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P. CHIOTTI

M e t a l l o g r a p h i c , t h e r m a l , and X - r a y techniques w e r e used to d e t e r m i n e the phase r e l a t i o n s in the Nd-Zn s y s t e m . Eight compounds, three e u t e c t i c s and a eutectoid w e r e found. The compounds NdZn, NdZne, and Nd2Zn17 m e l t congruently at 923 ~ 925 ~ and 981~ r e s p e c t i v e l y . The compounds Nd3Znn, NdZn4.46, and Nd3Zn2~ undergo p e r i t e c t i c decomposition at 870 ~ 902 ~ and 950~ r e s p e c t i v e l y , while NdZn3 undergoes p e r i t e c t o i d decomposition at 849~ The e u t e c t i c s occur at 12 wt pct Zn and 630~ 38 wt pct Zn and 868~ and 56 wt pct Zn and 854~ The eutectoid o c c u r s at 4 wt pct Zn and 622~ The existence of a NdZn~2 phase of the SmZn~2 type s t r u c t u r e has been confirmed. An a l l o t r o p i c t r a n s f o r m a t i o n between the t e t r a g o n a l NdZn~t s t r u c t u r e and the hexagonal NdZn~2 defect s t r u c t u r e is p r o p o s e d . A number of i n v e s t i g a t o r s have r e p o r t e d the e x i s t ence of one or more Nd-Zn compounds. K u z ' m a e t a l . ~'2 e s t a b l i s h e d the existence of NdZnu and Nd2Znlv by X - r a y diffraction techniques. IandeUi and P a l e n z o n a 3'4 used X - r a y single c r y s t a l and powder methods in studying the NdZn, Nd2Zn17, and NdZn~ compounds. F o r n a s i n i and Merlo 5 did a detailed m e t a l lographtc and X - r a y investigation of NdZn2 while Michel e t a l . ~ d e t e r m i n e d the melting point of NdZn2 to be 916~ An extensive investigation of the c o m pounds in the Nd-Zn s y s t e m has been made by Veleckis e t a l . 7 using effusion techniques and X - r a y powder methods. The compounds r e p o r t e d a r e NdZne, NdZn3, NdaZn11, NdZn4.3, NdZn6.s, Nd2Zn17, and NdZn11. Another extensive investigation of neodymium c o m pounds with i n t e r m e d i a t e zinc contents was made by Bruzzone e t al. a Some s t r u c t u r a l p r o p e r t i e s were r e p o r t e d for NdZn2, NdZn4.46, and NdaZn22. One other compound, NdZn~2, was r e p o r t e d by Veleckis e t a l . 9 f r o m X - r a y powder data. Johnson and Dillon ~~ have m e a s u r e d the solubility of neodymium in zinc and give the following equation for the t e m p e r a t u r e range of 425 ~ to 750~ log(at, pct Nd) = 6.071 - 6289T -~ The p u r p o s e of this work was to v e r i f y the v a r i o u s N d - Z n compounds as r e p o r t e d in the l i t e r a t u r e and to d e t e r m i n e the phase r e l a t i o n s in the s y s t e m . This is an extension of previous work on the phase d i a g r a m s , s t r u c t u r e a n a l y s i s , and t h e r m o d y n a m i c p r o p e r t i e s of r a r e e a r t h - z i n c s y s t e m s , n-~6 MATERIALS AND EXPERIMENTAL PROCEDURES The m a t e r i a l s used in this study w e r e Bunker Hill slab zinc 99.99 wt pct pure and A m e s L a b o r a t o r y neodymium 99.94 wt pct pure. The m a j o r i m p u r i t i e s in the neodymium by wt pct were tantalum and oxygen. The m a j o r i m p u r i t i e s by at. pct w