Further study of the electrochemical deoxidation of induction-stirred copper melts
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R. ODLE
AND
ROBERT
A. RAPP
P r e v i o u s s t u d i e s by O b e r g , F r i e d m a n , B o o r s t e i n and Rapp on the e l e c t r o c h e m i c a l d e o x i d a t i o n of i n d u c t i o n - s t i r r e d c o p p e r m e l t s have b e e n e x t e n d e d b y the m e a s u r e m e n t and int e r p r e t a t i o n of the p u m p i n g c u r r e n t and the e m f of an a u x i l i a r y g a l v a n i c c e l l to m o n i t o r oxygen c o n t e n t s at the p u m p i n g s u r f a c e . I m p e r f e c t s e a l s in the h i g h - t e m p e r a t u r e a p p a r a tus a l l o w e d the pickup of g a s e o u s oxygen by the m e l t to c o u n t e r a c t p a r t l y the e l e c t r o c h e m i c a l d e o x i d a t i o n of the m e l t . T h e o b s e r v e d p u m p i n g c u r r e n t w a s d i v i d e d into f r a c tions a c c o u n t i n g f o r this o x y g e n pickup a s w e l l a s the o x y g e n r e m o v e d f r o m the b u l k of the m e l t . C o n s i s t e n t with the d e o x i d a t i o n m e c h a n i s m of O b e r g , et al, the d e o x i d a t i o n r a t e is l i m i t e d by ionic c o n d u c t i o n in the z i r c o n t a e l e c t r o l y t e c r u c i b l e at high oxygen c o n t e n t s , and by the m a s s t r a n s p o r t of oxygen in the i n d u c t i o n - s t i r r e d m e l t a t low oxygen c o n t e n t s . A m a s s t r a n s p o r t c o e f f i c i e n t f o r o x y g e n was c a l c u l a t e d by s e v e r a l m e t h o d s .
KIUKKOLA
and W a g n e r ~ and P e t e r s et al 2,3 i n t r o d u c e d s t a b i l i z e d z i r c o n i a and t h o r i a - b a s e s o l i d e l e c t r o l y t e s for the o p e n - c i r c u i t e l e c t r o c h e m i c a l m e a s u r e m e n t s , The p e r t i n e n t e x p e r i m e n t a l m e t h o d s f o r the m e a s u r e m e n t of oxygen a c t i v i t i e s and s o l u b i l i t i e s h a v e b e e n r e v i e w e d p r e v i o u s l y . 4-6 K o r o u s i c and M a r i n c e k 7 u s e d a c l o s e d - e n d - z i r c o n i a tube to p u m p oxygen into and out of s t a g n a n t c o p p e r m e l t s at 1150~ a s i m i l a r tube s e r v e d a s a c e l l for m o n i t o r i n g the oxygen c o n t e n t s . U s i n g a z i r c o n i a tube at 1600~ F i s c h e r and J a n k e ~ e l e c t r o c h e m i c a l l y d e o x i d i z e d m e c h a n i c a l l y s t i r r e d m e l t s of F e , Co, Ni, and Cu c o n t a i n e d in a l u m i n a c r u c i b l e s . Upon the a p p l i c a tion of 7.5 V a c r o s s the e l e c t r o l y t e , the oxygen content of 450 g of m o l t e n c o p p e r was r e d u c e d in 80 min f r o m about 500 p p m O to about 25 p p m O. A c u r r e n t of a p p r o x i m a t e l y 2 . 5 - a m p s flowed t h r o u g h the e l e c t r o l y t e , but c a l c u l a t i o n s b a s e d on F a r a d a y ' s law i n d i c a t e that 100 pet c u r r e n t e f f i c i e n c y was only m a i n t a i n e d f o r a b o u t the f i r s t ten m i n u t e s . C l e a r l y , m e c h a n i c a l s t i r r i n g cannot
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