Operating experiences with electrolytes containing lithium fluoride
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the f o r e s e e a b l e f u t u r e s o d i u m c r y o l i t e w i l l be t h e m a i n c o m p o n e n t o f the e l e c t r o l y t e u s e d i n the e l e c t r o l y s i s o f a l u m i n u m . F r o m the v e r y b e g i n n i n g o f i n d u s t r i a l a l u m i n u m production, however, there have been many proposals and investigations to improve the prop e r t i e s o f t h e e l e c t r o l y t e t h r o u g h a d d i t i o n of o t h e r s a l t s . T o d a y CaF~ a n d AIFa a r e commonly used additions. A d d i t i o n s of N a C 1 , M g F 2 , KF, a n d B a F z h a v e b e e n t e s t e d in e x p e r i m e n t a l r e d u c t i o n c e i l s , w i t h o u t c o n v i n c i n g s u c c e s s . A l s o , a d d i t i o n s o f L i F w e r e s u g g e s t e d by H a l l z i n the f i r s t p a t e n t s c o n c e r n i n g the r e d u c t i o n o f a l u m i n a , a n d v a r i o u s l a b o r a t o r y t e s t s i n d i c a t e d f a v o r a b l e aspects for operating units. This material, however, had t o be c o n s i d e r e d u n s u i t a b l e f o r c o m m e r c i a l u s e b e c a u s e of i t s h i g h c o s t . O n l y w h e n t h e p r o d u c t i o n of l i t h i u m i n c r e a s e d , due t o the d e v e l o p m e n t o f n u c l e a r t e c h n o l o g y , did f a v o r a b l e c o n d i t i o n s r e s u l t f o r t h e a p p l i c a t i o n of l i t h i u m - s a l t s i n the a l u m i n u m e l e c t r o l y s i s , z T h u s , a l m o s t 10 y e a r s a g o , V A W s t a r t e d e x p e r i m e n t s by a d d i n g l i t h i u m - s a l t s t o the e l e c t r o l y t e . S i n c e t h e successful c o m p l e t i o n o f t h e s e e x p e r i m e n t s s o m e y e a r s a g o , a l l p o t l i n e s of t h e a l u m i n u m p l a n t L i p p e w e r k h a v e been operating with LiF modified electrolyte,
l ) Holrn ( I 9 6 6 ) 23 Gustow (1945) 3 )Edoyon, Monvelyon, Boboyon (1965) 4 ) Chin. Hoflmgsheod ( t 9 6 6 ) 5)Moho$ovsky, Melinovsky (1966) 6 ) Tschu - Yon- An, Beijojew 0959)
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Graphs can readily d e m o n s t r a t e h o w physical c h a r acteristics of a melt change when LiF and o t h e r s a l t s a r e a d d e d a n d w h a t i n f l u e n c e m i g h t be e x p e c t e d o n the o p e r a t i o n of the r e d u c t i o n c e l l . T h e m a i n t a r g e t of a l l s a l t a d d i t i o n s i s the l o w e r i n g o f the f r e e z i n g p o i n t a n d w i t h i t the o p e r a t i n g t e m p e r a ture b e c a u s e a s e r i e s o f factors, such as c u r r e n t effic i e n c y a n d c o n s u m p t i o n o f a n o d e s a n d b a t h , d e p e n d on t e m p e r a t u r e . F i g . 1 s h o w s t h e i n f l u e n c e of v a r i o u s add i t i o n s o n the f r e e z i n g t e m p e r a t u r e . 3-8 T h e r e d u c t i o n o f the f r e e z i n g t e m p e r a t u r e t h r o u g h t h e a d d i t i o n o f l i t h i u m c r y o l i t e i s m u c h m o r e p r o n o u n c e d than t h r o u g h the c o m m
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