Facundo J. Castro

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.

Thermal desorption spectroscopy (TDS) method for hydrogen desorption characterization (I): theoretical aspects

Abstract We present a theoretical study of thermal desorption spectroscopy applied to the characterization of hydrogen desorption kinetics from hydride forming materials. We propose a model that considers bulk and surface processes during desorption in the solid solution+hydride field of a metal–hydrogen system. We consider as possible rate limiting steps: diffusion, phase transformation, bulk to surface passage and two-atom recombination on the surface of the sample.

Catalytic effect of Ge on hydrogen desorption from MgH2

Abstract We studied the influence of Ge on hydrogen desorption from MgH 2 produced by mechanical alloying at room temperature under a hydrogen atmosphere. The structural and morphological properties, and the desorption kinetics of the products were examined by X-ray diffraction, differential scanning calorimetry, thermal desorption spectroscopy and scanning electron microscopy. The mechanical milling of Mg–Ge mixtures under hydrogen leads to the formation of Mg 2 Ge and MgH 2 . The presence of Ge decreases the hydride decomposition temperature in a range from 50 to 150°C, depending on the Ge amount. On the contrary, Mg 2 Ge does not show any effect on hydrogen desorption.