Influence of the Ti/Zr ratio and the synthesis route on hydrogen absorbing properties of (Ti1−xZrx)Mn1.5V0.5 alloys

The hydrogenation properties of two pseudo-binary Ti1−xZrxMn1.5V0.5 alloys with x=0.15 and 0.5 obtained by arc melting and mechanical alloying have been studied. All alloys crystallize in the hexagonal C14 Laves phase. Arc-melted alloys are microcrystralline and exhibit local variations of Ti and Zr contents which are not overcome by annealing treatments. As for milled alloys, agglomerated nanocrystallites (∼9 nm in diameter) are obtained after subsequent thermal annealing at 800 °C. For high Zr-contents, a better chemical homogeneity is obtained by the milling route. Whatever the synthesis route is, the hydrogen equilibrium pressure decreases with increasing Zr content due to cell-volume increase of the intermetallic compound. As concerns kinetics, very fast hydrogenation rates of few seconds are obtained at room temperature, particularly for milled alloys.