Hydriding kinetics of LaNi5 using Nucleation-growth and Diffusion Models

Abstract

In this paper, the hydriding kinetics of a LaNi5 alloy have been measured with a thermo-gravimetric system. The rate controlling steps have been analyzed. In the α + β phase, a first order Johnson-Mehl-Avrami model provides a good agreement with the measurements. In the ? phase, the previous approach shows that the reaction becomes progressively controlled by the diffusion of hydrogen atoms through the hydride. In order to support this hypothesis, a Crank-Nicholson diffusion model has also been applied and achieved good results. The results show that the transition in the rate controlling mechanism takes place before the static pressure-composition isotherms are reached.