Xiaojiang Hou

Dehydrogenation behavior and microstructure evolution of hydrogenated magnesium–nickel–yttrium melt-spun ribbons

This paper reports porous Mg67Ni33−xYx (x = 0, 1, 3, 6) ribbons which are prepared by a melt spinning method. The dehydrogenation behaviors, including the thermal decomposition process, dehydrogenation capacities, percentage and kinetics, are investigated in a temperature range of 523–623 K. The microstructure evolution during the dehydrogenation process of metal melt-spun ribbons is discussed with respect to the microstructures of hydrogenated and dehydrogenated ribbons. It is considered that the porous structure in the as-prepared ribbons accelerates the diffusion of hydrogen gas and atoms, and increases dehydrogenation nucleation locations and decreases the diffusion distance. Additionally, the addition of yttrium and melt-spinning decreases the activation energy of dehydrogenation. A low activation energy and a refined microstructure play dominant roles in decreasing the dehydrogenation temperature and increasing the kinetics of Mg-based metal melt-spun ribbons.

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

Abstract In order to enhance the hydrogen absorption kinetics of the Mg 2 Ni-based alloys, metal elements (Nd, Zn, and Ti) were added during melting process, respectively. The Mg 2 Ni-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 Mg 2 Ni results in the formation of minor phases Mg 6 Ni and Ni 3 Ti. Nd and Zn are dissolved in α -Mg, Mg 2 Ni and MgNi 2 phases in Mg 2 Ni-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 Mg 2 Ni. Hydrogen absorption kinetics and activation properties of Mg 2 Ni-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.