Effect of hydrogen pressure on the combustion synthesis of Mg₂NiH₄

The aim of this work is to study the experimental production of a hydrogen storage alloy (Mg₂NiH₄) directly from a magnesium and nickel mixture without activation treatment by combustion synthesis in hydrogen. In this paper, the effect of hydrogen pressure on the hydriding combustion synthesis of Mg₂NiH₄ at 0.5, 1.0, 2.0 and 4.0 MPa has been studied by differential scanning calorimeter (DSC) and by X-ray diffraction (XRD). The XRD results showed that the combustion products of all samples were composed mainly of Mg₂NiH_0.3 and Mg₂NiH₄ in spite of a slight remainder of Ni, in which the amount of Mg₂NiH₄ increased with increasing hydrogen pressure, but not very drastically. In addition, the DSC results showed several sharp heat-flow peaks during heating and cooling periods between room temperature and 850 K. It is suggested that the reaction mechanism of the hydriding combustion synthesis is not simple, but complicated with several endothermic and exothermic reactions with pressure dependence.