Modeling and analyzing the hydriding kinetics of Mg–LaNi 5 composites by Chou model

Abstract

Chou model was used to analyze the influences of LaNi 5 content, preparation method, temperature and initial hydrogen pressure on the hydriding kinetics of Mg–LaNi 5 composites. Higher LaNi 5 content could improve hydriding kinetics of Mg but not change hydrogen diffusion as the rate-controlling step, which was validated by characteristic reaction time t c. The rate-controlling step was hydrogen diffusion in the hydriding reaction of Mg–30 wt.% LaNi 5 prepared by microwave sintering (MS) and hydriding combustion synthesis (HCS), and surface penetration was the rate-controlling step of sample prepared by mechanical milling (MM). Rising temperature and initial hydrogen pressure could accelerate the absorption rate. The rate-controlling step of Mg–30 wt.% LaNi 5 remained hydrogen diffusion at temperatures ranging from 302 to 573 K, while that of Mg–50 wt.% LaNi 5 changed from surface penetration to hydrogen diffusion with increasing initial hydrogen pressure ranging from 0.2 to 1.5 MPa. Apparent activation energies of absorption for Mg–30 wt.% LaNi 5 prepared by MS and MM were respectively 25.2 and 28.0 kJ/mol H 2 calculated by Chou model. Kinetic curves fitted and predicted by Chou model using temperature and hydrogen pressure were well exhibited.