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Different types of particle size analyzers are electrozone sensors, laser diffraction, and microscopes. The type of analyzer used generally depends on the specific data required and the size of the particles to be assessed. Manufacturers, people in research and development, product testers, and quality control workers all use various types of particle size analyzers to determine size and distribution.
Electrozone sensing involves particle samples immersed in a conducting aqueous solution. Within the solution is an anode and a cathode containing the sensor. The particles are attracted to the sensor by electrical charge. Each particle displaces some amount of liquid as it passes through the sensor and causes a disruption in the electric field. The extent of the disruption corresponds to the size of the particle, and by measuring the number and size of the changes in impedance, it is possible to track particle distribution.
This type of particle size analysis was originally designed for testing blood samples and is not necessarily suitable for industrial applications. The technique is expensive and may be time consuming when analyzing larger particles. It is also ineffective for extremely small particles. Organic materials may be a problem because they may not be attracted by an electrical charge. Dense or porous substances can provide false readings.
Size and distribution can also be obtained using laser diffraction, commonly called low angle light scattering (LALLS). The instrumentation generally includes one or more laser light beams, back and angle scatter detectors, and a focal plane detector. As particles pass through laser beams, the light is dispersed, and sensors detect the deflection pattern. The effectiveness of this type of particle size analyzer largely depends on the number of sensors. Large particles tend to scatter brighter light in narrow angles, and small particles spread dimmer light in larger angles.
Industries often prefer LALLS above other types of analyzers for particle characterization and quality control. This method can be used for dry powders, emulsions, or liquid suspensions. Laser particle size analyzers typically provide results quickly and require little to no calibration.
Microscopy is the most cost effective of all the particle system analyzers and allows direct visualization of the particles in question. The small random sampling used in this method is generally not adequate to produce accurate accounts of particle size or distribution. Before valid results can be obtained from this method of testing, the National Bureau of Standards suggests that at least 10,000 different randomized tests be performed.
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