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Laser diffraction is a widely used particle sizing technique for materials ranging from hundreds of nanometers up to several millimeters in size. The main reasons for its success are:
Laser diffraction measures particle size distributions by measuring the angular variation in intensity of light scattered as a laser beam passes through a dispersed particulate sample. Large particles scatter light at small angles relative to the laser beam and small particles scatter light at large angles, as illustrated below. The angular scattering intensity data is then analyzed to calculate the size of the particles responsible for creating the scattering pattern, using the Mie theory of light scattering. The particle size is reported as a volume equivalent sphere diameter.
Laser diffraction uses Mie theory of light scattering to calculate the particle size distribution, assuming a volume equivalent sphere model.
Mie theory requires knowledge of the optical properties (refractive index and imaginary component) of both the sample being measured, along with the refractive index of the dispersant. Usually the optical properties of the dispersant are relatively easy to find from published data, and many modern instruments will have in-built databases that include common dispersants. For samples where the optical properties are not known, the user can either measure them or estimate them using an iterative approach based upon the goodness of fit between the modeled data and the actual data collected for the sample.
A simplified approach is to use the Fraunhofer approximation, which does not require knowledge of the optical properties of the sample. This can provide accurate results for large particles. However it should be used with caution whenever working with samples which might have particles below 50µm or where the particles are relatively transparent.
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This webinar deals with the routes of verifying laser diffraction instrument performance dealing with the optical set-up, software, and dispersion units.
Who should attend? Anyone involved in the verification of laser diffraction equipment. This co...
In fossil fuel power generation the usage of online particle sizing in the optimization of the combustion process takes on a greater significance. Pulverized coal is typically used to fire the boiler of power plants. The right particle size distribut...
The Dispersion Index and Dispersion Index RSD measured by Hydro Sight allow a user to monitor changes in the dispersion state of their samples by detecting subtle changes in the disorder of sample image frames. Hydro Sight therefore provides a valuab...
Getting a sample to a stable and reproducible state of dispersion is an important part of method development when carrying out particle size analysis. In this application note we show how the Mastersizer’s Hydro Sight accessory can be used to visuali...
In this article we take a look at how, from the starting point of an appropriate wet sensor, laser diffraction systems can be engineered to deliver to the needs of different process applications. A case study involving the control of an emulsificatio...
(Webinar - Recorded)
Mastersizer 3000 is turning three!
(October 9 2014)
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