What are the main ways in which particles are dispersed in air and liquid?

Particles present different ways of dispersion in air and liquid. What are the main ways to disperse in air and liquid?

First, the main way to disperse particles in the air

1, mechanical dispersion

Mechanical dispersion refers to the mechanical agglomeration of particles. The necessary condition for mechanical dispersion is that the mechanical force (referring to the shear and compressive stress of the fluid) should be greater than the adhesion between the particles. Usually, the mechanical force is caused by the strong turbulent motion of the airflow caused by the high-speed rotating impeller disk or the jetting and impact of the high-speed airflow.

Features:

Mechanical dispersion is easier to achieve, but since the force between them does not change, it is possible to re-adhere the agglomerates when the particles are removed from the disperser. In addition, mechanical dispersion may cause brittle particles to be pulverized, and the dispersion effect is reduced when the mechanical equipment is worn.

2, dry and dispersed

The liquid bridge force is often ten or ten times that of the intermolecular force. In humid air, the liquid bridge formed by the particles is the main cause of particle agglomeration. Therefore, the elimination of the liquid bridge or the destruction of the formed liquid bridge is one of the main means of ensuring the particles. In the production process, heating and drying are often used. For example, the ore particles are often heated to about 200 ° C before electrostatic separation. In the production process, heating and drying are often used.

3. Surface modification

Surface modification refers to the physical or chemical treatment of particles, purposefully changing the physical and chemical properties of the surface, so that the particles have new skills and improve their dispersion.

4, static dispersion

For homogenous particles, the electrostatic force acts as a repulsive force because the surface is charged the same. Therefore, it is possible to use electricity for particle dispersion, and the key to the problem is how to fully charge the particle group. The particles can be charged by contact charging, inductive charging, etc., but the most effective method is corona charging, so that the continuously supplied particles pass through the ion curtain formed by corona discharge to charge the particles.

Second, the main way to disperse particles in liquid

The means of dispersion control of particles in liquid can be roughly divided into medium regulation, dispersant regulation, ultrasonic regulation and mechanical regulation.

1, medium regulation

A well-dispersed suspension can be obtained by selecting an appropriate medium depending on the surface properties of the particles. The basic principle for selecting a dispersion medium is that non-polar particles are easily dispersed in a non-polar liquid; polar particles are easily dispersed in a polar liquid, that is, all the same polarity principles.

Typical dispersion medium and dispersed phase

1 surfactant

Anionic, cationic and nonionic surfactants can be used as the dispersing agent. Surfactants have found wide application in the coatings industry. The dispersion of the surfactant is mainly manifested by its adjustment of the surface wettability of the particles.

2 polymer dispersant

The adsorption film has a very significant effect on the aggregation state of the particles. This is because its film thickness often reaches several tens of nanometers, which is almost equivalent to the thickness of the electric double layer. Therefore, its effect begins to appear when the particles are far apart. Polymer dispersants are commonly used chemicals that regulate particle agglomeration and dispersion.

2, ultrasound regulation

Ultrasonic regulation is to directly place the industrial suspension to be treated in the ultrasonic field, and control the appropriate ultrasonic frequency and action time to fully disperse the particles. Ultrasonic dispersion is mainly determined by the correlation between ultrasonic frequency and particle size.

1-PbS 2-CuS 3-Fe2O3 4-SiO2

Boundary of ultrasonic dispersion of particles

The role of ultrasound is mainly in two aspects: First, the cavitation effect. Second, by the absorption of ultrasonic waves, various components in the suspension produce resonance effects.

3, mechanical mixing control

Mechanical agitation dispersion refers to the mechanical agitation of shearing, shearing and stretching caused by strong mechanical agitation to cause particle agglomeration to be disintegrated. Strong mechanical agitation is an effective means of disintegrating agglomerates, which is widely used in industrial processes.

The main problem with mechanical agitation is that once the particles leave the turbulent flow field generated by mechanical agitation and the external environment recovers, they may re-form a new agglomeration. Therefore, the dual effect of mechanical agitation plus chemical dispersant tends to result in better dispersion.

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