Transport process the main transport takes place in

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transport process. The main transport takes place in the center, but chemical signature at the rim follows the central trend except at a lower concentration. Imaging Micro-XRF, Texture, and Lattice Strain Mapping XRF analysis determines the relative amounts of elements within the probed sample volume. Material properties of solids, however, not only depend on the concentration of elements, but also on the phases as well as on the arrangement of crystallites and their orientation distribution, the crystal texture . Polymor- phism for instance, i.e., crystal forms of the same chemical composition but of different crystal lattices, cannot be detected by any analytical method. Therefore, analytical investigations must often be complemented by using additional techniques to reveal the morphology, the grain orientations, and the distribution of internal stress. In the 1990s, SEM in combination with elemental analysis by energy-dispersive spectroscopy (EDS) and backscat- ter Kikuchi diffraction (BKD, also known as “Automated EBSD (electron backscatter diffraction)”) has evolved into the standard technique to provide conveniently these complementary aspects of microstructure [460]. Typical spatial resolutions are 5 nm in SEM images with secondary electrons, 0.5 µ m in EDS microanalysis, and 50 nm in BKD. Better resolutions of about one order of magnitude are obtained from thin specimens in the transmission electron microscope (TEM) using EDS analysis and transmission Kikuchi dif- fraction [461]. Electron microscopy is not a universal technique to meet all require- ments of microstructure characterization. Many applications in mineralogy only require, at a moderate resolution from macroscopic areas in the speci- men surface or from cross-sections, the knowledge of the element distribution and the spatial distribution of certain crystal lattice directions (i.e., pole den- sities rather than the full crystal lattice orientation of each grain). In these cases, XRF and XRD are the methods of choice. These X-ray techniques are principally superior by about two orders of magnitude in accuracy over their electron microscopical counterparts, namely, EDS analysis and Kikuchi dif- fraction. Continuous background is almost negligible in XRF. The dispersion, ϑ/ϑ s in XRD is excellent as compared to electron diffraction, since spectral linewidth, ∆ λ/λ , is extremely small and the characteristic X-ray wavelengths, λ , are in the range of the lattice spacings, thus producing large Bragg angles, ϑ . Almost all X-ray analyses in the laboratory are nonimaging. Conventional lenses are not available for X-rays. To obtain microstructural images from a localized specimen region of the morphology, the spatial distributions of ele- ments, the type of crystal lattice (i.e., phases), grain orientations, and residual stress rather than an average over the whole illuminated area, a mapping tech- nique is required whereby a small spot-size X-ray beam is generated, and the specimen is mechanically scanned under the stationary beam spot. A syn-
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  • Spring '14
  • MichaelDudley

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