Study of hydrogen absorption kinetics of Mg2Ni-based powders produced by high-injected shock power mechanical alloying and subsequent annealing

Mg2Ni-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 Mg2Ni phase was obtained after 10 milling hours, in addition to Ni phase. Increasing the ball-milling 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 Mg2Ni-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 Mg2Ni phases. The particle size of Mg2Ni/Ni particles is estimated at 25 μm after 10 milling hours and drops to 5 μm at longer times. The scanning electron microscopy images of Mg2Ni/Ni particles demonstrated a drastic increase of their sizes up to 100 μm upon annealing. The hydrogenation reactivity and kinetic of Mg2Ni/Ni were both characterized by solid–gas reactions. The hydrogen absorption capacity value was about 3.5 H/f.u for milled and annealed Mg2Ni/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.