The measurement of liquidus temperatures by a stationary interface technique
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d e v e l o p e d f o r the d e t e r m i n a t i o n of liquidus t e m p e r a a s t a t i o n a r y s o l i d - l i q u i d i n t e r f a c e . Its a p p l i c a t i o n to V a l u e s for the l i q u i d u s t e m p e r a t u r e s w e r e obtained, distribution coefficient.
T H E l i q u i d u s t e m p e r a t u r e in an a l l o y which c o n t a i n s up to a few p e r c e n t of s e c o n d e l e m e n t can be u s e d to c a l c u l a t e the c o r r e s p o n d i n g d i s t r i b u t i o n c o e f f i c i e n t , k o. The m e a s u r e m e n t of l i q u i d u s t e m p e r a t u r e s could p r o v i d e a f a i r l y e a s y , r a p i d m e t h o d f o r finding k o in dilute alloys. However, very accurate data are essential for the d i s t r i b u t i o n c o e f f i c i e n t c a l c u l a t i o n s to b e m e a n i n g ful,* and the p r e c i s e d e t e r m i n a t i o n of liquidus t e m p e r a t u r e s h a s p r o v e d difficult. Two m a i n a p p r o a c h e s , both of which use c o o l i n g c u r v e s , have b e e n u s e d in the p a s t . In the f i r s t a p p r o a c h , 2 a l a r g e quantity of a l l o y , of the o r d e r of a k i l o g r a m , is c o o l e d v e r y s l o w l y t h r o u g h the liquidus r a n g e and the t e m p e r a t u r e is m e a s u r e d with a f a i r l y l a r g e s e n s o r such a s a p l a t i n u m r e s i s t a n c e t h e r m o m e t e r . The m a i n a d v a n t a g e s of the m e t h o d a r e the t h e r m a l s t a b i l i t y of the l a r g e m a s s of a l l o y , and the a b i l i t y to use l a r g e s e n s o r s , which a r e m o r e s t a b l e and r e l i a b l e than s m a l l t h e r m o c o u p l e s . A d r a w b a c k is that v e r y low t e m p e r a t u r e g r a d i e n t s m u s t be m a i n t a i n e d in the m e l t to k e e p the s o l i d - l i q u i d i n t e r f a c e t e m p e r a t u r e n e a r l y equal to that at the s e n s o r . This h a s two c o n s e q u e n c e s . F i r s t , the s a m p l e m u s t b e c o o l e d v e r y s l o w l y . F o r s a m p l e s a few c e n t i m e t e r s in d i a m e t e r to be e s s e n t i a l l y i s o t h e r m a l , the cooling r a t e m u s t not e x c e e d about 0.1 K / r a i n . Second, with such low t e m p e r a t u r e g r a d i e n t s it i s i m p o s s i b l e to m a i n t a i n a p l a n a r i n t e r f a c e a t n o r m a l s o l i d i f i c a t i o n r a t e s , u n l e s s the a l l o y is v e r y dilute o r the m e l t is s t i r r e d v i g o r o u s l y . In the s e c o n d a p p r o a c h , s m a l l s a m p l e s , a few g r a m s in weight, a r e c o o l e d . F i n e t h e r m o c o u p l e s a r e u s e d a s s e n s o r s . The a d v a n t a g e s a r e t w o - f o l d . F i r s t , the s e n s o r is n e a r the s o l i d - l i q u i d i n t e r f a c e when n u c l e a t i o n t a k e s p l a c e , and p i c k s up any h e a t output c a u s e d b y the p h a s e change without d e l a y . Second, the s m a l l s i z e of both the s a m p l e and th
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