Equilibria in reactions of CO and CO 2 with dissolved oxygen and carbon in liquid iron
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A knowledge of the e q u i l i b r i a i n v o l v i n g c a r b o n and oxygen in m o l t e n i r o n is a p r e r e q u i s i t e to u n d e r s t a n d i n g the s t e e l m a k i n g p r o c e s s . As a r e s u l t t h e r e has b e e n a g r e a t deal of work on m e a s u r i n g a c t i v i t i e s in m o l t e n F e - C , 1-7 F e - O , 8-12 and F e - C - O (Refs. 1, 4, 6, 13-15) a l l o y s . In the m a j o r i t y of c a s e s gas m i x t u r e s of known c a r b o n p o t e n t i a l (CH4/H2), oxygen p o t e n t i a l (H20//H2), or both (CO/CO2) were e q u i l i b r a t e d with m o l t e n i r o n held i n a l u m i n a or m a g n e s i a c r u c i b l e s at 1 atm total p r e s s u r e . However, t h e s e m e a s u r e m e n t s have b e e n r e s t r i c t e d to s m a l l r a n g e s of c a r b o n c o m position. The CO/COs m i x t u r e s can be used to study the t e r n a r y F e - C - O s y s t e m . The a c t i v i t y of c a r b o n can be defined by the r e a c t i o n CO2 + C ~ 2
CO
KI = ( P c o ) 2 / [ P c o 2 ac ]
[1] [21
and the a c t i v i t y of oxygen by the r e a c t i o n CO
+ 0 -~ CO2
K2 = P C O z / [ P c o a o ].
[3l [4]
Since c a r b o n and oxygen i n m o l t e n i r o n r e a c t with each other to f o r m CO C + 0 ~ CO
[5]
K3 : P c o / [ a c a o ] .
[6]
L e v i t a t i o n at high p r e s s u r e p r o v i d e d an a p p r o p r i a t e technique for the study of the e q u i l i b r i u m b e t w e e n the m o l t e n F e - C - O s y s t e m and CO-CO2 gas m i x t u r e s . L a c k of a g r e e m e n t b e t w e e n the r e s u l t s of p r e v i o u s w o r k e r s r e l a t e s to the e x p e r i m e n t a l d i f f i c u l t i e s i n h e r e n t in the c o n v e n t i o n a l c r u c i b l e t e c h n i q u e at a t m o s p h e r i c p r e s s u r e . In the following p a r a g r a p h s the a d v a n t a g e s and d i s a d v a n t a g e s of the new t e c h n i q u e a r e given in o r d e r to a s s e s s the a c c u r a c y of the r e sulting measurements. N. H. EL-KADDAHis Lecturer, Department of Mining, Petroleum and Metallurgy, University of Cairo, Egypt, and D. G. C. ROBERTSON is Lecturer, Department of Metallurgy and Material Science, Imperial College, London, S.W. 7, England. Manuscript submitted November 29, 1976. METALLURGICALTRANSACTIONSB
It follows f r o m Eq. [2] that the a c t i v i t y of c a r b o n f o r a p a r t i c u l a r CO/COs r a t i o is p r o p o r t i o n a l to the t o t a l p r e s s u r e . T h e u s e of p r e s s u r e s up to 70 a t m allowed the use of r e l a t i v e l y high COs c o n t e n t s in CO-CO2 m i x t u r e s (CO2/CO > 0.0076) to m e a s u r e c a r b o n a c t i v i t i e s in a l l o y s c o n t a i n i n g up to 4.6 wt pct c a r b o n at 1550~ Since the oxygen p o t e n t i a l i n the gas p h a s e i s i n d e p e n d e n t of the t o t a l p r e s s u r e u s e d (Eq. [4]), it was p o s s i b l e , by u s i n g any one gas m i x t u r e , to keep the oxygen p o t e n t i a l c o n s t a n t while v a r y i n
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