Hydrogenation and Dehydrogenation Behaviors of Mg2Ni Synthesized by Sintering Pelletized Mixtures Under an Ar Atmosphere

A Mg2Ni intermetallic compound was synthesized by sintering under an argon atmosphere in a stainless steel crucible at 823 K. The hydrogenation and dehydrogenation features of the synthesized samples were investigated. Hydrogenation and dehydrogenation behaviors of Mg2Ni were plotted using the Johnson-Mehl equation for the nucleation and growth mechanism. In addition, we analyzed the dependences of hydrogenation rates on hydrogen pressure and temperature and a rate-controlling step for the hydrogenation of Mg2Ni after the nucleation of Mg2Ni hydride. The XRD pattern of the Mg2Ni sample synthesized by sintering pelletized mixtures under an Ar atmosphere in a stainless-steel crucible showed a well crystallized Mg2Ni phase, revealing hardly any impurities. At 571 K under 30 bar H-2, the Mg2Ni sample was activated completely at the number of cycles, n, of three. As the temperature increased form 474 K to 522 K, the initial hydrogenation rate and the quantity of hydrogen absorbed for 10 min increased. The rate-controlling step of the hydrogenation of Mg2Ni after the nucleation of Mg2Ni hydride was found to be the forced flow of hydrogen molecules through pores, interparticle channels, or cracks. The dehydrogenation after activation proceeded by a nucleation and growth mechanism and could be expressed by a Johnson-Mehl equation.