Study of PCT and kinetic properties for LaNi_4.7Al_0.3 hydrogen storage alloy

The PCT properties and hydriding/dehydriding kinetics were simulated for LaNi_4.7Al_0.3 under quasi-isothermal and variable pressure conditions. An ideal kinetic expression for the hydriding/dehydriding reaction is an important tool in the designing process of reaction unit. This paper is based on PCT polynomial equation and nucleation and growth model, and appropriate model equations were obtained for hydriding/dehydriding reaction of LaNi_4.7Al_0.3 hydrogen storage alloy. There was a large slope in the PCT plateau of the alloy. The plateau was divided into three regions according to hydrogen content of hydriding/dehydriding, and enthalpy and entropy values are calculated for each regions using Van't Hoff equation. The results show that the activation energy value was E_a=32 kJ/mol, and the Avrami index n were within the narrow range of 1.1-1.33 in the model equation. The theoretical curves and the experimental data show a good agreement. The mechanism of hydriding/dehydriding changes from one-dimensional nucleation and growth in the prior period to lower diffusion in the later period for controlling reaction process.