PSD measurement: Laser diffractometry
The following collection of "very brief abstracts" (VBAs) represents selected recent papers on the subject named in the title of this page.
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- If elongated particles are substantantially aligned during a measurement of the PSD with a laser diffractometer (LD), the result may be biased for diffractometers with certain detector geometries (Berthold C et al 2006). In particular, if the detector measures a vertical section of the diffraction pattern of particles that are vertically aligned, the particle size retrieved by the LD will be representative of the particle width. If the detector measures a horizontal section of that pattern, the particle size will represent the particle length.
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- Laser diffractometer with an axially-symmetric multi-element detector (semi-circular rings) of scattered light yields PSD independent of systematic particle orientation for nonspherical particles (Köhler U et al 2007). In contrast, laser diffractometers with asymmetric detectors yield PSD that depends on the prevalent orientation of the particles in the measuring zone.
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- Measurement of soil particle size distribution (PSD) with laser diffraction and transmission electron microscopy (TEM) reveals that laser diffraction overestimates the mean diameter of the small particle fraction (< 2 µm; clay), in comparison to TEM (Pieri L et al 2006).
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- Limits of size resolution of the optical techniques of particle size measurement for transparent spherical particles (Rysakov VA and Rejmund 2008).
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- Particle shape / orientation effects
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- A rectangular particle with breadth (width) B and length L contributes to an "apparent" size distribution measured by a laser diffractometer, assuming that the particles are spheres, at two apparent particle sizes: B and L. These contributions are proportional to A2/B to A2/L respectively. This explains an overestimation of the small size (particle width) contribution and an underestimation of the large size (particle length) contribution (Tinke AP et al 2008).
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- Static image analysis (SIA) using the diameter of the largest inscribed disc as the particle size measure is superior to laser diffraction (LD) for nonspherical particles or particles with complex optical properties (Michel F et al 2007). The PSD obtained with LD for elongated particles is wider than that obtained with SIA and is more sensitive than the latter to the presence of a few large particles (outliers) in an analyzed sample.
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- An empirical kernel for non-spherical particles was used for the first time in inversion into particle size distribution of the small-angle light scattering patterns measured with a laser diffractometer (Agrawal YC et al 2008). The use of such kernel is shown to virtually elliminate inversion artifacts, such as overestimation of the small particle concentration, for seawater dispersions.
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