Kinetics of solid vanadium-nitrogen reactions at high temperatures
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have b e e n conducted c o n c e r n i n g the r e a c t i o n b e t w e e n n i t r o g e n and solid v a n a d i u m . Howe v e r , only a l i m i t e d n u m b e r of these h2 have dealt with the k i n e t i c s and m e c h a n i s m s of the n t t r t d i n g r e a c t i o n . The p u r p o s e of the p r e s e n t work was to a c q u i r e a b e t t e r u n d e r s t a n d i n g of this r e a c t i o n . G u l b r a n s e n and Andrew ~ exposed p u r e v a n a d i u m sheet to n i t r o g e n gas between 873 and 1173 K for 2 h m a x i m u m . Most r e a c t i o n s were c a r r i e d out at a p r e s s u r e of 1.01 x 104 Pa (76 t o r r ) , but at 1173 K they also n i t r i d e d s a m p l e s at p r e s s u r e s of 2.0 • 102 and 1.01 • 10 z Pa (1.5 and 7.6 t o r r ) . Except for the i n i t i a l stage of the r e a c t i o n , the weight gain followed a p a r a b o l i c t i m e dependence. They concluded that the weight gain was caused by the diffusion of n i t r o g e n into the m e t a l to f o r m a solid solution. However, the r e a c t i o n was not s e n s i t i v e to p r e s s u r e , and this g e n e r a l l y indicates the p r e s e n c e of a n i t r i d e l a y e r on the m e t a l s u r f a c e d u r i n g n i t r i d i n g . They i n f e r r e d that a thin n i t r i d e l a y e r was p r e s e n t d u r i n g the r e a c t i o n but d i s s o l v e d into the m e t a l after the n i t r o g e n gas had b e e n r e m o v e d . They r e p o r t e d an a c t i v a t i o n e n e r g y of 131 k J / m o l (31.4 k c a l / m o l e ) for the r e a c t i o n . Others 3 l a t e r r e p o r t e d an a c t i v a t i o n e n e r g y of 142 k J / m o l (34 k c a l / m o l e ) for the diffusion of n i t r o g e n in v a n a d i u m . Verkhoglyadova, Dubovik, and Samsonov a exposed v a n a d i u m powder to n i t r o g e n gas at 1 atm for 4 h m a x i m u m . T h e i r t e s t s were in the t e m p e r a t u r e r a n g e of 773 to 1773 K. Above 1073 K they r e p o r t e d a p a r a b o l i c r a t e law for all r e a c t i o n s , but no k i n e t i c data were p r e s e n t e d for the t e s t s above 1473 K. The hexagonal c l o s e - p a c k e d v a n a d i u m n i t r i d e VaN and the f a c e c e n t e r e d cubic v a n a d i u m n i t r i d e VN were identified. These n i t r i d e s a r e the only ones to be expected at high t e m p e r a t u r e s . 4
P. MUIJE is Associate Professor, School of Chemical Engineering, Georgie Institute of Technology, Atlanta, Ga. 30332. R. M. HORTON and S. A. DURANare Associate Professor and Professor, respectively, Department of Materials Science and Engineering,Washington State University,Pullman, Wash. 99163. Manuscript submitted March 2 l, 1973. METALLURGICALTRANSACTIONS
At low t e m p e r a t u r e s , a t h i r d v a n a d i u m - n i t r o g e n phase could f o r m a c c o r d i n g to the work of Henry et al. 5 They o b s e r v e d a sluggish t r a n s f o r m a t i o n between 773 and 873 K in s o m e v a n a d i u m - n i t r o g e n alloys, wher
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