Small-angle scattering investigations of magnesium hydride used as a hydrogen storage material


In this work, high-energy ball-milled magnesium hydride samples used for hydrogen storage are investigated using small- and ultra-small-angle neutron scattering (SANS) as well as small-angle X-ray scattering (SAXS). Size distributions of inhomogeneities with dimensions from 10 A ˚ up to more than 10 mm, corresponding to crystallite and particle sizes obtained by X-ray diffraction and electron microscopy, are determined as a function of milling time, milling tool material and added metal oxide catalysts in order to study the influence of the microstructure on the sorption kinetics. Significant changes of the volume fraction distributions are found for samples containing the catalyst chromium oxide, particularly when the catalyst particles are nanometre-sized. Cr2O3 is an effective agent for breaking up particles during the milling process. The comparison of SANS and SAXS curves give some of the first information about the distribution of hydrogen-containing structures. Using anomalous small-angle X-ray scattering, an energy-dependent scattering is found for an MgHx sample with 1 mol% Fe2O3. From the separated scattering curve a size distribution of hard spheres is obtained with a size range which is expected for crystallite and particle sizes of the Fe2O3 catalyst. Chemical shifts in the absorption spectra give information about the stability of the metal oxide catalysts during the milling process.
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