GRAIN BOUNDARY MOBILITIES IN POLYCRYSTALS A high-throughput method of measuring grain boundary mobilities has been developed that uses a direct comparison of a 3D experimental movie to simulations of grain growth during annealing of an iron polycrystal with 1501 grains. The mobilities are used to investigate the dependence of the grain boundary mobility on the crystallography of grain boundaries. The results suggest that other driving mechanisms besides crystallography are at play.
STRUCTURE OF MATERIALS
Pd-LaFeO3 catalysts in aqueous ethanol: Pd reduction, leaching, and structural transformations in the presence of a base, S. Checchia (a), C.J. Mulligan (b), H. Emerich (a), I. Alxneit (c), F. Krumeich (d),
M. Di Michiel (a), P.B.J. Thompson (a), K.K. Hii (b), D. Ferri (c) and M.A. Newton (d), ACS Catal. 10, 3933-3944, (2020); https:// doi.org/10.1021/acscatal.9b04869. (a) ESRF
(b) Department of Chemistry, Imperial College London (UK) (c) Paul Scherrer Institut, Villigen (Switzerland) (d) ETH Zurich (Switzerland)
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PRINCIPAL PUBLICATION AND AUTHORS
reduced Pd nanoparticles, around a core of the starting structure.
In summary, the base can be a potent agent for leaching of palladium and the integrity of
this type of functional materials cannot be guaranteed in the presence of some of the species that are required under the typical operation conditions of the material, for example, for carbon-carbon coupling chemistry.
Fig. 125: Schematic description of how the
LaFe1-xPdxO3 catalyst behaves as a result of
heating in aqueous ethanol and in basified
aqueous ethanol, as determined through the combined use of Pd and
Fe K-edge XAS and HXRD/ PDF methods.
Most crystalline materials are composed of many small crystallites, grains, with lattices in different orientations. Since many mechanical and physical properties of materials, from tensile strength in structural materials to resistivity in electronic materials, are a function of the local grain morphology, grain growth can be used to design materials with a given set of properties. The predictive power of models of this grain growth process are critically dependent on understanding the mechanisms governing the grain boundary movement and measurements of the relevant material parameters. The crystallography of a grain boundary is traditionally described by five degrees of freedom representing the misorientation (the orientation difference between the two grains that share the boundary) and the inclination
of the grain boundary plane. Measuring grain boundary mobilities for a large number of boundaries in the interior of a polycrystal is essential in understanding the mechanisms controlling grain growth in the polycrystalline systems found in real-life materials.
To address this problem, a novel approach was developed to extract grain boundary mobilities from time-resolved X-ray diffraction tomography. By introducing a unique coupling with 3D phase-field modelling, it was possible to simultaneously fit the reduced mobilities (the product of the grain boundary mobility and energy) for a large number of grain boundaries of grain growth in a 99.9% pure iron polycrystalline sample resulting in a rapid throughput technique for measuring grain