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Mg 2 Ni-based compounds were prepared using a high-energy milling technique, with a planetary ball mill, and subsequent annealing at 350°C. X-ray diffraction analyses revealed that Mg 2 Ni phase was obtained after 10 milling hours, in addition to Ni phase. Increasing the ballmilling duration from 10 to 17 h causes a decrease in the crystal size of particles from 93 to 76 nm. However, the subsequent annealing of all Mg 2 Ni-based materials highly increases their crystallite sizes with calculated values in the range of 261-235 nm. In the same way, X-ray diffraction patterns of annealed compounds show the presence of highly crystallized Mg 2 Ni phases. The particle size of Mg 2 Ni/Ni particles is estimated at 25 lm after 10 milling hours and drops to 5 lm at longer times. The scanning electron microscopy images of Mg 2 Ni/Ni particles demonstrated a drastic increase of their sizes up to 100 lm upon annealing. The hydrogenation reactivity and kinetic of Mg 2 Ni/Ni were both characterized by solid-gas reactions. The hydrogen absorption capacity value was about 3.5 H/f.u for milled and annealed Mg 2 Ni/Ni compound. The highest hydrogen absorption kinetic was obtained during the first 5 h of absorption time, where 95 % of the maximum absorption capacity was reached.

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