Effect of Milling Time on Hydrogen Desorption Properties of Nanocrystalline MgH2

Nanocrystalline magnesium hydride powder was synthesized by mechanical milling of MgH2 in a planetary ball mill for various times. The effect of MgH2 structure, i.e. crystallite size, lattice strain, particle size and specific surface area on the hydrogen desorption properties was investigated. A single peak of hydrogen desorption was observed for as-received powder, exhibiting an average particle size of 30 µm. In contrast, all milled powders with much reduced particle size exhibited desorption peak doublet in DTA. It was shown that the dehydrogenation temperature of MgH2 decreased from 421 ºC to 319 ºC after 30 h mechanical milling. Here, the average crystallite size, specific surface area and accumulated lattice strain were 18 nm, 9.3 m2/g and 0.7%, respectively. There was no significant difference on the onset temperature of dehydrogenation between powders milled in different times. However, the amount of hydrogen release was decreased, i.e. from 5.9 wt.% to 4 wt.% with increasing the milling time from 5 h to 30 h.