A magnetization-chemisorption study of hydrogen and sulfur dioxide on iron
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known ~'2~ that h y d r o g e n a f f e c t s the m e c h a n i c a l p r o p e r t i e s of many s t e e l s . C h a n g e s in d u c t i l i t y , and c r a c k g r o w t h r a t e s f r o m t h e i r v a l u e s in a i r to l o w e r v a l u e s in the p r e s e n c e of h y d r o g e n a r e w e l l d o c u m e n t e d . T h e h y d r o g e n m a y be p r e s e n t as a r e s u l t of c h a r g i n g ( i n t e r n a l h y d r o g e n e m b r i t t l e m e n t ) o r a s a r e s u l t of h y d r o g e n gas in the e n v i r o n m e n t ( e x t e r n a l or environmental hydrogen embrittlement). Previous s t u d i e s of the effect of low p r e s s u r e He gas ( - 1 a i m ) on 4340, ~'2 4130, 2 and 4335 V 4,5 s t e e l s d e m o n s t r a t e that a d s o r p t i o n and s u b s e q u e n t s u r f a c e r e a c t i o n s a r e e x t r e m e l y c r u c i a l s t e p s in t h e h y d r o g e n e m b r i t t l e m e n t p r o c e s s . T h i s b e c o m e s m o r e obvious when the e f f e c t s of the g a s e s s u c h a s SOs o r H2S a r e c o n s i d e r e d . T h e s e g a s e s have b e e n shown 1'2 to i n h i b i t o r p r o m o t e h y d r o gen e m b r i t t l e m e n t , r e s p e c t i v e l y . S r i k r i s h n a n ~ has shown that He a d s o r p t i o n on F e f o i l s was c o m p l e t e l y inhibited if the s a m p l e had p r i o r e x p o s u r e to SO2 and that H2S d e s t r o y e d that i n h i b i t i n g a b i l i t y . T h e s e r e s u l t s a r e in c o m p l e t e a c c o r d with e m b r i t t l e m e n t findings ~,2 and i n d e e d help to e x p l a i n t h e m . T h e r e f o r e , a g r e a t e r knowledge of the bonding of H2 and o t h e r g a s e s to the s u r f a c e of F e would be of g r e a t v a l u e . One m e t h o d to s t u d y b o n d i n g on s u r f a c e s of f e r r o m a g n e t i c s u b s t a n c e s i s to m e a s u r e t h e change of m a g n e t i z a t i o n with a d s o r p t i o n . U n d e r the r i g h t c o n d i t i o n s t h i s can s h e d light on t h e t y p e of b o n d i n g b e t w e e n a d s o r b a t e and a d s o r b e n t . Selwood 7 h a s d e v e l o p e d a low f i e l d a . c . method to s t u d y the effect of the a d s o r p tion of v a r i o u s g a s e s on f e r r o m a g n e t i c m a t e r i a l s . A c o l l e c t i o n of s m a l l d i a m e t e r p a r t i c l e s of any f e r r o m a g n e t i c m a t e r i a l w i l l a c t s u p e r p a r a m a g n e t i c a l l y and can be t r e a t e d in t e r m s of s i m p l e L a n g e v i n e q u a t i o n s (which can often be l i n e a r i z e d ) . In this way Selwood was a b l e to t r e a t the b o n d i n g of an a d s o r b a t e on a f e r r o m a g n e t i c m a t e r i a l in a s i m p l e m a n n e r . T h e change m e a s u r e d in the m a g n e t i z a t i o n e x p e r i m e n t s was t a k e n to b e due s o l e l y to the e f f e c t of b o n d i n g on the m a g n e t i c m o m e n t ( s ) of the a t o m ( s ) . Selwood went s o f a r a s to define th
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