Structure and hydrogenation properties of nanocrystalline Mg₂Ni prepared by hydriding combustion synthesis and mechanical milling

In the present work, a nanocrystalline Mg₂Ni alloy was prepared by hydriding combustion synthesis followed by mechanical milling (HCS + MM), and its structure as well as hydrogenation properties, especially the thermodynamic properties were studied by means of X-ray diffraction (XRD), scanning electron microscopy (SEM) and pressure-concentration isotherms (PCIs). It was found that the product milled for the optimized duration of 40 h absorbed 2.76 wt.% of hydrogen within 100 s at 313 K. However, this excellent hydriding property degenerated fast with cycling. The enthalpy derived from the Van't Hoff equation of this product was -53.13 kJ/mol for hydrogenation, which was slightly higher than that reported for the HCS product. From the results of SEM and XRD the dimensions of particle and grains of Mg₂Ni hydride were drastically reduced after MM, and the nanostructured alloy Mg₂Ni experienced noticeable grain growth during dehydring/rehydriding reactions.