Guillermina Urretavizcaya

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.

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.

Thermal transformation of sol-gel alumina into α-phase. Effect of α-Al2O3 seeding

Abstract The kinetics of thermal transformation of alumina gels prepared from alkoxide precursors are studied both in the as-prepared gel and in samples seeded with α-Al 2 O 3 particles of controlled size. The seeding enhances the reactivity of the gel, by providing sites for the nucleation and growth of the product phase, processes which control the kinetics of the transformation. The densification and the microstructure evolution along the transformation are discussed, and the kinetic parameters determined in the temperature range 1050–1100°C.