Effect of Ball-Milling on the Properties of Mg₂Cu Hydrogen Storage Alloy

抄録

We investigated by differential scanning calorimetry the effect of ball milling on the hydrogenation properties of Mg₂Cu, a hydrogen storage alloy, prepared by two methods: One is mechanically alloyed Mg₂Cu using Mg and Cu powders as starting materials. Eight hours (=28.8 ks) of ball milling transformed the Mg:Cu=2:1 mixture into Mg₂Cu single phase which reacts reversibly with hydrogen. The other is prepared by ball milling a cast Mg₂Cu alloy. While the as-cast Mg₂Cu undergoes neither hydrogenation nor dehydrogenation under 3 MPa of hydrogen in the temperature range of 300–773 K, just an hour of ball milling activates the inert Mg₂Cu to react with hydrogen reversibly. Examining the milling period dependency of the particle size, crystallite size, activation energy and the apparent heat of dehydrogenation which reflects the fraction of activated part in a specimen, we found that the ball milling firstly influenced the particle size and the activated fraction of the sample, and then followed the effect on the crystallite size and kinetic properties. We also found that a trace amount of oxygen could significantly spoil the benefits brought by the ball milling for longer period of milling.