Hydrogen charging kinetics of Mg - 10wt% Fe2O3 prepared via MgH2-forming mechanical milling

Abstract

The rate-determining steps in the hydrogen charging of Mg-10Fe2O3, prepared by mechanical milling in hydrogen (MgH2-forming mechanical milling), were analyzed by comparing dependences of hydrogen charging rate on hydrogen pressure and temperature with those of previously established theoretical rate equations. Hydrogen charging of the activated Mg-10Fe2O3 can be classified into dissociative chemisorption of hydrogen molecules on particle surfaces, diffusion of hydrogen atoms through a thickening Mg hydride layer, and chemical reaction of Mg with hydrogen at the interface. The dependences of the initial hydrogen charging rates on hydrogen pressure (linear) and temperature (Arrhenius equation / T1/2) showed that the rate-determining step of the hydrogen charging of Mg-10Fe2O3 was the dissociative chemisorption of hydrogen molecules on the surfaces of Mg and/or Fe in the initial hydrogen charging stage. In the later stage, the diffusion of hydrogen atoms through the thickening Mg hydride layer determined the hydrogen charging rate of Mg-10Fe2O3.