Electrochemical deoxidation of induction-stirred copper melts
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M.
FRIEDMAN, WILLIAM M. BOORSTEIN, AND
I n d u c t i o n - s t i r r e d m e l t s of copper contained in z i r c o n i a - b a s e e l e c t r o l y t e c r u c i b l e s w e r e d e oxidized by e l e c t r o c h e m i c a l p u m p i n g of oxygen. The r a t e - c o n t r o l l i n g step for the deoxidation r e a c t i o n was found to be t r a n s p o r t of oxygen in the e l e c t r o l y t e in the higher oxygen c o n c e n t r a t i o n r a n g e s , and t r a n s p o r t a c r o s s a b o u n d a r y l a y e r in the m e l t at the m e l t / e l e c t r o l y t e i n t e r f a c e for the lower c o n c e n t r a t i o n r a n g e s . The m a s s t r a n s f e r coefficient for t r a n s p o r t of oxygen a c r o s s the b o u n d a r y l a y e r at the m e l t / c r u c i b l e i n t e r f a c e was d e t e r m i n e d to be aOcu = 1.7. exp ( - 1 2 , 9 0 0 / R T ) c m / s The o p t i m i z a t i o n of the e x p e r i m e n t a l p a r a m e t e r s for this new deoxidation method a r e discussed.
IN r e c e n t
y e a r s a n u m b e r of h i g h - t e m p e r a t u r e e l e c t r o c h e m i c a l i n v e s t i g a t i o n s 1-4 of the t r a n s p o r t of oxygen out of or into q u i e s c e n t liquid m e t a l - o x y g e n a l l o y s have been made in o r d e r to d e t e r m i n e the d i f f u s i v i t i e s and s o l u b i l i t i e s of oxygen. In this work, analogous e x p e r i m e n t s a r e extended to i n d u c t i o n - s t i r r e d m e l t s of copper to study the k i n e t i c s of e l e c t r o c h e m i c a l oxygen r e m o v a l and d i r e c t l y d e t e r m i n e m a s s t r a n s f e r coeffic i e n t s for oxygen between s t i r r e d homogeneous m e t a l m e l t s and the e l e c t r o l y t e ( c r u c i b l e ) at the m e l t / e l e c trolyte interface. The e l e c t r o c h e m i c a l cell i n c o r p o r a t e d a p a r t i a l l y s t a b i l i z e d z i r c o n i a e l e c t r o l y t e ( c r u c i b l e ) and is s c h e matically described as Cu(/) + Q
ZrO2(CaO)
(dissolved) I solid e l e c t r o l y t e
P t - A i r (P~o~ = 0.21 atm)
dr~
dt
= a i ' A " AC i
[1]
r e f e r e n c e gas
[1] F o r the case of p o t e n t i o s t a t i c e l e c t r o c h e m i c a l p u m p i n g of oxygen f r o m a q u i e s c e n t m e l t , the r a t e c o n t r o l l i n g step i s e s s e n t i a l l y a l w a y s the diffusion of oxygen in the m e l t , and by m o n i t o r i n g the ionic cell c u r r e n t d u r ing the t r a n s i e n t p e r i o d of deoxidation, the diffusivity and the s o l u b i l i t y of oxygen in the m e t a l can be c o m puted f r o m an i n t e r p r e t a t i o n of data in t e r m s of the a p p r o p r i a t e solution to the diffusion equation. The e l e c t r o c h e m i c a l t i t r a t i o n (pumping) of oxygen f r o m an i n d u c t i o n - s t i r r e d m e l t i s different b e c a u s e , through inductive s t i r r i n g , the oxygen c o n c e n t r a t i o n is m a i n t a i n e d u n i f o r m throughout the m e l t except a c
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