Effect of Milling Time on Hydrogen Desorption Properties of Nanocrystalline MgH۲

Nanocrystalline magnesium hydride powder was synthesized by mechanical milling of MgH۲ in a planetary ball mill for various times. The effect of MgH۲ 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 ۳۰ 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 MgH۲ decreased from ۴۲۱ ºC to ۳۱۹ ºC after ۳۰ h mechanical milling. Here, the average crystallite size, specific surface area and accumulated lattice strain were ۱۸ nm, ۹.۳ m۲/g and ۰.۷%, 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 ۵.۹ wt.% to ۴ wt.% with increasing the milling time from ۵ h to ۳۰ h.