Hydrogenation properties of Mg2AlNi2 and mechanical alloying in the Mg–Al–Ni system

Samples with MgmAlNin composition (m, n ≤ 3) were synthesized by ball milling in form of crystalline nanoparticles, and were found to be a single phase with partially disordered CsCl-type cubic structure. For compositions with large m and small n, minor quantities of Mg and Mg2Ni are segregated. XRD Rietveld refinements indicate that the two Pm3¯m sublattices basically have (Mg, Al) and (Mg, Al, Ni) occupations, respectively. Hydrogenation experiments on the Mg2AlNi2 sample by the PCI technique showed a reversible absorption/desorption of 1.4 wt% H2 with formation/decomposition of the MgH2 and Mg2NiH4 hydrides. The van’t Hoff plot gives ΔrH = 67.7 kJ mol−1 (enthalpy of dehydrogenation), and T0 = 524 K (temperature of dehydrogenation at p = 0.1 MPa). A kinetic study of the gas release at 535 K showed a satisfactory behaviour, with a first fast step followed by a slower one in both the absorption and desorption processes.