ISO 13320-2020 pdf download

ISO 13320-2020 pdf download.Particle size analysis一Laser diffraction methods. 4 Principle 4.1 General The laser diffraction or scattering technique’) for the determination of particle size distributions. PSDs, is based upon the phenomenon that the angular distribution of the intensity of scattered light by a particle (scattering pattern) is dependent on the particle size. When the scattering is from a cloud or ensemble of particles the intensity of scattering for any given size class is related to the number of particles and their optical properties, present in that size classllIN. A test sample, dispersed at an adequate concentration in a suitable liquid or gas, is passed through the beam of a monochromatic light source, usually a laser. The light scattered by the particles, at various angles, is measured by an array of photo detectors. The numerical values from each detector are recorded for subsequent analysis. Within certain limits, such as of particle concentration in measuring zone, the scattering pattern of an ensemble of particles is identical to the sum of the individual scattering patterns of all particles. The theoretical scattering patterns of unit volumes of particles in selected size classes are used to build a matrix and together with a mathematical procedure are used to solve the inverse problem, providing a volumetric particle size distribution (PSD), iterated to provide a best fit to the measured scattering patternl1.l. 4.2 Theory The theoretical scattering pattern of a single spherical homogeneous particle is given by Mie-theory in generall). If the particle size is relatively large (in terms of size parameter, a = it x > 10) and is opaque, Fraunhofer diffraction theory is available only for small angle forward scatteringl1lll. The Fraunhofer approximation is an analytical method that does not require the optical properties of the material. Some other theoretical approximations are available for numerical realization of the Mie-theory. and these are called optical models in general. Choosing a relevant optical model for the inverse problem to yield a proper PSD is important. Laser diffraction records the scattering pattern from the particles presented. This composite pattern is converted to a size distribution of spherical particles that would provide the same composite scattering pattern using an appropriate optical model and data inversion routine, It therefore provides a size distribution of laser diffraction equivalent spheres. If the test sample is not spherical, the same basic procedure is used and the resulting size distribution Is formed. Thus, PSDs...