Electrochemical investigtion of solubility and chemical diffusion of lithium in aluminum
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WEN,
W. WEPPNER,
B. A. BOUKAMP,
AND
R. A. HUGGINS
The s o l u b i l i t y of l i t h i u m in a l u m i n u m and the c h e m i c a l diffusion coefficient in this solid s o l u t i o n have b e e n i n v e s t i g a t e d as a function of t e m p e r a t u r e between 400 and 600~ using the e l e c t r o c h e m i c a l cell:
(--)Al, "LiAI"/LiC1-KCI(eut.)/AI(Li)(+) The s o l u b i l i t y l i m i t of l i t h i u m in a l u m i n u m was found to d e c r e a s e f r o m 13.8 at. pct at 595~ to 8.0 at. pct at 395~ in good a g r e e m e n t with data p r e v i o u s l y r e p o r t e d by other i n v e s t i g a t o r s using d i f f e r e n t t e c h n i q u e s . The c h e m i c a l diffusion coefficient has b e e n m e a s u r e d by two different e l e c t r o c h e m i c a l t r a n s i e n t t e c h n i q u e s . The data can be r e p r e sented by the r e l a t i o n :
= O.155exp
(-AII/RT) cm2/s
where ~ is 119.2 k J / m o l . T h i s e l e c t r o c h e m i c a l technique has also b e e n used to obtain v a l u e s of the c o m p o s i t i o n dependence of the Gibbs free e n e r g y of mixing and the e n h a n c e ment factor d In aLi/dlnXLi which r e l a t e s the c h e m i c a l diffusion coefficient and the self diffusion coefficients within the Li-A1 solid solution.
T
HERE is c u r r e n t l y a c o n s i d e r a b l e amount of i n t e r e s t in l i f h i u m - a l u m i n u m alloys as anode (negative e l e c t r o d e ) m a t e r i a l s in new types of high p e r f o r m a n c e s e c o n d a r y b a t t e r i e s , e.g., the AI,"LiAI"/FeS x (where x ~ 1 or 2), 1-s and as high s t i f f n e s s light weight cons t r u c t i o n m a t e r i a l s for a i r c r a f t . 7-~~ The solid s o l u b i l i t y of l i t h i u m in a l u m i n u m has b e e n studied by a n u m b e r of i n v e s t i g a t o r s . ~-~7 However, the a g r e e m e n t among r e s u l t s has been v e r y poor, except in the two most r e c e n t studies.16'~7 T h i s lack of a g r e e m e n t has been a t t r i b u t e d to the use of m a t e r i a l s of different p u r i t y , and to c o n t a m i n a t i o n d u r i n g the s a m p l e p r e p a r a t i o n p r o c e s s . One should be able to avoid these p r o b l e m s by e l e c t r o c h e m i c a l l y i n c o r p o r ating l i t h i u m into a l u m i n u m of high p u r i t y f r o m an a p p r o p r i a t e m o l t e n s a l t . T h i s study d e m o n s t r a t e s that this can indeed be r e a l i z e d for this s y s t e m . The only p r e v i o u s data on the c h e m i c a l diffusion of l i t h i u m in a l u m i n u m a p p e a r to be those r e p o r t e d by Costas, ~8 along with one point by Melendres.~9 The second a s p e c t of the p r e s e n t work was the m e a s u r e ment of the c h e m i c a l diffusion coefficient, D, in this phase f r o m 400 to 600~ by the use of two different e l e c t r o c h e m i c a l t e c h n i q u e s , a p o t e n t i o s t a t i c method, in which the l i t h i u m c o n c e n t r a t i o n at the s u r f a c
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