Hydrogen desorption behavior from magnesium hydrides synthesized by reactive mechanical alloying

Abstract

The β- and γ-phases of MgH 2 were synthesized by reactive mechanical alloying (RMA) at room temperature under hydrogen atmosphere. The structural and desorption properties of the products obtained were examined by X-ray diffraction (XRD), differential scanning calorimetry (DSC), thermogravimetric analysis (TG) and scanning electron microscopy (SEM). Reactive mechanical alloying of Mg leads to the formation of about 50 wt.% of MgH 2 (β- and γ-phases) after 50 h of milling. Different thermal behaviors are observed depending on the milling time. Hydrogen thermal desorption shows a sharp endothermic peak for MgH 2 milled up to 30 h associated with β-MgH 2. For longer milling times, two endothermic peaks (or a double peak) are observed and are associated with hydrogen desorption from the γ-MgH 2–β-MgH 2 mixture and the β-MgH 2 phase. The presence of γ-MgH 2 destabilizes the β-MgH 2 phase, reducing its desorption temperature. The results of this study are consistent with hydrogen desorption from γ-MgH 2 prior to the γ→β-MgH 2 transformation.