Rates of evaporation of silver, lead, and bismuth from copper alloys in vacuum induction melting
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I ~ M E D A and Y a z a w a 1 c a r r i e d out s o m e e x p e r i m e n t s on the r e f i n i n g of c r u d e c o p p e r by v a c u u m m e l t i n g and d i s c u s s e d the e v a p o r a t i o n of i m p u r i t i e s f r o m a t h e r m o d y n a m i c standpoint, finding that l e a d and b i s m u t h could be e a s i l y r e m o v e d . T h e p r e s e n t study w a s u n d e r t a k e n in o r d e r to inv e s t i g a t e the r a t e of r e m o v a l of i m p u r i t i e s f r o m c r u d e c o p p e r in v a c u u m m e l t i n g . M o l t e n c o p p e r a l loys containing e a c h of s i l v e r , lead, and b i s m u t h w e r e m a i n t a i n e d at 1473 and 1573 K o r 1573 K under v a c u u m wh i l e b e i n g s t i r r e d i n d u c t i v e l y at d i f f e r e n t speeds. Their evaporation-rate constants were det e r m i n e d and the e f f e c t s of t e m p e r a t u r e and the s t i r r i n g r a t e of t h e m e l t on t h e m w e r e i n v e s t i g a t e d . F u r t h e r m o r e , the e f f e c t s of oxygen and s u l f u r on the e v a p o r a t i o n - r a t e c o n s t a n t of b i s m u t h and the f o r m e r e f f e c t on that of s i l v e r w e r e i n v e s t i g a t e d . T h e r a t e c o n t r o l l i n g s t e p f o r e v a p o r a t i o n in e a c h e x p e r i m e n t a l r u n was d i s c u s s e d .
v a c u u m m e l t i n g w as m e a s u r e d by an i o n i z a t i o n gage, b e i n g in the r a n g e 10 -1 to 1 P a . T a b l e I shows e x p e r i m e n t a l c o n d i t i o n s in e a c h e x p e r i m e n t a l r u n . A c y l i n d r i c a l a l u m i n a c r u c i b l e w as u s e d e x c e p t f o r the v a c u u m m e l t i n g of C u - P b a l l o y s (Run N u m b e r s H - 5 and H - 8 ) , in which a m a g n e s i a c r u c i b l e was us e d. T h i s a l u m i n a o r m a g n e s i a c r u c i b l e w as p l a c e d in an o u t e r a l u m i n a c r u c i b l e as shown in F i g . l ( a) . T h i s h e a t i n g condition is d e s i g n a t e d H C - A . F o r the p u r p o s e of r e d u c i n g the s t i r r i n g r a t e of t h e m e l t , the a l u m i n a c r u c i b l e w as p l a c e d in a c y l i n d r i c a l g r a p h i t e c r u c i b l e and t h e s e two c r u c i b l e s w e r e p l a c e d in an o u t e r a l u m i n a c r u c i b l e as shown in F i g . l(b). T h i s h e a t i n g condition is d e s i g n a t e d H C - B . It was obs e r v e d that the m o v e m e n t of p a r t i c l e s f l o a t i n g on top of the m e l t s u n d e r H C - B w as f a i r l y s l o w c o m p a r e d with that u n d e r H C - A . T h e m e t h o d s of d e t e r m i n a t i o n of the c o n c e n t r a EVACUATION SYSTEM
EXPERIMENTAL 1) A p p a r a t u s and P r o c e d u r e C u - A g , C u - P b , C u - B i , C u - A g - O , C u - B i - O , and CuB i - S a l l o y s w e r e v a c u u m - m e l t e d by an induction f u r n a c e . H e a t i n g w a s c a r r i e d out by a 430 KHz induc t i o n c u r r e n t and e v a c u a t i o n was c a r r i e d out by
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