fulltext_009 - Chapter 10 Laser Diffraction Contents 10.1...

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259 ±10.1± ±Characteristics±of±Laser±Diffraction±Technique±± Chapter 10 Laser Diffraction Contents 10.1 Characteristics of Laser Diffraction Technique . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 259 10.2 Principle of Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 260 10.3 Light Scattering Theories . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 261 10.4 Instrument Set up . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 268 10.5 Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 271 10.6 Operational Parameters. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 273 10.7 Quality Aspects. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 273 10.8 Qualification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 275 10.9 Limitations and Problems. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 275 10.10 Error Sources and Diagnosis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 279 10.11 Practical Notes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 280 10.12 Future Prospects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 280 10.13 Definitions, Abbreviations and Symbols . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 281 10.14 List of Instrument Manufacturers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 284 Bibliography. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 285 Principle model-based PSD calculation from angular pattern of scat- tered light intensities Type of diameter (set of) equivalent light scatter diameter(s) Type of distribution volume based size distribution of a collective of spherical particles, having approximately the same scattering pattern as the dispersed sample Measurement range - overall 0.1–3,000 μm (in special set-ups up to about 10 mm or down to about 0.03 μm) - per measurement depending on optics and type of instrument Calibration no; manufacturer calibrates detector elements; qualification/validation recommended Sample types dispersed dry powders, sprays, suspensions, emulsions Sample size mg to gram quantities depending on particle size; larger quantities allowed for dispersed dry powders Measurement time 0.01–30 s Repeatability D 50 about 0.5% relative Bias D 50 smaller than 2% relative Resolution 10–40% relative, depends on size of detector elements and particles Sensitivity better than 5% (w/w) Traceability only indirectly H.G. Merkus, Particle Size Measurements, DOI 10.1007/978-1-4020-9015-8_10, © Springer Science+Business Media B.V. 2009
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260 10 Laser Diffraction ±10.2± ±Principle±of±Operation± At present, the standard name of the technique is laser diffraction (LD). Other names are: static light scattering (SLS), (near-) forward light scattering, low-angle laser light scattering (LALLS) and Fraunhofer diffraction. In this technique, the scattering pattern of monochromatic laser light by an ensemble of dispersed particles is measured on a series of detector elements posi- tioned at different angles, mostly in the forward direction. The measured detector signals are then converted (deconvoluted) to a particle size distribution (PSD), by using a model-based matrix. This matrix contains the calculated signals at all detector elements per unit volume of spherical particles for each of a defined set of size classes. Several theoretical models are being used: Fraunhofer, anoma- lous diffraction and Mie (see Sect. 10.3). The latter model requires knowledge of the real and imaginary part of the refractive index (RI). In some instruments, data obtained with different wavelengths or polarization directions are taken into account as well. Always, the particles are assumed to be spherical. For non-spher- ical particles, this leads to a distribution of equivalent light scatter diameters, which depends on particle orientation.
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This note was uploaded on 05/06/2010 for the course MECH. 28197 taught by Professor Dr.shafii during the Spring '10 term at Sharif University of Technology.

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fulltext_009 - Chapter 10 Laser Diffraction Contents 10.1...

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