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IN P a r t

II of t h i s s e r i e s 1 we showed that n i t r o g e n a t e d F e - A1 a l l o y s , c o n s i s t i n g of n u m e r o u s , e x t r e m e l y s m a l l A1N p a r t i c l e s and of f e r r i t e p h a s e containing a v e r y l a r g e d e n s i t y of d i s l o c a t i o n s , a b s o r b c o n s i d e r a b l e a m o u n t s of n i t r o g e n in e x c e s s of the n o r m a l l a t t i c e s o l ubi l i t y . P a r t of the e x c e s s n i t r o g e n w a s i d e n t i f i e d as be in g a d s o r b e d at the A 1 N - f e r r i t e i n t e r f a c e , and a n o t h e r p a r t w a s c h a r a c t e r i z e d a s being held at the c o r e s and a s s o c i a t e d s t r e s s f i e l d s of d i s l o c a t i o n s . The d i s l o c a t i o n - h e l d n i t r o g e n w a s e x p e r i m e n t a l l y shown to exhibit r e v e r s i b l e i s o t h e r m s at v a r i o u s t e m p e r a t u r e s , and Li and Chou la d e m o n s t r a t e d r e m a r k a b l y good a g r e e m e n t b e t w e e n the e x p e r i m e n t a l i s o t h e r m s and i s o t h e r m s c a l c u l a t e d f r o m t h e t h e r m o d y n a m i c s of s t r e s s e d b o d i e s .2 It is c l e a r l y of i n t e r e s t to i n v e s t i g a t e the extent and the m a n n e r of the l o w e r - t e m p e r a t u r e a b s o r p t i o n of h y d r o g e n at v a r i o u s f u g a c i t i e s by n i t r o g e n a t e d a l l o y s conta in i n g d i f f e r e n t , known a m o u n t s of a b s o r b e d n i t r o g e n c o r r e s p o n d i n g to m e a s u r e d a c t i v i t i e s . The i n i t i a l i d e a w a s that the p r e a b s o r b e d n i t r o g e n would p r e e m p t d i s l o c a t i o n - c o r e s i t e s f r o m o c c u p a n c y by h y d r o g e n at r o o m t e m p e r a t u r e , but that i n t e r f e r e n c e by n i t r o g e n would be n e g l i g i b l e away f r o m the c o r e s . The p r e s e n t i n v e s t i g a t i o n c o n s i s t s of n i t r o g e n a t i n g an F e - 2 pct (by weight) a l u m i n u m a l l o y , e s t a b l i s h i n g the r e v e r s i b l e n i t r o g e n c o n t e n t - a c t i v i t y i s o t h e r m at 500~ and e s t a b l i s h i n g the r o o m - t e m p e r a t u r e r e v e r s i b l e h y d r o g e n cont e n t - f u g a c i t y i s o t h e r m s f o r a l l o y s with v a r i o u s a m o u n t s of f r o z e n - i n n i t r o g e n , which at 500~ is r e v e r s i b l y a b s o r b e d . We c o m p a r e the e x p e r i m e n t a l n i t r o g e n i s o t h e r m s with i s o t h e r m s c a l c u l a t e d by the L i - C h o u p r o c e d u r e , and the e x p e r i m e n t a l h y d r o g e n i s o t h e r m s and i s o b a r s with c u r v e s c a l c u l a t e d by the L i - C h o u t e c h n i q u e but m o d i f i e d to acc o u n t f o r s i t e s p r e e m p t e d by n i t r o g e n . E X P E R I M E N T A L D E T A I L S AND R E S U L T S A) N i t r o g e n a t i o n and N i t r o g e n I s o t h e r m s In o r d e r to p r o d u c e a l l o y s wi