Hydrogen sorption behavior of CaAl_1.5Li_0.5

The hydrogen sorption properties of an alloy with nominal composition CaAl_1.5Li_0.5 have been investigated in a pursuit for hydrogen-absorbing Li-containing intermetallics. X-ray analysis of the original alloy indicated a coexistence of three closely related Laves phases. The maximum hydrogen capacity, recorded at about 6 MPa and 300 °C, was approximately 2.5 H atoms per formula unit (f.u.). Pressure-composition (p-c) isotherm measurements were taken in the temperature range between 350 and 450 °C up to pressures of 133 kPa. Thermodynamic parameters are derived for two plateau regions in the p-c isotherms. Analysis of these parameters and supporting evidence from X-ray patterns of hydrogenated and dehydrogenated samples suggest: (a) an initial irreversible disproportionation of the original alloy and (b) subsequent reversible hydrogenations, featuring reversible disproportionations of CaAl₂ and LiAl intermetallic compounds. Attempts to form additional Li-containing intermetallics, namely CaAlLi, TiMn_2−xLi_x (x = 0.2, 0.3, 0.4, 0.6) and TiAl_2−xLi_x (x = 0.3, 0.5), and to hydrogenate them, are reported in brief.