A study of stability of MgH2 in Mg–8at%Al alloy powder

To investigate the effect of Al addition on the stability of magnesium hydride, the hydrogenation characteristics of a Mg–8at%Al alloy powder synthesized using the electrodeposition technique were evaluated. The characterization of the hydrogenation behavior within the 180 °C–280 °C temperature range and the subsequent microstructural analysis elucidated that the amount of Al present in the hydride decreased with increasing temperature. This observation suggests that Al has very low solubility in magnesium hydride but Al can be accommodated in MgH2 by processing under non-equilibrium conditions. Pressure–composition isotherms were developed at different temperatures for the Mg–Al powder as well as pure Mg powder. The results indicate that the enthalpy of formation was slightly lower for the Mg–8at%Al powder while the enthalpy of dissociation did not change. The absence of noticeable influence of Al addition on the stability of magnesium hydride is attributed to its lack of solubility.