Measurement and modelling of hydriding and dehydriding kinetics

The rates of hydriding and dehydriding were measured for LaNi5Hx under isothermal and isobaric conditions. Obtained data of hydriding rates indicated that the rate controlling step was the nucleation and growth process of the hydride phase and then changed to hydrogen diffusion through the hydride phase at the later stage. On the other hand, for the desorption of hydrogen, the rate controlling step was only the homogeneous chemical reaction of the hydride phase. Theoretical rate equations were derived on the basis of the kinetic model of hydriding and dehydriding reaction proposed in this study. A satisfactory agreement between the theoretical and experimental results was obtained. (C) 1998 Elsevier Science S.A. All rights reserved.