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e a r l i e r p a p e r1 h a s g i v e n t h e r m o d y n a m i c f u n c t i o n s for s o l i d a n d l i q u i d LiF-A1F3 mixtures at temperatures up t o 1073 K . T h e y w e r e b a s e d o n v a r i o u s e l e c t r o c h e m i c a l measurements. At h i g h e r temperatures the p r o b l e m a r i s e s that A1203 b e g i n s t o be a p p r e c i a b l y s o l u b l e i n Li~A1F6 m e l t s , so that i t i s no l o n g e r s u i t a b l e as a d i a p h r a g m m a t e r i a l in c o n c e n t r a t i o n c e l l s . T h e p r e s e n t w o r k was t h e r e f o r e b a s e d o n m e a s u r e m e n t s o f t h e equilibrium:

[1]

3 L i F + AI(1) ~ - A1Fa + 3 L i (A1),

T a b l e I . L i C o n t e n t o f A I i n E q u i l i b r i u m w i t h L i F - A I F 3 Melts

Temp, K

NAIF3,mol fraction

1073 1073 1293+-2 " " " " "

0.253 0.251 0o255 0.390 0.382 0.233 0.219 0.312 0.306 0.330 0.351 0.405 0.460 0.464 0.480 0.224

" " " " " "

IOe'NLi, atom fraction

6.5 5.5 36 30 6.5 7.5 42 40 19 18 14 10 6.4 2.05 2.2 1.95 48

0.255

"

t h e c o n c e n t r a t i o n of L i d i s s o l v e d i n m e t a l l i c A1 i n contact with the m e l t s b e i n g m e a s u r e d . A s i m i l a r m e t h o d h a s b e e n u s e d t o d e t e r m i n e a c t i v i t i e s i n the N a F - A 1 F a s y s t e m ;2 e s s e n t i a l l y , m i x t u r e s a r e e q u i l i b r a t e d in t h i n w a l l e d g r a p h i t e c r u c i b l e s a n d q u e n c h e d .

Li,ppm wt

25 21 140 116 25 29 163 155 74 70 54 39 25 7.9 8.5 7.5 186

RESULTS AND THERMODYNAMIC TREATMENT T a b l e I s h o w s the experimental r e s u l t s . The m e l t s were f o u n d to c o n t a i n a r o u n d 1 m o l p e t N a F ( i n t r o d u c e d a s a n i m p u r i t y i n t h e A1Fa); i t h a s b e e n c o u n t e d a s t h e e q u i v a l e n t a m o u n t of L i F s i n c e e x a m i n a t i o n of r e s u l t s for the t e r n a r y LiF-NaF-A1F3 s y s t e m3 i n d i c a t e s t h a t r e p l a c e m e n t of L i F w i t h N a F a t that l e v e l has little influence o n the L i content of the metal. T h e m e l t s a l s o c o n t a i n a l i t t l e A 1 2 O s - i t w a s f o u n d that t h e r e p o r t e d r a t i o of c a t i o n s / a n i o n s w a s > 1 . It h a s b e e n a s s u m e d that the m i s s i n g anions are oxygen, and the A12Os h a s b e e n s u b t r a c t e d b e f o r e c o m p u t i n g m o l a r fractions. T h e r e s u l t s a r e p l o t t e d in Fig. 1. The f o r m o f t h e c u r v e a t t h e l o w e r e n d h a s b e e n c h o s e n t o m a k e the a c t i v i t y of A 1 F s e q u a l t o o n e a t the l i q u i d u s c o m p o s i t i o n . (see below.) T h e L i c o n t e n t m e a s u r e m e n t s i n t h e m s e l v e s do not give sufficient information t o d e d u c e activities of LiF a n d A 1 F a , t h e m o r e so s i n c e t h e a c t i v i t y c o e f f i c i e n t of L i i n A1 i s not k n o w n a t t h i s t e m p e r a t u r e a n d c o n sequently only relative v a l u e s o f a L i are available. E a r l