Sieve particle size analysis:

The sieving method is the most common and intuitive method for particle size measurement. The implementation of screening is very simple: According to different needs, select a series of standard sieves with different mesh diameters, stack them in order from small to large, with the bottom sieve at the bottom and the screen cover at the top, and then fix them on the vibrating screen machine , select the appropriate mode and length, and automatically vibrate to achieve screening; after the screening is completed, record the mass of particles obtained in each layer of standard sieves by weighing, and thereby obtain the particle size distribution represented by mass fraction. .

The advantages of the screening method are simple and intuitive principle, convenient operation and easy implementation, which is also an important reason for its wide application. The shortcomings of the screening method cannot be ignored. Generally speaking, because the division of particle size segments by the sieving method is limited by the number of sieve layers, the measurement of particle size distribution is slightly rough, which affects the accuracy of the results to a certain extent. In addition, due to strong vibration during the screening process, some particle types may be easily damaged, thereby destroying the particle size distribution and affecting the measurement results; some particles (such as fly ash particles in this test) have a strong mutual adsorption effect , the phenomenon of aggregation and agglomeration often occurs during screening, which also affects the accuracy of screening results.

Based on the characteristics of the sieving method, its application is mainly in the measurement of particle size distribution of large-size particles, such as above 45 μm. For particles with smaller particle sizes, the screening method is less reliable unless special methods are used.

The screening method has poor ability to distinguish fine particles, but it is more accurate when used for large particles, and the screening results are clear and have good practical guidance significance.

Determination of the average particle size of powder by Fisher's method:

Fisher's method is a relatively simple particle size measurement method. It is based on measuring the speed of air penetrating the powder accumulation and calculating the average particle size of the powder based on the Kozeny-Carman formula. The instrument used was a Fisher's instrument, developed by Fisher Scientific Co. in the United States and named after the company's first character. The instrument has a simple structure, easy operation and low price. It does not require any calculation and the particle size value can be read directly from the reading plate. The full English name of the instrument is Fisher Sub-sieve Sizer. There are different translations in my country, some are translated as "Fisher Sub-sieve Sizer", others are translated as "Fisher Sub-sieve Sizer" and so on. Some people misunderstand this name and think it is a kind of sieve. In fact, it has nothing to do with sieves. The sub-sieve refers to powders whose particle size range measured by this method is sub-sieve level (usually less than 5 Qum), that is, which cannot be sieved by ordinary mechanical sieving methods. powder. Strictly speaking, this instrument should be translated as "Fischer Subsieve Powder Particle Size Analyzer". Our country's standards call this method "Fisher's method", and this term is used here.

This method is a relative measurement method and cannot accurately determine the true particle size of the powder. It is only used to control the process and product quality. This method can only accurately measure the transmittance of air passing through a powder accumulation, and the value depends on its pore structure. The porosity, particle shape, particle size, particle size composition, particle size distribution and pressing method of the powder accumulation all affect the pore structure. Therefore, this method is only suitable for powders with the same chemical composition and similar particle size composition. For powders with the same chemical composition but different particle size compositions, large measurement errors will occur. Sometimes two powders with the same chemical composition but different particle size compositions will have the same Fisher value because they have the same transmittance. Therefore, the particle size values measured by this method cannot be compared with other particle size measurements.

Laser particle size analysis:

A method of analyzing particle size through the spatial distribution (scattering spectrum) of diffracted or scattered light produced by particles irradiated by a laser beam.

The laser particle size analyzer uses the principle of light scattering to measure the size of powder particles. It is the most widely used particle size analyzer in the current field of particle size measurement. It is characterized by a wide dynamic range of measurement, fast measurement speed, and easy operation. It is especially suitable for measuring powder and liquid droplets with a wide particle size distribution range. As a particle size testing instrument with excellent testing performance and a wide range of applications, the laser particle size analyzer has been widely used in other powder processing and application fields.

The laser particle size analyzer uses the fact that when light is propagating, the wave front is limited by pores or particles equivalent to the wavelength scale. The emission with each element wave at the restricted wave front as the source interferes in space to produce diffraction and scattering. Diffraction and scattering The spatial (angular) distribution of scattered light energy is related to the wavelength of the light wave and the size of the pores or particles. According to this characteristic, when the light source is changed to laser, the spatial (angular) distribution of diffracted and scattered light energy is only related to the particle size. Therefore, based on this characteristic, the proportion of different particles in the sample can be analyzed to obtain the total laser particle size of the sample.