Homogeneous nucleation of CO bubbles in Fe-C-O melts
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T H E f o r m a t i o n of c a r b o n monoxide b u b b l e s in liquid i r o n a l l o y s i s often o b s e r v e d a s a c a r b o n boil or d r o p let explosion d u r i n g s p r a y - d e c a r b u r i z a t i o n o p e r a t i o n s in oxygen. Although this i n t e r e s t i n g p h e n o m e n o n is of p r a c t i c a l i n t e r e s t in other i n d u s t r i a l p r o c e s s e s , 1'2 and has b e e n the s u b j e c t of e x t e n s i v e r e s e a r c h , 3-~~ no s a t i s f a c t o r y t h e o r e t i c a l e x p l a n a t i o n of the bubble f o r m a t i o n p r o c e s s had been developed u n t i l r e c e n t l y , n'~2 In p a r t i c u l a r , c l a s s i c a l n u c l e a t i o n t h e o r i e s have been unable to r e c o n c i l e the f o r m a t i o n of c r i t i c a l vapor e m b r y o s in t h e s e m e t a l l i c s y s t e m s with the high s u r f a c e or i n t e r f a c i a l t e n s i o n s and the r e l a t i v e l y low vapor p r e s s u r e s involved. 9'12 M o r e o v e r , the n a t u r e of the a l t e r native p r o c e s s that has been m o d e l e d to r a t i o n a l i z e bubble f o r m a t i o n , v o r t e x n u c l e a t i o n , l~ is u n c l e a r . While other p o s s i b i l i t i e s , such as h e t e r o g e n e o u s n u c l e a t i o n , a r e not excluded, it s e e m s m o s t p r o b a b l e that bubble f o r m a t i o n o c c u r s in this i r o n alloy s y s t e m by a h o m o g e n e o u s n u c l e a t i o n p r o c e s s in spite of the high s u r f a c e t e n s i o n , low vapor p r e s s u r e paradox. T h i s s t r o n g i n f e r e n c e c o m e s f r o m the explosion and sac f o r m a t i o n s t u d i e s in the z i r c o n i u m s y s t e m ~4-~6 w h e r e the v e r y high t e m p e r a t u r e s involved, the r e a c t i vity of the s y s t e m , and the expected wide homogeneity r a n g e of the Z r - O - N m e l t a p p e a r to deny the e x i s t e n c e of h e t e r o g e n e o u s p r o c e s s e s . M o r e o v e r , the s y s t e m a t i c c h a n g e s in the sac f o r m a t i o n b e h a v i o r with d r o p l e t s i z e and n i t r o g e n content is s u g g e s t i v e of a homogeneous n u c l e a t i o n p r o c e s s . T h i s i n f e r e n c e i m p l i e s that the c l a s s i c a l t h e o r i e s that have been used a r e o v e r s i m p l i fied and a r e not a p p l i c a b l e to t h e s e m u l t i c o m p o n e n t s y s t e m s without s o m e m o d i f i c a t i o n . In p a r t i c u l a r , a m o r e complete d e s c r i p t i o n of the s u r f a c e l a y e r i s r e q u i r e d in o r d e r to a c c o u n t for the effects of c h e m i s o r b e d ions n'12 s i n c e the t h e r m o d y n a m i c p r o p e r t i e s of the s y s t e m will depend s t r o n g l y on the p r e s e n c e of e l e c t r i c a l c h a r g e s in the s u r f a c e l a y e r . In this r e p o r t , we n e g l e c t many f e a t u r e s of the d e c a r b u r i z a t i o n p r o c e s s , which have been i n v e s t i g a t e d and t r e a
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