Effect of heat treatment on microstructure and hydrogen storage properties of mass-produced Ti0.85Zr0.13(Fex–V)0.56Mn1.47Ni0.05 alloy

Abstract

Hydrogen storage as a metal hydride is the most promising alternative because of its relatively large hydrogen storage capacities near room temperature. TiMn2-based C14 Laves phases alloys are one of the promising hydrogen storage materials with easy activation, good hydriding-dehydriding kinetics, high hydrogen storage capacity and relatively low cost. In this work, multi-component, hyper-stoichiometric TiMn2-based C14 Laves phase alloys were prepared by a vacuum induction melting method for a hydrogen storage tank and electrochemical applications. Since TiMn2 alloy shows high equilibrium plateau pressure, Ti and Mn were partially replaced by other metallic elements such as Zr, V, and Ni. Since pure vanadium (V) is quite expensive, the substitution of the V element in these alloys has been tried and some interesting results were achieved by replacing V by commercial ferrovanadium, FeV, raw material. XRD pattern and SEM analysis of the as-cast VIM Ti0.85Zr0.13(Fex–V)0.56Mn1.47Ni0.05 alloy revealed that the main phase of the C14 Laves phase and the secondary phase of FeO formed along the grain boundary. Also, the as-cast VIM Ti0.85Zr0.13(Fex–V)0.56Mn1.47Ni0.05 alloy showed a high plateau pressure slope from measurement of P–C-isotherms, which led to a decrease in reversible hydrogen storage capacity. It was found that a suitable heat treatment was very effective in the formation of the C14 single phase and improving the sloping properties. The improvement of sloping properties was mainly attributed to the strain energy effect and the homogeneity of chemical composition. In this work, hydrogen storage capacity was evaluated by a volumetric method using P–C-isotherms and a gravimetric method using magnetic suspension balance.