NSWC/WOL TR 77.67

SLITHIUM-BORON ALLOY ANODES FORSMOLTEN SALT BATTERIES (1)

BY S. DALLECD. W. ERNSTB. F. LARRICK

' RESEARCH AND TECHNOLOGY DEPARTMENT

11 JANUARY 1978

Appoved for public ree. disitrbutim. urdhmtdD D C

NAVAL SURFACE WEAPONS CENTERDd*Mu. V~runl 2244 0 SIlve Spring. Maryla 2010

UNCLASSIFIEDECUI"ITY CLASSIFICATION OF THIS PAGE (When, Data Entered)

REPOT DCUMNTATON AGEREAD INSTRUCTIONSREPOT DCUMNTATON AGEBEFORE COMPLETING FORM

2GOVT ACCESSION NO. 3. RECIPIENT'S CATALOG MUMmER

(t: NSWC/W L rR-7?7-67

~ITIU-AORONALLOY AODES FORPOLE Progres

SAT-ATTERIES M1' Rnfinu.

7. T B. CONTRACT OR GRANT NUMER(s)

/ = ./Dallek, D. W.g'4rnst andB. F. arrick

9. PERFORMING ORGANIZATION NAME AND ADDRESS 10O. PROGRA14 ELEMENT, PROJECT, TASKAREA & WORK UNIT NUMUERS

Naval Surface Weapons CenterV' NIF;0;0;wR33JA(1);White Oak LaboratoryWhite Oak. Silver Spring, Maryland 20910____________

11. CONTROLLING OFFICE NAME AND ADDRESS

14 AONIT IN E & ADDRESS(Uf different from Controlflng Office) IS. SECURI TY CLASS. (of this report)

UNCLASSIFIEDISa. DECL ASSI FICATION/ DOWNGRADING

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Approved for public release.Distribution unlimited

17. DISTRIBUTION STATEMENT of the abstract entered in Block 20. it different from, Report)

IS. SUPPLEMENTARY MOTES

I$. KEY WORDS (Continue an reverse ade it necessary md identify by block numiber)

Lithium Alloys, Boron Alloys, Anodes, Batteries

0. ABSTRACT (Continue an reverse aid* if necessary and Identily by block mmnber)

NThe current work is concerned with the development of a procedurefor the preparation of a lithium-boron alloy suitable for use asan anode in thermal batteries. lMetallography, thermal analysis,and X-ray diffraction techniques are being developed as tools forstudying this multiphase material. A chemical analysis is plannedto identify the composition of the various phases. Once the phasediagram for the system has been determined, we will be able to

DD JN31473 EIONONv 66 Is 00SOLETS NLSSFE

.6URITY CLASSIPICATION OP T141S PAGE (ften Dae et

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repare material having optimum electrochemical properties for useas an anode material.

UNCLAS iFIsuSECURITY CLASSIPICATION o@PHIS PA@S(mum Data Ente'*0

NSWC/WOL TR 77-67

SUMMARY

This is the first of a series of progress reports on thedevelopment of a lithium-boron alloy for use as an anode in thermalbatteries. A preparation procedure is being developed and the phasediagram for the alloy system is being determined. This alloy system,utilizing the electrochemical superiority of lithium as an anodematerial, will be used in the development of an improved thermalbattery.

This work is being performed under Program Element NIF TaskArea Number 0, work unit number WR335A (1).

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NSWC/WOL TR 77-67

ACKNOWLEDGEMENTS

The authors wish to thank L. Kowalchik for assistance in thetechniques of the alloy preparation and many valuable discussionson the system. The helpful advice of L. E. DeVries and F. M. Bowersis also gratefully acknowledged.

2'A

NSWC/WOL TR 77-67

CONTENTS

Page

I. INTRODUCTION ...................... ..... . ...... ..... . .. .. 5

II. LITERATURE SURVEY OF INITIAL STUDIES ...................... 6

III. REPORT OF CURRENT WORK ........ ..................... 11A. Alloy Preparation.............. .. . ..... .. .. .. . ... .. . .. 11B. Metallographic Studies .................. .. .. .. .. .. .. .. . .. 13

C. Thermal Analysis.................. .. ...... .. ......... 14D. X-ray Analysis................................. ......... 15

IV. FUTURE WORK ......................... o....... 15

V. SUMM1ARY ........ ................................. 16

REFERENCES ........................................ ...... 18

ILLUSTRATIONS

Figure Page

1 Discharge Potentials of Lithium-Boron Alloy Anodesin Molten LiCl-KCl Eutectic at 773K (5000 C) ......... 19

2 Heat of Crystallization of Lithium-Boron Alloys ... 23 Photomicrograph of Li-B Alloy (80 atomic

percent Li)...................... 21

APPENDIX A PREPARATION METHOD USED AT NSWC FOR LITHIUM-BORON ALLOY INGOTS (80 ATOMIC PERCENT Li) Al

3

NSWC/WOL TR 77-67

TABLES

Table Page

1 Density of Lithium-Boron Alloys...................... 72 Electrical Resistivity of Lithium-Boron Alloys........... 83 Thermal Conductivity of Lithium-Boron Alloys........... 94 Heat Capacity of Lithium-Boron Alloys...................... 95 Heat Evolved During Exothermic Transition ............ 106 Electrochemical Equivalents of Some Metals and

Lithium-Boron Alloys ................................ 17

4

NSWC/WOL TR 77-67

I. INTRODUCTION

Most thermal batteries employ solid calcium metal anodesdischarging in a molten lithium chloride-potassium chloride eutecticelectrolyte. Thermal batteries typically deliver less than 30 percentof the available discharge capacity because the anode reaction product(KCl*CaCI2) forms a solid, non-conducl-ing barrier between the anodeand the molten salt electrolyte.

The electrochemical superiority of lithium as an anode materialis well known. Its reaction product (LiCI) is soluble, and it isknown that lithium could provide a twofold to threefold improvementin both the specific energy and specific power of thermal batteries.However, lithium melts at 453K (1800C), well below the 800K (5270C)operating temperature of thermal batteries. The escape of lithiumduring discharge and the difficulty of maintaining the physical integ-rity of a liquid metal anode have precluded the use of lithium inmolten salt batteries. This problem may be solved by utilizing thelithium in the form of an alloy having a high melting point. Alloysof lithium with such metals as Al, Mg, Si, Zn, Cu, and Pb have beenexamined as high-temperature anode materials1 . Their deficienciesinclude low melting points, severe polarization at high current,and poor lithium utilization.

The lithium-boron alloy system, which was first prepared atNSWC2 , does not have these deficiencies and has shown great promisefor use as an anode material in molten salt batteries.

A large amount of information has been accumulated on this alloysystem but has never been written down in one place. This reportserves two purposes; first, it will attempt to describe the early

1. Selman, J. R., Steunenberg, R. K., Barghusen, J. J. andW. G. Howard (ED), Proceedings of the Symosium and Workshopon Advanced Battery Research and Desin, Argonne NationalLaboratory, Report No. 76-8 (1914"..

2. Wang, F. A., Invention Disclosure, Navy Case #60,721, NSWC,Silver Spring, Maryland (1974).

5

NSWC/WOL TR 77-67

work done on the Li-B system, and, second, it will summarize currentprogress and serve as the first in a series of progress reports.

II. LITERATURE SURVEY OF INITIAL STUDIES

The first reported work (1932) on LiB alloys was by Andrieuxand Barbetti3 who electrolyzed fused borate solutions and obtainedboron and lithium hexaboride as products. In 1959, two Russians,Markovskii and Kondrashev4 , reported that they prepared a blackpowder from the direct mixing of lithium and boron in a 1 to 6 ratio.An unidentified boride and free boron were found to be present inthe X-ray patterns. Secrist 5 , in 1962, studied the LiB systembetween 3 and 55 atomic percent Li and found a compound at 32 at.% Li.In 1967, he also reported the existence of a brownish colored phase6

identified as LiB 10 .85+0.35. In 1965, Casanova7 reported the

existence of LiB 4 in a-French patent. His compounds were prepared 0by reduction of boron carbide with lithium metal between 973.3K (700 C)and 1273.3K (10000 C). In most of these early preparations, blackor brownish colored powders were formed. It is generally believedthat these powders were borides and not metallic alloys of lithiumand boron.

Wang2 , in 1972, states that he prepared a metallic alloy insteadof the borides made by previous investigators. In preparing thealloy, a solution of boron in liquid lithium was first preparedat a temperature below 670K (3970C); then, as the solution was grad-ually heated to about 823K (5500 C), its viscosity spontaneouslyincreased until the material solidified. On continued heating, anexothermic reaction occurred and the alloy changed from one having ametallic luster to one with a whitish non-metallic luster. It isimportant that the alloy be completely solidified before proceeding 0to the last step in order to produce an alloy stable above 823K (550 C).

Sutula, while working on a lithium/chlorine type battery whichwas being developed at NSWC as a future high rate primary battery,suggested that this alloy might be useful as an anode material

3. Andrieux, L. and Barbetti, A., Compt. Rendu, 194, 1573 (1932).

4. Markovskii, L. Ya. and Kondrashev, Yu. D., Zh. Neorgan. Khim.,2, 34-41 (1957).

5. Secrist, D. R. and Childs, W. J., USAEC TID-17149/Secrist, D. R.

USAEC KAPL-2182 (1962).

6. Secrist, D. R., J. Amer. Cer. Soc., 50, 520 (1967).

7. Casanova, J., French Patent No. 1461878 (1965).

6

NSWC/WOL TR 77-67

Table 1. Density (kg m- ) of Li-B Alloys

Atomic TEMP. (K)Percent Li 293 373 473

70 935 926.3 915.3

78 795 783.8 '769.8

78 805 788 780

87 1005 990 975

7

NSWC/WOL TR 77-67

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NSWC/WOL TR 77-67

-l1-Table 3. Thermal Conductivity (W m K- ) of Li-B Alloys

Atomic TEMP.(K)percent Li 373 473 573 673 773 873 973 1073

70 72 62 51 38 35 30 28

70 78 65 56.5 48 39 28 25 25

78 75 63 55 45 38 33 30

78 77 73 70 66 62 56 48

87 71 66 58 53 50 47 43

Table 4. Heat Capacity (J kg- K- ) of Li-B Alloys

Atomic TEMP.(K)percent Li 373 473 573 673 773 873 973 1073

70 3450 3550 3690 3750 3850

78 3650 3700 3800 3900 4000

78 3450 3500 3660 3700 3850

87 3700 3730 3840 3950 4000

JANAF TABLES

TEMP. (K)298 300 400 500 600 700 800 900 1000 1100

Li 3549 3555 3978 4341 4257 4177 4170 4163 4156 4148

B 1025 1031 1438 1736 1930 2057 2150 2227 2301 2367

9

NSWC/WOL TR 77-67

Table 5. Heat Evolved During Exothermic Transition

ATOMIC PERCENTAGES HEAT EVOLVEDLi B cal/g cal/mole of alloy

90.3 9.7 1.56 11.482.4 17.6 2.46 18.875.7 24.3 4.70 37.067.5 32.5 8.37 22.466.3 33.7 7.47 61.660.9 39.1 11.4 96.457.7 42.3 14.3 122.657.2 42.8 13.2 113.454.8 45.2 15.9 138.053.9 46.1 15.4 134.351.0 49.0 16.0 141.548.3 51.7 15.2 135.844.8 55.2 14.3 129.641.8 58.2 14.9 136.8

10

NSWC/WOL TR 77-67

(Electronol). James and DeVries 8 reported on the anodic dischargebehavior of Electronol alloys in TLiCl-KCl eutectic melts. They showedthat current densities up to 8 A/cm2 could be sustained without anydetectable diffusional limitations at temperatures between 750K (4770C)and 870K (597 0C). They also concluded that the end discharge productwas Li2B and that the Li2B matrix solid held the molten lithium inplace during the discharge. Figure 1 is a plot of their data. Morerecently, Mitchell and Sutula 9 have reported on the density, Hallcoefficient, and electrical resistivity of alloys containing up to60 atomic percent boron. Wang et al. 10 have also reported on thecrystal structure of the Li5B4 compound.

Over the years, other properties of the Li-B system have beendetermined. As part of the lithium/chlorine battery developmentprogram, the electrical resistivity, thermal conductivity, heat capa-city, and density of several Electronol alloys were measured. Thesedata are summarized in Tables 1-4. Wang 2, in his patent, givesheat of reaction data. These data and the heat of reaction per moleare tabulated in Table 5 with a plot of the data given in Figure 2.

III. REPORT OF CURRENT WORK

A major goal of the current work is the preparation of a suitableLi-B alloy for use as an anode in thermal batteries. One of theproblems is that there is a lack of information on how to make thematerial. Wang's patent gives a general procedure with no informationconcerning phases or phase boundaries. One objective of this workis to determine the phases present in the system and their electro-chemical and physical properties. Further electrochemical measure-ments are needed to identify the lithium transport mechanism withinthe alloy structure during discharge. It is especially importantto know whether loss of lithium can be avoided in molten salt electro-lytes at high temperatures. Knowledge of the physical propertiesis necessary to guide in the design, fabrication, and use of thesealloys as battery anodes. Among the measurements needed are strength,dctility, and electrical resistance at both high and low temperatures.7 e second objective of the work is to set up specifications on howoest to make the anode.

A. ALLOY PREPARATION. Sutula, using essentially Wang's 2

method, made the first Electronol anodes by dissolving the boronin molten lithium, stirring until the grittiness in the crucible

8. James, S. D. and DeVries, L. E., J. Electrochem. Soc., 123,321-27 (1976).

9. Mitchell, M. A. and Sutila, R. A., The Density,ElectricalResistivity, and Hall Coefficient of LiB Alloys. To be pub-lished in J. Less Common Metals.

10. Wang, F. A., Mitchell, M. A., Sutula, R. A., Holden, J. R.,and Bennett, L. H., Li5B4: The Structure Study Of. To bepublished in Acta Cryst.

~11

i

NSWC/WOL TR 77-67

was gone, raising the temperature until the solution thickened, andthen increasing the temperature until a visible exothermic reactionwas observed. The crucible was then removed from the furnace andallowed to qool. This was the type of Electronol supplied to Jamesand DeVries and used in their work. Analysis showed that thismaterial was inhomogeneous, with the lithium content varying by 6to 8% from one part of the ingot to another. The process was refinedto create a more homogeneous material by stirring more thoroughlyand using a smaller particle size boron. Subsequent analysis onthis material showed improved homogeneity with only a 1 to 1.5% vari-ation and indicated that Fe, Ni, Cr, and Mn were also present upto a total of 0.14%11.

Since the behavior of this system is unknown and complex,preparation procedures were varied from one composition to the nextin order to obtain an overall understanding of the system. A listof equipment used and the method of preparation of ingots of 80 atomicpercent lithium are presented in the appendix. (This compositionwas chosen for development of a battery anode material because itstheoretical coulombic capacity, as shown in Table 6, is about thesame as that of calcium.) Due to the unusual nature of the alloysystem, and until a phase diagram can be determined, the best wayto present the data is to describe the general facts gathered sofar.

1. Boron is wetted by lithium at around 623K (3500 C). At lowertemperatures, lithium forms a ball in the crucible; the meniscus ofthe molten lithium is tightly curved.

2. Boron reacts completely with molten lithium at 673K (4000 C).If lower temperatures are used, a longer time is required for completereaction. The nature of this reaction process is not yet understood.It apparently involves both a slightly exothermic chemical reactionand a physical mixing of the reaction product with excess lithium.Whether the mixing also includes the formation of solid or liquidsolutions is not yet known.

3. At 773K (500 C), the melt becomes extremely fluid, andthe meniscus starts to creep up the container walls. No solidparticles are present that are large enough to be detected by ordinarystirring of the fluid mixture.

4. Between 803K (530 C) and 853K (580°C), the melt graduallythickens. At approximately 853K (580 0C), an exothermic transitionoccurs, during which the melt solidifies and contracts from the wallsof the crucible. The heat liberated is enough to cause the crucible

11. DeVries, L. E. and Gubner, E., Analytical Procedure For MainComponents and Major Impurities in Lithium-Boron Alloys. Tobe published in Analytical Chemistry.

12

NSWC/WOL TR 77-67

temperature to be visibly increased above that of the furnace. Wang2

and Sutula both report seeing the exotherm in samples of 80 atomicpercent lithium. Our studies indicate that the exotherm is notobserved if the lithium content is high or if the heating is doneslowly.

5. The observations described above apply principally to alloysmade with more than about 50 atomic percent lithium. The behaviorof alloys made with less than about 50 atomic percent lithium isdifferent. For example, great difficulty in achieving complete reac-tion of the boron is one significant difference. Alloy ingots withhigh boron content and of uniform composition have not beensuccessfully prepared. Because they contain relatively less lithium,such alloys would be of little interest as battery anode materials.

B. METALLOGRAPHIC STUDIES. Metallographic studies were conductedon ingot samples in an effort to determine the presence of variousphases in the alloy. The alloy, being a reactive material, posedsome problems in its handling, and it was first thought that theactual work would have to be carried out in an inert atmosphereglove box. However, if one works fast (10-15 minutes), photomicro-graphs taken with a metallurgical microscope can be made before thealloy deteriorates.

Mounting the specimen was the first problem to overcome. It

is not possible to use mounting compounds which have a liquid asone of the ingredients. The reaction of the alloy with the liquidcreates bubbles before the-mounting compound hardens, resulting ina poorly adherent mount. A series of Epoxy-Patch kits (white, blue,clear) wece tried. The white and blue were found to be satisfactory,the clear less so because of its long set-up time (1 hour) and reac-tion of the alloy during this time. The blue is hard to work withbecause of its fast set-up time (4 minutes) but gave very good mounts.The white is also very good because it sets up in 1/2 hour and canbe heated to set up faster, but with some alloys a slight reactionwas observed.

Another type of epoxy system (Biggs Epoxy Putty), in which twosolids are mixed together like dough until a uniform color isobtained, offered a convenient and satisfactory method for mountingthe alloy and is currently being used.

The second problem involved finding a lubricant for use on thesilicon carbide grinding paper. A number of organic fluids weretried, including alcohols, glycols, mineral oil, and Kel F polymeroil. Mineral oil was found not to react with the alloy, but itsviscosity makes grinding difficult. However, mineral oil is usedwith the 600 grit paper and is also put on the specimen after ithas been etched to slow down the reaction with air. Kel F polymeroil was the best lubricant used but is dangerous because of thereaction of halogenated hydrocarbons with lithium, which leads toa reaction product that can explode when shocked. Propylene carbon-ate, a commonly used solvent in lithium batteries, was finally chosenas the lubricant in the polishing stages down to 600 grit.

13

NSWC/WOL TR 77-67

The next problem solved was what to use for an etchant. Again, anumber of organic solvents were tried. Three, with different reactionrates, were found to be suitable. They were methanol, ethanol, andethylene glycol, and their reactivity decreased in that order. Awater etch was found to be much more reactive than methanol and notsuitable for alloys containing 66 atomic percent or more lithium.

Since we are still in the early investigation stages, we havenot identified phases as to their composition and under what condi-tions they are formed, but can only give a description of what wehave observed. Compositions below 50 atomic percent lithium arenot covered because of uncertainties in their preparation. All ofthe alloys discussed have been taken high enough in temperature tohave gone through the exothermic reaction but have not been allowedto remain at high temperatures long enough to ensure equilibriumconditions. However, we are now in the process of carrying out thatexperiment.

The results of our metallographic study suggest that four phasesmay exist between 50 and 80 atomic percent lithium. There is a creamy-white, lithium-rich phase, a steel-gray phase, a black-gray phase,and a brownish color phase. Between 50 and 66 atomic percent lithium,the steel-gray and black-gray phases coexist. From 66 to 69 atomicpercent lithium, the black-gray and brownish phases coexist. Above69 atomic percent lithium, the creamy-white, lithium-rich phase coexistswith the black-gray and brownish phases. It has not been possibleto determine the relative amounts of the two phases that are presentfrom the photomicrographs of the alloys. The lever arm rule doesnot seem to apply; one would expect more of the black-gray phaseto be present at 66 atomic percent lithium than at 55 atomic percentlithium, or vice versa, but this does not appear to be the case.Instead, the two phases always seem to be present in the same pro-portions. The same situation exists for the two phases between 66and 69 atomic percent lithium. However, above 69 atomic percentlithium, it is possible to see the difference in relative amountsof the lithium rich phase and the coexisting black and brownishphases. The possibility has been considered that the material isa single phase of variable composition. However, this does not fitin with the different colored phases observed.

A typical photomicrograph of an 80 atomic percent Li(B) alloyis presented in Figure 3.

C. THERMAL ANALYSIS. Initial thermal analysis work using theDuPont 990 Modular Thermal Analysis System has included differentialthermal analysis (DTA) and differential scanning calorimetry (DSC)studies. These techniques will be used as a tool for constructingthe phase diagram. A major difficulty in working with this systemis the extreme reactivity of lithium. Lithium reacts with the plat-inum and aluminum sample cups and alumina cup liners supplied withthe instrument, and so sample cups of other materials have to beconstructed. We are now on the process of having Armco iron cupsmade for the DSC apparatus.

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NSWC/WOL TR 77-67

An observation made in the metallographic work was that oneof the phases was more reactive than the others, and if the specimenswere over-etched, hills and valleys appeared. This led us to thinkthat, maybe, if the material were dissolved in the etchant, one ofthe phases would be dissolved away from the other. Water and methanolwere the primary reagents (etchant) used in our separation techniques.Ethanol was also tried but was much slower in its reaction than meth-anol, and no benefit was derived from its use. The alloy phase thatis most reactive is the black-gray phase followed by the creamy-whitelithium-rich phase. After reaction with the reagent, two differentmaterials remained, a black compound obtained from the alloys between50 and 66 atomic percent lithium and a brownish compound obtainedfrom alloys containing more than 66 atomic percent lithium. Acentrifuge was used to separate the material from the reagent.Transitions characteristic of these hase-separated materials havebeen obtained using DTA and DSC methods but have not yet beenidentified.

D. X-RAY ANALYSIS. X-ray diffraction techniques are frequentlyused in the determination of phase diagrams, and we planned to make

extensive use of this method. The samples X-rayed were the sameones used in the metallographic work. The diffractometer shieldwas enclosed in Saran Wrap and Drierite placed in the sample areato remove water vapor. The combination of Saran Wrap shield andmineral oil on the sample permitted X-ray exposure up to 3 hourswithout deterioration of sample surface. However, metallographicexamination revealed that the material is multiphase, and thereforeit is not possible to tell which peaks belong to which phase.X-ray patterns taken on the phase-separated material have not beenideal for several reasons. The powders are finely divided materialwhich does not give well-defined diffraction peaks. Both lithiumand boron are fairly transparent to X-rays and most of the beam passesthrough the material rather than being diffracted. The Debye-Scherrer film method gave more satisfactory results due to integra-tion of the peak intensities. At present, all of the separatedcompounds have not been X-rayed, but it is noted that there are atleast three different patterns present. It is necessary to improveX-ray techniques used before the peaks can be indexed or the latticeparameters determined.

IV. FUTURE WORK

The goal of the present research is the development of a lithium-boron alloy suitable for use as an anode in thermal batteries. Byvarying the preparation procedure, we will be able to better under-stand the reactions occurring in the formation of the alloy. Thus,the use of different amounts of starting materials and differenttemperatures during the preparation should result in the formationof different phases in varying proportions. We plan to identifythese various phases using metallography, thermal analysis, and X-raydiffraction techniques. A chemical analysis will be performed onphase-separated material. We also plan to anneal alloy samples at

15

NSWC/WOL TR 77-67

700 C for several weeks to see if an equilibrium can be achievedamong the various phases we have seen. A comparison will then bemade between this material and newly prepared material using thetechniques mentioned above. Studies are also planned on materialwhich has not undergone the exothermic transition. Valuable infor-mation will be obtained by comparing phases present before and afterthis exothermic reaction.

General Electric Neutron Devices (GEND), under contract to thisCenter, has made thermal battery cells using the Li-B alloy systemas an anode. Correlations will be made between the alloys we prepareand GEND results on cell fabrication and testing.

V. SUMMARY

The procedure for the preparation of lithium-boron alloys isbeing studied and the phase diagram for the system is being determinedusing metallography, X-ray, and thermal analysis techniques.

Metallographic results indicate that as many as four phasesmay exist in the composition range 50-80 atomic percent lithium.These phases are probably formed under non-equilibrium conditionssince the phase rule is not obeyed.

The X-ray patterns of the alloy have been difficult to interpretsince the material is multiphase and relatively transparent to X-rays.However, several good patterns have been obtained on phase-separatedmaterial.

Differential thermal analysis (DTA) and differential scanningcalorimetry (DSC) are being developed as tools for characterizingthe material and developing the phase diagram.

The combination of a chemical analysis on phase-separatedmaterial with metallography, X-ray and thermal analysis is plannedfor characterizing the alloy for use as an anode in thermalbatteries.

j. 16

I-IVa

NSWC/WOL TR 77-67

Table 6. Electrochemical Equivalents of SomeMetals and Li-B Alloys

Metal or Alloy Equivalent weight, grams

66.7 at % Li O

70 -81.00

75 31.63

80 19.28

85 13.67

90 10.47

100 6.939

Al 8.99

Mg 12.16

Ca 20.04

Na 22.99

Fe 27.92

Zn 32.68

Cd 56.20

Pb 103.60

*Equivalent weight of allay based on the reaction

Li B-*pL + (n-2)Li~ + (n-2)e-.n i2B

17

NSWC/WOL TR 77-67

REFERENCES

1. Selman, J. R., Steunenberg, R. K., Barghusen, J. J. andW. G. Howard (ED), Proceedings of the Symposium and Workshopon Advanced Battery Research and Design, Argonne NationalLaboratory, Report No. 76-8 (1976).

2. Wang, F. A., Invention Disclosure, Navy Case #60,721, NSWC,Silver Spring, Maryland (1974).

3. Andrieux, L. and Barbetti, A., Compt. Rendu, 194, 1573 (1932).

4. Markovskii, L. Ya. and Kondrashev, Yu. D., Zh. Neorgan. Khim.,2, 34-41 (1957).

5. Secrist, D. R. and Childs, W. J., USAEC TID-17149/Secrist, D. R.USAEC KAPL-2182 (1962).

6. Secrist, D. R., J. Amer. Cer. Soc., 50, 520 (1967).

7. Casanova, J., French Patent No. 1461878 (1965).

8. James, S. D. and DeVries, L. E., J. Electrochem. Soc., 123,321-27 (1976).

9. Mitchell, M. A. and Sutula, R. A., The Density, ElectricalResistivity, and Hall Coefficient of LiB Alloys. To be pub-lished in J. Less Common Metals.

10. Wang, F. A., Mitchell, M. A., Sutula, R. A., Holden, J. R.,and Bennett, L. H., Li5B4 : The Structure Study Of. To bepublished in Acta Cryst.

11. DeVries, L. E. and Gubner, E., Analytical Procedure for MainComponents and Major Impurities in Lithium-Boron Alloys. Tobe published in Analytical Chemistry.

18

NSWCIWOL TR 77-47

0-

U- W

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II

33MM31311-1314q3 SAJIOI3

19:

NSWC/WOL TR 77-67

120

00

100

P 80

Go-

U

00

20-

0.4 0.5 0.6 0.7 0.8 0.9 1.0

ATOM FRACTION LITHIUM

FIGURE 2 HEAT OF CRYSTALLIZATION OF LITHIUM-BORON ALLOYS

20

NSWCIWOL TR 77-67

FIGURE 3 80 ATOMIC PERCENT U (8) ALLOY 1150X)

21

NSWC/WOL TR 77-67

Appendix A

Preparation Method used at NSWC for Lithium-BoronAlloy Ingots (80 atomic percent Li)

I. Equipment and Apparatus

A. Inert atmosphere glove box

1. Vacuum Atmosphere Company - model HE 553-2 DRI-LAB

2. He atmosphere vacuum 3x10-10 cc/sec or better

B. Furnace

1. Sybron Corporation, Thermolyne type 1300

2. 0-1200oC, temperature control knob (percent time on)

C. Reaction Vessel

1. 318 Stainless Steel tube with screw-on bottom capinner diameter 3.90 cminside depth 3.49 cmouter diameter 4.13 cmcap outer diameter 4.45 cm

D. Balance

1. Mettler - model P163N

2. Capacity, 160 g

3. Accuracy, 1 mg

II. Materials

A. Lithium, 99.9%

1. Foote Mineral Company, standard grade

2. 113 g - ingot or ribbon

A-1

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II. Materials (Cont.)

B. Boron

1. Atomergic Chemetals Corporation

2. Boron, crystalline lump, 99.9%

III. Procedure for Alloy Preparation

1. Because the volume of the reaction vessel is only about40 cm3 , the amount of starting material which can be convenientlyused is generally in the range of 15-18 g. Thus, to prepare an ingotof 80 atomic percent lithium, 11.102 g of lithium and 4.324 g ofboron are weighed out and placed in the reaction vessel. The boron,which had been ground into small chunks or powder, is placed in thecrucible first, and then the lithium is added.

2. The reaction vessel is placed in the furnace, and thetemperature is raised to approximately 623K (350 0C). After thelithium is molten, the mixture is stirred with a stainless steelstirring rod.

3. As the temperature is slowly raised, the reaction vesselis occasionally removed from the furnace, and the melt is thoroughlystirred to facilitate reaction of the boron with lithium and to insurehomogeneity.

4. Gradually, the boron is wetted by the lithium and beginsto react. It is assumed that the boron is completely reacted whenthe grittiness felt during stirring is gone at about 673K (4000C).

5. Coinciding with the reaction of the boron is the appearanceof a new solid phase at the bottom of the reaction vessel. Withstirring, this phase is dispersed in the remainder of the melt, anda smooth, syrupy material results.

6. The temperature is slowly raised, and the melt is thoroughlystirred u8 til it becomes extremely viscous. Then, at approximately853K (580 C), solidification occurs, and the ingot contracts awayfrom the walls of the reaction vessel. When the melt first solidifies,the solid has a silvery, metallic appearance. This changes to anon-metallic, grey-violet appearance during the contraction.

7. After the contraction, the reaction vessel is removed fromthe furnace, the bottom of the container is unscrewed with pliers,and the ingot is removed and allowed to cool. When cool, the alloyis placed in a plastic zip-lock bag for removal from the glove box.

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NSWC/WOL TR 77-67

IV. Notes

1. The furnace temperature and crucible temperature are assumedto be identical.

2. The heating and stirring procedure is designed to producea homogeneous mixture, formed under near-equilibrium conditions.Thus, no definite length of time is specified for the process. (Afterthe boron dissolves, the remaining procedure takes approximately onehour.)

3. Coinciding with, or slightly above, the solidificationtemperature is the appearance of an exothermic transition in thesystem if the alloy is formed too quickly.

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