The solution rate of alumina in CaF 2 -Al 2 O 3 slags
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The r a t e of s o l u t i o n of A1203 in C a F 2 + 30 wt pct A120 s (at 1518 ~ and 1509~ and C a F 2 + 20 wt pct A1203 (at 1500~ liquids has been d e t e r m i n e d . The o p e r a t i v e p r o c e s s is d i f f u s i o n - c o n t r o l l e d , with an i n t e r d i f f u s i o n coefficient, D for the p r o c e s s v a r y i n g b e t w e e n 8.5 and 8.1 • 10-5 sq c m s -1 in the C a F 2 + 30 wt pct A12Oa slags, and 4.0 • 10 -5 sq cm s -I in the C a F z + 20 wt pct A1203 slag. E s t i m a t i o n s of the r a t e at which a l u m i n a i n c l u s i o n s would r e a c t with t h e s e slag d u r i n g the e l e c t r o s l a g p r o c e s s i n g of s t e e l s , indicate that e l e c t r o d e i n c l u s i o n s a p p r o a c h i n g 100/~ i n d i a m will be d i s s o l v e d .
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r a t e at which a l u m i n a i n c l u s i o n s d i s s o l v e in the s l a g r e g i o n of an e l e c t r o s l a g m e l t is a d e t e r m i n i n g factor in f o r m of the ingot i n c l u s i o n d i s t r i b u t i o n . In g e n e r a l , the e l e c t r o d e m a t e r i a l is a cast, or wrought, p r o d u c t and will contain n o n m e t a l l i c i n c l u s i o n s which m a y be quite l a r g e (100/~ d i a m ) in a cast m a t e r i a l . When such i n c l u s i o n s contact the slag at the e l e c t r o d e / s l a g i n t e r f a c e , the r a t e of s o l u t i o n is d e t e r m i n e d by t h r e e f a c t o r s , n a m e l y , the h y d r o d y n a m i c r e g i m e , the o p e r a t i v e diffusion coefficients, and the c h e m i c a l p o t e n t i a l g r a d i e n t . The p r e s e n t work r e l a t e s to a l u m i n a d i s s o l v i n g into a CaF~-Al203 liquid at a l u m i n a c o n c e n t r a t i o n s close to s a t u r a t i o n , and is studied using the r o t a t i n g disc technique. We also p r e s e n t some s u g g e s t i o n s as to the r a t e of s o l u t i o n to be expected for a l u m i n a i n c l u s i o n s in e l e c t r o d e s r e m e l t e d by the e l e c t r o s l a g method through the r e l e v a n t s l a g c o m positions.
Alumina Discs D i s c s w e r e cut u l t r a s o n i c a l l y f r o m p l a t e s of e l e c t r o n i c g r a d e r e c r y s t a l l i z e d a l u m i n a , and were 20.5 m m diam b y 0.50 m m thick with a 0.39 m m sq hole in the c e n t e r . As the d i s c and the s q u a r e hole were cut s i m u l t a n e o u s l y , any s o u r c e of r o t a t i o n a l e c c e n t r i c i t y was m i n i m i z e d . Apparatus The a p p a r a t u s used is shown in Fig. 2. The slag is contained in a g r a p h i t e c r u c i b l e , which is i n s u l a t e d by
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EXPERIMENTAL A n u m b e r of e x p e r i m e n t a l p r o b l e m s exist in a p p l y ing the r o t a t i n g disc technique ~ to the d e t e r m i n a t i o n of high t e m p e r a t u r e diffusion coefficients. The m o s t s e r i o u s of these is the m e c h a n i c a l one of e n s u r i n g that the d i s c r o t a t e s without e c c e n t r i c i t y and
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