The rate of chlorination of metals and oxide: part II. iron and nickel in HCL(g)
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I N a p r e v i o u s p u b li c a ti o n ~ s e v e r a l e x a m p l e s of m e t a l l u r g i c a l p r o c e s s e s w e r e g iv e n in which v o l a t i l e c h l o r i d e s a r e i m p o r t a n t . In that p u b l i c a t i o n one of the au t h o r s r e p o r t e d on the r a t e s of c h l o r i n a t i o n of iron, n i c k e l , and tin to v o l a t i l e c h l o r i d e s in c h l o r i n e . In this i n v e s t i g a t i o n the r a t e of c h l o r i n a t i o n of i r o n and n i c k e l by HC1 (g) has b e e n d e t e r m i n e d . The s t a n d a r d f r e e e n e r g i e s of the r e a c t i o n s i n v e s t i gated a r e s Ni (s) + 2HC1 (g) = NiC12 (g) + H2 (g)
R E S U L T S AND DISCUSSION
[1]
(800 to 1400K) AF ~ = 24,725 + 15.13T - 6.15T log T (cal) and f e (s) + 2HC1 (g) = FeC12 (g) + H2 (g)
in m o l e c u l a r w ei g h t s of He and HC1, i.e., the d i f f u s i v i t y d e c r e a s e s with i n c r e a s i n g HC1/He. H o w e v e r , the d i f f u s i v i t y is e s s e n t i a l l y independent of c o n c e n t r a t i o n f o r Ar-HC1 m i x t u r e s , b e c a u s e Ar and HC1 have s i m i l a r t r a n s p o r t p r o p e r t i e s . Since m a s s t r a n s f e r is i m p o r t a n t in the r e a c t i o n s studied, m o s t e x p e r i m e n t s w e r e c a r r i e d out using Ar-HC1 m i x t u r e s .
[2]
(800 to 1200) ~xF~ = 18,290 - 79.10T + 21.10T log T (cal) E v e n though the v a p o r p r e s s u r e of FeCls, as (FeC13) 2 (g) is c o n s i d e r a b l y h i g h e r than that of FeC12, its e q u i l i b r i u m v a p o r p r e s s u r e is c o n s i d e r a b l y l e s s than that f o r FeCI~ f o r the p r e s s u r e s of HC1 i n v e s t i ga ted and does not c o n t r i b u t e to the r a t e .
Nickel At low t e m p e r a t u r e s (850 to 920 K) and high p r e s s u r e s of HC1 the c h l o r i n a t i o n b e h a v i o r of n i c k e l in HCI is s i m i l a r to that in c h l o r i n e d i s c u s s e d tn d e t a i l p r e v i o u s l y , x B r i e f l y , HC1 i n i t i a l l y r e a c t s with the n i c k e l to f o r m a thin l a y e r of NIC12 (s) on the s u r f a c e , r e s u l t ing in a net weight gain of the s a m p l e . A f t e r a few m i n u t e s of r e a c t i o n , the c h l o r i d e l a y e r at t ai n s a s t e a d y st at e t h i c k n e s s (~ 5/~m), and then a s t e a d y r a t e of weight l o s s is o b s e r v e d . The r a t e is dependent on gas v e l o c i t y , e s s e n t i a l l y independent of PHC1 at high PHC1 (Fig. l(a)) and c h a n g e s a p p r e c i a b l y with t e m p e r a t u r e . The r a t e s (kNi) a r e l i s t e d in Table I f o r a gas flow r a t e
EXPERIMENTAL The apparatus and the experimental technique were essentially the same as those used previously. I The samples were of high purity (99.99 pet) iron or nickel strips 0.I cm thick ranging from 2.5 • 1.5 cm to 1.0 • 1.0 c m . E l e c t r o n i c g r a d e HC1 (g) (99.99 pct) was m i x e d with p u r i f i e d h e l i u m o r a r g o n u s i n g c o n v e n t i o n a l
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