Phase separation of Mg2Ni by hydriding-dehydriding cycling

The intermetallic compound Mg2Ni was prepared by sintering in a closed alumina tube furnace in order to reduce the quantity of evaporated Mg. A small amount of MgO and MgNi2 was formed in the Mg2Ni as prepared, and their quantities increased as the number of cycles increased. Electron diffraction analysis showed that the particle on the sample surface was MgO. The magnetic measurements showed that Ni segregated after hydriding-dehydriding cycling and its quantity increased as the number of cycles increased. A small amount of O-2 in the H-2 reacts with Mg2Ni to form MgO and to segregate Ni: Mg2Ni+O-2-->2 MgO+Ni. The segregated Ni reacts with Mg2Ni to form MgNi2: Mg2Ni+3Ni-->2MgNi(2). These two reactions decrease hydrogen-storage capacity of Mg2Ni as the number of the hydriding-dehydriding cycles increases. (C) 1999 Elsevier Science S.A. All rights reserved.