High temperature oxidation of tungsten wires in CO 2 -argon mixtures
- PDF / 318,308 Bytes
- 4 Pages / 613 x 788.28 pts Page_size
- 86 Downloads / 198 Views
The oxidation k i n e t i c s of t u n g s t e n w i r e s in n a t u r a l convection has b e e n i n v e s t i g a t e d in CO 2a r g o n m i x t u r e s in the t e m p e r a t u r e r a n g e b e t w e e n 2450 and 3000 K and the COs p a r t i a l p r e s s u r e r a n g e between 2.13 • 10 -5 to 1.28 • 10 -4 atm at 0.789 a t m total p r e s s u r e . The r a t e g e n e r a l l y d e c r e a s e s with i n c r e a s i n g t e m p e r a t u r e at c o n s t a n t bulk CO2 p r e s s u r e with a m a g n i tude r a n g i n g between 0.5 to 5 • 10 -8 g / c m s s. The oxidation r e a c t i o n is gas t r a n s p o r t cont r o l l e d as d e m o n s t r a t e d b y s u p p l e m e n t a l m e a s u r e m e n t s at 0.395 a i m total p r e s s u r e . A v o l a t i l e oxide c o u n t e r diffusion model, which has b e e n p r e v i o u s l y p r o p o s e d to explain the oxidation k i n e t i c s of t u n g s t e n w i r e s in O2-argon m i x t u r e s , is in r e a s o n a b l e a g r e e m e n t with the data. T H E r a t e of v o l a t i l i z a t i o n of t u n g s t e n w i r e s b y high t e m p e r a t u r e oxidation in CO2-argon a t m o s p h e r e s has b e e n m e a s u r e d as a p a r t of a s e r i e s of s t u d i e s on the effect of g a s e o u s i m p u r i t i e s on the l i f e t i m e and effic i e n c y of i n c a n d e s c e n t lamp f i l a m e n t s . In a p r e v i o u s i n v e s t i g a t i o n1 the oxidation k i n e t i c s of t u n g s t e n w i r e s in O~-argon m i x t u r e s was r e p o r t e d . The r a t e of this oxidation r e a c t i o n g e n e r a l l y d e c r e a s e s with i n c r e a s i n g t e m p e r a t u r e and the o v e r a l l r e a c t i o n is gas t r a n s p o r t c o n t r o l l e d . A model b a s e d on c o u n t e r diffusion of v o l a tile oxides In the g a s e o u s b o u n d a r y l a y e r was shown to give a r e a s o n a b l e d e s c r i p t i o n of the o b s e r v e d k i n e t i c s . The b a s i c a s s u m p t i o n of the v o l a t i l e o x l d e - c o u n t e r diff u s i o n is no h o m o g e n e o u s c h e m i c a l r e a c t i o n s in the b o u n d a r y l a y e r . In the p r e s e n t study, the r a t e of v o l a t i l i z a t i o n of t u n g s t e n w i r e s in f r e e c o n v e c t i v e flow was i n v e s t i g a t e d in the t e m p e r a t u r e r a n g e between 2450 and 3000 K and in the COs p a r t i a l p r e s s u r e r a n g e b e t w e e n 2.13 x 10 -s and 1.28 • 10 -4 atm at 0.789 a i m total p r e s s u r e . Under t h e s e conditions only v o l a t i l e oxides of t u n g s t e n can f o r m as a r e s u l t of the r e a c t i o n between CO2 and t u n g s t e n . M e a s u r e m e n t s were a l s o c a r r i e d at 0.395 a t m total p r e s s u r e . These s u p p l e m e n t a l m e a s u r e m e n t s d e m o n s t r a t e that the oxidation of t u n g s t e n w i r e s b y COs in n a t u r a l convection is g a s - t r a n s p o r t c o n t r o l l e d . EXPERIMENTAL The e x p e r i m e n t a l approach used in
Data Loading...
