Evolution of microstructure in MgH2 powder particles during high energy ball milling and hydrogen cycling

Abstract We investigated in details the evolution of microstructure by electron microscopy when powder MgH 2 particles were ball milled up to 60 h. The average particle size reduced to less than 5 μm within 5 h of milling from an average size of 38 μm measured before milling. The grain size reduced from an average of ∼750 nm in the un-milled powder to below 100 nm after milling. Particle size, as well as the grain size of milled powders followed log-normal distribution. Lattice strain was introduced significantly in the milled powder as a result of milling. Upon hydrogen cycling, this strain was reduced and the grain size was increased.