Hydrogen desorption behavior of magnesium hydrides synthesized by reactive mechanical alloying

F. GENNARI; F. CASTRO; G. URRETAVIZCAYA

JOURNAL OF ALLOYS AND COMPOUNDS

Elsevier

Lugar: Amsterdam; Año: 2001 vol. 321 p. 46 - 53

0925-8388

The b- and g-phases of MgH were synthesized by reactive mechanical alloying (RMA) at room temperature under hydrogen 2b- and g-phases of MgH were synthesized by reactive mechanical alloying (RMA) at room temperature under hydrogen 2 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 (b- and g-phases) after 50 h of milling. Different thermal behaviors are observed 2b- and g-phases) after 50 h of milling. Different thermal behaviors are observed 2 depending on the milling time. Hydrogen thermal desorption shows a sharp endothermic peak for MgH milled up to 30 h associated with 22 b-MgH . For longer milling times, two endothermic peaks (or a double peak) are observed and are associated with hydrogen desorption 2-MgH . For longer milling times, two endothermic peaks (or a double peak) are observed and are associated with hydrogen desorption 2 from the g-MgH –b-MgH mixture and the b-MgH phase. The presence of g-MgH destabilizes the b-MgH phase, reducing its 2 2 2 2 2g-MgH –b-MgH mixture and the b-MgH phase. The presence of g-MgH destabilizes the b-MgH phase, reducing its 2 2 2 2 2 desorption temperature. The results of this study are consistent with hydrogen desorption from g-MgH prior to the g®b-MgH 2 2g-MgH prior to the g®b-MgH 2 2 transformation.