Nanocrystallization and hydrogen storage in rapidly solidified Mg–Ni–RE alloys
Abstract Hydrogen storage in rapidly solidified magnesium based Mg–Ni–RE (RE=Y or Mm) alloys was studied. The as-quenched alloys were amorphous or nano-/amorphous, consisting of nanocrystals (with average size of 3 nm) embedded in large amounts of amorphous phase. The hydrogenation properties (hydrogen storage capacity and hydrogenation kinetics) of Mg 76 Ni 19 Y 5 and Mg 78 Ni 18 Y 4 alloys were compared mainly with those of Mg 75 Ni 20 Mm 5 (Mm=Ce, La-rich mischmetal), reported recently. Alloys with the above mentioned compositions were found to attain the best hydriding characteristics among the Mg–Ni–RE alloys. A more beneficial effect on the hydrogen storage capacity of Mm (La,Ce-rich mischmetal) than Y was detected. Crystallization of these alloys leads to a nanocrystalline material through a metastable fcc Mg 6 Ni phase, as for the Mg 78 Ni 18 Y 4 alloy the nanostructure and the intermediate phase are thermally more stable. The kinetics of crystallization was studied at non-isothermal conditions and the kinetic parameters for different magnesium alloys were compared. The results from previous and the present study show that stable nanocrystalline microstructures appropriate for hydrogen storage can be produced by controlled crystallization of amorphous or nano-/amorphous magnesium based Mg–Ni–RE precursors.