The Bi-MnBi eutectic region of the Bi-Mn phase diagram
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e n t i a l b e t w e e n the B i / M n B i s a m p l e s and a Cu r e f e r ence s t a n d a r d was m o n i t o r e d f r o m 25 to 350~ A flowing a t m o s p h e r e of a r g o n was used throughout. The m a s s of each s a m p l e and the Cu r e f e r e n c e s t a n d a r d were 5 mg so as to m i n i m i z e the r e s p o n s e t i m e d u r ing m e l t i n g and yet r e t a i n a r e a s o n a b l e s i g n a l to n o i s e r a t i o . By c o m p a r i n g the r e s u l t i n g t h e r m o g r a m s a g a i n s t those of p u r e Bi, the s y s t e m a t i c c o m p o n e n t of the m e l t i n g e n d o t h e r m was d e t e r m i n e d . The s o l i d u s (initial d e v i a t i o n of the m e l t i n g e n d o t h e r m ) and l i q uidus (initial d e v i a t i o n plus the effective width of the e n d o t h e r m ) t e m p e r a t u r e s of e a c h s a m p l e w e r e obt a i n e d by c o r r e c t i n g for the s y s t e m a t i c c o m p o n e n t . Using this a p p r o a c h we e s t i m a t e that the t e m p e r a t u r e s of i n t e r e s t can be d e t e r m i n e d to b e t t e r than +0.3~ A f t e r a n a l y s i s by d i f f e r e n t i a l s c a n n i n g c a l o r i m e t r y , each s a m p l e ' s c h e m i c a l c o m p o s i t i o n was d e t e r m i n e d by m e a n s of c h e m i c a l s p e c t r o p h o t o m e t r i c a b s o r b a n c e . E a c h s a m p l e was f i r s t d i s s o l v e d in a s o l u t i o n c o n t a i n ing 50 pct H20 and 50 pct n i t r i c acid. M n i n this s o l u tion is t r i v a l e n t s i n c e this i s the m o s t t h e r m o d y n a m i c a l l y f a v o r e d state for the m o l a r i t y of t h e s e s o l u t i o n s . It a p p e a r s that the Mn 3. ions a r e r e l a t i v e l y f r e e and that any i o n - i o n exchange, ion coupling or s o l v a t i o n of ions has a n e g l i b i b l e effect on the Mn ~ a b s o r p t i v i t y . Using the B e e r - L a m b e r t a p p r o a c h (since our s o l u t i o n s a r e dilute), we d e t e r m i n e d the c o n c e n t r a t i o n of Mn ions by m o n i t o r i n g the r a t i o of light t r a n s m i t t e d by each s a m p l e to that t r a n s m i t t e d by a specified r e f e r e n c e s o l u t i o n . T h i s t e c h n i q u e has a s e n s i t i v i t y of +0.001 wt pct Mn and p r o v i d e d an e f f i c i e n t t e c h n i q u e for m o n i t o r i n g the c h e m i c a l c o m p o s i t i o n . In addition, m i c r o c h e m i c a l a n a l y s i s of the Bi r i c h m a t r i x of e a c h s a m p l e was p e r f o r m e d u s i n g e n e r g y d i s p e r s i v e X - r a y a n a l y s i s (EDAX) in c o n j u n c t i o n with an AMR-1000 s c a n n i n g e l e c t r o n m i c r o s c o p e in o r d e r to d e t e r m i n e the extent of Mn t e r m i n a l solid s o l u b i l ity. S t a n d a r d s of pure Mn and Bi and each s a m p l e were p l a c e d in the SEM and an X - r a y e n e r g y s p e c t r u m g e n e r a t e d for each u s i n g a 30 keV a c c e l e r a t i n g p o
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