European Powder Diffraction EPDIC 8

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Authors: S. Naamen, H. Ben Rhaiem, A. Ben Haj Amara
Abstract: The intercalation complex of nacrite with an alkali halide (Caesium chloride: CsCl) has been successfully prepared by mixing a CsCl saturated solution with a 8.4Å-hydrated nacrite. The homogeneous nacrite/CsCl complex has been studied by X-ray diffraction (XRD). Using an oriented clay aggregate, 10 basal reflections were obtained. The XRD pattern showed basal spacing of 10.5Å with integral series of 00l reflections indicating an ordered stacking of parallel 1:1 layers. A direct method involving a monodimensional electron density projection, along the normal to the layers, is used to determine the number and the position of intercalated compounds. The best agreement between observed and simulated p(Z) (R = 5%) is obtained by placing one Cl- ion at Z=6.7Å; one Cs+ ion at Z=8.3Å and two H O molecules at 6.3 and 7.4Å.
Authors: David Rafaja
Abstract: Capability of the X-ray scattering for study of low-dimensional structures is illustrated on few examples. They are focused to the phase analysis, residual stress measurement, calculation of the stress-free lattice parameters, investigation of the anisotropic lattice deformation and preferred orientation in UN thin films. Further, the study of concentration profiles in functionally graded hard-metals and investigation of the multilayer degradation caused by soft annealing are discussed.
Authors: Nathalie Audebrand, Daniel Louër
Abstract: The theoretical background currently used in line profile analysis is reviewed. It covers the size and structure imperfection effects at the origin of diffraction line broadening. The propagation of errors, i.e. old errors and new errors related to profile fitting techniques, is commented. The experimental conditions for minimising errors are described. Representative examples of microstructure characterisation of nanopowders are presented.
Authors: Paolo Scardi, Matteo Leoni, M. Loch, G. Barbezat
Abstract: The residual stress in thin coatings of yttria stabilised-zirconia produced by Low Pressure Plasma Spraying were measured by X-ray Diffraction, using laboratory as well as synchrotron radiation sources. The specific microstructure, with absence of texture and fine distribution of nearly equiaxed grains, point out that despite the markedly anisotropic nature of cubic zirconia, coatings can be considered as macroscopically isotropic. This picture is also confirmed by the results of a parallel study, where the X-ray elastic constants were measured in-situ along two crystallographic directions ([440] and [620]): measured values agree fairly well with those calculated from single-crystal data under the Neerfeld-Hill assumptions. SR XRD provided a detailed information on the stress field across the thickness of the zirconia coatings. In particular the presence of a stress gradient was observed and modelled. The average stress is compressive, and increases with the coating thickness. Compression tend to increase from the surface toward the inside of the coating reaching a maximum of ~-1.0 GPa in a 24 µm coating.
Authors: Giovanni Berti, U. Bartoli, G. Basile, P. Becker, Andrew N. Fitch
Abstract: Three blocks of silicon have been crashed in this experiment in order to verify the crashing effects on specimens having distinct original micro-structural arrangements. One of them comes from a rod bar of mono-crystal silicon, two others were from polycrystalline silicon manufactured by two distinct manufacturers with distinct growing process. Several specimens of powders, differing in type and grain size, were obtained by treating these source samples. This paper reports on data collected from synchrotron and conventional radiation and the results show that powders obtained from mono-crystalline silicon provide diffraction profiles, where the structural contribution is smaller than for polycrystalline silicon specimens. The peaks from the 'mono-crystal powder' resulted even narrower than peaks from SRM Silicon 640b by NIST.
Authors: S.V. Cherepanova, S.V. Tsybulya
Abstract: Software for the simulation of X-ray powder diffraction (XRPD) patterns for ultrafine-grained materials with some kinds of imperfections has been developed. These calculations are performed on the base of the model of one-dimensionally disordered (1D-disordered) crystal [1]. Such a model can describe stacking faults (SF) and other planar defects (PD) and also finite size of coherently scattering domains. Simulated XRPD pattern is compared with experimental one and can be fitted to it. Potentialities of the software are illustrated by several examples.
Authors: Thomas L. Christiansen, Marcel A.J. Somers
Abstract: On evaluating lattice strain-depth or stress-depth profiles with X-ray diffraction, the variation of the information depth while combining various tilt angles, in combination with lattice spacing gradients leads to artefacts, so-called ghost or fictitious stresses. X-ray diffraction lattice-strain analysis was simulated for a model stress-depth profile combined with a composition-depth profile. Two principally different methods were investigated for the reconstruction of the actual stress and composition profiles from the simulated data: - considering the stress/strain determined at a specific depth as a weighted average over the actual stress/strain depth profile - considering the lattice spacing determined at a specific depth, for a specific value for as a weighted average over the actual lattice spacing profile for this direction. On the basis of the results it is possible to propose a preferred method for the evaluation of stress/strain and composition profiles, while minimising the risk for ghost stresses.
Authors: Iuliana C. Dragomir, András Borbély, Tamás Ungár
Abstract: Anisotropic strain broadening of diffraction peaks can be parameterised by dislocation contrast factors. A comprehensive software has been developed and made available through the internet to determine the individual and averaged contrast factors which are also compiled for cubic and hexagonal crystals. Using the theoretical and the measured values of contrast factor the microstructure of the specimen can be characterised in terms of active slip systems, Burgers vector populations, dislocation densities and crystallite size- and size distribution.
Authors: Nariman A. Enikeev, Igor V. Alexandrov, Ruslan Valiev
Abstract: A computer simulation-based approach has been developed in order to reveal grain boundary defect structure of nanomaterials, which is described in terms of extrinsic grain boundary dislocations. On the basis of comparative analysis of numerically obtained results to experimental data, the defect structure parameters of nanostructured materials produced by severe plastic deformation have been evaluated.
Authors: Jenő Gubicza, Magdy Kassem, Tamás Ungár
Abstract: The effect of the nominal Mg content and the milling time on the microstructure of mechanically alloyed Al(Mg) solid solutions is studied. The crystallite size distribution and the dislocation structure are determined by X-ray diffraction peak profile analysis. Magnesium gradually goes into solid solution during ball milling and after 3 h almost all of the Mg atoms are soluted into the Al matrix. With increasing milling time the Mg content in solid solution, the dislocation density as well as the hardness are increasing, whereas the crystallite size is decreasing. A similar tendency of these parameters is observed at a particular duration of ball milling with increasing of the nominal Mg content. At the same time for a long milling period the dislocation density slightly decreases together with a slight reduction of the hardness.

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