| Abstract: | It has recently been shown that the hydriding properties of the nanocrystalline metal hydrides are far superior to those of the polycrystalline ones. Especially in the case of the Mg-based hydrogen storage alloys, nanostructural modifications have been studied for the purpose of improving their hydrogenation kinetics. In previous studies, I reported on the successful fabrication of Mg2NiHx from Mg and Ni chips with hydrogen induced mechanical alloying (HIMA). Observation of the microstructure showed that the synthesized particles (processed with a 66:1 ball to chips mass ratio and 96 hr HIMA) are composed of amorphous and nanocrystalline composite phases with a grain size of less than 10 nm. The aim of the present work was to examine the hydriding/dehydriding behavior of nanocrystalline metal hydrides using a Sieverts type automatic pressure-composition-isotherm (PCI) apparatus at 393, 423, 453, 483, 513 and 543 K. The specimen was characterized by X-ray diffraction after PCI measurement. The influence of hydrogenation behavior on the phase transition of nano-/amorphous Mg2Ni is a key factor in commercial application. The particles synthesized at 66:1 BCR and 96 hr HIMA revealed a good hydrogen capacity of 2.25 mass% at 483 K. |
