Hydrogen sorption behavior of some Pd-containing compounds

Highlights: • Pd substitution destabilizes the hydrides in the Zr(Pd_xV_1-x)₂ system, 0 ≤ x ≤ 0.2. • The Zr(Pd_xV_1-x)₂ hydride stabilities obey the rule of reversed stability. • Heats of alloy formation and cell volumes show joint effect on hydride stabilities. • Hydrogen absorption capacity correlates inversely with shear to bulk moduli ratio. • Ti(Pd_xNi_1−x)₃ compounds do not absorb significant amounts of hydrogen. New pseudobinary Zr(Pd_xV_1−x)₂, x = 0.1, 0.15, 0.2, intermetallic compounds have been synthesized and characterized by X-ray diffraction and their shear, G, and bulk, B, moduli have been measured. Hydrogen absorption isotherms of the x = 0.1 and 0.2 alloys have been determined at temperatures between 200 °C and 500 °C in the pressure range 10⁻⁷-1.3 atm. An increase of the Pd content causes a decrease of both the hydrogen absorption capacity and the stability of the corresponding hydrides. The latter behavior is attributed mainly to the Pd-induced increase of the stability of the starting intermetallics (rule of reversed stability). A combined effect of the heats of alloy formation, ΔH_alloy, and the crystal cell volumes, V, on the stabilities of the hydrogenated compounds is shown for Zr(Pd_xV_1−x)₂ and Zr(Al_xV_1−x)₂ in terms of correlation factor ΔH_alloy + bV, where b is a fitted constant. The decrease of the hydrogen absorption capacity with x in Zr(Pd_xV_1−x)₂ correlates well with an increase of the G/B ratio, as previously suggested. We have also tried to produce and hydrogenate alloys of the systems Ti(Pd_xNi_1−x)₃, Zr(Pd_xFe_1−x)₂ and Zr(Pd_xNi_1−x)₃ but did not find significant hydrogen absorption.