Influence of elemental diffusion on low temperature formation of MgH₂ in TiMn_1.3T_0.2Mg (T = 3d-transition elements)

In order to examine the influence of the elemental diffusion from the host compound into the Mg region on low temperature formation of MgH₂, we have investigated the hydriding properties and the microstructures of the composite materials TiMn_1.3T_0.2-Mg (T=V, Cr, Mn, Fe, Co, Ni and Cu). MgH₂ is formed at 353 K in all composite materials. Of all the substitutions, the amount of MgH₂ is the largest in the case of the Cu substitution, which originates from the existence of the Mg-Mg₂Cu eutectic formed by Cu diffusion from the host compound TiMn_1.3Cu_0.2 into the Mg region during the liquid phase sintering. In addition, the hydrogen capacity of TiMn_1.3Cu_0.2-Mg (that is TiMn_1.3Cu_0.1-(Mg+Mg₂Cu) after the sintering) easily saturates in comparison with TiMn_1.5-(Mg+Mg₂Cu) without Cu diffusion. It is concluded that Cu diffusion promotes the mobility of hydrogen atoms at the complex interface between the host compound and the Mg region.