The device does not directly measure the size of the particle but the angle and intensity of light scattering from the particles.
This is made use of in every analyzer ever made, from the basic prototype to the latest LA-960 particle size analyzer.
The larger the particle, the smaller the angle and the higher the intensity of the scattering. The principle of laser diffraction is the relationship that exists between light scattering (its angle and intensity) and particle size. While such analysis was then limited to labs which had built customized equipment for this purpose, several new developments have led to laser diffraction becoming a part of the arsenal of research laboratories and production processes all over the world. It was Gustav Mie, author of the Mie Scattering Theory, who studied gold nanoparticles in pursuit of his doctoral degree. Light scattering as the basis for size determination of many objects has been explored for a long time. D 1 or D 99).Sponsored by HORIBA Scientific Jun 14 2018 The beginning and end of the distribution are commonly defined by D 10 and D 90, although other D values can be used to define the cumulative distribution as well (e.g. D 50 defines the point where 50 % of the particles are smaller and 50 % bigger than that certain diameter. In either direction, the cumulative curve always ranges from 0 % to 100 %, with the middle point D 50 being the most commonly reported result of particle sizing by laser diffraction. This is done either from the smallest to the biggest diameter (called the "undersize curve") or in the opposite direction (called the "oversize curve"). To get this distribution, values for all previous classes are added to the next. For this reason, usually the cumulative distribution is analyzed. spikey, flat, etc.), so peak values are rather unreliable. However, there might be more peaks or the peak might be weakly defined (e.g. The D mode value defines the position of the highest peak. The basic particle size distribution might have one or more peaks for size classes, which indicate the most common particle sizes. The sample de-agglomerates (breaks down into smaller sized particles) as particles collide with each other or with the wall of the dispersion unit.Ī typical result of a laser diffraction measurement is shown in Figure 11. In dry mode the powder is put into motion either by compressed air or by gravity, creating a dry flow which is positioned in front of the laser beam.
The liquid dispersion unit is usually equipped with a mechanical stirrer with adjustable speed and with a sonicator with adjustable duration and power.
The sample keeps circulating until the measurement is done. In liquid mode the particles are dispersed in a liquid and pumped into a glass measurement cell which is placed in front of the laser. it should be measured in liquid mode if the final product is a liquid dispersion and in dry mode if the final product is a powder. Usually a sample should be analyzed in a state relevant to its application, i.e. This means that each particle should be visible as a single particle in front of the laser, moving through either liquid medium or air. In order to get a clear diffraction, it is necessary to have a proper dispersion of the sample.
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