Introduction To The Measurement Method of White Corundum Powder And Silicon Carbide Powder

Sedimentation method

The sedimentation method is based on the principle that the sedimentation of particles in the liquid conforms to Stokes’ law, and the particle size of the particles is calculated according to the final sedimentation velocity of the particles in the liquid. In actual operation, it is difficult to hesitate to test the sedimentation velocity of particles. Therefore, all sedimentation instruments measure other physical parameters related to the final sedimentation velocity, such as pressure, density, weight concentration or light transmittance, etc. The particle size distribution of the obtained particles.

The sedimentation method is divided into two types: gravity sedimentation and centrifugal sedimentation. The test range of gravity sedimentation is usually 0.5~100μm, and the measurable particle size range of centrifugal sedimentation is 0.05~5μm. At present, sedimentation particle analyzers generally use gravity sedimentation and centrifugal sedimentation. The combination of subsidence.

The resistance method, also known as the Coulter counting method, is suitable for the measurement of particles with a relatively narrow particle size distribution. Its working principle is relatively simple: the particles suspended in the electrolyte pass through a small hole made of ruby under the action of negative pressure, and the resistive sensors composed of two platinum electrodes are inserted into the two sides of the small hole respectively. The resistance between electrodes increases when passing through the small hole, generating a voltage pulse. The amplitude of the pulse corresponds to the volume of the particles and the corresponding particle size, and the number of pulses corresponds to the number of particles. By counting all the individual measured pulses and determining their amplitudes, the particle size can be obtained and the distribution of the particles can be counted. The electrical resistance method is by far the highest resolution particle size analysis count.

The laser diffraction method (also known as the small-angle forward scattering method) is the most mature and widely used method in the scattering laser particle measurement technology. , using the classical Mien scattering theory and the Fraunhofer theory applicable to large particles to obtain the size and distribution of particle size. For particles with larger particle size, the scattering in the forward small angle range is dominated by diffraction. Therefore, the small-angle forward scattering method is also called diffraction method. The laser diffraction method has wide applicability, wide particle size measurement range, accurate measurement, high precision, good repeatability, fast measurement speed, few physical parameters to be provided, and can be measured online, so it is widely used.

Comparing the test results of the three most commonly used particle size analyzers, the laser particle size analyzer (laser diffraction method), the Coulter counter (resistance method) and the centrifugal particle size analyzer (sedimentation method), the median diameter D50 value was compared. Statistical analysis can be obtained: the standard deviation of the laser particle size analyzer is 0.08 on average; the standard deviation of the Coulter counter is 0.097; the standard deviation of the centrifugal particle size analyzer is 0.219. The measured D50 value has a small standard deviation, and the measurement results have good repeatability and high precision. The measurement repeatability and measurement accuracy of the centrifugal particle size analyzer are relatively poor.

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