Electrochemical characteristics of nanocrystalline ZrCr_2 and Mg_2Ni type metal hydrides prepared by mechanical alloying

摘要

The mechanical alloying process (MA) has beenintroduced to produce nanocrystalline ZrCr_2 and Mg_2Ni typemetal hydride. MA has recently emerged as a novel technique forproducing alloy powders whose structures are nanocrystalline. TheZr-Cr-Ni and Mg-Ni systems were prepared using a planetary ballmill, starting from mixtures of elemental powders. In the Zr-Cr-Nisystem, nanocrystalline C14 structure could not be obtained afterball-milling but could be obtained from heat-treatment of ball-milled powders. The heat-treated Zr-Cr-Ni powders showed asimilar discharge capacity to the arc-melted alloy, but theactivation was much easier. In contrast to Zr-Cr-Ni system,nanocrystalline Mg_2Ni alloy could be formed by ball-milling. Incomparison with the polycrystalline one, nanocrystalline Mg_2Nishowed a lower temperature for hydrogenation and a much higherdischarge capacity at 30 deg C. The partial substitution of Zr forMg resulted in a icrostructure different from mechanically alloyedMg_2Ni and greatly improved the discharge capacity at 30 deg C.The discharge capacity of 120 h-milled 1.8Mg-0.2Zr-Ni electrodewas 465 mAh g~-1. 1999 Elsevier Science S.A. All rights reserved