Kinetics of reaction of zirconium tetrachloride vapors with solid sodium chloride spheres
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This compound Na2ZrCI 6 is of much i n d u s t r i a l i m p o r tance. 3,4 Single c r y s t a l p l a t e s of sodium c h l o r i d e w e r e e m ployed in the two p r e v i o u s studies %6 on the k i n e t i c s of f o r m a t i o n of sodium h e x a c h l o r o z i r c o n a t e . In the p r e s e n t i n v e s t i g a t i o n the k i n e t i c s have been studied using p o l y c r y s t a l l i n e s o d i u m c h l o r i d e s p h e r e s . The weight gain, due to f o r m a t i o n of the c o h e r e n t and nonporous product, was m e a s u r e d using a q u a r t z s p r i n g in an all p y r e x c l o s e d s y s t e m . The k i n e t i c s of the r e a c tion w e r e i n v e s t i g a t e d under v a r i o u s conditions of t e t r a c h l o r i d e v a p o r p r e s s u r e (175 to 1033 m m Hg) and r e a c t i o n t e m p e r a t u r e (415 to 525~ Sodium c h l o r i d e s p h e r e s of t h r e e d i f f e r e n t s i z e s w e r e used. In addition, s o m e m a r k e r e x p e r i m e n t s have been c a r r i e d out to s u b s t a n t i a t e the p o s t u l a t e d r a t e l i m i t i n g diffusion step in the r e a c t i o n . EXPERIMENTAL
t u r e fluctuations w e r e as l a r g e as ~3~ which r e s u l t e d in an u n c e r t a i n t y of about 4-69 m m p r e s s u r e s at 330~ S p h e r i c a l s a m p l e s (nominal diam 6.6, 9.2 and 12.2 mm) w e r e obtained by p o u r i n g m o l t e n s o d i u m c h l o r i d e in a p r e h e a t e d s t a i n l e s s s t e e l mold followed by slow cooling. For all sizes, the bulk porosity was around 13 pct. It was, however, noticed that the porosity was almost entirely confined to the central region. A calibrated quartz spring and the sample were suspended from a cap with a book and this cap was joined to the top of the reaction chamber. The top was heated by a separate cover. The high temperature spring constant, usually 4 to 4.25 pet higher than the r o o m temperature value, was determined for every run. All weight gain m e a s u r e m e n t s were computed from the calibrated high temperature spring constant values. For starting a run, the reaction c h a m b e r was maintained at 400 to 450~ and evacuated for about 24 h for removal of any traces of moisture. Twice distilled zirconium tetrachloride was filled in a bulb inside a dry box, the bulb was then joined to the rest of the system in the minimum possible time (2 to 3 min) and the trolley furnace pushed over it. The bulb was then heated to about 160~ and the entire system was evacuated for 2 to 3 h. Finally, the system was vacuum sealed from the top.
The glass set up used is shown in Fig. I. It is similar to the one described earlier by Dutrizac and Flengas. s The temperatures of the bulb and that of the reaction chamber were controlled to within •176 and J:2~ respectively. The vapor pressure of tetrachloride was calculated using the relationship 7 logP
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5400 T + 11.766 (480 to 689K)
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w h e r e P is p r e s s u r e of t e t r a c h l o r i d e in m m Hg and T the bulb t e m p e r a t
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