Hydrogen reaction kinetics of Mg-based alloys synthesized by mechanical milling

The influence of mechanical milling of Mg-based mixtures on the structure and hydrogen sorption properties was investigated by measuring the rate of hydrogen absorption, nuclear magnetic resonance and X-ray diffraction. In order to separate different factors responsible for hydrogenation kinetics, we compare the results of milling of both pure Mg and the mixture of Mg with different metallic and oxide additives in argon at 77 K and in hydrogen atmosphere at room temperature, with the milling tools made of steel and brass. It was established that the role of grain size and different catalytic additives is considerable only for an initial formation of MgH2 phase during mechanical activation in hydrogen. The most important effect of mechanical activation at the late stages of milling consists of the formation of a special structural state of the hydrogen-containing phase, independently on the type of the catalyst. The observed enhancement of the proton spin-lattice relaxation rate in the samples prepared by ball milling in hydrogen is attributed to the effect of paramagnetic centers which are an intrinsic feature of such a structural state.