Modeling and analyzing the hydriding kinetics of Mg-LaNi5 composites by Chou model

Chou model was used to analyze the influences of LaNi₅ content, preparation method, temperature and initial hydrogen pressure on the hydriding kinetics of Mg-LaNi₅ composites. Higher LaNi₅ 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.% LaNi₅ 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.% LaNi₅ remained hydrogen diffusion at temperatures ranging from 302 to 573 K, while that of Mg-50 wt.% LaNi₅ 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.% LaNi₅ prepared by MS and MM were respectively 25.2 and 28.0 kJ/mol H₂ calculated by Chou model. Kinetic curves fitted and predicted by Chou model using temperature and hydrogen pressure were well exhibited.