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1、laParticle size analysis-Laser diffraction methods (ISO-13320-1) IntroductionLaser diffraction methods are nowadays widely used for particle sizing in many different applications. The success of the technique is based on the tact that it can be applied to various kinds of particulate systems, is fas
2、t and can be automated and that a variety of commercial instruments is available. Nevertheless, the proper use of the instrument and the interpretation of the results require the necessary caution.Therefore, there is a need for establishing an international standard for particle size analysis by las
3、er diffraction methods. Its purpose is to provide a methodology for adequate quality control in particle size analysis.Historically, the laser diffraction technique started by taking only scattering at small angles into consideration and, thus, has been known by the following names:- fraunhofer diff
4、raction;- (near-) forward light scattering;- low-angle laser light scattering (LALLS).However, the technique has been broadened to include light scattering in a wider angular range and application of the Mie theory in addition to approximating theories such as Fraunhofer and anomalous diffraction.Th
5、e laser diffraction technique is based on the phenomenon that particles scatter light in all directions with an intensity pattern that is dependent on particle size. All present instruments assume a spherical shape for the particle. Figure 1 illustrates the characteristics of single particle scatter
6、ing patterns: alternation of high and low intensities, with patterns that extend for smaller particles to wider angles than for larger particles2-7,10,15 in the bibliography.Within certain limits the scattering pattern of an ensemble of particles is identical to the sum of the individual scattering
7、patterns of all particles present. By using an optical model to compute scattering for unit volumes of particles in selected size classes and a mathematical deconvolution procedure, a volumetric particle size distribution is calculated, the scattering pattern of which fits best with the measured pat
8、tern (see also annex A).A typical diffraction instrument consists of a light beam (usually a laser), a particulate dispersing device, a detector for measuring the scattering pattern and a computer for both control of the instrument and calculation of the particle size distribution. Note that the las
9、er diffraction technique cannot distinguish between scattering by single particles and scattering by clusters of primary particles forming an agglomerate or an aggregate. Usually, the resulting particle size for agglomerates is related to the cluster size, but sometimes the size of the primary parti
10、cles is reflected in the particle size distribution as well. As most particulate samples contain agglomerates or aggregates and one is generally interested in the size distribution of the primary particles, the clusters are usually dispersed into primary particles before measurement.Historically, in
11、struments only used scattering angles smaller than 14 ,which limited the application to a lower size of about 1 卩 m. The reason for this limitation is that smaller particles show most of their distinctive scattering at larger angles (see also annex Z).Many recent instruments allow measurement at lar
12、ger scattering angles, some up to about 150 ,for example through application of a converging beam, more or larger lenses, a second laser beam or more detectors. Thus smaller particles down to about 0.1卩 m canbe sized. Some instruments incorporate additional information from scattering intensities an
13、d intensity differences at various wavelengths and polarization planes in order to improve the characterization of particle sizes in the submicrometre range.Particle size an alysis Laser di ffractio nmethods-Part 1:General principles1 scopeThis part of ISO 13320 provides guidance on the measurement
14、of size distributions of particles in any two- phase system, for example powders, sprays, aerosols, suspensions, emulsions and gas bubbles in liquids, through analysis of their angular light scattering patterns. It does not address the specific requirements of particle size measurement of specific p
15、roducts. This part of ISO13320 is applicable to particle sizes ranging from approximately 0.1a m to 3 卩 m.For non-spherical particles, an equivalent-sphere size distribution is obtained because the technique uses the assumption of spherical particles in its optical model. The resulting particle size
16、 distribution may be different from those obtained by methods based on other physical principles (e.g. Sedimentation, sieving).3,terms, definitions and symbolsFor the purposes of this part of ISO 13320, the following terms, definitions and symbols apply.3.1 terms, definitions3.1.1 absorptionintroduction of intensity of a light beam traversing a medium through energy conversion in the medium3.1.2 coefficient of variation ( 变异系数 ) Noative
