Solid state reaction and formation of nano-phase composite hydrogen storage alloy by mechanical alloying of MmNi3.5(CoMnAl)1.5 and Mg

Abstract

In this work MmNi3.5(CoMnAl)1.5 and Mg were mechanically alloyed to prepare composite hydrogen storage alloys. The microstructural variation of the alloy resulted from the mechanical alloying was characterized by X-ray diffraction, SEM and TEM analysis. It was found that solid state reaction occurred between MmNi3.5(CoMnAl)1.5 and Mg components, resulting in Mm2Mg17 phase formation. The alloy obtained by ball milling contains homogeneously distributed Mg, MmNi3.5(CoMnAl)1.5 and Mm2Mg17 phases of nanometer size. It was also found that Mg2Ni was formed after the mechanically alloyed samples were annealed. The mechanism of the reaction has been proposed based on the estimation of the heat of formation using Miedema's theory and is in accordance with the experiment result of lattice constant measurement of ball milled sample and its structure variation during annealing.