Diffusion layer interpretation of the interaction of electrorefining addition agents
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r i t y . Surface r o u g h n e s s leads to e l e c t r i c a l s h o r t s b e t w e e n the anodes and cathodes in the c o m m e r c i a l o p e r a t i o n . I m p u r i t i e s lower e l e c t r i c a l conductivity. P u r i t y is affected by o c c l u s i o n of e l e c t r o l y t e s , cod e p o s i t i o n of ions and p a r t i c l e s , and i n c o r p o r a t i o n of n o n d e p o s i t i n g anions and cations. Severe c o n c e n t r a tion p o l a r i z a t i o n f a v o r s codeposition of i m p u r i t i e s . Surface r o u g h n e s s as r e l a t e d to g r a i n s i z e , s m o o t h n e s s , and c o m p a c t n e s s of the deposit affect o c c l u s i o n of i m p u r i t i e s . T h e s e f a c t o r s a r e a l s o r e l a t e d to the a m o u n t of c o n c e n t r a t i o n p o l a r i z a t i o n at the cathode and the a m o u n t and types of addition agents used. Both c u r r e n t and power a r e i m p o r t a n t cost f a c t o r s in c o m m e r c i a l o p e r a t i o n s . The c u r r e n t d e t e r m i n e s the r a t e of copper deposition. F a r a d a y ' s Law, 96,487 c o u l o m b s will deposit one e q u i v a l e n t , r e l a t e s c u r r e n t to d e p o s i t i o n r a t e . Power (IV = IZR) is i m p o r t a n t s i n c e it, not c u r r e n t , is the e n e r g y that is paid for. E l e c t r o r e f i n i n g f a c i l i t i e s could be used m o r e effic i e n t l y and p r o f i t a b l y if high c u r r e n t d e n s i t i e s could be used. Low c u r r e n t e f f i c i e n c y and i n c r e a s e d s u r f a c e r o u g h n e s s at higher c u r r e n t d e n s i t i e s l i m i t the use of higher c u r r e n t d e n s i t i e s . Addition a g e n t s such as glue, salt, and wetting agents a r e used to c o n t r o l s u r f a c e r o u g h n e s s , t h e r e b y p e r m i t t i n g higher c u r r e n t d e n s i t i e s , even though these higher c u r r e n t d e n s i t i e s i n c r e a s e power c o n s u m p t i o n p e r unit of m e t a l deposited. Organic addition agents have b e e n t r a d i t i o n a l l y used in copper d e p o s i t i o n to p r o m o t e s m o o t h n e s s of the cathode. 5 These o r g a n i c m a t e r i a l s , u s u a l l y with a m i n e groups or other e l e c t r o n e g a t i v e groups a r e supposed to a d s o r b at peaks on the cathode due to higher c h a r g e d e n s i t i e s or t h i n n e r diffusion l a y e r s . 1'6,7 The a d s o r p tion of the glue then i n h i b i t s deposition at these peaks c a u s i n g l e s s f a v o r a b l e lower s i t e s to be a c t i v a t e d u n t i l the a d s o r b e d addition agent b r e a k s down or is cove r e d over d u r i n g deposition. The r e p e t i t i o n of this a d s o r p t i o n - i n c l u s i o n p r o c e s s o c c a s i o n a l l y is so s e v e r e as to r e s u l t in a l a m i n a t e d a p p e a r a n c e in the c r o s s - s e c t i o n a l view of the peak. 8 Small a m o u n t s of o r g a n i c m a t t e r have been r e p o r t e d to r e d u c e
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