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

Abstract

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 Å up to more than 10 µm, 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.

Review of magnesium hydride-based materials: development and optimisation

“…This finding, that in the presence of transition metal oxides the nanostructure is stabilised, has clearly been confirmed by small-angle scattering measurements performed by Pranzas et al [106,107]. In addition to these findings which by themselves could explain the enhanced hydrogen absorption in transition metal-doped MgH 2 , measurements of Corey et al [108] Obviously, a shift in the rate-limiting steps from surface reaction towards a two-dimensional growth of the Mg phase with constant interface velocity occurs.…”

Protection of organic carbon in soil microaggregates via restructuring of aggregate porosity and filling of pores with accumulating organic matter

“…We should also point out that the method we are using here is really only another application of the contrast matching technique used extensively in small angle neutron studies to analyze multicomponent systems (Avdeev, 2007) or anomalous small angle X-ray scattering studies (Kirby et al, 2007;Lee et al, 2007;Pranzas et al, 2007); each of these studies employed these routinely applied neutron contrast methods, In analyses of multiphase systems with a complicated small angle scattering profile, the contrast of one phase is changed and the difference in scattering data is attributed to the change in the contrast of that phase. This phase is then analyzed using a two-phase approximation.…”

Thermodynamics of Metal Hydrides: Tailoring Reaction Enthalpies of Hydrogen Storage Materials

“…Furthermore, different additives, such as liquid milling agents and hard particles like oxides, borides, etc. , can positively influence the particle size evolution during the milling process (Pranzas et al, 2006;Pranzas et al, 2007;Dornheim et al, 2007) and prevent grain i.e. crystallite growth.…”