Activation behaviors of Mg₂NiH₄ at different hydrogen pressures in hydriding combustion synthesis

For the industrialization of the process of hydriding combustion synthesis of Mg₂NiH₄, the activation behaviors of Mg₂NiH₄ at different hydrogen pressures were measured by means of DSC (differential scanning calorimeter) and XRD (X-ray diffraction). The profiles of heat flow of DSC were very different at 0.5,1.0,2.0 and 4.0 MPa hydrogen pressures within three cycles of temperature scanning at a rate of 0.1 K/s in hydriding combustion synthesis of Mg₂NiH₄. It is apparent that an activation behavior existed in the hydriding combustion synthesis since the height of DSC peak from the hydriding reaction of Mg₂NiH₄ increased with the cycling of temperature scanning. The pressure of hydrogen strongly affected this kind of an activation. The peak height increased as hydrogen pressure increased. It reached maximum values after the second cycle of temperature scanning at 4.0 MPa of hydrogen pressure and after the third cycle at 2.0 MPa. The patterns of XRD revealed that pure products of Mg₂NiH₄ were obtained after the third cycle of temperature scanning at 2.0 MPa of hydrogen pressure and after the second cycle at 4.0 MPa. These results are significant for developing the industrial process of hydriding combustion synthesis of hydrogen storage alloy Mg₂NiH₄ within only one temperature scanning without any activation process.