Hydrogen absorption properties of the γ-Mg17Al12 phase and its Al-richer domain

In order to modulate the thermodynamic properties of the (Mg-Al)-H-2 system, the extended homogeneity range of the gamma-Mg17Al12] 12 intermetallic phase has been studied in Al-richer domain. In this paper, the two compounds at the nominal composition MgxAl100-x, X = 50 and 58.6 are presented. The samples were prepared by the bulk mechanical alloying (BMA) technique. This method was used because of its great advantages for industrial applications (reducing time process, solid preform, large scale production...). The structures and phase's homogeneity of alloying compounds were analyzed by several experimental measurements. The hydrogen absorption properties are presented at 350 degrees C. Samples X = 50 and 58.6 show a maximum hydrogen capacity of 3.5 and 3.7 wt%, respectively. For these two compounds, the pressure-composition isotherm (PCT) curves show two absorption plateaux, with equilibriums around 10 bar which are higher than that of pure MgH2. The shape discontinuity corresponds to the transformation Of gamma-Mg17Al12 to MgH2 and to the intermediate beta-Al3Mg2 phase, before the completed decomposition in MgH2 hydride and pure Al-fcc in a second step. After final desorption, the initial compounds are recovered, indicates that the reactions are reversible. These behaviors are confirmed by X-ray diffraction (XRD) patterns refined by the Rietveld method. (C) 2007 Elsevier B.V. All rights reserved.