Investigation on kinetics mechanism of hydrogen absorption in the La2Mg17-based composites

A new model has been successfully used to investigate the hydrogen absorption kinetics mechanism of La2Mg17-based composites. The results indicate that different preparation conditions lead to different rate-controlling steps during hydrogen absorption process. For La2Mg17–LaNi5 composite synthesized by the method of melting, the rate-controlling step is the surface penetration of hydrogen atoms, which does not change by addition agent (LaNi5). However, mechanical milling can change the rate-limiting steps of hydriding reaction in the La2Mg17–LaNi5 composite from surface penetration to diffusion of hydrogen in the hydride layer. With the enhancement of milling intensity, the rate-controlling step in La1.8Ca0.2Mg14Ni3 alloy changes from surface penetration to diffusion. In addition, the activation energies of hydrogen absorption for La2Mg17−20 wt%LaNi5 and La1.8Ca0.2Mg14Ni3 are obtained by this model.