Effects of Milling in Hydrogen on Magnesium Hydride with a Hydride-Forming Titanium Additive

Abstract

A hydride-forming element titanium (Ti) was selected as an additive to improve the hydrogen uptake and release properties of MgH₂. The hydrogen uptake and release properties of three Ti-added MgH₂ alloys [named MgH₂-xTi (x = 6, 12, and 15)] prepared by milling in hydrogen (reactive mechanical grinding) were investigated and those of MgH₂-12Ti were studied in more detail because it had the highest initial hydrogen uptake and release rates and the largest quantities of hydrogen absorbed and released for 60 min. At the cycle number, n, of one (n = 1), MgH₂-12Ti absorbed 4.01 wt.% H for 2.5 min and 6.39 wt.% H for 60 min at 573 K in 12 bar H₂, having an effective hydrogen storage capacity of 6.39 wt.%. MgH₂-12Ti released 0.44 wt.% H for 2.5 min and 1.86 wt.% H for 60 min at 593 K in 1.0 bar H₂. γ-MgH₂, TiH_1.924, and MgO were formed during reactive mechanical grinding. We believe that the brute forces and tensile, compressive, or shear stresses, which are applied to the materials during reactive mechanical grinding, introduce imperfections, fabricate cracks, expose fresh and clean surfaces, decrease the particle size, and disperse the additive among the particles. The γ-MgH₂, TiH_1.924, and MgO formed during reactive mechanical grinding and their pulverization during reactive mechanical grinding are believed to make these effects stronger.