Abstract
In order to modulate the thermodynamic properties of the (Mg-Al)-H_2 system, the extended homogeneity range of the intermetallic γ-phase Mg_<17>Al_<12> has been studied. Several Mg_xAl_<100-x> samples were prepared by the bulk mechanical alloying (BMA) process. This method was used because of its great advantages for industrial applications (reducing time process, solid preform, large scale production, reducing the surface exposition to the oxidation...). The structures and phase's homogeneity of alloying compounds were analyzed by several experimental measurements and are in mutual agreement with properties of existing phases. The hydrogen absorption properties are presented at 350℃. At 2MPa, samples X=50 and X=58.6 show a maximum hydrogen capacity of 3.5 and 3.7wt% respectively. For these two compounds, the pressure-composition isotherm (PCT) curves show two absorption plateaux. The shape discontinuity corresponds to the transformation of γ-Mg_<17>Al_<12> to the intermediate β-phase (Al_3Mg_2) before the complete decomposition in MgH_2 hydride and pure Al-fcc in a second step. After complete desorption, the initial compounds are recovered, indicates that the reactions are reversible. Theses behaviors are confirmed by X-Rays diffraction (XRD) patterns refined by the Rietveld method.
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