Nitrogen diffusion and solubility in tungsten
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for m e t a l l i c c E o m p o n e n t s u s e f u l at high T t e m p e r a t u r e s as claddings for c e r a m i c n u c l e a r r e a c t o r f u e l s l i m i t s the s e l e c t i o n to r e f r a c t o r y m e t a l s . Such s e l e c t i o n s depend in p a r t on the ability of the c l a d ding to contain and not i n t e r a c t d e l e t e r i o u s l y with the c e r a m i c f u e l s and t h e i r d e c o m p o s i t i o n p r o d u c t s such as oxygen, c a r b o n , and n i t r o g e n . The i n t e r a c t i o n s of a r e f r a c t o r y m e t a l with r e a c t i v e g a s e s at low p r e s s u r e between 1000 ~ and 2000~ can r e s u l t in the c o n t a m i n a t i o n of the m e t a l by the i n t e r s t i t i a l l y d i s s o l v e d g a s e s a n d / o r r e a c t i o n s which lead to the f o r m a t i o n of s e c o n d p h a s e s . Of p a r t i c u l a r i n t e r e s t , at p r e s e n t , is the u s e of a u r a n i u m n i t r i d e fuel. L i t e r a t u r e i n f o r m a t i o n i n d i c a t e s t u n g s t e n to be a candidate cladding m a t e r i a l and the p u r p o s e of t h i s study was to a s s e s s the ability of t u n g s t e n to contain n i t r o g e n . The p e r m e a t i o n of n i t r o g e n t h r o u g h t u n g s t e n has been m e a s u r e d by F r a u e n f e l d e r z and Corm 2 et al., diffusion in t u n g s t e n by F r a u e n f e l d e r , z and solution in t u n g s t e n by Norton and M a r s h a l l s and F r o m m and Jehn. 4 C a l c u l a t e d v a l u e s for the s o l u b i l i t y of n i t r o g e n in t u n g s t e n has been given by F r a u e n f e l d e r . Z The fact that the a f o r e m e n t i o n e d w o r k s a r e not in a g r e e m e n t p r o m p t e d this study p a r t i c u l a r l y with r e g a r d to s o l u bility v a l u e s . In the p r e s e n t work, diffusion c o n s t a n t s , D, and s o l u b i l i t y c o n s t a n t s , S, w e r e m e a s u r e d in the t e m p e r a t u r e r a n g e of 1000 ~ to 1800~ and the n i t r o g e n p r e s s u r e r a n g e of 1 to 25 t o r r . P e r m e a t i o n c o n s t a n t s , K, w e r e c a l c u l a t e d f r o m K = DS. P r e v i o u s work s has shown that n o r e a c t i o n t a k e s p l a c e b e t w e e n solid t u n g s t e n and n i t r o g e n to f o r m a n i t r i d e at any t e m p e r a t u r e . K i e s s l i n g and Liu s r e p o r t that t u n g s t e n n i t r i d e m a y be o b t a i n e d by heating t u n g sten in a m m o n i a at 825 ~ to 875~ However, this r e a c tion p r o c e e d s slowly and at 900~ the n i t r i d e d e c o m R. L. WAGNER, formerly with Oak Ridge National Laboratory, Oak Ridge, Tenn., is now with Stellite Division, Cabot Corp., Kokomo, Ind. Research sponsored by the U. S. Atomic Energy Commissionunder contract with the Union Carbide Corp. Manuscript submitted September 15, 1969. METALLURGICALTRANSACTIONS
p o s e s into the e l e m e n t s . In view of this i n f o r m a t i o n it would appear that in the t e m p e r a t u r e and p r
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