Effects of hydrogen pressure and cooling rate on the hydriding combustion synthesis of Mg₂NiH₄ studied by thermogravimetry and X-ray diffraction

The purpose of this study is to produce Mg₂NiH₄, directly from mixture of elemental magnesium and nickel by means of hydriding combustion synthesis method without any activation treatment. In the method, cooling rate and hydrogen pressure were selected as two major parameters, and the effects of these two parameters on the product composition were mainly investigated. The results demonstrated that we could produce pure Mg₂NiH₄ by controlling thermal and pressure condition accurately within only one cycle of temperature scanning, according to overall reaction: 2Mg+Ni+2H₂→Mg₂NiH₄. The selected conditions of the two parameters for obtaining pure product are 4.0 MPa in hydrogen pressure and 16.7 × 10^-3 K/s in cooling rate.