Hydrogen diffusivities in molten iron between 0.1 and 1.5 atm H 2
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Hydrogen Diffusivities in Molten Iron Between 0.1 and 1.5 Atm H 2 M . Y. S O L A R AND R. I. L. GUTHRIE
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a r e c e n t p u b l i c a t i o n , ' the a u t h o r s d e s c r i b e d a n e w e x p e r i m e n t a l m e t h o d f o r s t u d y i n g the k i n e t i c s o f g a s a b s o r p t i o n in l i q u i d m e t a l s . T h e t e c h n i q u e i n v o l v e s s u d d e n a d m i s s i o n o f p u r e g a s into a p r e v i o u s l y e v a c u a t e d a l u m i n a t u b e c o n t a i n i n g a c o l u m n of s t a g n a n t molten m e t a l . Following a short initial p e r i o d of p r e s s u r e i n s t a b i l i t y ( ~ 1 0 s e c ) , a b s o r p t i o n r a t e s c a n be a c c u r a t e l y f o l l o w e d by m o n i t o r i n g t h e r e s u l t a n t c h a n g e s i n p r e s s u r e o f a f i x e d v o l u m e of g a s . U s i n g t h e a b o v e t e c h n i q u e , the s o l u t i o n o f h y d r o g e n in p u r e l i q u i d i r o n was s t u d i e d at 1 a t m p r e s s u r e a n d c o n f i r m e d t o be a d i f f u s i o n - c o n t r o l l e d p r o c e s s . T h e t e m p e r a t u r e d e p e n d e n c e o f the h y d r o g e n d i f f u s i o n c o e f f i c i e n t i n t h e r a n g e 1550 ° t o 1 7 2 0 ° C w a s r e p o r t e d a s D=
2 . 5 7 × 1 0 -3
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to a H e w l e t t - P a c k a r d M o d e l 7 1 0 1 B p o t e n t i o m e t r i c recorder. P r o v i d e d the rate controlling m e c h a n i s m for h y d r o g e n a b s o r p t i o n i n m o l t e n i r o n o v e r the r a n g e o f p r e s s u r e s i n v e s t i g a t e d is diffusion in t h e l i q u i d p h a s e , t h e c u m u l a t i v e p r e s s u r e d r o p , A p , a f t e r t s e c o f gasl i q u i d m e t a l c o n t a c t , s h o u l d be r e l a t e d t o t h e s y s t e m v a r i a b l e s by t h e e q u a t i o n C*oARTr ( l + a ) Vr
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w h e r e R is t h e i d e a l gas c o n s t a n t , C,0 is t h e i n t e r f a c i a l c o n c e n t r a t i o n of d i s s o l v e d h y d r o g e n g i v e n by S i e v e r t ' s L a w ( g - a t o m - c m - 3 ) , D is t h e diffusion c o e f f i c i e n t o f h y d r o g e n (sq c m . s e e - l ) , A is t h e c r o s s s e c t i o n a l a r e a o f t h e m e l t ( s q c m ) , Vr ( c u c m ) i s t h e v o l u m e o f t h e cold z o n e o f t h e gas p h a s e at t e m p e r a t u r e T r (°K) a n d a i s a hot z o n e c o r r e c t i o n f a c t o r w h i c h t a k e s into a c c o u n t the f a c t t h a t p r e s s u r e c h a n g e s o c c u r in a n o n i s o t h e r m a l c l o s e d s y s t e m . ' E q . [2] a s s u m e s that t h e i n i t i a l bulk h y d r o g e n c o n c e n t r a t i o n is z e r o a n d p r e d i c t s a l i n e a r r e l a t i o n s h i p b e t w e e n A p a n d 14-fi-~-~. T h u s e x p e r i m e n t a l d a t a w e r e t r a n s f o r m e d into A p VS ~ c u r v e s . Fig. 1 s h o w s s u c h a c u r v e ( c u r v e 1) o b t a i n e d f o r a r u n c o n d u c t e d a t 1 6 0 4 ° C a n d a t 0 . 1 2 3 6 a i m i
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