Oxidation rates of liquid copper and liquid copper sulfide
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ALTHOUGHt h e r e
have b e e n m a n y s t u d i e s on the t h e r m o d y n a m i c s of copper s m e l t i n g a s d e m o n s t r a t e d in the r e v i e w s of Schuhmann, 1 Ruddle, 2 and the m o r e r e c e n t review by T o g u r i , T h e m e l i s , and J e n n i n g s , 3 v e r y l i t t l e data a r e a v a i l a b l e on the k i n e t i c a s p e c t s of this p r o c e s s . The p r e s e n t i n v e s t i g a t i o n was t h e r e f o r e u n d e r taken a s p a r t of a study on the k i n e t i c s of copper s m e l t i n g and c o n v e r t i n g r e a c t i o n s . Any r a t e p r o c e s s can be b r o k e n down into a n u m b e r of p h y s i c a l t r a n s p o r t and c h e m i c a l r e a c t i o n s t e p s . In g e n e r a l , t h e r e a r e t h r e e b a s i c steps between r e a c t i n g s p e c i e s in s e p a r a t e p h a s e s : 1) Diffusion of the r e a c t a n t through a b o u n d a r y l a y e r to the g a s - l i q u i d or l i q u i d - l i q u i d i n t e r f a c e . 2) The r e a c t i o n step at the i n t e r f a c e . This i n c l u d e s a b s o r p t i o n , a d s o r p t i o n , d i s s o c i a t i o n or a c t i v a t e d c o m plex m e c h a n i s m s which d e t e r m i n e the o v e r a l l c h e m i c a l reaction rate. 3) Diffusion of the r e a c t i o n p r o d u c t s away f r o m the interface. The o v e r a l l r e a c t i o n r a t e i s equal to the s u m of the diffusion s t e p s , the c h e m i c a l r e a c t i o n steps, and the p h y s i c a l k i n e t i c p r o c e s s e s affecting the diffusion p a t h s . The step p r e s e n t i n g the l a r g e s t r e s i s t a n c e can be cons i d e r e d to be r a t e c o n t r o l l i n g . At high t e m p e r a t u r e s it i s expected that the s p e c i e s at the r e a c t i o n i n t e r f a c e a r e v e r y n e a r c h e m i c a l e q u i l i b r i u m , thus diffusion in the liquid or gas p h a s e i s v e r y often the r a t e l i m i t i n g step. In m a n y c a s e s , a c o n t r o l l i n g step can be isolated and its rate d e t e r m i n e d by an a p p r o p r i a t e e x p e r i m e n t a l t e c h n i q u e . In the p r e s e n t study the oxidation r a t e of m o l t e n c u p r o u s sulfide was studied u n d e r conditions of gas diffusion c o n t r o l . EXPERIMENTAL A) Method The t e c h n i q u e adopted to m e a s u r e the r a t e s of oxidation was b a s e d on the weight change of a m o l t e n s a m p l e F. AJERSCH and J. M. TOGURI are Graduate Student and Professor, respectively, Department of Metallurgyand Materials Science, Univeristy of Toronto, Toronto, Ontario, Canada. Manuscript submitted January 13, 1972. METALLURGICALTRANSACTIONS
held in a tube of known length. If an i n e r t gas or a gas of different c o m p o s i t i o n f r o m the e q u i l i b r i u m v a p o r p r e s s u r e is p a s s e d over the s u r f a c e of an open tube, c o n c e n t r a t i o n g r a d i e n t s i n s i d e the tube will be e s t a b l i s h e d . At the g a s - l i q u i d i n t
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