Metallic oxides are brittle and halides have low melting points. They are expected to increase the reaction rates of Mg with hydrogen when added. Samples with compositions of 95 wt% Mg+5 wt% TiCl3 (designated as Mg-5TiCl3), 90 wt% Mg+10 wt% TiCl3 (Mg-10TiCl3), and 80 wt% Mg+14 wt% Ni+6 wt% TiCl3 (Mg-14Ni-6TiCl3) were prepared by high-energy ball milling in hydrogen (reactive mechanical grinding). At the first cycle (n = 1), Mg-5TiCl3 had the highest initial hydrogen uptake rate and the largest quantity of hydrogen absorbed for 60 min at 593 K in 12 bar H2, followed by Mg-10TiCl3 and Mg- 14Ni-6TiCl3. Mg-5TiCl3 had an effective hydrogen storage capacity (a quantity of hydrogen absorbed for 60 min) of about 6.3 wt% at n = 1. Mg-5TiCl3 absorbed 4.84 wt% H for 5 min and 6.27 wt% H for 60 min. Decrease in the Mg proportion in Mg-14Ni-6TiCl3, compared with those in Mg-5TiCl3 and Mg-10TiCl3, and the formation of Mg2Ni, with a lower hydrogen storage capacity than Mg, are thought to decrease the initial hydrogen uptake rate and the quantity of hydrogen absorbed for 60 min for Mg-14Ni-6TiCl3. At n = 1, Mg-14Ni-6TiCl3 has the highest initial hydrogen release rate at 593 K in 1.0 bar H2, followed by Mg-10TiCl3 and Mg-5TiCl3. The Mg2Ni formed in Mg-14Ni-6TiCl3 and the larger content of additives (favoring the nucleation of Mg-H solid solution) are believed to make Mg-14Ni-6TiCl3 have the highest initial hydrogen release rate among these three samples. The hydrogen storage properties of Mg-14Ni-6TiCl3 were compared with those of Fe2O3 and Niadded Mg, which were prepared under the conditions similar to those to prepare Mg-14Ni-6TiCl3.

Keywords: Hydrogen absorbing materials, Phase transition-accompanying milling, Phase transition, Microstructure, TiCl3 or Fe2O3 addition to Mg.