Dehydrogenation properties of nano-/amorphous Mg2NiHx by hydrogen induced mechanical alloying

In recent years, nanocrystalline materials have been of interest for hydrog en storage applications. Especially, the great improvement of the hydrogena tion properties of Mg alloys that can be achieved by nanocrystallization. I n this study, nanocrystalline Mg2NiHx is fabricated from Mg and Ni chips by hydrogen induced mechanical alloying (MA) for 96 h under a high-pressure h ydrogen atmosphere. The balls to chips mass ratios (BCR) are 30:1 and 66:1. The particles obtained are characterized by XRD and TEM,and absorbed hydro gen contents (AHC) were measured by TGA. For dehydrogenation kinetics, acti vation energies are calculated by isothermal thermogravimetry analysis (ITG A) and pressure-composition-isotherm (PCI) analysis. The results of XRD and TEM revealed that the Mg2NiHx peaks are broadened in the case of high BCR and the particles are composed of the nanocrystalline phases less than 10 n m with the amorphous phase. The results of ITGA and PCI analysis show that the dehydrogenation kinetics are greatly improved by nanocrystallization. T he results show that BCR conditions mainly affect the size and fraction of the nanocrystalline phases, the resultant AHC and the dehydrogenation kinet ics. (C) 2000 Elsevier Science B.V. All rights reserved.