In situ synchrotron X-ray diffraction studies of hydrogen desorption and absorption properties of Mg and Mg–Mm–Ni after reactive ball milling in hydrogen

Reactive ball milling in hydrogen was applied to synthesize nanocrystalline Mg- and Mg8Mm20Ni-based hydrides with crystallite size below 10 nm. These hydrides were studied by in situ synchrotron X-ray diffraction performed at the Swiss–Norwegian Beam Lines of the European Synchrotron Radiation Facility, Grenoble. Characterization of the phase-structural and microstructural state of the constituents during the reversible processes of synthesis and decomposition of the hydrides upon application of hydrogen pressure or vacuum at temperatures 20–350 °C and kinetics of hydrogen uptake was performed. Details of the mechanism of the phase-structural transformations were provided by high time resolution of the synchrotron X-ray diffraction data, high sensitivity in determining formation of the phase constituents, excellent accuracy in yielding the crystallographic characteristics and in probing the microstructural evolution of the constituents formed.