Hydrogen storage in Mg–10 at.% LaNi5 nanocomposites, synthesized by ball milling at different conditions

Three Mg–10 at.% LaNi5 nanocomposites were synthesized by high-energy ball milling at different conditions. One of the composites was prepared by milling MgH2 and LaNi5, whereas for the other two composites pure Mg and LaNi5 were used as starting materials. The last two composites were milled at different conditions—dry milling and with heptane. Relatively narrow particle size distribution has been determined by scanning electron microscopy for all composites. Mean particle size of about 2 μm has been obtained for the first two composites, while the composite milled at milder mechanochemical conditions (in heptane) shows substantially larger average particle size of about 6 μm. All composites have shown nanocrystalline microstructure (28–33 nm), which appeared to be quite stable during hydriding/dehydriding cycling, slightly increasing the mean crystallite size regardless the high-temperature of annealing (300 °C). Formation of new phases has been detected during the milling and further annealing—Mg2Ni and Mg6Ni were formed. Hydriding and dehydriding kinetics were found to be very fast for the composites with finer particle and grain sizes. Partial low-temperature hydrogen absorption has been observed and “pump-getter” mechanism was suggested and proved.