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

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 H₂, 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.