Effects of anthracite calcination and formulation variables on properties of bench scale aluminum smelting cell cathodes
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a n t h r a c i t e has for many y e a r s b e e n the p r i m a r y m a t e r i a l used in Hall cell l i n i n g s (cathodes). G r a p h i t e o r m e t a l l u r g i c a l coke a l s o m a y be added in s i g n i f i c a n t q u a n t i t i e s and 10 pct or m o r e of the cathode c a r b o n is coke f o r m e d by c a r b o n i z a t i o n of the b i n d e r . Of p r i m e i m p o r t a n c e in cathode p e r f o r m a n c e is u s e f u l life. The l i n i n g in s o m e c a s e s f a i l s c a t a s t r o p h i c a l l y ; i.e., a l u m i n u m and bath tap out t h r o u g h c r a c k s or holes in the lining. In other c a s e s , the a l u m i n u m p r o duct b e c o m e s i n t o l e r a b l y high in i r o n content due to attack on cathode c o l l e c t o r b a r s exposed due to l i n i n g d e t e r i o r a t i o n and the cell m u s t be r e m o v e d f r o m s e r vice. A n o t h e r m a j o r factor in cathode p e r f o r m a n c e is e l e c t r i c a l r e s i s t a n c e over the l i n i n g life s i n c e this is an i m p o r t a n t c o n t r i b u t o r to e n e r g y c o n s u m p t i o n . The f a c t o r s affecting l i n i n g life and e l e c t r i c a l r e s i s t a n c e a r e complex. E x a m i n a t i o n of v a r i a b l e s aff e c t i n g them a r e , in p r i n c i p l e , b e s t d e t e r m i n e d in o p e r a t i n g c e l l s . Such d e t e r m i n a t i o n s , however, a r e i n h e r e n t l y difficult to conduct with s t a t i s t i c a l s i g n i f i cance without l a r g e s c a l e , e x p e n s i v e t e s t s . Hence, b e n c h s c a l e t e s t s can prove useful. R a p o p o r t and Samoilenko 1 f i r s t r e p o r t e d the d e v e l o p m e n t of a r e v e r s e d p o l a r i t y l a b o r a t o r y t e s t cell to a c c u r a t e l y d e t e r m i n e the a m o u n t of cathode s w e l l i n g that o c c u r s d u r i n g e l e c t r o l y s i s due to a b s o r p t i o n of s o d i u m . A n u m b e r of w o r k e r s have s i n c e r e p o r t e d an i n v e r s e c o r r e l a t i o n b e t w e e n l i n i n g life and e x p a n s i o n o c c u r r i n g d u r i n g such a t e s t . I n i t i a l cathode e l e c t r i c a l r e s i s t i v i t y can be m e a s u r e d r e a d i l y at r o o m t e m p e r a t u r e . In addition, m e a s u r e m e n t of r e s i s t a n c e change d u r i n g t e s t cell o p e r a t i o n gives an i n d i c a t i o n of r e l a tive cathode voltage d r o p s to be expected f r o m d i f f e r ent cathode m a t e r i a l s . The author has r e v i e w e d 2 e a r l i e r work on the effects of v a r i o u s p a r a m e t e r s on cathode s w e l l i n g and e l e c t r i cal r e s i s t i v i t y and has r e p o r t e d work on b e n c h s c a l e cathodes made f r o m a blend of 70 pct a n t h r a c i t e c a l cined at 1135~ and 30 pct graphite. T h e p r e s e n t work DAVID BELITSKUSis Scientific Associate, Physical Chemistry Division, Alcoa Laboratories, Alcoa Center, PA 15069. Manuscript submitted Ma
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