A mass- spectrometric investigation of the high temperature thermodynamic stabilities of Pd- Ti alloys
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C C O R D I N G to the E n g e l - B r e w e r c o r r e l a t i o n , ~,2 c o n s i d e r a b l e bond s t r e n g t h e n i n g is expected due to e l e c t r o n t r a n s f e r when d - e l e c t r o n - d e f i c i e n t T i is a l l o y e d with a d - e l e c t r o n - r i c h p l a t i n u m f a m i l y elem e n t such as Pd. The p r e s e n t i n v e s t i g a t i o n was u n d e r t a k e n to m e a s u r e the t h e r m o d y n a m i c and m e c h a n i c a l p r o p e r t i e s of T i - P d alloys which were expected to have high b o n d i n g e n e r g i e s and to c o r r e l a t e these p r o p e r t i e s , with due c o n s i d e r a t i o n of o t h e r f a c t o r s , with the m e c h a n i c a l b e h a v i o r . A d d i t i o n a l f a c t o r s such as expected high c o r r o s i o n r e s i s t a n c e , low d e n s i t y and the a v a i l a b i l i t y of f a i r l y e x t e n s i v e s t u d i e s of the phase d i a g r a m , ~8 have been i n s t r u m e n t a l in the i n v e s t i g a t i o n of T i - P d a l l o y s . E v e n 0.2 at. pct Pd has b e e n known to confer high c o r r o s i o n r e s i s t a n c e to T i in the p r e s e n c e of b o i l i n g a c i d s , hot c h l o r i d e s and fused s a l t s o l u t i o n s . 9 P a l l a d i u m is a ~ - s t a b i l i z e r and p r o d u c e s a n eutectoid at 868 K and 19.5 wt pct Pd. ~ T h e r e a r e a n u m b e r of i n t e r m e t a l l i c compounds in this s y s t e m , i n c l u d i n g TiPd~ and TiPd; the l a t t e r is expected to show i n d u s t r i a l l y i m p o r t a n t " s h a p e m e m o r y e f f e c t s " analogous to those of T i N i . 1~ As could be i n f e r r e d f r o m E n g e l - B r e w e r concepts and the phase d i a g r a m , the highly s t a b l e t i t a n i u m alloys will be p a l l a d i u m - r i c h . In this study, the t h e r m o d y n a m i c s t a b i l i t i e s of T i - P d a l l o y s for N p d --> 0.5 a r e r e p o r t e d , and the s u b s e q u e n t i n v e s t i g a t i o n s will deal with the m e c h a n i c a l and t h e r m o d y n a m i c p r o p e r t i e s of t i t a n i u m rich alloys. Since the K n u d s e n cell m a s s s p e c t r o m e t r i c t e c h nique offers a c o n v e n i e n t choice for high t e m p e r a t u r e t h e r m o d y n a m i c i n v e s t i g a t i o n s of E n g e l - B r e w e r type t r a n s i t i o n m e t a l alloys, the p r e s e n t d e t e r m i n a t i o n of the s t a b i l i t i e s of P d - r i c h t i t a n i u m a l l o y s has been c a r r i e d out by m e a s u r i n g the ion c u r r e n t s of T i and Pd. The d i s p a r i t y in the v a p o r p r e s s u r e s of T i and Pd coupled with the r e a c t i v e n a t u r e of the a l l o y s at high t e m p e r a t u r e s , l i m i t s the a p p l i c a b i l i t y of the " i o n c u r r e n t r a t i o t r e a t m e n t ''1~,12 for the i n v e s t i g a t i o n of the T i - P d s y s t e m . Hence, p r e s s u r e c a l i b r a t i o n was U. V, CHOUDARY, formerly with Texas A & M Universi
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