Electrotransport and thermotransport of oxygen and nitrogen in vanadium metal
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t r a n s p o r t of i n t e r s t i t i a l s o l u t e s in a m e t a l m a t r i x u n d e r the influence of e i t h e r an e l e c t r i c field or a t e m p e r a t u r e g r a d i e n t is of i n t e r e s t to a b a s i c u n d e r s t a n d i n g of the b e h a v i o r of s o l u t e s in m e t a l s as well as to the e n g i n e e r i n g a p p l i c a t i o n of m e t a l s and a l l o y s . The t r a n s p o r t b e h a v i o r of oxygen and n i t r o g e n in the group V t r a n s i t i o n m e t a l s is of p a r t i c u l a r i n t e r e s t b e c a u s e of the d e t r i m e n t a l effect that t h e s e s o l u t e s have on the m e c h a n i c a l p r o p e r t i e s of t h e s e bcc r e f r a c t o r y metals. R e c e n t s t u d i e s by F r o m m and c o w o r k e r s 1-a on the e l e c t r o - and t h e r m o t r a n s p o r t of oxygen and n i t r o g e n in n i o b i u m (columbium) and t a n t a l u m have r e v e a l e d two r a t h e r i n t e r e s t i n g effects: i) a p r o n o u n c e d t e m p e r a t u r e dependence of the effective v a l e n c e i n c l u d i n g a change in sign at e l e v a t e d t e m p e r a t u r e s and ii) a m a r k e d conc e n t r a t i o n d e p e n d e n c e of the heat of t r a n s p o r t . Since v a n a d i u m is also a group V t r a n s i t i o n m e t a l , an i n v e s t i g a t i o n of t h e s e p o s s i b l e effects on the t r a n s p o r t p r o p e r t i e s of oxygen and n i t r o g e n in v a n a d i u m was i n stigated. E a r l i e r work by Schmidt and W a r n e r s showed little evidence for any t e m p e r a t u r e dependence of Z* for oxygen, n i t r o g e n , or c a r b o n i n v a n a d i u m but t h e i r m e a s u r e m e n t s w e r e m a d e at only t h r e e t e m p e r a t u r e s and over a r a t h e r l i m i t e d t e m p e r a t u r e r a n g e (1650 to 1825~ No t h e r m o t r a n s p o r t data have b e e n r e p o r t e d for e i t h e r oxygen or n i t r o g e n in v a n a d i u m but Shaw and O a t e s 6 r e p o r t a Q* value of - 4 . 9 k c a l / m o l e for c a r b o n in v a n a d i u m . Another objective of this i n v e s t i g a t i o n was to c o m p a r e v a l u e s of the effective v a l e n c e for the s a m e s o l u t e - m e t a l s y s t e m obtained by the i s o t h e r m a l nonsteady s t a t e technique employed by Schmidt and W a r n e r with those by the n o n - i s o t h e r m a l steady state t e c h nique developed by F r o m m and c o w o r k e r s .
J. MATHUNI is a Graduate Research Assistant, and E. FROMM and R KIRCttHEIM are Research Scientists in the Max-PlanckInstltut ft'lr Metallforschung,Institut far Werkstoffwlssenschaften,Stuttgart, Germany. O N. CARLSON is Senior Metallurgistand Professor, Ames Laboratory, ERDA, and Iowa State University, Ames, IA 50010. This work was done while O N Carlson was a visiting scientist with the Max-Planck Inshtut. Manuscript submitted September 12, 1975. METALLURGICALTRANSACTIONSA
PRINCIPLES The flux of solute a t o m s for a s y s t e m u n d
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