Kinetics of reaction of ZrCl 4 -HfCl 4 vapor mixtures with solid sodium chloride spheres
- PDF / 476,932 Bytes
- 6 Pages / 604 x 784 pts Page_size
- 99 Downloads / 204 Views
H E T E R O G E N E O U S g a s - s o l i d r e a c t i o n b e t w e e n ZrC14 o r HfCI 4 v a p o r s with solid s o d i u m c h l o r i d e is known to f o r m the h e x a c h l o r o compound. 1 If the g a s e o u s phase i n v o l v e s both z i r c o n i u m t e t r a c h l o r i d e and h a f n i u m t e t r a c h l o r i d e then the r e a c t i o n p r o d u c t should be a solid s o l u t i o n of the compounds (Ref. 2), Na2ZrC16 and Na2HfC16. In the p r e s e n t work the k i n e t i c s of s i m u l t a neous f o r m a t i o n of t h e s e two c o m p o u n d s have b e e n studied e m p l o y i n g p o l y c r y s t a l l i n e s p h e r e s of s o d i u m c h l o r i d e and a s t a n d a r d gas m i x t u r e . The k i n e t i c a n a l y s i s of s o l i d - g a s r e a c t i o n s y s t e m s i n v o l v i n g s i m u l t a n e o u s f o r m a t i o n of m o r e than one compound would depend on the n a t u r e of a s s o c i a t i o n of the p r o d u c t s . The m i c r o s t r u c t u r e of the p r o d u c t l a y e r m a y c o m p r i s e of d i s p e r s e d p h a s e s , l a y e r e d p h a s e s o r a s i n g l e s o l i d s o l u t i o n phase. Even if a s i n g l e solid solution p h a s e f o r m s one cannot r u l e out the p o s s i b i l ity of n o n u n i f o r m i t y in the p r o d u c t l a y e r c o m p o s i t i o n . Obviously, however, the a n a l y s i s is s i m p l e r if the p r o d u c t is a h o m o g e n e o u s s i n g l e phase. Subsequently, it is shown that the p r e s e n t m i x e d g a s - s o l i d s y s t e m falls u n d e r t h i s c a t e g o r y . Studies on the r e a c t i o n of i n d i v i d u a l t e t r a c h l o r i d e g a s e s and s o d i u m c h l o r i d e have shown ~-5 that the f o r m a t i o n of both c h l o r o z i r c o n a t e and c h l o r o h a f n a t e o c c u r s by the outward diffusion of s o d i u m and c h l o r i n e ions by a v a c a n c y m e c h a n i s m . A s i m i l a r m e c h a n i s m should be o p e r a t i v e in the p r e s e n t c a s e also. In o t h e r words, it is p o s t u l a t e d that the s o d i u m and c h l o r i n e ions m i g r a t i n g through the p r o d u c t l a t t i c e , r e a c t with a d s o r b e d z i r c o n i u m t e t r a c h l o r i d e and h a f n i u m t e t r a c h l o r i d e m o l e c u l e s on the o u t e r s o l i d - g a s i n t e r f a c e to f o r m the r e a c t i o n p r o d u c t s with g e n e r a t i o n of v a c a n c i e s r e q u i r e d for the r e a c t i o n . The r a t e data, t h e r e f o r e , have b e e n a n a l y z e d in t e r m s of a v a c a n c y diffusion model developed in a c c o r d a n c e with the p o s t u l a t e d mechanism.
EXPERIMENTAL P r e p a r a t i o n of Sodium C h l o r i d e Spheres The s p h e r e s of n o m i n a l d i a m e t e r s , 6.6, 9.2 and 12.2 c m w e r e m a d e by c a s t i n g in s t a i n l e s s s t e e l s p l i t mold. Kinetic M e a s u r e m e n t s The a p p a r a t u s for k i n e t i c m e a s u r e m e n t s , whic
Data Loading...
