Application of a new kinetic model for the hydriding kinetics of LaNi 5− xAl x (0 ≤ x ≤ 1.0) alloys

Abstract

The hydriding kinetic mechanism of LaNi 5− x Al x (0 ≤ x ≤ 1.0) is clarified using Chou model, involving the influence of temperature, pressure and Al content. The results indicate that the rate-controlling step of the hydriding reaction in LaNi 5 and LaNi 4.7Al 0.3 is diffusion, but in LaNi 4Al, it is surface penetration at the temperature range of 30–80 °C. Moreover, the hydriding reaction rates increase with increasing temperature for the three alloys. Based on the results calculated using the Chou model, the rate-controlling steps for LaNi 5 and LaNi 4.7Al 0.3 correspond to surface penetration and diffusion under different pressures ranging from 0.47 to 1.0 MPa, and the hydrogenation rate increases with an increase in pressure. A suitable addition of Al can obviously improve the hydrogen absorption reaction rate. For LaNi 5− x Al x ( x = 0, 0.15, 0.5 and 1.0) under a hydrogen pressure of 1.00 MPa at 30 °C, the hydrogen absorption reaction rate is as follows: LaNi 5 < LaNi 4Al < LaNi 4.5Al 0.5 < LaNi 4.85Al 0.15.