IMPROVEMENT IN HYDROGEN STORAGE CHARACTERISTICS OF MAGNESIUM BY MECHANICAL ALLOYING WITH NICKEL

The hydriding and dehydriding kinetics of Mg are reviewed. It is reported that the hydriding and dehydriding reactions of Mg are nucleation-controlled under certain conditions and progress by a mechanism of nucleation and growth, and that the hydriding rates of Mg are controlled by the diffusion of hydrogen through a growing Mg hydride layer. The hydriding and dehydriding kinetics of Mg can be improved in consequence by a treatment such as mechanical alloying, which can facilitate the nucleation by creating defects and shorten diffusion distances by reducing the effective particle size of Mg. The hydriding and dehydriding characteristics of mechanically-treated Mg and mechanically-alloyed mixtures with the compositions Mg-x wt % Ni (x = 5, 10, 25 and 55) are studied. The Mg2Ni phase develops in the mechanically-alloyed mixtures. The Mg-10 wt % Ni and Mg-25 wt % Ni mixtures are activated easily, show much larger hydrogen storage capacities and much higher hydriding rates, and higher dehydriding rates, than other magnesium-based alloys or mixtures.