Hydriding kinetics of the La1.5Ni0.5Mg17–H system prepared by mechanical alloying

Abstract

In the study of reaction kinetics between hydrogen and hydriding alloys, what is the most important is to obtain intrinsic kinetic data. The hydriding kinetics of 0.5 g La1.5Ni0.5Mg17 sample in the two-phase (α-β) region was investigated as a function of temperature and pressure in the ranges 553–573 K and 0.256–0.992 MPa H2 respectively. Mathematical analyses of the time-dependent hydrogen absorption curves indicate agreement with Jander diffusion model, [1 − (1 − ξ)1/3]2 = k(T, P)t, which suggests that the rate-controlling step for hydrogen absorption is three-dimensional diffusion. An apparent activation energy for such diffusion process of 83 ± 1 kJ/mol H2 has been obtained from the absorption data.