Fisher's method is a relatively simple particle size measurement method, which is based on measuring the speed of air passing through the powder accumulation, and then obtaining the average particle size of the powder according to the Kozeny-Carman formula. However, the Fisher method is a relative measurement method, which cannot accurately determine the true particle size of the powder, and is only used to control the quality of the process and product. Fisher's method is consistent with the results of microscopic determination for relatively regular powders.

The average particle size Dsv measured by the Fisher particle size analyzer is similar to D(3,2) calculated by the laser particle size measurement. However, the Fisher particle size analyzer is actually measured, and the laser particle size is based on the particle size distribution, and D(3,2) is calculated according to the spherical shape of the particles. That is to say, when the particles to be tested are close to spherical, the difference is small, and the more irregular the particle shape is, the greater the difference is. That is to say, the laser particle size distribution analyzer measures the size distribution of the particle group. So the two are not necessarily related. When the particles in the particle group are all spherical, the Fisher mean particle size = D(3,2) in the laser particle size distribution data (surface area mean diameter)

In order to obtain the correct data of the primary particle size, it is often necessary to open the agglomerated particles in the particle size test to form particle monomers and uniformly disperse them in the medium. This operation is called "dispersion". The requirement of the laser particle size analyzer for the dispersion system is "dispersion without segregation". Share the sample dispersion method in particle size testing here.

The wet dispersion techniques that can be used for particles in a liquid medium are:

Ultrasonic dispersion: use the cavitation effect of ultrasonic waves to disperse in the liquid to deaggregate the agglomerates;
Mechanical stirring and dispersion: the mechanical action of the blade rotation is used to disintegrate the agglomerated particles and distribute the particles evenly in the liquid;
Liquid circulation: use a pump to drive the high-speed flow of the suspension to keep the particles evenly distributed throughout the dispersion system and prevent large particles from settling;
Dispersant: Some samples need to use chemical dispersion method, that is, adding an appropriate amount of dispersant to improve the electrical properties of the particle surface to maintain the dispersed state;
Surface pretreatment: Some samples are incompatible with the medium and appear to float on the water surface. It is necessary to add a small amount of ethanol or other surface treatment agents before entering the water for pretreatment to make them easy to disperse in water.

Particles can be dispersed in air by dry dispersion techniques.

The core component of dry dispersion is the dispersion pump. The functions of the dispersion pump:

1. Using the negative pressure formed by the high-speed airflow of the air source, the dry powder is sucked into the pump body and mixed with the gas;

2. High-speed airflow is also known as turbulent flow. The particles are subjected to complex hydrodynamic effects in the turbulent flow, including the impact of normal shock waves, the shearing of rotating airflow, the collision between particles and the wall and the collision between particles, etc., which make the particles agglomerate. It is separated into monomers to achieve the purpose of dispersion.