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

Abstract 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.