Browsing by Author "Rowles, MR"

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    Fluorine substitution in magnesium hydride as a tool for thermodynamic control
    (American Chemical Society, 2020-04-01) Humphries, TD; Yang, J; Mole, RA; Paskevicius, M; Bird, JE; Rowles, MR; Tortoza, MS; Sofianos, MV; Yu, DH; Buckley, CE
    Metal hydrides continue to vie for attention as materials in multiple technological applications including hydrogen storage media, thermal energy storage (TES) materials, and hydrogen compressors. These applications depend on the temperature at which the materials desorb and reabsorb hydrogen. Magnesium hydride is ideal as a TES material, although its practical operating temperature is capped at ∼450 °C because of material degradation and high operating pressure. Fluorine substitution for hydrogen in magnesium hydride has previously been shown to increase the operating temperature of the metal hydride while limiting degradation, although full characterization is required before technological application can be ensured. The present study characterizes Mg(HxF1-x)2 solid solutions (x = 1, 0.95, 0.70, 0.85, 0.50, and 0) by inelastic neutron spectroscopy, powder X-ray diffraction, and thermal conductivity measurements, with the results being verified by density functional theory. For each experiment, a clear trend is observed throughout a series of solid solutions, showing the possibility of tuning the properties of MgH2. As F- substitution increases, the average Mg-H(F) bond distance elongates along the axial positions of the Mg-H(F) octahedra. Overall, this leads to an increase in Mg-H bond strength and thermal stability, improving the viability of Mg-H-F as potential TES materials. © 2020 American Chemical Society.
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    Polycrystalline materials analysis using the Maia pixelated energy-dispersive x-ray area detector
    (Cambridge University Press, 2017-09-26) Kirkwood, HJ; De Jonge, MD; Howard, DL; Ryan, CG; van Riessen, GA; Hofmann, F; Rowles, MR; Paradowska, AM; Abbey, B
    Elemental, chemical, and structural analysis of polycrystalline materials at the micron scale is frequently carried out using microfocused synchrotron X-ray beams, sometimes on multiple instruments. The Maia pixelated energy-dispersive X-ray area detector enables the simultaneous collection of X-ray fluorescence (XRF) and diffraction because of the relatively large solid angle and number of pixels when compared with other systems. The large solid angle also permits extraction of surface topography because of changes in self-absorption. This work demonstrates the capability of the Maia detector for simultaneous measurement of XRF and diffraction for mapping the short- and long-range order across the grain structure in a Ni polycrystalline foil. Copyright © International Centre for Diffraction Data 2017
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    Simultaneous X-ray diffraction, crystallography and fluorescence mapping using the Maia detector
    (Elsevier, 2018-02-01) Kirkwood, HJ; de Jonge, MD; Muránsky, O; Hofmann, F; Howard, DL; Ryan, CG; van Riessen, GA; Rowles, MR; Paradowska, AM; Abbey, B
    Interactions between neighboring grains influence the macroscale behavior of polycrystalline materials, particularly their deformation behavior, damage initiation and propagation mechanisms. However, mapping all of the critical material properties normally requires that several independent measurements are performed. Here we report the first grain mapping of a polycrystalline foil using a pixelated energy-dispersive X-ray area detector, simultaneously measuring X-ray fluorescence and diffraction with the Maia detector in order to determine grain orientation and estimate lattice strain. These results demonstrate the potential of the next generation of X-ray area detectors for materials characterization. By scanning the incident X-ray energy we investigate these detectors as a complete solution for simultaneously mapping the crystallographic and chemical properties of the sample. The extension of these techniques to broadband X-ray sources is also discussed. © 2017 Acta Materialia Inc. Published by Elsevier Ltd.