The particle size and particle size distribution of talc powder are important indicators of this type of product, and particle size testing is a very important quality inspection task in the production and application of talc powder.
Repeatability and accuracy of particle size testing: Repeatability refers to the average deviation between each test value when a sample is tested for multiple times. There are many factors that affect the repeatability. In addition to the instrument itself, it is also closely related to the degree of dispersion of the sample, the dispersant, the medium, the sampling method, the operation technique and other test factors. Repeatability is the primary indicator for measuring a particle size analyzer. If the repeatability of a particle size analyzer is not good, then it has no practical value. So how to ensure the repeatability of the instrument? First, there must be an instrument with stable performance, and second, there must be a standardized sample preparation and operation method. Both are equally important and indispensable. The accuracy of the particle size test is relative to a recognized test method or a standard sample. In the macro measurement work, accuracy is the first; in the process of particle size testing, the repeatability of the test is the first, and the accuracy is the second.
Dispersant and medium: Dispersant is a small amount of substance that can significantly reduce the surface tension of the liquid, so that the surface of the particles can be well wetted. The role of the dispersant has two aspects: one is to accelerate the decomposition of agglomerates, the other is to prevent or delay the re-agglomeration of monomer particles. There are two commonly used dispersants in talc particle size testing: sodium pyrophosphate and sodium hexametaphosphate. The commonly used media are water (distilled water, purified water or deionized water) 30% ethanol aqueous solution and ethanol. When water is used as the medium, the ratio of the above two dispersants is 0.3%. When 30% ethanol aqueous solution and ethanol are used as the medium, no dispersant is needed.
The relationship between ultrasonic dispersion time and particle size: Ultrasonic dispersion is a commonly used dispersion method, and it is also widely used in the particle size test of talc powder. It is generally believed that the longer the ultrasonic dispersion time, the better the dispersion effect. In fact, for a specific talcum powder sample, the ultrasonic dispersion time has an optimal period. Beyond this period, the dispersion effect is not obvious, but it has a tendency to promote the agglomeration of small particles, which makes the test result tend to increase.