 1. Schematic Diagram of Apparatus. Flow rates were controlled with calibrated capillary flow meters. To obtain gas mixtures, a sepera.,e flow meter was used for each gas and the gases were mixed in a vessel situated in the line immediately before the moisture saturation. A Chainomatic balance was employed for the studic Provision for automatic recording was made by using two opposed photoelectric cells situated behind avented vane mounted xat the end of the balance pointer. The imbalanced voltage from^the photocells was used to drive a Minimax recorder. Mechanical linkage between the recorder and the balance was provided by a pair of synchro-motors, one of which was geared to the drive-shaft of the recorder and the other to the chain drive of the balance. The 'accuracy of the balance, assessed by using calibrated weights to drive the balance up and down scale, was within-*: 0.3 milligrams. B. SPECIMEN PREPARATION. The lithium used was obtained in the form of a cast 1 pound ingot from the Foote Mineral Company. The manufacturer's chemical analysis with respect to potassium and sodium was 340 and 70 ppm respectively. The ingot v/as sectioned, and pieces were die-pressed into rectangular blocks 2"x l"x 0.6". The blocks were cleaned by immersion in a methyl hydrate-benzene solution and were then stored in a glove-box under an atmosphere of argon. Specimens used in the experiment were prepared in the glove-box by cutting wafers approximately .040 inches in thickness of rom the rectangular slabs prepared previously,. Piano wire .006 inch in diameter was used for the cutting operation. Circular disks were then cut from the wafers with the aid of a cork-borer. The disks were washed in lithium- dried benzene before being introduced into the reaction vesselo Co. PROCEDURE The specimens were positioned in the basket and lowered into the reaction chamber which was charged with the reaction gas. A period of approximately 2 minutes was required before the first, weight reading could be taken. Weight gains which occured: during this period were not recorded. Circular disks were used for most of the experiments, but for runs in which it was desired also to observe the condition of the specimen surface, rectangular specimens were used. These specimens were supported from a platinum hook and periodic visual observations were made by momentarily lifting the specimen to the upper part'of the reaction chamber. Generally, reactims involving nitrogen were followed "to completion while those involving water vapour were followed for approximately 24 hours. However, some runs ' were interrupted in order to obtain photographs of the samples. 9* The reaction products were identified with the aid cf an X-ray diffractometer. During analysis, the specimen surface was protected from further reaction by a light coating of paraffin wax. Some diffraction lines from the wax coating were always observed but these were easily identified1. Ill RESULTS FOR REACTIONS IN DRY AND MOIST NITROGEN Ao REACTION WITH DRY NITROGEN lo Results Specimens were reacted with dry nitrogen at 110°Co Weight-time data are tabulated in Table 1 of Appendix I. A typical reaction curve is shown in Figure 3• The shapes of the reaction curves were characteristically alike,involving a period during which no weight increase was observed followed by a period during which the rate of the reaction increased sharply to a maximum value and then gradually decreased to zero o During the initial period of zero weight increase, the surface of a specimen, remained untarnished. However, soon after weight increases were recorded massive patches, reddish-brown in colour were' visible at corners' and edges of a rectangular specimen. These patches' extended through the thickness of a specimen, and as the reaction proceeded they grew radially across the specimen. The surface appearance of a specimen early in a run is shown in Figure 4. Several runs were made at 110*C, and in all cases nuclei were formed preferentially at corners or at the edges of a specimen. Nucleus formation remote from the edges was never observed. The reaction product was analysed using an X-ray diffractometer and the results are given in Table 2 of Appendix I All calculated "d" spacings. correspond to the values given in the A- S. T.. M. file for lithium nitride ( Li, Ni ). 11. 2h0 0 50 100 150 200 250 300 Reaction Time (minutes) Figure 3» Reaction Curve for a Rectangular Specimen Heated in Dry Nitrogen at 110°C. 12 Fi gure 4« Specimen Reacted in Dry Nitrogen at 110 G. x 1«5 Figure 5. Specimen Reacted in Moist Nitrogen at 40 C (Pli 0« 4.6 mm Hg. ). x 1.5 Figure 6^. Reaction Initiated in Moist Nitrogen at 40 G and then continued in Dry Gas. x L5 13.. .2, Discussion of Results for the Reaction in Dry Nitrogen. In a previous study of the reaction between lithium and dry nitrogen (9), lithium nitride was observed to form uniformly over the surface of the specimen. The reaction apparently proceeded by diffusion of nitrogen molecules' through a porous, but gradually thickening, lithium nitride layer. An incubation period was not observed, but in other respects the reaction curves were similar in shape to those obtained in the present studies. The period of increasing rate was interpreted as corresponding to the formation of lithium nitride over the plane surface of the specimen. The period of gradually decreasing rate was interpreted as resulting from the gradual increase in the length of the diffusion path for nitrogen molecules as the reaction proceeded. In the present investigation, lithium nitride was observed to form by a process of nucleation and growth. Nucleation occured preferentially at the edges and corners of the specimen. The nitride then formed by lateral growth across the specimen, and hence the length of the diffusion path for nitrogen molecules was constant throughout the duration of the run. Thus the previous results are distinguished from those of the present investigation in that, in the former case " nucleation " may be regarded as having occurred randomly over the surface of the specimen. This result is surprising in view of the fact that distilled metal had been employed„ A kinetic analysis of the present results using weight gain vs. time data alone was impossible, because the 14, . formation of nitride nuclei was random with respect to time. A kinetic analysis would require measurements of radial growth-velocities for individual nuclei. It was decided to employ -moisture additions to the reaction gas to determine whether or not a uniform surface•reaction would result. B. REACTION WITH MOIST.NITROGEN Whereas reaction curves for runs carried out in dry nitrogen exhibited an-initial period during which no weight increase was recorded, those for runs in" moist nitrogen rose immediately upon beginning the run. The initial weight increases were associated with the formation of a glassy black film over the.entire surface of the specimen. X-ray .examination identified the film as lithium hydroxide (Li-OH)., Early during the runs, the reaction curves rose steeply, corresponding to the appearance- of nitride nuclei at the edges of the specimens. Unlike the case for specimens reacted in dry nitrogen, however, nucleation occured all along the edges and, for a circular disk led to the formation of a nearly perfect ring around the periphery of the specimen. A photograph of a rectangular specimen showing the black hydroxide layer and the lithium nitride ring about its periphery is shown in Figure 5. Nucleus formation on the plane surfaces of a specimen was commonly observed and is visible in Figure 5» 1. The Effect of Reaction Temperature Specimens were reacted with moist nitrogen ( partial pressure of water 4.6 mm Hg. ) at temperatures 15. from 22 to 70 degrees Centigrade. The results are given in Tables 2 and 3 of Appendix 1. "Because the thickness of the circular disk varied from specimen to - specimen, the total weight gains exhibited for reactions carried to completion also differed. Hence, in order to allow graphical comparison of the results, the curves have been re-plotted with the.percentage of the specimen transformed as the ordinates against time as abscessa.'Typical curves so obtained are -shown in Figures 7 and. 6\ 2... . The Effect, of the Moisture Content of the Reaction Gas. Specimens were reacted at 45°C with nitrogen gas at various moisture levels. These results are given in Table 5 of Appendix 1. • Also, some runs were carried out in which moist nitrogen was used to obtain a nearly perfect ring of nitride around the perimeter of a specimen. Then, dry nitrogen was flushed through the system and the specimen was reacted to completion•in dry gas. This procedure was effective in ssoapressing the formation of surface nuclei. A photograph of a rectangular specimen treated in this manner is shown in Figure 6. The results of these experiments are given in Table 9 of Appendix 1 and are shown graphically in Figure 9. 3. Effect of Partial Pressure of Nitrogen Using a constant moisture content (2.6 mm Hg) and a constant temperature (45°C) specimens were reacted in nitrogen-argon gas mixtures at various nitrogen partial pressures^ The results are given in Table 4 of Appendix 1 and some reaction curves are included in Figure 9« 0 50 100 150 200 250 300 Reaction Time (minutes) Figure 7• Reaction Curves for Samples Reacted in Moist Nitrogen at Various Temperatures. ( Pllgo = 4,6 mm. Hg) 17- 50 100 150 200 250 Reaction Time ( minutes ) Figure 8- Reaction Curves for Three Samples Reacted in Moist Nitrogen at koOC ( PH20 = k.6 mm. Hg ) 18. 19. C. ANALYSIS OF THE RESULTS USING MOIST NITROGEN fb a first approximation, the results should conform to the simple geometric model shown in Figure 10. Figure 10. Schematic Representation ( Ignoring Nucleation Remote from the edges of a Specimen ) of the Formation of Lithium Nitride during a Reaction. A concentric ring of lithium nitride is observed to form around the periphery and to grow radially across the specimen. At any particular reaction temperature, the velocity at which the interface advances may be considered to be constant and represents the rate constant for the reaction. ( It is assumed that the interface velocity corresponds to';*the radial growth velocity of an individual nucleus ). During-an interval of time t to t+ At the interface advances a distance/iir giving rise to a weight change Aw, where dw= [trr2 - TT(r - dr)2]h (P Li-^N - /Li) 20. where h is the thickness of the disk and /^Li^N and /-*Li are respectively the densities of lithium nitride and of lithium. This expression, neglecting square terms in Ar, reduces to Aw = 27rrAr x (PlijN - />Li)h The distance, r, of the nitride-metal interface from the centre of the disk at any time t is given by r - R - Vt where R i.s the diameter of the disk. Substituting this value- for r in the above equation the following expression for the weight increment in time At results: ) Aw = (27TRAr - 2 TT vt Ar) (/ Li3N - y°Li)h whence (-^r)t = - 2 Tfvt ^£) (/°Li3N - />Li)h A T or since J~ *> V A t ( } = (27rRV 2 2 5 T? t " TrV t)(/ Li3N - >PLi)h which, divided through by 7fR2h (/^Li^N - /°Li)h gives transformed _v _ a _ ^ At. t 2 where a = ' and b = Thus the geometric model considered above requires that a plot o.f the slopes of the reaction curves at various times during the reaction against time should give a straight line. This'requirement was tested using experimental data with results as shown in Figure 11. 21, ,' 116.4 I Reaction Time (minutes) Figure 11. Reaction Rate vs. Reaction Time for Samples Reacted at 45°C. 22. The results of runs carried out entirely in moist . nitrogen do not conform to the phenomenological relationship because surface nuclei formed during the experimental runs but were diregarded in the geometric model. However, for runs in which a shift to dry gas was made before surface nuclei could form, the curves rise sharply to a maximum and then decrease at a constant rate. The period of increasing rate corresponds to the period during which a roughly concentric ring of nitride was forming and the results fit the theoretical relationship increasingly better after the nuclei impinge and then grow inwards-., It is appargnt that from the above considerations that, whereas runs carried out partly in dry nitrogen can be treated adequately in terms of a simple geometric model, further elaboration is required to analyze the reaction curves obtained using moist nitrogen only and for which surface nucleation was involved. 1. Analysis of Results for Runs in Which Surface Nucleation' Was Absent. These runs include those in which a shift was' made from moist to dry gas early during the reaction. The reaction curves were analyzed in terms of the simple geometric model described above. Curves, similar to those shown in Figure 14 were constructed from the reaction curves and the constant 2. 2 b (= 2v / R ) was determined from the linear portions of these graphs..Interface velocities were then calculated and the results are listed in Table 10 of Appendix 1 and are shown graphically in Figure 12. The interface velocities 23. Figure 12. Dependence of Interface Velocity on Reaction Temperature. 24* rose quite rapidly with increasing temperature but it was impossible to extend the data beyond 50°0 because above this temperature extensive surface nucleation gave rise to reaction curves which could not be analyzed in terms of the geometric model. An Arrenhius plot of the logarithms of interface velocities against the reciprocals.of the absolute reaction temperatures is shown in Figure 13. The data conform to a linear relation and the corresponding activation energy is equal to -7,300 calories per mole of lithium nitride formed 2, Analysis of Results of Runs in Which Surface Nucleation was Present. Surface nucleation of lithium nitride was an important factor in all the runs carried out in moist nitrogen Figure 8 shows transformation-time data for three runs carried out at 40°G. In one run the maximum reaction rate attained was considerably greater than in the other runs, and it is considered that a greater number of surface nuclei are responsible for the increased rate. Discrepancies of this type were observed in duplicate runs at all temperatures and since the number and distribution of surface nuclei in each case are unknown, a geometric analysis of the kind used previously is impossible. In spite of these difficulties, however, some quantitative data should be obtainable from the transformation time curves since the approximate geometric arrangement of nuclei early during a reaction is known. That is, nuclei form first at the periphery of the specimen, and during the early part of the reaction most of the weight-gains recorded are due 25- Figure 13. Arrenhius Plots for Interface Velocities. 26. to these nuclei rather than to surface nuclei which form, later. Thus in Figure 8" referred to previously, the slopes of the reaction curves at the 20 percent transformation points are approximately equal, even though the curves deviate at later stages.- Ignoring surface nuclei the fraction, f, of the sample transformed to nitride at any given time is f - 1 ^ where r is the inner radius of the nitride ring at the time in question and R is the original radius of the lithium' disk ( = 6.66mm. for all specimens). Differentiation of the above expression gives df = _2r _dr_ dt " R2 dt dr The quantity is the interface velocity, V. then -df = i& v In order to include the contribution to the overall reaction rate of nuclei which form at the surface, a correcting term would have to be added to the above expression. However, at the time corresponding to 20 percent of complete transformation the contribution made by surface nuclei is small and'the equation above can be taken to describe the reaction. At this point the expression above reduces to mm m±n V = 3.73 (•^*)f_0 2 / ° 27- Figure 15• Effect of Nitrogen Partial Pressure on Eeaction Velocity. 29. Figure 16„ Hypothetical Arrangement of Lithium Nitride for a Sample Reacted Partially to Completion in Moist Nitrogen. Thus for all reaction curves obtained by using wet nitrogen only, slopes were measured at.the point corresponding to 20 percent'of complete transformation. Interface velocities were calculated and were given in Tables 3 and 4 of Appendix 1. The results are presented graphically in Figures 12, 13, 15 and 16. As shown in Figure 12 the interface velocity rose o rapidly from 25 to 50 C but dropped with further increase in temperature. The activation energy for the reaction between 25 and 50°C was 11,500 cals. per mode of lithium nitride formed. 30. D. DISCUSSION OF RESULTS 1, Factors Influencing Nucleation Rate The rate of formation of nitride nuclei depended on several factors including the surface condition of the sample, the reaction temperature and the composition of the reaction gas. It has been mentioned previously that nitrogen nuclei formed preferentially at sites of high surface energy such as the edges and corners of a specimen. For duplicate runs under the same apparent conditions the number of surface nuclei which formed varied from specimen to specimen. This result probably derived from the presence of areas of high surface energy such as scratches at the surface of the specimen. It appears therefore that the contribution of surface energies to the thermodynamic free energy required for nucleation was a dominant factor. That surface energies should exert an important influence is generally indicated by a consideration of the widely different lattice constants for lithium nitride ( cubic; a= 5.50 ), and lithium ( body- centred-cubic; a= 3«50 ) It is significant that nucleation of lithium nitride was promoted by the presence of water vapour in the reaction gas ( and hence of lithium-hydroxide at the surface of the specimen ). The free energy for nucleation of lithium hydroxide on a lithium surface should involve a relatively small surface - energy component ( lithium hydroxide is tetragonal with a= 3.55 and c=4.34 compared with the body- centred cubic lattice of lithium with a = 3.50). It is not unlikely that nitride nucleation was promoted by the presence of lithium hydroxide by some mechanism involving surface energies* However at high reaction temperatures or for high partial pressures of water in the reaction gas, nitride nuclei did not form and the lithium —»• lithium-hydroxide reaction predominated.(Consideration of the relative chemical free energies involved indicates that the reaction lithium nitride plus water —»• lithium hydroxide should occur. This reaction did not proceed under the conditions studied; however, a pulverized lithium nitride' sample in the laboratory atmosphere did react to lithium hydroxide over a period of weeks.) 2, Factors influencing growth rate. In moist nitrogen two simultaneous reactions were - involved. Lithium nitride formed by a process of nucleation and growth while lithium hydroxide formed independently at the plane surface of the specimen. The arrangement of the phases during the reaction is shown in Figure 16. This model is based upon visual observation and x-ray diffraction data and suggests the following sequence of reaction steps: 1. ) Transport of nitrogen molecules to the gas phase- lithium hydroxide interface. 2. ) Adsorption of nitrogen molecules at the interface. 3. ) Dissociation and diffusion of nitrogen in the atomic form across the hydroxide layer. 4. ) Diffusion through ( porous ) lithium nitride or through lithium metal to the reaction Interface. 5. ) Chemical combination at the interface. It is desired to determine which of these steps is the slowest and hence the rate controlling step for the reaction. Step- 1 normally occurs rapidly and is unlikely to control the reaction rate. The results to be interpreted include: 1. ) The general shape ( Figure 14 ) of the curve showing the dependence of growth velocity on the partial pressure of water vapour in the reaction gas. The curve rose slightly with an increase in water pressure from 2.6 to 4.6 mm-Hg. and then dropped rapidly with further increases in the aqueous tension. Nucleation did not occur in dry gas or at a water pressure of 12.6 mm Hg. 2. ) The general shape ( Figure 12 ) of the curve of reaction velocity against the5reaction temperature for moist gas. This curve increased rapidly at temperatures from 25 to 50°C but dropped with further increases in temperature. 3. ) The fact that the growth velocities in moist gas were higher than those which obtained when a shift was made to dry gas after initiating the run in moist gas. ( Figure 12 ) 4. ) The dependence ( Figure 15 ) of the curve showing the dependence of growth velocity on the partial pressure of nitrogen. At 45°C and with a partial pressure of water of 2.6 mm Hg., the reaction velocity increased with the square root of nitrogen partial pressure. 33. First consider the curve in Figure 14 showing the dependence at 45°C of the interface velocity on the moisture content of the reaction gas. These velocities decreased rapidly for partial pressures of water in excess of 2.6 mm Hg0 This result'suggests that the rate of formation of lithium nitride is controlled by the rate of diffusion of nitrogen atoms across the lithium hydroxide layer at the surface of the specimen. It is shown in the next section that the rate of thickening of the hydroxide layers increases with increasing partial pressures of water vapour. Consequently, for a particular stage of the lithium nitride reaction, the length, of the diffusion path for nitrogen atoms across the lithium hydroxide barrier increases with increasing water pressures. If diffusion across this barrier is the rate controlling step for the reaction, then the rate should decrease with increasing water pressure as observed. Two other results support the notion that diffusion across a lithium hydroxide barrier is rate-controlling. As is shown in Figure 12, interface velocities decreased at temperature above 50°C. This result is considered to derive from the fact that the hydroxide film thickened more rapidly at higher temperatures. Again, in Figure 15 the interface velocity is shown to depend upon the square root of the nitrogen partial pressure. This behavior is characteristic of cases in which a diatomic molecule dissociates on absorption and then diffuses in the atomic form. It is likely that nitrogen would diffuse through lithium hydroxide in the atomic form and hence the result above conforms to the notion of a 34. reaction controlled by the rate of diffusion across a lithium hydroxide layer at the surface. On the other hand some of the results oppose this conclusiono The growth rates which were observed >/hen a shift, was made to dry gas after initiating the run in moist gas were lower than those which were obtained when the reaction was carried out entirely in moist gas. In the fonac • case, the hydroxide layer was thinner and the rates should have been much higher. A possible explanation for this discrepancy follows from a consideration of the heat liberated during the reaction It is shown in the section concerned with analysis of errors that a considerable amount: of heat is liberated and that a significant.difference between the measured ( reaction gas ) temperature and the actual reaction ( interface ) temperature could be expected. It may be presumed that the thicker hydroxide'layer present when the reaction was carried out entirely in moist gas presented an increased resistance to the dissipation of heat to the reaction gas. This would result in higher temperatures at the reaction interface and correspondingly faster rates.-A difference in temperature of 10°C would account for the difference in the rates shown in Figure 12 and this is not impossible. Experimental activation energies of 7,300 and 11,300 cals were observed according to whether the runs were made partially in dry gas or entirely in moist gas. In the former case the thickness of the hydroxide layer was approximately the same regardless of the reaction temperature 3 5-. ( the shift to dry gas was made at a time corresponding to a weight gain of 5 percent of the total expected increase ). However for specimens reacted entirely in moist gas the thickness of the hydroxide film increased with the reaction temperatureo The resultant increase in the diffusion path for nitrogen atoms across the barrier thus accounts for the increased activation energy. E. SOURCES OF ERROR The geometric model employed in order to determine interface velocities was an approximate representation of the actual arrangement of lithium nitride nuclei during the reaction. Variations in the experimental values must therefore be expected but reasonable reproducibility was realized. For example, the calculated interface velocities for four P o runs in moist ( H2O = 4»6 mm Hg.) nitrogen at 40 C were 0.010, 0.010, 0.0090, and 0.00&7 mm./min. Another source of error resulted from the weight increases associated with the formation of lithium hydroxide over the surface of the specimen. This contribution to the overall weight change was ignored when calculating interface velocities. However, a simple calculation ( in terms of the measured rates for the hydroxide reaction as described in the next section ) shows that the calculated growth velocities for the nitride reaction are in error by less than 5 percent due to this factor. A further source of error becomes apparent by a consideration of the rate at which heat is evolved during the reaction. The heat liberated during the reaction 3 Li + 5 —*- Li-^N is 15.7 k cals per mole of lithium. For a standard specimen 0.1 cm. in thickness it is.readily shown that, at-the time for which the reaction is 20 percent complete, the rate at which heat is liberated is given by Q ( cals/mln ). = 445 V (cals/min ) where V is the interface velocity expressed in cm/min. For the reaction in moist ( ^H20 - 4.6 mm Hg. ) nitrogen the reaction velocities;; at 25 and 45°C were respectively .0011 and . .0042.. cm/min. Then during one minute the heats liberated for the reactions at 25 and 45°C are respectively 0.49 and 1.8*7 cals;.. These amounts :-of heat if distributed without loss throughout the unreacted•portion of the specimen ( .specific heat of lithium metal - 0.96 cals/gram ) are sufficient to cause a temperature increase of 9 or 34 degrees Centigrade respectively. Such drastic temperature increases would not actually occur because most of the reaction heat would be transferred to the gas. However, the reaction occurs at an interface of relatively small area and it is likely that the temperature increase at the interface would be considerable. In all the experiments therefore, the actual reaction temperatures ( at the lithium-lithium nitride interface ) were greater by unknown amounts than the measured temperature ( ie. the temperature of the reaction gas ). This source of error could drastically influence the shape of the reaction rate vs. " temperature " curve as suggested in the discussion. 37. F. CONCLUSIONS The reaction of lithium with nitrogen proceeds with nucleation and growth of lithium nitride. The presence of moisture in the reaction gas promotes nucleus formation but also leads to the formation of lithium hydroxide at the plane surface of the specimen. The results suggest that the rate of nitride formation is controlled by diffusion of nitrogen atoms across the lithium hydroxide layer. IV REACTION WITH WATER VAPOUR A. . REACTION WITH DRY AND MOIST OXYGEN A specimen heated in dry oxygen at 40°C exhibited! no increase in weight over a period of 16 hours. In agreement with this observation, it is reported that lithium does not react with dry oxygen below 100°C although it reacts rapidly at higher temperatures. (5) It is shown later that, so far as X-ray diffraction data could show lithium oxide did not form in moist oxygen at temperatures from 22-42°C, but that, instead, the reaction product was lithium hydroxide. Accordingly, runs carried out in moist oxygen are reported below as reactions with water vapour and oxygen is classed with argon and helium as an inert carrier gas. B. REACTION WITH WATER VAPOUR 1. General Characteristics of the Reaction Some typical reaction curves obtained using moist ( ^^0 = 4.6 mm Hg. ) oxygen at temperatures from 2 5 to 40°C are shown in Figure 17. A comparison of the reaction rates in moist oxygen, argon and helium is made in Figure 18. It is apparent from these curves that the reaction proceeded in three distinct stages:. 1. ) an initial stage, in duration lasting from 3 to 4 hours and in which the reaction rate was approximately constant. 2. ) an intermediate stage during which, over a period of 50 o Reaction Time (minutes) Figure 18. Reaction Curves for Specimens Reacted in Moist Gases at 35°C ( PR2O = k-6 mm. Hg* ; Specimen Area = 2,79 on?*)- 41.. 1 to 4 hours depending on the temperature, the reaction rate increased continuously. 3.) a third stage during which the reaction proceeded at a constant rate approximately l| times that of the initial stage. Visual examination of the specimens revealed a characteristic sequence of changes in the appearance of the specimens which corresponded with the observed changes in reaction rates. Some runs were interrupted in order to obtain photographs of the samples and these are shown in Figures 19a-e. During the initial stage of approximately constant rate, the specimens acquired a black glassy tarnish (Figure 14a) reminiscent cf the surface film which has been observed to form in moist- nitrogen. At a time corresponding approximately to the commencement of the intermediate ( rate-increasing ) stage, a white reaction product formed on the surface of the specimen. This product often formed first at the edges of the specimen and grew laterally across the surface. Photographs are shown in Figures 19 b and d. The final stage of constant rate commenced when the entire surface was covered with the white product ( Figure 14c ) which then thickened uniformly over the surface as the reaction proceeded. The specimen swelled slightly during this period and the appearance of a specimen oxidized to completion is shown in Figure 19e. The grea.tly enlarged size of the specimen at this stage is to be noted. X-ray diffraction patterns were obtained of the reaction film at various stages of the reaction and these Reaction Time Figure 19* Changes in Surface Appearance of Rectangular and Circular Specimens in Relation to a Typical Reaction Curve. 43. results are given in Tables 5 and 6 of Appendix 11. For the black film characteristic of early stages of the reaction, the calculated d spacings for each of the diffraction lines compared closely with those given for lithium hydroxide ( LiOE ) in the A..S.T.M.card files. The white layer which was present at advanced stages gave two sets of diffraction lines corresponding to lithium hydroxide ( Li OH ) and lithium monohydrate ( LiOH • H2O ). A sample reacted to completion at P 35°C ( H20 = 8.2 mm. ) was entirely LiOH * H20 2. Comparison of Oxygen, Argon and Helium as Carrier Gases. Although the initial reaction rates -for runs carried out in moist argon or oxygen were very nearly constant, those for helium were more rapid at first and decreased slightly as the reaction proceeded. It is considered that, some separation of helium and water occured which resulted in increased partial pressures of water in the reaction tube. The results'for all runs carried out in moist helium are included in Table 3 of Appendix 11 but are considered untrustworthy and are not included in the discussion of results. 3. Effect of Temperature. Lithium specimens in the form of circular disks were reacted with moist oxygen at temperatures from 22-42°C and the results are summarized in Table 2 of Appendix 11. Graphs ( Figure 20 ) of the logarithms of the rate constants against the reciprocal of the absolute reaction temperature gave straight lines in accordance with the.. Arrhenius relationship. The activation energies for the reaction were respectively 11,700 and 7,700 cals. for the Vapour Pressure. 46.. initial and final stages respectively. 4o Effect of the Partial. Pressure of Water Vapour Samples were reacted at 35°C in.argon gas saturated to give moisture levels of 2.6, 4.6, S.2 and 12.6 mm Hg. All reactions displayed, the three characteristic stages as before. The reaction rate constants were determined and a graph showing- the dependence of these rates on the partial pressures of water is shown in Figure 21. In another run, a specimen was reacted in moist (4.6 mm. Hg.) oxygen at 35°C until the white product characteristic of an advanced reaction had formed. A shift was then made to dry oxygen. The rate dropped to zero thus indicating that lithium oxide would not form under these conditions. Co DISCUSSION OF RESULTS 1. General Considerations It was mentioned earlier that the white product which first appeared during the "intermediate" stage of the reaction, formed first at the edges of the specimen and then spread inwards across the face. This- behavior suggests that a recrystallization process is involved. The occurence of recrystallization implies :that the initial film was in a state thermodynamically less stable than the recrystallized product. From a comparison of the lattice constants of lithium hydroxide ( tetragonal; c = 4".34 A, a = 3.55 A ) and lithium .( cubic; a = 3 • 50 A ) it is at least possible that the initial film was coherent with the underlying 47. metallic lattice. Such a film would necessarily be in a state of lateral compression and as the film thickened the gradual increase in strain energy might provide a driving force for recrystallization. • Another important result was that, whereas the initial black film was entirely lithium hydroxide ( LiOH ), the recrystallization layer incorporatedamounts of lithium monohydrate ( LiOH°H20 ). A considerable increase in the compressive stresses acting on the lithium hydroxide film should accompany hydration and these stresses may have provided an additional.driving force for recrystallization. Although the disposition of lithium hydroxide and monohydrate in the recrystallized layer could not be inferred from the X-ray diffraction data obtained, it is reasonable to suppose that a concentration gradient with respect to water of hydration existed such that the outer portion of the layer was essentially lithium monohydrate while the' inner portion was lithium hydroxide. At completion of a reaction ( at least for a partial pressure of water of 12.6 mm ) the entire sample had transformed to lithium monohydrate. The relative magnitude of the reaction rates at advanced stages can be explained from the above considerations. The increase in weight due to hydration of the hydroxide film may be considered to proceed at a constant rate which is superimposed upon the initial rate. Then the new rate would be approximately 2 times the initial rate. In Tables 2 and 4 of Appendix 11 it is shown that the ratios of final 48. to initial reaction rate constants vary from 1.3-1.9, the higher values being associated with low reaction temperatures. The only exceptional result is the value of 3.1 which obtained at 3 5°C and at a water partial pressure of 2.6 mm Hg. The latter result was obtained in the region of extreme pressuredtpendence and its significance is not understood. 2. The Effect of the Partial Pressure of Water in the Reaction Gas. In a previous investigation concerned with the reaction of lithium with water vapour (4) it was reported that the rate constant for the reaction ( the initial rate constant only was determined ) was pressure independent at moisture levels from 22-55 mm Hg. The rates increased with pressure above 55 mm Hg but a lower limit to the pressure range was not encountered, the lowest pressure investigated being 22 mm Hg. For the present study, the dependence of the reaction rate constants on the partial pressure of water in the reaction gas is shown in Figure 21. The rate constants for both the initial and final stages of oxidation increased rapidly with pressure in the range 2.6-4.6 mm Hg but with further increases in pressure the rate constants appear to increase according to a linear relationship. 3. Suggested Mechanism It is desired to determine the rate controlling step for the reaction. Early during the reaction the consecutive steps involved should include: 1.) transport of water molecules to the lithium hydroxide- gas interface. 49 o 2. ) adsorption at the interface. 3. ) diffusion through the hydroxide layer. 4. ) adsorption at and reaction with lithium at the interface. Later during the reaction another step, that of lithium hydroxide to lithium monohydrate, must be considered but this step may be assumed to proceed independently. Now, if step (1) above were rate controlling, then the rate of the reaction would be controlled by the rate of impingement of water molecules onto the specimen surface and a linear^rate law would be expected to persist throughout the reaction. However since the rate actually increased at a later stage, it must be concluded that step (1) is not rate- controlling. It is likely that step (3) above may also be eliminated as rate-controlling. It is reported (4) that the reaction of lithium with water vapour in the pressure range 22-100 mm. proceeds according to a logarithmic rate law and, moreover, that the rates were pressure-independent in the • range 22-55 mm. Hg. These results were interpreted in terms of a diffusion-controlled reaction and,if this interpretation is co'rrect, the present results at low partial pressures of water preclude diffusion through a hydroxide film as the rate-controlling step for the reaction. It should be pointed out that the previous investigators followed the reaction rates by measuring the increase in pressure in a static system due to hydrogen evolved during the reaction LitH2P —*• LiOH+ gHl, Although the investigation was concerned only with the early stages of the reaction during which, according to the present i 5.0). results, no lithium monohydrate was formed it is clear +-hat the method used could not have sensed that the reaction LiOH + H2O —>LiOH was occuring simultaneously. The authors state that " with the appearance of the white product, the rate of the-• reaction becomes completely unpredictable This observation is significant because no such unpredictability was encountered in the present studies. It now seems likely that a network of cracks developed in the film during recrystallization. If diffusion across the film was rate- controlling then the development of cracks on the film would certainly disrupt the reaction rate as observed previously. That no disruption was observed offers further support to the conclusion that diffusion was not rate-controlling at the low water levels employed in the present investigation. Referring back again to the reaction steps involved , it seems likely that, besides steps (1) and (3), step (4) is not rate-controlling because actual chemical reactions normally proceed rapidly. • It' is probable then that the rate of the reaction was limited by the rate of uptake of water molecules at the surface of the specimen. The reaction rate vs. water partial pressure curve gives general support to this notion. It can be shown (£), using the Langmuir Adsorption Isotherm that the rate of uptake of gas molecules ( which then diffuse into the body of the material ) depends on the equilibrium betweem the rate at which gas molecules condense onto the surface and the rates of evaporation away from the surface ( either back to the gas phase or into the body of the material ). At 51.- equilibrium the fraction, Q , of the surface covered with water molecules is given by the expression e -- 06 u v+»<:u where u is the number of molecules c&tmilfciiBg; unit area of surface per second, c*C is the proportion of these molecules which adhere ( the accomodation coefficient ) and v is a constant for a given gas and surface. The rate, u , at which molecules strike the surface is directly proportional to the gas pressure. Hence, the expression above may be written << P e = k v+<< P which has the limits Q - k —<^=. p at low pressures v or Q - k at high pressures. That is, at low temperatures for which the specimen surface is only sparsely covered by molecules the proportion of the surface actually covered ( and hence the reaction rate ) is directly proportional to the gas pressure. The reaction between lithium and water vapour was pressure dependent at partial pressures from 4.6 to 12.6 mm. Hg. At higher gas pressures the specimen surface is completely covered by water molecules and the reaction rate becomes independent of gas pressure as observed by Deal and Svec for partial pressures of water above 22 mm. Hg. However, considerations above do not account for 52. the fact that water molecules were available in sufficient amounts to allow the formation of lithium monohydrate. In-order to account for this result it is necessary to presume that the accomodation coefficient ,°<, increases up< n. recrystallization of the lithium hydroxide film to alloxv a greater number of water molecules to condense at the surface. The overall reaction rate then increases with the formation of lithium monohydrate at the specimen surface. D. SOURCES OF ERROR 1. Errors due to Variations in Surface Condition. The geometric areas of the samples were used for calculating rate constants. Although the geometric areas were less then true areas by an unknown amount' ( the roughness factor ), the results were reproducible and it is assumed that all specimens possessed the same roughness factor. Then, although this source of error affects the values of the measured rate constants, it would not affect the experimental activation energies. 2. Error in Temperature Measurement due to Liberated Reaction Heats. The heat liberated during the reaction Li+OH —?LiOH is 116.4 k cals. per mole of lithium reacted. Then, for the P reaction at 35°C ( H20 = 4.6 mm. Hg. ) heat is liberated at the rate of 0.2 cals./min. This amount of heat if distributed without loss throughout the specimen is sufficient to cause a temperature increase of approximately 3°C/min. but most of the heat would be dissipated by transfer to the carrier gas. 53 Also, since the area of the surface interface is relatively large, the- difference between the measured temperature nd the actual temperature would certainly be less than that for the lithium nitride reaction - discussed previov ly„ 3. Zero Point Error In all cases, a zero point error was present because a few minutes elapsed between the time of initiating the run.and the time at which the first weight reading was taken. This error does not affect the measured values for the rate constants. 4. Errors due to Transport of Water Molecules to the Lithium- Hydroxide Gas Interface. It is instructive to consider the possibility that reaction rates could have been influenced by transport of water molecules from the gas phase to the specimen. The fastest rates recorded involved the consumption of approximately 0.3 mg. water per minute. For a water partial pressure.of 4.6 mm. Hg." this amount of water is contained in a volume of approximately 60 cc. of the reaction gas. However,reaction gas entered the system at a rate of 150 cc./min. and this was probably sufficient to ensure against depletion of water in the system. E. CONCLUSIONS The reaction of lithium with water vapour proceeds in three distinct stages. Initially, a lithium hydroxide film forms which is coherent with the underlying lithium lattice. At the low 54. partial pressures used in the investigation the results suggest that adsorption of water is rate-controlling. At water partial pressures higher than 22 mm. Hg. the rate, according to a previous investigation (4), becomes pressure independent and the rate is controlled by diffusion across the lithium hydroxide layer. As the reaction proceeds, sufficient strain energy is built up to provide a driving force for recrystallization of the film. During recrystallization the film develops a network of cracks. Simultaneously with recrystallization, the outer portions of the reaction layer undergo partial hydration to lithium monohydrate. The increased weight gains associated with water-of-hydration are superimposed upon those due to reaction to lithium hydroxide and the overall rate of the reaction increases by approximately 1| times the initial rate. This was not observed by the previous investigators (4) because of the insensitivity of the manometric method used to hydration of the film.' ¥ BIBLIOGRAPHY 1. Pilling and Bedworth, J.Institute of Metals, Vol. 29 529 ( 1923 ). 2. A..R. Evans, J Electrochem. Soc, 91, 547 ( 1947 ). 3. Gregg and Jepson, j.institute of Metals, 91, 351 (1959 )• 4. B.E. Deal and H.J. Svec, J.Am. Chem. Soc, 75, 6173-5 ( 1953 ). 5o Foote Mineral Company Bulletin. 6. S.. Yamaguti, Nature, 145, 742 ( 1940 ). 7. A.I. Belyaev, L.A. Firanova and I.N. Pomerantsev, paper reviewed in Chemical Abstracts, 50, 155400-1 ( 1956 ),. 8. K.J. Laidler, Chemical Kinetics, first edition, McGraw-Hill, 1950. p. 177. 9. V/. Frankenburger, F. Electrochem., 32, 481-91 ( 1926 ). VI APPENDICES APPENDIX 1 Table 1. Reaction Rates with Dry Nitrogen at 110°C, (Rectangular Specimens; 1= l.OOy w= 0.500" ). Reaction Time Weight Gain of Samples (minutes) ( mg. ) 1 2 1 0 0 0 0 15 0 0.2 0 30 0 0..6 . 0 45 0 1-5 2,2 60 1..9 3 ..0 3.6 75 4.7 5.3 5.2 90 7.-5 9.6 7.5 105 10.8 14.6 I0:..4 120 15..4 24.8 14.2 135 21.2 37.0 18.7 150 27.4 55.5 24.5 165 35.2 73.-8 31..7 180 43. a 107.7 39.-9 195 54.1 144 „3> 49.0 210 65..0, 59..0 225 68,2 69.9 240 80.5 2 55 90.0 270 97.-3 235 104 ..3 300 110.9 315 116.5 • Table 2 '' v,':•*'., Reaction Rates•of,Circular Lithium'Disks with Moist Nitrogen ( .Partial Pressure of Water = 4-6 mm. ).. Temp. React. Percentage of the Sample Time.mins. .' Transformed '. . 25°C • '. 30°C 35°C •' 35°C ' ; 35°C o •0 o; •'• 0 : 0 • : 0 ' 15 • . • 0.9 •• • 0..2 ' 0.8 ., • ' Q)„2 ' , : 0.2 30 . 1.5 •; 0.6 : 0.5 0.8 0...7 "45 1.4 •• , 1.1 . . 1.9 '• • ' 1.4- 60 2..7 . 2,4 '1.6 •3.7 2..5 75 '•• • 3.1 • • 3.3, 2 ..3 , 7.-8 . . , '3.8 9.0 . ' 3.5 , 4.5 • 3.4 •. 15..2 .' 6,7 105. 3 ..9 ; 6.5 26.4' .11.6 120. 4.4 .. 9 ..2 ' ' 7.9 •: • '42,0 18,9. 135 4 »<8 • 13-9 12.1 61 o.0 27.4 150 • 5.2 , • • .' 20.. 8 18 ...5 • 81. ..0 ' 40,.l. 1165 5..6 31.-2 27.3 95..1 52,7 130 • . 5.9 , 43.0 . '37.8 99.5 •. 64 »77 195 . 57.2: 50.0 • 99 ..8 ' 77.7 210; 6.6 7 2..2. 65..2 100 . 88 .A 225 6.9 85..2 77.2 96 d 240 7.2 93 ..4 '• 89.. 5 99.-9 255 7..5 ' 9 8..6 97.6 270 7.7 99.8 99.6 285 100.0 99.8 300 8.4 100 315 8.8? 330 9 o2. 345 9.7 465 21.2 480' 24.9 495 30,4 510 37.3 Table 2 (continued) Temp. React. Percentage of the Specimen Time . mins. Transformed 40°C 40J°C 40°C • •' 45°C 45°C 50°C •o 0 0 0 0 0 0 15 0.4 . 0.6 0.2 0..7 • 0.2 30 0.8 •' 1.6 2.5 . 2.3 2.5 2.5 45 2.5 3.0 5.6 V .7.3 6.4 7.8 60 6.1 .5.5 ' 12.2 .,• 17.7. 15.5 22.5 65 •30.0 70 20.9 25.6 . 38.5 75 13.3 10.1 26.1 36.6 31.2 48.0 80 31.8 36.4 57.9 35 37.6 42.3 68.2 90 25.4 19.1 43 .4 65.0 47.3 77.7 95 48.9 74.7 53 .0 86.9 100 54.4 84.9 53.1 94.4 105 39.5 35.0 60.0 91.0 63.3 98.2 110 65.4 95.5 63.5 99.6 115 70.8 98.4 73.5 99.8 120 53.7 58.0 76.2 99.4 73.1 100 125 81.2 99.8 32.6 100 130 86.1 87.0 13 5 67.2 83.4 100 90.5 140 94.0 93.6 145 97.0 96.1 150 79.1 97.6 98.9 98.2 155 99.6 99.1 160 99.8 99.7 165 88.6 99.8 100 99.9 180 96.8 100 100 195 99.5 210 99.8 225 100 59 Table. 3 Analysis, of Results of Runs Carried out in Nitrogen at a Water Level of 4.6 mm. Hg, T°C df 20 V (mm./mini.) dT *u -0033 55 25 ..ooao .0112 .003300 30) .00 57/ .0213; .004+8$ -0.179 ..003 246 35 .0063; .02.35 ..0065 .0242 ..0067 .02 50) .0067// .02.50) ..003194+ 40 .010 0) .0373 ..0100 .0373 ..0090 -0336 -0087# ..032 5 ,.003144 45 .0110) -0410) -011? .0436 -0116 -043-2 ..003100) 50 .0150 .0540 -0560 -00304.9 55 .0132// ..0490 ..0.12.6// .04-72! ..003007 60 -0117# .0438 ..00291-8 70 .00645 .0.2 50 $ Values taken directly from Curves Obtained on Recording Balance. 60 Table 4 Effect of Nitrogen Pressure on Reaction Velocity at 45°C •( Moisture Level = 2.6 mm. Hg.; Values, taken directly from Curves Obtained on Recording Balance ). i P Nitrogen Partial (, N2 ) V ( mm ./min.. ). Pressure 1 atom 1 ..0393 0..77 0>38 ..0327 0.73 0.85 .0310 0.64 0.80 .0311 0;. 50 0 ..71 .02:61 0.31 0.56 .0209 0.20 0.45 .0149 Table 5 Effect of Water Partial Pressure on Reaction Velocity in Nitrogen at 45°C ( Values taken directly from Curves Obtained in Recording Balance ). Partial Pressure of Water (mm.) V" ( mm./min. ) 0 No Nucleation 2.6 .0393 4.6 .0427 8.2 ..0134 12.6 No Nucleation 61.. Table 6 Effect of Temperature and Gas Composition on Nucleation Rate ( expressed as the Time required for the Reaction to Proceed to 20 percent of completion ). P a. . Effect of Temperature ( N2 = 1 atm.; , ^HgO = 4.6 mm. ). T°C t ( minutes ) 2 5 460 30 148, 160, 97 35 123, 154, 120 40 92, 68, 84, 85 45 63, 65„ 63 50 58 55 62, 62 60 55 70 78 110 No Nucleatiom P b. . Effect of Moisture Content ( N2 = 1 atm.; T = 45°C ) P H2Q (mm.) t ( minutes ) 0 NJO Nucleation 2.6 48 4-6 63, 65, 63 8.2 13 8 12 ..6 No Nucleation P Co Effect of Nitrogen Partial Pressure ( H20 = 2.6 mm.; T = 45°C ) P M2 (mm.) t ( minutes ) 1 63 0..77 58 0..73 52 0.64 56 0.50 78 0.31 105 0.20 175 62. Table 7 Reaction Rates of Circular and Rectangular Specimens in Moist Nitrogen Gas at 30°C (Gas saturated to a moisture content of 4.6 mm. Hg.) Reaction Time Percentage of (minutes) Sample Transformed Circular Rectangular 0 0 0 15 0.2 0.7 30 0.6 1.3 45 1.4 2.4 60 2.4 5.0 75 3.3 8.9 90 4.5 13.9 105 6,.5 13.9 120 9.2 24.2! 13 5 13.9 30.3 150 20.8 38.7 165 31.2 46.5 180 43.0 56.1 195 57.2 66.5 210 72.2 76.9 225 85.2 86.4 240 93.4 93.2 255 98.6 98.1 270 99.8 99.6 285 100 99.9 300 100 Rectangular Specimen: length = 1.00" ; width = 0.598 Circular Specimen: diameter =6.66 mm. 63 Table 8 X-ray Diffraction data for Specimens Reacted in Moist Nitrogen (4.6 mm. water) at 45°C. (Cu K>< radiation, Ni filter) a. Reddish Brown Product ( Prepared Surface ) Line Intensity Measured Corresponding Line in d spacing Card No. 2-0301 1 100 3.90 A Li3N 3.90 2 88 3 .16 A !» 3.18 3 20 2.73 A ft 2.75 4> 20 2.45 A tr 2.49 5 48 2.32 A Aluminum Holder 6 64 2.01 A rt it A 7 34 1.94 Li3N 1.95 8 48 1.82 A it 1.83 9 40 1.65 A tt 1.66 10 86 1.42 A Aluminum Holder 11 28 1.33 A Li3N 1.33 12 90 1.21 A tt 1,22 13 16 1.16 A tt 1.20 14 18 1.05 A it 1.06 b. Black Film Line Intensity Measured Corresponding Line in d spacing ASm Card No. 4-0708 and 1-1131 1 64 4.41 A LiOH 4.34 (001) 2 100 4.19 A Paraffin Wax 3 46 3.96 A Paraffin Wax 4 100 3.75 A Paraffin Wax 5, 70 2.78 A LiOH 2.75 (101) 6 50 2.53 A LiOH 2.51 (110) 7 46 2.49 A Li 2.48 8 72 2.24 A LiOH 2.17 (002) 64. Table 9 Reaction Rates of Lithium Disks in Dry Nitrogen after Initiating the Run in Moist Nitrogen ( ^h^Q r 4°6 mm.. ) Temp. Fraction of the Specimen Tra-nsformed React. Time 35°G 40°G 45°C 45°G 50°G 50°C 0 min, 0 0 0 0 0 0 15 0,5 0.3 0.7 0.9 0.8 0-4 30 2.2 1-3 2.1 3..5 3-5 1,8 45 4.1 3.9 6-5 13 -o# 9-6 4.7 60 6.8 9.6# 18 .1# 25..0 20.8# 11 -4 75 1.3 .0# 19-2 28.6 34-7 30.2. 19-5 90 21.7 27.2 33.9 43 -2 38-4 26.9 105 29«8 34.7 47.6 51.1 47-3 3 5.3 120 36.7 41.3 57.2 53-4 52 „.6 43 0.3 135 42.9 43.4 65.I 65.1 59.3 510.9 150 48. L. 54.8 72 ...5 7/0-9 67-0 59 .-3 165 53 -5 60 06 78..0 75-9 73-5, 67 -6, 180 5 8..4 67.0 33.5 30.6 79^3 74,-2 195 62.3 7 2 0.5 36-9 85 0.2 85-2 79-4 2110 66.3 77.6 90-6 88.6 84-6 225 70-2 82-5 94 ..0 89 -1 240 73 .4 86.6 96-6 92.2 255 76.4 90-0 98-4 96.0 270 79-4 93 o.4 99-6 99-2 285 81.7 960.4 100 100 300 84 0.2 98-5 100 315 86.6 99-4 330 88-9 99.8 390; 960.2 100 495 100 # Moment at which the Shift to Dry Gas was Carried out. 65'. Table 10 Analysis of Runs in Dry Nitrogen Which were Initiated ' in Moist Nitrogen ( b Determined from the Data in Table 9 using the Relation - a_bt; R _ 6e66 ranu ) # a. Determination of Growth Velocities. Temp t b V - • k ,SL 3 5°G .000183 .016 mm./min. 40°0 ,00028 „020 45°C . 000 50 5 =027 45°G ,00043 ,02 5 50°G ..00057 -029 b. Determination of Activation Energy 1 T. T° K V^_ 3 5-pC .,003246 „016 mm,/min, 40°G o 003194 .020 45QC .,003144 c027 45°C .003144 =.025 50°G ,003100 =029 Activation Energy Q r -7,300 cals, _APPEN.D,IX„,11 .Tabl.e_l Weight Incfeasffs of Lithium Disks Reacted with Moist Oxygen at Vari-SUs Temperatures ( Water Pressure = 4.6 mm.. Hg.; Specimen Area = 2.792 em . ), React. Time Min. 22°C; 22?_,Q . 25 °C 2,8°,G 3Q°.C. 3_Q°,C 32°C 35°C 3 5°C. 4,Q°,C. 4:IJG OJ 0 0 0 0 0) 0 0 0 0 0 9) 15 0.45 0..2 0.4 O..65 0*4 0,.4 0.4 0.3 5 0,3 Q)*-4 Q,„3 5 30 0.9 0.3 0*7 0.8 0.9 0..7 0.7 0.80 0,7 0*7 0 = 7 45 1..2 5 0.55 0.9- 1.-05 1.4 1,0 1..0 1..15 1*1 1,2 60 1,1. 1.-5 0.8 1..1 1.3 2*0 1.3 5 1.6 1.55 1,7 1*9 75 1.75 1.1 1,3 1.55 2..5 1..3 2;.l 2:..0 2,2 . 2*7 90 2.05 1.3 1..5 1,.8 3.05 2.15 2.15 2..5 2*4 3.45 105 2.3 1.5 1..7 2..05 3.5 2. -55 2;. 5 3.0 3*25 4-2 120 2.6 1.7 1.9 2.25 3.9 2..9 2.85 3.45 3.4 3*8 4-* 81 13 5 2.8 1.9 2.1 2.5 4,..2 3.25 3 ..20; 3.85 4.3 5.5 150 2.95 2.2 5 2...6 5 4.55 3.6 3.55 4.2 4.2 6,1| 165 3..2 2,1-5 2..85 2.,4 5 4,9 3. -95 3.9 4.65 4*55 5*2 |s8 180 3.-4 2.25 3 a. 5.-2 4.2 4.25 5,.6 7.4 195 3.6 2.-45 2-,.85 3.3 5 4.55 4.60 5.5 5.5 6 ..2; 210 3.75 2,6 3.0 3.-6 4.85 4.95 5.95 6,75 8,0 225 3*95" 2.75 3.35 6,1 5.2 5.20 6..4 7.3 8,7 240 2.9 33..4.2 4.1 6..3 5-5 5.6 6..9 7.35 10.2 255 4.3 3 ..05 3.55 4.3 5 6.55 5.-9 6.0 7-3 5 8^45 10.9 270 3 ..2 4.45 3.75 4.6 6,8 6,35 6.3 7.35, 7.7 9.05 11.6 285 4*65 3.4 4.0 4.85 7,0 6.75 6.7 9.7 12,4 300 4.85 3.55 4.3 5*1 7.35 7.2 7.0 8.7 10.4 13*15 315 5.0 3.75 4.55 5*4 7.6, 9*0 ,0 7.7 7.4 11 13*9 330 5.1-5 4.0 4 .8 5.7 8,05 7.85 9*7 11.55 7*9 1-4.6 345 5,-3 5.-65 6^0 8 a 8.5 8.3 10,2 12'.-2 5 360 : 5.5 4.4 5.3 8L 9 5 15.3 6.3 5 8.5 8.7 11.2 12 s9 375 5.6 4.65 5.65 6.7 9..4 9.1 11,8 11.2 13.5 16,0 390 5-8 4.-9 6.0 7.1 9.9 9.5 14.2- 16,7 405 6.0 5.1-5 6,*3 7*5 10.35 9.9 12.2 17.4 420 6.2 5.35 6.6 7.-9 9.7 10.9 10.4 15.6 18.15 43 5 6,3 5.55 6.95 8.3 11.35 10..8 14.2 13.3 18,85 450 6.5 5,8: 8,7 10... 3, II.85 11 ..2 5 14.7 465 6.75 6.05 7*3.6,5 9.-1 12,3 11.7 480 6.9 6.2-5 8.0 9.-.5 11.1 12.8 12.2 14-4 495 7.0 6..4 5 8.4 9.9 13 ..25 12.7 510 7.15 6.7 8..8 10 ..3 11. ..8 13.15 15.5 525 7.3 6.95 9.1-5 10.7 13 ..6 24*2 16,.6 540 7.5 7 *2 11.1 12.6 14.1 2-5*35 555 7.8 7.45" 9.9 14.55 570 8.0 7.7 10s2 5 13.4 15.0 585 8.2-: 10 ,.6 15.5 18..8 600 10,.9 5 14.3 16.0 645 16.5 2 5.9 705 19.-9- 28.5 720 10.4 19.95 745 Table 1 ( continued ). React. £7^ Time Min. 22° C 765 17.2 780 11.4 17.6 795 27 ..5 825 28.5 840 12.5 900 13.8 960 15.1 990 15..6 1215 34.7 1230 1245 42.2 1260 68.7 1275 54.65- 1320 22.4 1365 47.0 1395 32.,1 48.I 1470 44.3 1530 27..4 68. Table 2 . Summary of Data for Reaction in Moist ( 4.6 mm. HigO ) Oxygen. Rate Constants. k2 Temp. k2 kl 22°C ..004l7nig. / cm^ -min. . 007l6mg,/cm^-mjh. 1.7 22 .00391 .00738 1.9 25 .00461 .00837 1.8 28 .00573 .00955 1.7 30 .00674 .0118 1.8 30 # .0107- 32 .00836 .0114 -1.4 35 .0107 ..0126 1.2 35 .0104 .0131 1.3- 40 ..0122 .0158 1.-3 42 # it — # Non-linear Reactions. 69. Table 3 Reaction Rates of Lithium Disks with Moist Helium at Various 2 Temperatures (P H20 =4.6 mm. Hg.; Specimen Area = 2.792cm ) .Weight Gain (mg.) React. Time. 28°C 28°C 30°C 32°C 3 5°C 45°c 28°C # 0 0 0 0 0 0 0 0 15 0.2 0.45 .0.75 0.3 0.3 0,.6 0,3 30 0.55 0.6 1.0 1.0 0.65 1.2 1.4 45 0.9 0.8 1.35 1.5 1.15 2.05 2,1 60 1.2 1.1 1.6 2.0 1.7 3.1 2.7 75 1.6 1.4' 1.85 2.45 4.2 3.3 90 2.0 1.7 2.1 2.9 2,8 5.3 105 2.2 2.1 2.4' 3.4 3.4 6.4 4.2 120 2.45 2.7 3.8 4.0 7.6 4.8 13 5 2.8 3.1 4.4 4.45 8,8 5.25 150 3.3 3.4 4.8 4.9 9.9 5.8 165 3.65 3.45 3.7 5.2 5.4 10,85 6,2 180 4.0 4.0 5.6 5.8 11.95 6.6 195 4.1 4.3 6.0 13.0 7.0 210 4.6 4.55 6.5 6.8 14.1 7.4 225~ 4.9 4.85 4.9 6.8 15.1 7.75 • 24a 5.2 5.2 7.2 7.75 16.15 7.95 255 5.55 5.6 5.5 8,1 270 5.85 5.8 7.6 8.6 285 6.25 6.2 7.9 18.95 8,3 300 6.5 6.6/ 8.2 9.45 19.85 315 6.9 7.0 8,6 20.75 8.5 330 7.35 9.0 9.9 345 7 .-6 5 9.3 360 8.8 375 8.35 10.0 11.05 390 10.4 11.45 9.0 405 9.05 10.7 12.0 25.3 420 11.0 12.4 9.1 435 10*3 11.4 12.8 450 11.75 13.2 465 11.0 12.0 13.65 480 12.2 14.1 495 14.6 510 1.5.1 525 540 34.25 555 13.4 570 13.7 585 600 615 / . 18.9 645 20.05 795 25.15 70. Table 3 (continued) Weight Gain (mg.) R.S 6. C t o Time.° 28°C 28°C 30°C 32°C 3 5°C 45°C 28°C # 1170 30.8 1185 31.3 1200 31.8 1260 22.5 1290 23.3 1320 1380 36.9 # Reaction Gas a Mixture of 50$ He, 50$ 02 . Table 4 Effect of Water Pressure on Reaction Rate Constants in Wet Argon at 3 5°C ( v/alues taken directly from recorder-chart ) Pressure of Water-Vapour (mm. Hg.) 2.6 .00389 .0122 3.1 4.6 .0108 .0147 1.4 8.2 .0100 .0152 1.5 12.6 .0116 .0162 1.4 71. Table 5 X- ray Diffraction Data for Specimens Reacted with Water-Vapour (4.6 mm.) (Cu K Radiation; Ni filter) a. Black Film (specimen Reacted with Moist Oxygen 2 hours at 40°C) Gorresp. Line in Calc. d A.S.T.M. Cards No. Line Inten. Spacing 4-0708 and 1-1131 1 14 4.39 A LiOH 4.34 (001) 2 13 4.15 Paraffin } 11 3.91 Paraffin 4 8 3.73 Paraffin 5 14 2.76 LiOH. 2.75 (101) 6 100 2.51 LiOH 2.51 (HO) 7 13 1-99 Unknown 8 16 1.245 Li 1.24 b„ White Reaction Product ( Specimen Reacted in Moist Oxygen for 24 hours at 40°C ). Corresp. Line in Calc. d A.S.T.Mo Cards No. line Inten. Spacing 4-0708,1-1131,1-1062 1 28 4.57 A Paraffin Wax 2: 65 4.37 LiOH; 4.34 (001) 3 47 4.19 Paraffin Wax 4 30 3.75 Paraffin Wax 5 53 2.81 Li0H>H20 2..80 6 100 2.74 LiOffi 2.75 (100) 7 35 2.57 LiOK'H'oO 2.59 8 100 2.52 LiOH 2.51 (110) 9 85 2.49 Li 2.48 10 22 1.85 LiOffi 1.85 (102) 11 55 1.77 LiOffi 1.78 (200) 12 23 1.67 LiOH 1..65 (201) 13 36 1.64 LiOH 1.64 (112) 14 21 1.51 LiOH.H20 1.50 15 35 1.49 LiOH 1.49 (211) 16 17 1.45 Li 1.43 17 16 1.26 LiOH 1.26 (220) 72. Table 5 ( continued ). Co Black Film ( Specimen Heated in Moist Argon 2 hours at 40°C ). Corresp. Line in Calc. d A .S .T.M. Cards No. Line inten„ Spacing 4'-0708, and 1-1131. 1 52 4.39 LiOH 4.34 (ool) 2 100 4.15 Paraffim Wax 3 32 3.95 Paraffin Wax 4 84 3.74 Paraffin Wax 5 24 2.85 Li0Hi»H~20 2.80 6 42: 2.75 LiOH 2.75 (100) 7 72 2.54 LiOH 2.50 (110) 8 100 2.49 Li 2.48 9 16 1.77 LiOH 1.78 (200) 10, 16 1..45 Li 1.43 11 28 1.11 LiOH 1,12 (.004) do White Reaction Product (Specimen Reacted in Moist Argon for 20 hours at 40°C ). Corresp. Line in Calc. d A .S .T.M. Cards No. Line Inten. Spacing 4-0708,1-1131.1-1062 1 31 4.59 Paraffin Wax 2 68 4.37 LiOffi 4.34 (001) 3 100 4.15 Paraffin Wax 4 72 3.73 Paraffin Wax 5 47 2o83 LiOH°H20 6 100 2„76 LiOH 2.75 (101) 7 30 2.57 Li0H°H?0 2.59 8 88 2.51 LiOH 2.51 (110) 9 20 2.24 Li0H°H20 2.24 10 18 2.18 LiOH 2.17 (002) 11 26 1.86 LiOH 1.85 (102) 12 24 1.81 Li0H°H20 1.79 13 86 1.78 LiOH 1.78 (200) 14 24 1.67 LiOH 1.65 (201) 15 42 1.65 LiOH 1.64 (112) 16 21 1.51 LiOH->H20 1.50 1-7 35 1.49 LiOH 1.49 (211) 18 25 1.43 Li 1.43 19 21 1.26 LiOH 1.26 (220) 20 13 1.207 LiOHI 1.21 (221) 21 12 1.144 LiOH 1.14 (301) 22 13 1.144 LiOH 1.12 (310) 23 13 1.041 LiOH 1.04 (104) 24 11 0.998 LiOH 0.998 (312) 25 11 0o96l LiOH 0.962 (321) Table 5 (continued). eo X-ray Diffraction Data for a Sample Reacted to Completion in Moist Oxygen ( PH20 - 8.2 mm. Hg. ) at 35°C. Calc. d Corresp. Line in A.S Line Inten. Spacing Cards No. 1-1062 1 63 2.92 i LiOH°H20 2.97 : 21 52 2.79 tt 2.80 3 44 2.70 ft 2.67 1* 52 2.47 tt 2.44 5 63 2.41 Unknown 6 48 2.25 LiOH°H20 2.24 7 48 1.86 tf 1 o 85 8 42 1.73 1.75 9, 55 1.66 it 1.66 10 44 1.58 tt 1.60 11 48 1.51 it 1.50