The solubility of nitrogen in liquid manganese
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IN the production of m a n g a n e s e by the
aluminothermic p r o c e s s , the f i n a l a l u m i n u m content of the m a n g a n e s e is about 1 pct for the s t o i c h i o m e t r i c a m o u n t of a l u m i n u m added.* One p o s s i b l e method of r e m o v i n g a l u m i n u m f r o m the m a n g a n e s e is to n i t r i d e the a l u m i n u m by blowing n i t r o g e n , or gas m i x t u r e s c o n t a i n i n g n i t r o gen, through the Mn-A1 m e l t . Knowledge of the t h e r m o d y n a m i c s of liquid m a n g a n e s e - a l u m i n u m - n i t r o g e n alloys will a s s i s t the d e v e l o p m e n t of such a p r o c e s s . The s o l u b i l i t y of n i t r o g e n in liquid m a n g a n e s e in e q u i l i b r i u m with n i t r o g e n of 1 arm p r e s s u r e has b e e n d e t e r m i n e d by Gokcen z b e t w e e n 1273 and 1500~ and by B a r a t s h v i l i , e t a l s b e t w e e n 1380 and 1800~ t h e s e two s e t s of data a r e in s u b s t a n t i a l a g r e e m e n t . The p r e s e n t work was done to d e t e r m i n e the effect of p r e s s u r e on n i t r o g e n s o l u b i l i t y in molten m a n g a n e s e . EXPERIMENTAL
About 5.5 g of m a n g a n e s e of 99.9 pet p u r i t y was m e l t e d in a r e c r y s t a l l i z e d a l u m i n a boat and e q u i l i b r a t e d in o x y g e n - f r e e N2 or N2-He m i x t u r e s in a h o r i z o n t a l m o l y b d e n u m - w o u n d f u r n a c e . The g a s e s were mixed by m e a n s of the u s u a l a r r a n g e m e n t of p r e c a l i b r a t e d c a p i l l a r y flow m e t e r s ; the total gas flow r a t e v a r i e d between 300 and 400 cm 3 (STP) min. p t / 6 per The t e m p e r a t u r e was m e a s u r e d with a pct RhP t / 3 0 pct Rh t h e r m o c o u p l e in close p r o x i m i t y of the boat c o n t a i n i n g the m e l t . The boat c o n t a i n i n g the m a n g a n e s e was pushed slowly into the hot zone while He was flowing. A f t e r the t e m p e r a t u r e in the hot zone had r e a c h e d its d e s i r e d value again, N2 was a d m i t t e d to the s y s t e m and the r u n was s t a r t e d . A few t i m e e x p e r i m e n t s at 1300 and 1500~ (Fig. 1) showed that e q u i l i b r i u m was r e a c h e d after 60 rain; for 0.025 arm N2 about 120 rain was needed to r e a c h e q u i l i b r i u m . In a l l s u b s e q u e n t e x p e r i m e n t s where pN 2 > 0.1 atm, the e q u i l i b r a t i o n t i m e was 1 h; when pN 2 < 0.1 arm the t i m e was i n c r e a s e d to 3 h. At the end of a run, the n i t r o g e n was switched off and the boat was quickly pulled into the cool p a r t of the r e a c t i o n tube for r a p i d cooling. The solidified s a m p l e s were a n a l y z e d for n i t r o g e n by two methods: 1) F o r n i t r o g e n contents below about 1 pct, the n i t r o -
gen was d e t e r m i n e d by the s o - c a l l e d i n e r t gas fusion method. 2) F o r n i t r o g e n contents above about 1 pct the K j e l d a h l method was used. F o r s o m e s a m p l e
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