Hysteresis and related irreversible phenomena in CeNi5-based intermetallic hydrides -: I.: Peculiarities of the first hydrogenation

The effect of alloy annealing, particle size and hydrogenation temperature on the behaviour of CeNi5 during the first absorption-desorption cycles has been studied using pressure-composition isotherm measurement and XRD analysis. It has been shown that the particle size of the sample did not affect the thermodynamic parameters of the activation and different behaviour of the as-cast and annealed samples very likely was caused by initial strain and crystallite size of the virgin alloys. Enthalpy and entropy changes in the first hydrogenation and dehydrogenation reactions have been calculated from the temperature dependence of the fugacity values corresponding to the plateau pressures. Activation peculiarities of the CeNi5-H-2 system have been discussed in comparison with the literature data on LaNi5. (C) 2003 Elsevier B.V. All rights reserved.