Abstract
In the present work, the Mg-Al system was studied towards hydrogen absorption properties.
Several MgxAl100-x compounds from X=47.5 to 70 by incremental step of 2.5 were prepared by ball-milling with post-annealing. Different experimental measurements were performed and are in mutual agreement with properties of existing phases. They show that deviation from the ideal composition of Mg17Al12 (X=58.62) leads to a decrease of the homogeneity. The single γ-phase range is extended at room temperature for initial 55≤X≤62.5 atomic % of Mg.
The hydrogenation properties have been investigated for two compounds at the nominal composition X=50 and X=58.6. The hydrogen absorption is presented at 350°C and shows 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 bars which are higher than that of pure MgH2. The shape discontinuity corresponds to a transformation into a 2-step process as described in this work. After final desorption, the initial compounds are recovered, indicates that the reactions are reversible.
