Solubility of nitrogen and carbon in CaO-Al 2 O 3 melts in the presence of graphite
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KLAUS SCHWERDTFEGERand HANS GEORG SCHUBERT are with Max-Planck-Institutfor Eisenforschung GmbH, Metallurgical Department, 4000 Diisseldorf, Germany. Manuscript submitted October 26, 1976. METALLURGICALTRANSACTIONSB
p u r e CO and held u n d e r the s a m e gas for 1 h. T h e n the N 2 - C O - A r gas was a d m i t t e d . T o t a l r e a c t i o n t i m e was b e t w e e n 30 and 100 h, d u r i n g which s a m p l e s of about 3 g w e r e t a k e n f r o m the m e l t by s u c t i o n into 4 m m ID g r a p h i t e t u b e s , in r e g u l a r i n t e r v a l s . T h e s a m ples wer, e s a n d b l a s t e d (to r e m o v e a d h e r i n g g r a p h i t e ) and a n a l y z e d for t o t a l c a r b o n , total n i t r o g e n , a n d cyanide c o n t e n t s . In s o m e of the s a m p l e s a l s o the acid s o l u b l e c a r b o n was d e t e r m i n e d which was p r a c t i cally i d e n t i c a l to total c a r b o n , i n a g r e e m e n t with p r e vious m e a s u r e m e n t s . 3 Hence, the a m o u n t s of g r a p h i t e in the s l a g a r e n e g l i g i b l y s m a l l . T h e a p p l i e d a n a l y t i cal p r o c e d u r e s have b e e n d e s c r i b e d i n a p r e c e d i n g p a p e r . 1 F u r t h e r , the Ca and A1 c o n t e n t s w e r e a n a l y z e d in o r d e r to check w h e t h e r c h a n g e s of Ca/A1 r a t i o occ u r r e d d u r i n g the long r e a c t i o n t i m e s . EXPERIMENTAL
RESULTS
AND DISCUSSION
The typical concentration-time curves are shown in Figs. 1 and 2. The zero point of the time scale is at the time when the carbon monoxide atmosphere was changed to the N2-CO-Ar gas mixture. In the upper diagrams the contents of total nitrogen (N)total, of cyanide (CN) and of total carbon (C) total are shown. Similar curves were obtained for all the other experiments. In the lower diagrams the analyzed Ca/Al ratios are plotted against time. Because of the relative unprecision of the individual Ca/A1 values average values are given for all the experiments conducted with the same master slag. Error bars indicate the scatter of the individual points. With slags of nominal composition 40 wt pct CaO/60 wt pct A1203 constant (N) total, (CN) and (C) total c o n t e n t s a r e a t t a i n e d a f t e r s o m e t i m e (e.g. F i g . 1), and the Ca/A1 r a t i o does not change within the e x p e r i m e n t a l e r r o r . With the CaOr i c h s l a g of 50 wt pct C a O / 5 0 wt pct A1203, h o w e v e r , the c u r v e s for c a r b o n and c y a n i d e have m a x i m a (e.g. F i g . 2). F u r t h e r the Ca/A1 r a t i o s d e c r e a s e with t i m e which is a p p a r e n t l y due to v o l a t i l i z a t i o n of s o m e Ca c o n t a i n i n g s p e c i e s . The s i m i l a r o b s e r v a t i o n s have b e e n made in the .previous e x p e r i m e n t s 1'2 u s i n g s l a g of 55 wt pct CAO/45 wt pct A1203. With the s l a g of 45 wt pct CAO/55 wt pct A1203 t h e r e w e r e v e r y s l i g h t c a r bon and c y a n i d e m a x i m a v i s i b l e only in the e x p e r i m e
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