Mechanical alloying of the Mg-Ge-H system: hydriding properties

F. GENNARI; F. CASTRO; G. URRETAVIZCAYA; G. MEYER

Annecy, Francia

Simposio; International Symposium on Metal-Hydrogen Systems; 2002

D. Fruchart, Université de Grenoble

We study the reactive mechanical alloying (RMA) of Mg and Mg-Ge mixtures at room temperature under hydrogen atmosphere. We evaluate the structural and morphological properties, and the hydrogen absorption/desorption kinetics of the products by XRD, DSC, TDS, SEM and volumetric measurements. Reactive mechanical alloying of Mg leads to the formation of about 50 wt.% of MgH2 (b and g phases) after 50 h of milling. During hydrogen desorption, different thermal behaviors are observed depending on the milling time and the presence of b-MgH2 or a g-MgH2-b-MgH2 mixture [1]. The metastable g-MgH2 destabilizes the b-MgH2 phase, reducing its desorption temperature. When Ge is added, Mg2Ge and MgH2 are formed after RMA. The presence of Ge decreases the MgH2 decomposition temperature in 50 °C to 150 °C, depending on the Ge amount. On the contrary, Mg2Ge does not produce an effect on hydrogen desorption. The degradation of the catalytic effect of Ge was also studied by performing hydrogen absorption/desorption cycling.   F. C. Gennari, F. J. Castro, G. Urretavizcaya, J. Alloys Comp. 321 (2001) 461.