The rate of CO bubble nucleation at oxide metal interfaces within liquid iron alloys
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AND
W. O. PHILBROOK
B a k e r , W a r n e r , and J e n k i n s found that levitated d r o p l e t s of F e - 0 . 8 pct C a l l o y s exploded when d e c a r b u r i z e d at 1660~ w h e r e a s d u r i n g the p r e s e n t i n v e s t i g a t i o n , the drops r e m a i n e d intact d u r i n g d e c a r b u r i z a t i o n at t e m p e r a t u r e s above 1850~ T h e r e f o r e , the object of this work was to d e t e r m i n e w h e t h e r h e t e r o g e n e o u s n u c l e a t i o n of CO b u b b l e s at a n i r o n - i r o n oxide i n t e r f a c e could o c c u r at 1900~ but could not o c c u r at 2200~ An equation was developed to c a l c u l a t e the n u c l e a tion r a t e of CO b u b b l e s at a n i r o n - i r o n oxide i n t e r f a c e in i r o n at 1900~ c o n t a i n i n g 0.8 pct C and in i r o n at 2200~ containing 0.1 pct C. The r e s u l t s of the c a l c u l a t i o n showed that an i r o n - i r o n oxide i n t e r f a c e could not s e r v e as a s i t e for CO bubble n u c l e a t i o n . T h e r e f o r e , a new m e c h a n i s m is p o s t u l a t e d in which c a v i t i e s swept into the levitated d r o p l e t f r o m the s u r f a c e s e r v e a s n u c l e i for CO bubble f o r m a t i o n i n s t e a d of n u c l e i f o r m e d at the i r o n - i r o n oxide i n t e r f a c e .
IN a p r e v i o u s p a p e r ,
K a p l a n and P h i l b r o o k 1 r e p o r t e d on the r e s u l t s of e x p e r i m e n t s in which F e - C a l l o y s w e r e d e c a r b u r i z e d while levitated in a h e l i n m - o x y g e n atmosphere. These experiments were performed within the t e m p e r a t u r e r a n g e 1850 ~ to 2050~ In a l l of the e x p e r i m e n t s the c a r b o n content d e c r e a s e d l i n e a r l y with t i m e . When the c a r b o n content b e c a m e l e s s than some c r i t i c a l level, which was in the r a n g e 0 to 0.2 pct and depended on the t e m p e r a t u r e and c o m p o s i t i o n of the s p e c i m e n , the drop b e c a m e u n s t a b l e and fell f r o m within the coil. In no c a s e did the s p e c i m e n explode. However, B a k e r , W a r n e r , and J e n k i n s 2'a p e r f o r m e d s i m i l a r e x p e r i m e n t s at 1660~ with v a r i o u s oxidizing a t m o s p h e r e s and found that t h e i r l e v i t a t e d drops did explode when the c a r b o n content d e c r e a s e d to the v i c i n i t y of 0.8 pct. To explain both t h e i r own e x p e r i m e n t a l r e s u l t s as well as those of B a k e r , W a r n e r , and J e n k i n s , 2'3 K a p lan and Philbrook ~ p r o p o s e d a m e c h a n i s m to a c c o u n t for the oxidation k i n e t i c s of c a r b o n f r o m l e v i t a t e d F e C a l l o y s . A c c o r d i n g to this m e c h a n i s m , oxygen is t r a n s p o r t e d towards the m e t a l s u r f a c e through t h e r m a l and diffusion b o u n d a r y l a y e r s s u r r o u n d i n g the levitated drop. S i m u l t a n e o u s l y , CO is being g e n e r a t e d at the g a s - m e t a l i n
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