Internal sulfidation of iron
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7. E. Rudyand St. Windisch:Trans. TMS-AIME, 1968,vol.242,p. 953.
Internal Sulfidation of Iron ROSS F . BOLAND AND OWEN F . DEVEREUX
A r m c o i r o n in hydrogen sulfide a t m o s p h e r e s in the t e m p e r a t u r e r a n g e 850 to 950~ The s t u d i e s r e p o r t e d were conducted in a m a n o m e t r i c a p p a r a t u s in which gas v o l u m e and p r e s s u r e were c o n t r o l l e d by m e r c u r y - i n - g l a s s b u r e t t e s . A r m c o i r o n s p e c i m e n s * were p r e p a r e d as flat s t r i p s , a p p r o x *Reference 1 providesthe followinganalysisfor Armcoiron(in pct): Fe = 99.94, S = 0.025,Mn= 0.017, C= 0.012,P = 0.005. i m a t e l y 0.36 x 10 x 38 m m , and were m e c h a n i c a l l y polished to 600 g r i t and d e g r e a s e d with toluene p r i o r to u s e . Sulfidation s t u d i e s were conducted at 850 and 950~ with i n i t i a l hydrogen sulfide p r e s s u r e s of 220 and 440 m m Hg, Static e n v i r o n m e n t s were employed; hence these p a r t i a l p r e s s u r e v a l u e s d e c r e a s e d in p r o p o r t i o n with the extent of r e a c t i o n , with a c o r r e sponding i n c r e a s e in hydrogen p r e s s u r e . R e a c t i o n o c c u r r e d in a c l e a n V y e o r f u r n a c e tube, following two v a c u u m (5 x 10 -~ t o r r ) / h y d r o g e n a n n e a l (700 m m Hg) c y c l e s at operating t e m p e r a t u r e , for p r e d e t e r m i n e d time intervals. As in the c a s e of p r e v i o u s i n v e s t i g a t i o n s the p r i m a r y m a n i f e s t a t i o n of the sulfidation r e a c t i o n was the f o r m a tion of a t w o - l a y e r s c a l e , the i n n e r l a y e r being d e n s e and the o u t e r l a y e r p o r o u s . Both l a y e r s were shown by X - r a y d i f f r a c t i o n to be p y r r h o t i t e (FeS). As noted, the i n t e r e s t i n g a s p e c t of these e x p e r i m e n t s was the a p p e a r a n c e of both i n t e r - and i n t r a g r a n u l a r sulfide p a r t i c l e s as shown in the a c c o m p a n y i n g p h o t o m i c r o g r a p h s . P r i o r to e x p o s u r e to a sulfidizing e n v i r o n m e n t , the A r m c o i r o n exhibits o c c a s i o n a l i n t e r - and i n t r a g r a n u l a r second phase p a r t i c l e s as s e e n in Fig. 1. E n e r g y d i s p e r s i o n X - r a y a n a l y s i s (EDX) showed these p a r t i c l e s to be of two types, one showing only t i t a n i u m and p r e s u m e d to be t i t a n i u m dioxide (oxygen cannot be d e tected by our i n s t r u m e n t ) and the other a t i t a n i u m , i r o n sulfide. Both the a s - r e c e i v e d and the sulfidized i r o n d i s p l a y e d r a i s e d g r a i n b o u n d a r i e s upon SEM e x a m i n a tion following a light n i t a l etch; EDX r e v e a l e d only i r o n
A n u m b e r of i n v e s t i g a t o r s have studied the s u l f i d a tion k i n e t i c s of i r o n and i r o n alloys in hydrogen s u l fide c o n t a i n i n g gas mixtures.l-13 T y p i c a l l y , a twol a y e r s c a l e
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