Hydrogen storage alloy of Mg₂NiH₄ hydride produced by hydriding combustion synthesis from powder of mixture metal

As previous results, we reported that hydrogen storage alloy of Mg₂NiH₄ was produced by process of hydriding combustion synthesis in laboratory scale and regardless of the compressive pressure of the compacts from 140 MPa, 280 MPa, 550 MPa to 1.10 GPa. In present work, at first, we study the effect of the hydrogen atmosphere on the synthesis of Mg₂NiH₄ by this process. It is confirmed that the hydrogen atmosphere in the heating period plays an important role to the synthesis of Mg₂NiH₄ in the cooling period due to the expansion of the compact in the heating period resulted from the hydriding reaction of Mg+H₂→MgH₂. Then, we use powder of the mixture metal of magnesium and nickel as raw material directly and use lower pressures of hydrogen from 2.0 MPa, 1.0 MPa and to 0.5 MPa to produce Mg₂NiH₄. It is found that pure Mg₂NiH₄ from X-ray diffraction (XRD) analysis results can be produced at only 1.0 MPa hydrogen atmosphere when powder of mixture metal was used, which is much lower than that of 4.0 MPa when compact of mixture metal was used.