Hydrogen storage properties of amorphous and nanocrystalline MmNi4.2Al0.8 alloys

The hydrogen storage properties of amorphous and nanocrystalline MmNi4.2Al0.8 alloys were studied. These materials were prepared by mechanical alloying (MA). The amorphous phase forms directly from the starting mixture of the elements, without other phase formation. Heating the MA powders at 750°C for 0.5 h resulted in the formation of the hexagonal CaCu5-type structure. Gas-phase hydrogen sorption in an amorphous as well as a nanocrystalline MmNi4.2Al0.8 alloy was also investigated. The nanocrystalline powders prepared by MA have a lower hydrogen storage capacity than powders from arc-melted ingots. The difference is mainly due to iron impurities trapped in the mechanically alloyed powders from erosion of the milling media.