Kinetics of interaction of Mg-based mechanically activated alloys with hydrogen

Parameters of interaction of hydrogen with magnesium powders and structure of powder magnesium alloys alloyed with different metals and oxides (such as Fe, Ni, Al, Cu, Ti, Pd, NiPd, V2O5, and VH2) prepared by mechanical activation under either argon or hydrogen atmosphere in a vibration mill have been studied. The mechanically activated alloys absorb to 7 wt% hydrogen at 300 degrees C for 20 min. For most of the additions used, the effect of the grain size and type of addition on the rate of hydrogen absorption was found to manifest itself only at the stage of the formation of the MgH2 phase upon mechanical activation in the hydrogen atmosphere; virtually no effect is observed upon subsequent hydrogenation. The temperature of the hydrogen desorption also depends only slightly on the addition kind. The increase in the hydrogenation rate of the Mg-based alloys resulting from the mechanical activation was shown to be due to the formation of a specific structural state of the particle surface, which exhibits a high catalytic activity for the hydrogen sorption. A study of the mechanically activated alloys by proton nuclear magnetic resonance showed a substantial increase in the rate of proton spin-lattice relaxation as compared to that observed for MgH2 produced by direct hydrogenation. This can be due to the interaction of protons with paramagnetic centers formed at the imperfect surface of mechanically activated Mg particles.