Dissolution of boron nitride in liquid iron
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AND
ROBERT
D. PEHLKE
The rate of d i s s o l u t i o n of b o r o n n i t r i d e in liquid iron and F e - B alloys has been m e a s u r e d using a v o l u m e t r i c technique. The solution p r o c e s s was found to be diffusion c o n t r o l l e d and d i r e c t l y r e l a t e d to the c o n c e n t r a t i o n of b o r o n in the liquid metal. Diffusion c o n t r o l was s u b s t a n t i a t e d f u r t h e r by e x p e r i m e n t s u t i l i z i n g b o r o n n i t r i d e rods which were r o t a t e d in liquid i r o n .
T H E objective of the p r e s e n t i n v e s t i g a t i o n has b e e n to study the solution rate of b o r o n n i t r i d e in liquid i r o n . The rate of solution of s i l i c o n n i t r i d e in m o l t e n i r o n has b e e n studied by Minowa et al. z who found that the solution rate was d e s c r i b e d by a f i r s t o r d e r r a t e law in t e r m s of s i l i c o n c o n c e n t r a t i o n s . R e l a t e d solution s t u d i e s have b e e n c a r r i e d out in some f e r r o u s s y s t e m s and i n t e r p r e t e d u t i l i z i n g a convective diffusion model. Shurygin and Kryuk 2 studied the solution r a t e s of c a r bon d i s c s in molten F e - C , F e - S i , F e - P , and F e - N i a l loys. Shurygin and S h a n t a r i n 3 have m e a s u r e d the s o l u tion r a t e s of m e t a l l i c i r o n , m o l y b d e n u m , t u n g s t e n , and c a r b i d e s of c h r o m i u m and t u n g s t e n in molten F e - C a l loys u s i n g a r o t a t i n g s a m p l e g e o m e t r y . T h e i r r e s u l t s c o n f i r m that the r e s i s t a n c e to m a s s - t r a n s f e r in these s y s t e m s r e s i d e s in the b o u n d a r y l a y e r adjacent to the i n t e r f a c e . R e c e n t l y O l s s o n et al.4 have m e a s u r e d the r a t e s of d i s s o l u t i o n of c y l i n d r i c a l graphite s a m p l e s in F e - C alloys. The m a s s - t r a n s f e r coefficients were c a l c u l a t e d using the r e l a t i o n of L o m m e l and C h a l m e r s 5 a s s u m i n g that the i n t e r r a c i a l liquid was s a t u r a t e d with carbon. The p r e s e n t work d e a l s with the solution r a t e s of b o r o n n i t r i d e d i s c s in N2 s a t u r a t e d liquid iron and dilute F e - B alloys. The t h e r m o d y n a m i c s and k i n e t i c s of N2 solution in liquid i r o n and dilute b i n a r y alloys of i r o n have been studied by Pehlke and Elliott. 6,7 F u r t h e r m o r e , the t h e r m o d y n a m i c s of f o r m a t i o n of b o r o n n i t r i d e in liquid F e - B a l l o y s in e q u i l i b r i u m with n i t r o g e n gas has been well e s t a b l i s h e d by E v a n s and Pehlke 8 and m o r e r e c e n t l y by Schenck and S t e i n metz. 9
r e s e r v o i r line in o r d e r to m a i n g a i n the N2 p r e s s u r e at 1 atm p r e s s u r e (ambient). As the m e r c u r y level fell in the b u r e t t e , its position and the r a t e of gas evolution were s i m u l t a n e o u s l y and continuously r e corde
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