Microstructure and hydrogenation kinetics of Mg2Ni-based alloys with addition of Nd, Zn and Ti

In order to enhance the hydrogen absorption kinetics of the Mg2Ni-based alloys, metal elements (Nd, Zn, and Ti) were added during melting process, respectively. The Mg2Ni-based alloys were melted using an electric resistance furnace under the protection of the covering reagent to prevent the oxidation and the evaporation of magnesium. Phase compositions and microstructures of as-cast alloys were characterized by XRD and SEM equipped with EDS. Hydrogenation kinetics of experimental alloys were investigated by the constant volume method using a Sievert-type apparatus. The addition of Nd, Zn or Ti elements to Mg2Ni results in the formation of minor phases Mg6Ni and Ni3Ti. Nd and Zn are dissolved in alpha-Mg, Mg2Ni and MgNi2 phases in Mg2Ni-based alloys. With the addition of Nd, the hydrogen content of the first absorption is 2.86% in mass fraction, which is higher than that of the Mg2Ni. Hydrogen absorption kinetics and activation properties of Mg2Ni-based alloys are improved evidently. During the initial three hydrogenation/dehydrogenation cycles, the hydrogen absorption capacity and kinetics properties have been improved for alloys with the addition of transition element Zn or Ti. The kinetics properties of the experimental alloys and absorbing reaction mechanism were also analyzed with the help of the Hirooka kinetics model.