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[1]

2FexOy(s) + C(s) ~2FexOy_t(s) + CO2(g)

[2]

in which when

x = 1, 2, o r 3 y = 1, 3, o r 4

The d i r e c t r ed u ct i o n m a y be v i s u a l i z e d as beginning at the points of contact between iron oxide and c a r b o n p a r t i c l e s ; and as oxygen is r e m o v e d f r o m the solid in the f o r m of CO and COs, i s l e t s of r e d u c e d iron a p p e a r on the oxide s u r f a c e and e v e n t u a l l y join t o g e t h e r to f o r m a continuous s h e l l a r o u n d the s t i l l u n r e d u c e d oxide. F u r t h e r r e d u c t i o n is a s s u m e d p o s s i b l e by the d i f fusion of carbon a t o m s t h r o u g h the r e d u c e d iron s h e l l to the i r o n / o x i d e i n t e r f a c e . The i n t e r r a c i a l c h e m i c a i

reaction involving oxide ~md carbon is presumed to occur relatively rapidly as compared to the diffusion process. Consistent with these views, Baukloh and D u r r e r 1 and Yun ~ have p r o p o s e d that diffusion through the p r o d u c t l a y e r , i . e . , r e d u c e d i r o n s h e l l , is the r a t e l i m i t i n g step in the d i r e c t r e d u c t i o n p r o c e s s . It was r e c o g n i z e d by the p r e v i o u s i n v e s t i g a t o r s ~-7 that " t r u e " d i r e c t r e d u c t i o n of i r o n oxide by c a r b o n is p o s s i b l e only when the g a s e o u s p r o d u c t s of r e a c t i o n s [1] and [2], i . e . , CO and CO~, a r e r e m o v e d f r o m the r e a c t i o n s y s t e m as f a s t as t h e s e a r e g e n e r a t e d . Baukloh et at.~ conducted d i r e c t r e d u c t i o n e x p e r i m e n t s in the r a n g e 700~ 1000~ in a vacuum of 2 x 10-z m m Hg Y. K. RAO is Assistant Professor, Henry Kmmb School of Mines, Columbia University, New York, N. Y. Manuscript submitted Augaust 26, 1970. METALLURGICAL TRANSACTIONS

and c l a i m e d to have o v e r c o m e the p r o b l e m of r e m o v ing the g a s e o u s p r o d u c t s . A r k h a r o v et at. ~ r e p o r t e d the r e s u l t s of a study in which d i r e c t r ed u ct i o n was c a r r i e d out o v e r the t e m p e r a t u r e r a n g e 1000 ~ to 1150~ in a vacuum of 1 x 10 -3 m m Hg. R e c e n t w o r k of Yun 7 was c o n c e r n e d with the k i n e t i c s of d i r e c t r ed u ct i on in m i x t u r e s of FezOs and g r a p h i t e p o w d e r s ; e x p e r i m e n t s c o v e r i n g the t e m p e r a t u r e r an g e between 700~ 1100~ w e r e c a r r i e d out in a v a c u u m of 5 x 10-4 m m Hg which, a p p a r e n t l y , e n s u r e d the r e m o v a l of g a s e o u s p r o d u c t s of p r i m a r y r e a c t i o n s [1] and [2]. The e x p e r i m e n t a l data w e r e a n a l y z e d by u s i n g the kinetic m o d e l s d e v e l o p e d f o r s o l i d - so l i d r e a c t i o n s . F o r s o l i d - s o l i d and s o l i d - g a s r e a c t i o n s that a r e d i f f u s i o n - c o n t r o l l e d , J a n d e r , ~ G i n s t l i n g and B r o u n shtein, ~~ and C a r t e r , :~ have d e v e l o p e d k i n e t i c eq u a t i ons to d