Particle size, grain size and γ-MgH2effects on the desorption properties of nanocrystalline commercial magnesium hydride processed by controlled mechanical milling

The hydrogen desorption properties of commercial nanocrystalline magnesium hydride (Tego Magnan ® from Degussa–Goldschmidt) processed by controlled mechanical milling (CMM) are investigated. A profound effect of the powder particle size on the hydrogen desorption characteristics has been observed. The onset ( T ON ) and peak hydrogen desorption temperatures measured by differential scanning calorimetry (DSC) decrease initially slowly with decreasing mean particle size of hydride, and when the particle size reaches a certain critical threshold value, the desorption temperatures start decreasing more rapidly with further decrease of particle size. The total drop of desorption temperature from its initial value for the as-received MgH 2 to the value attained for the milled MgH 2 having a particle size of ∼500–600 nm is within the range 40–60 °C. The metastable γ-MgH 2 hydride coexists with the stable nanocrystalline β-MgH 2 in the microstructure of the MgH 2 powders ball milled for 10 h and longer. Quantitative evidence shows that two factors, namely the refined powder particle size and the γ-MgH 2 phase residing within the powder particles, acting additively, are responsible for a substantial reduction of the hydrogen desorption temperature of MgH 2 hydride.