Hydrogenation characteristics of the Zr 1 − xTi xCr 1 − yFe 1 + y laves phase alloys

Abstract

The thermodynamic properties of the quarternary Zr 1 − x Ti x Cr 1 − y Fe 1 + y Laves phase alloys for the ranges 0 ⩽ x ⩽ 0.5 and 0 ⩽ y ⩽ 0.5 were investigated as a function of composition and temperature. The variations of hysteresis and plateau slope in the P-C isotherms were extensively studied, depending on alloy composition. The increasing iron substitution for chromium increases the extent of hysteresis and decreases hydride stability while there is no compositional dependence on plateau slopes. The titanium substitution, however, affects both hysteresis and slope. When the titanium concentration range is lower than 0.1, the slopes of the linearly increasing plateaux with hydrogen concentration become lower as the titanium concentration is increased. The well-defined plateaux appear at x = 0.1. However, a further increase in titanium concentration above x = 0.1 results in an increase in the plateau slope. The extent of hysteresis as a function of alloy composition is closely related to the cell volume but different in nature from titanium and iron substituents. The enthalpies are strongly affected by the iron substitution but the entropies are independent of iron concentration, while the replacement of zirconium by titanium changes both the enthalpies and the entropies. From the above results, it is suggested that the hydrogen site occupancy in the lattice is altered by titanium substitution and not by the replacement of chromium by iron.