Experiments on macrosegregation and freckle formation
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3. K. G. Denbighand G. Raumann:Proc. Roy. Soc. (London), 1952,vol.A210,pp. 377, 518. 4. A. Sieverts:Z. Metallk., 1929,vol. 21, p. 37. 5. A. Sievertsand G. Zapf: ,7..Phys. Chem., 1935,vol. 174A,p. 359.
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Experiments on Macrosegregation and Freckle Formation
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R. MEHRABIAN, M. A. KEANE, AND "o
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Fig. 2--1nPh/Pc as a function of time for the temperatures investigated. i n v e s t i g a t i o n s is shown s c h e m a t i c a l l y in Fig. 1. B a s i cally it c o n s i s t e d of a s p e c i m e n a s s e m b l y , which c o n t a i n e d the p a l l a d i u m m e m b r a n e (1.4 c m d i a m , 0.1 c m thick), a heating and a cooling b l o c k to p r o v i d e the t e m p e r a t u r e g r a d i e n t , and a hot and cold side gas v o l u m e . The p a l l a d i u m u s e d was 99.99 pct Pd and h y d r o gen was e m p l o y e d d i r e c t l y f r o m the c y l i n d e r . The p r o c e d u r e followed when m a k i n g a r u n c o n s i s t e d of a d j u s t i n g the hydrogen p r e s s u r e s on both s i d e s of the m e m b r a n e to v a l u e s close to the s t e a d y - s t a t e p r e s s u r e d i s t r i b u t i o n and then following the v a r i a t i o n of the q u a n t i t y In P h / P c with t i m e to the final s t a t i o n a r y state. F o r each p a r t i c u l a r m e a n m e m b r a n e t e m p e r a t u r e , the steady state was a p p r o a c h e d f r o m both d i r e c t i o n s . That is, f r o m i n i t i a l In P h / P c v a l u e s g r e a t e r than and s m a l l e r than the s t e a d y - s t a t e value. In this way an a v e r a g e In P h / P c w a s d e t e r m i n e d . Fig. 2 shows r e p r e s e n t a t i v e r e s u l t s for t e m p e r a t u r e s i n v e s t i g a t e d . E x p e r i m e n t a l d e t a i l s a r e l i s t e d in the t a b l e of this figure t o g e t h e r with the c a l c u l a t e d h e a t s of t r a n s p o r t . The s o l u b i l i t y d a t a of S i e v e r t s 4 and S i e v e r t s and Zapf 5 w e r e u s e d to e v a l u a t e the heat of s o l u t i o n at each t e m p e r a t u r e . It is e v i d e n t f r o m the t a b u l a t e d v a l u e s of Q* that o v e r the t e m p e r a t u r e r a n g e studied, t h e r m o m i g r a t i o n of h y d r o g e n in p a l l a d i u m i s s m a l l and effectively i n d e p e n d e n t of t e m p e r a t u r e . An a v e r a g e Q* of +1.5 ~: 0.5 k c a l p e r g atom can be a s s i g n e d to the s y s t e m for the e n t i r e r a n g e . One of the a u t h o
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