Hydrogen desorption behavior from magnesium hydrides synthesized by reactive mechanical alloying

摘要

The #beta#- and #gamma#-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. percent of MgH_2 (#beta#- and #gamma#-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 #beta#-MgH_2. For longer milling times, two endothermic peaks (or a double peak) are observed and are associated with hydrogen desorption from the #gamma#-MgH_2 -#beta#-MgH_2 mixture and the #beta#-MgH_2 phase. The presence of #gamma#-MgH_2 destabilizes the #beta#-MgH_2 phase, reducing its desorption temperature. The results of this study are consistent with hydrogen desorption from #gamma#-MgH_2 prior to the #gamma#->#beta#-MgH_2 transformation.