Phase relations and crystallographic data for the Pr-Zn system
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AND
P. CHIOTTI
M e t a l l o g r a p h i c , t h e r m a l , X - r a y , and r e s i s t i v i t y data were e m p l o y e d in e s t a b l i s h i n g the phase d i a g r a m of the P r - Z n s y s t e m . Eight c o m p o u n d s , three e u t e c t i c s , and a eutectoid were obs e r v e d . The compounds P r Z n , PrZn~, and Pr2Zn~7 melt c o n g r u e n t l y at 882 ~ 898 ~ and 978~ r e s p e c t i v e l y . The compounds P r Z n s , Pr3Zn11, PrZn4.46, PrsZn22, and P r Z n l , u n d e r g o p e r i t e c tic d e c o m p o s i t i o n at 833 ~ 855 ~ 891 ~ 956 ~ and 743~ r e s p e c t i v e l y . The eutectic t e m p e r a t u r e s and c o m p o s i t i o n s in wt pct Zn a r e 576~ and 11.9 pct, 833~ and 39.0 pct, and 830~ and 56.8 pct. The eutectoid r e a c t i o n o c c u r s at 558~ and 5.2 pct Zn. The lattice p a r a m e t e r s of the compounds in the s y s t e m were d e t e r m i n e d using X - r a y powder d i f f r a c t i o n methods. Single c r y s tal X - r a y t e c h n i q u e s were u s e d to show that PrZn3 has the YZn3 (space group P n m a ) type structure.
INVESTIGATIONS of v a r i o u s a s p e c t s of the P r - Z n s y s t e m have been r e p o r t e d in the l i t e r a t u r e . Most of the work has been d i r e c t e d at the identification and c r y s t a l s t r u c t u r e d e t e r m i n a t i o n of the i n t e r m e t a l l i c compounds. Veleckis et al. 1 u s e d an effusion t e c h nique and X - r a y powder methods in d e t e r m i n i n g the p r e s e n c e of the compounds, P r Z n , PrZn2, P r Z n s , PrsZn11, PrZn4.s, P r Z n s . s ( ? ) , PrZnT, Pr2Zn17, and PrZn~l. I a n d e l l i and P a l e n z o n a 2'3 have r e p o r t e d the compounds P r Z n , Pr2Zn17, and PrZnl~. The Pr3Zn22 and Pr2Zn17 compounds have been r e p o r t e d by K u z ' m a et al. 4,5 and B r u z z o n e et a l f i have identified the compound Pr3Zn11. T h e r e a r e other r a r e e a r t h zinc c o m pounds with s t r u c t u r e s analogous to those found in the P r - Z n s y s t e m . The m e l t i n g point of P r Z n 2 has been given by Michel et al. 7 Johnson and Dillon 8 have r e p o r t e d the solubility of p r a s e o d y m i u m in zinc to be log N p r = - 6 5 9 1 / T + 4.268 (425~ to 725~
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where Npr is the atom f r a c t i o n of p r a s e o d y m i u m . The purpose of this study was to d e t e r m i n e the phase d i a g r a m of the P r - Z n s y s t e m and to v e r i f y the c o m p o s i t i o n and s t r u c t u r e of the i n t e r m e t a l l i c c o m pounds found. T h i s is an e x t e n s i o n of the work done on other r a r e e a r t h - z i n c s y s t e m s , g- 12
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The materials used in this study were Bunker Hill slab zinc 99.99 pct pure and Ames Laboratory praseodymium. Analysis of the praseodymium gave in ppm, 0--380, H--14, N--f16, and Fe--90. The following impurities were present in amounts less than the detection limit indicated in ppm: Mg--50, Si--250, Ca--200, Cr--60, Ta--500, La--50, Ce-1000, Nd--600. The praseo
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