Re-examination of Zr7Ni10 single-phase region

In order to obtain information about the hydrogenation properties of Zr-rich Zr7Ni10 with orthorhombic Pbca symmetry, which can help to understand the mechanism of the unusual hydrogenation properties of stoichiometric Zr7Ni10 with orthorhombic Cmca symmetry, the synthesis of the Zr-rich compound was attempted by applying four alloying procedures: (1) alloying and cooling on water-cooled copper hearth in an arc melting furnace, (2) heat treatment at 1273 K in a vacuum for 86.2 ks for the as-cast samples prepared by arc melting, (3) remelting of as-cast alloys followed by quenching on copper wheel rotating at 4000 rpm in an argon atmosphere, and (4) heat treatment of quenched samples at 973 K or 1073 K under pressurized argon atmosphere for 7.2 ks. The target phase was not obtained by these four methods and, through the examinations, it was found that the single-phase region of Zr7Ni10 was quite narrow compared with the solubility range published in a binary phase diagram and the Zr7Ni10 compound with the tetragonal structure, which can also be obtained by hydrogenation to form the corresponding hydride Zr7Ni10H17 followed by dehydrogenation, was formed in the quenched samples prepared by procedure 3. The solubility of Zr7Ni10 and its phase stability are discussed. (C) 2004 Published by Elsevier B.V.