Effect of rapid solidification on phase structure and hydrogen storage properties of Mg70(Ni0.75La0.25)30 alloy

Abstract

The hydrogen absorption/desorption kinetics and P–C isotherm of Mg70(Ni0.75La0.25)30 alloy, both the as-melt and rapid solidification were carried out on a sievert-type apparatus. The experimental data of initial hydrogen absorption and desorption kinetics at 573 K are in good agreement with Avrami–Erofeev equation, which indicated a three-dimensional interface reaction process of nucleation and growth for the initial hydrogenation kinetics and ‘‘geometrical contraction model’’ for dehydrogenation kinetics. However, the third absorption process seems to have a different hydriding mechanism as chemical reaction. P–C isotherm curves show that the as-melt alloy has two distinct hydrogen absorption plateaus, while the rapid solidification alloy has only one, which attribute to the absent of LaMg3 phase by rapid solidification. It can be confirmed by DSC analysis that the as-melt alloy has two endothermic peaks, compared to one for the rapid solidification alloy. The dehydrogenation activation energies of Mg70(Ni0.75La0.25)30 alloy were calculated by Kissinger method, showing the values of 128.60 ± 13.79 and 112.89 ± 9.94 kJ/mol for the as-melt sample and 61.09 ± 6.28 kJ/mol for rapid solidification alloy respectively.