Hydrogen sorption behavior of mechanically synthesized Mg–Ag alloys

Abstract

A systematic study of the interactions between hydrogen and Mg–Ag alloys prepared by mechanical alloying is presented in this paper. The alloys were chosen to cover both the two-phase limited solubility and hypoeutectic regions (3, 5, 10, 20 wt. % Ag in Mg) as well as the intermetallic phases (γ′-AgMg4, ε-AgMg3 and AgMg). The hydrogen-absorption abilities of the samples were investigated for the two states: directly after mechanical alloying and after annealing. It was found that all of the chosen alloys could be very effectively synthesized with mechanical alloying, a process that also was found to extend the solubility limits compared to those on known phase diagrams. The synthesis is greatly enhanced by further annealing which allows us to obtain well crystallized samples with phase compositions in accordance with these phase diagrams. In most cases, the obtained alloys were able to absorb significant amounts of hydrogen while magnesium hydride and AgMg intermetallics were formed as a residual product and phase, respectively, that did not react with hydrogen under the chosen conditions. The magnesium hydride formed in such reactions seemed to have a very similar decomposition temperature and was not significantly influenced by the silver additive, which was not found to greatly catalyze the MgH2 decomposition reaction in such cases. Samples characterized directly after ball milling showed higher reaction kinetics with hydrogen.