The heat of vaporization and vapor pressure of liquid lead
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The Heat of Vaporization and Vapor Pressure of Liquid Lead DOUGLAS
H . SHIU A N D Z U H A I R A . M U N I R
NUMEROUS
M O R E E N
Williams and Hickman9 have r e p o r t e d on the t e m p e r i n g b e h a v i o r o f o r t h o r h o m b i c m a r t e n s i t e in t i t a n i u m a l l o y s c o n t a i n i n g 4 . 0 p e t M o , 4 . 2 5 p e t M o + 0 . 2 5 p e t Si a n d 4.0 p e t W . D u r i n g t e m p e r i n g i n t h e s e a l l o y s , W i l l i a m s and Hickman c l a i m that hexagonal a p h a s e precipitates as s m a l l n e e d l e s , with t h e l o n g dimension c o r r e s p o n d i n g t o t h e [001]o. T h e r e s u l t w a s b a s e d u p o n t h e i n t e r p r e t a t i o n of F i g . 2 o f R e f . 9 w h i c h s h o w e d a t r a n s m i s s i o n e l e c t r o n m i c r o g r a p h of t h e p r e c i p i t a t i o n o f a in o r t h o r h o m b i c m a r t e n s i t e a n d t h e c o r r e s p o n d i n g S A D p a t t e r n w h i c h i s i n d e x e d a s a 010 o r t h o r h o m b i c martensite zone. T h e S A D p a t t e r n , F i g . 2(b) o f R e f . 9 , s h o u l d be i n d e x e d a s 110 o r t h o r h o m b i c m a r t e n s i t e z o n e . T h i s m a y be s e e n by c o m p a r i n g d s p a c i n g r a t i o s d e r i v e d f r o m t h e SAD p a t t e r n t o t h o s e d e r i v e d f r o m t h e lattice p a r a m e t e r data, T a b l e I of Ref. 9 . If indexed a c c o r d i n g t o a 010 z o n e , t h e r a t i o dloo/doo~ o b t a i n e d by m e a s u r e m e n t s o f diffraction s p o t p o s i t i o n s o n Fig. 2 o f Ref. 9 w o u l d be 0.91 a s c o m p a r e d t o 0.65 f r o m t h e l a t t i c e p a r a m e t e r d a t a . I n d e x i n g a s a 110 z o n e y i e l d s doo2/d22o = 1.82 i n g o o d a g r e e m e n t w i t h t h e v a l u e o f 1 . 8 1 0 f r o m the lattice p a r a m e t e r d a t a . T h e r e v i s e d indexing c h a n g e s the directions i n d i c a t e d i n F i g . 2 o f R e f . 9 . T h e i n d i c a t e d [100]o i s [ 1 i 0 ] o a n d t h e i n d i c a t e d [001]o i s t h e [001]o. T h e a p r e c i p i t a t e p a r t i c l e s t h e n m a y be i n t e r p r e t e d a s n e e d l e s w h i c h l i e a l o n g [001 ]o. Consideration of the c r y s t a l s t r u c t u r e s of the orthorhombic martensite and a p h a s e s h o w s that the o b s e r v e d m o r p h o l o g y o f t h e p r e c i p i t a t e s is c o n s i s t e n t w i t h t h e a r r a n g e m e n t s of a t o m s w i t h i n t h e c r y s t a l s t r u c t u r e s . T h e g r o w t h d i r e c t i o n c o r r e s p o n d s to t h e direction of minimum lattice m i s m a t c h between the orthorhombic and hexagonal p h a s e s . T h e o r t h o r h o m b i c m a r t e n s i t e h a s b e e n r e p o r t e d by B r o w n , e t a l . , '° t o h a v e a s t r u c t u r e s i m i l a r t o a - U . T h e a t o m p o s i t i o n i n t h i s u n i t c e l l a r e O, y , a1 - ,. O, l - - y , ~3 ., ~I , ~I - - y , -1~ ., a n d ~ -I , ~ -1 + y , ~3- . B r o w n r e p o r t e d t h a t t h e v a l u
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