Particle size, grain size and γ-MgH2 effects on the desorption properties of nanocrystalline commercial magnesium hydrideprocessed by controlled mechanical milling

Abstract

The hydrogen desorption properties of commercial nanocrystalline magnesium hydride (TegoMagnan® from Degussa–Goldschmidt) processed by controlled mechanical milling(CMM) are investigated. A profound effect of the powder particle sizeon the hydrogen desorption characteristics has been observed. The onset(TON) and peak hydrogen desorption temperatures measured by differential scanningcalorimetry (DSC) decrease initially slowly with decreasing mean particle size of hydride,and when the particle size reaches a certain critical threshold value, the desorptiontemperatures start decreasing more rapidly with further decrease of particle size. Thetotal drop of desorption temperature from its initial value for the as-receivedMgH2 to the value attainedfor the milled MgH2 having aparticle size of ∼500–600 nm iswithin the range 40–60 °C. The metastable γ-MgH2 hydride coexists with the stable nanocrystallineβ-MgH2 in themicrostructure of the MgH2 powders ball milled for 10 h and longer. Quantitative evidence showsthat two factors, namely the refined powder particle size and theγ-MgH2 phase residing within the powder particles, acting additively, are responsiblefor a substantial reduction of the hydrogen desorption temperature ofMgH2 hydride.