Ultrafine powder particles have large specific surface area and high specific surface energy, and are in a very unstable state of thermodynamics. In the process of preparation and post-treatment, it is very easy for particles to coagulate and agglomerate, forming secondary particles, which makes the particle size larger. Zui eventually loses the unique functions of ultra-fine powder in use. In a sense, the dispersion technology of ultra-fine powder is ultra-fine Powder technology The key technology of zui. Therefore, detect Dispersion of ultrafine powder Performance has become an important item to evaluate the technical quality level of ultra-fine powder.

Ultrafine powder usually refers to small solid particles with a size of about 1nm~1 μ m. Because of the large surface energy of the powder particles in this state, a single physical or chemical dispersion has its own inevitable limitations. Physical dispersion cannot effectively maintain the stability of materials for a long time, while chemical dispersion requires the use of physical methods to solve the problem, The material is fully dispersed, and then dispersant is added to form stable dispersion through surface bonding. In practical operation, the dispersion of ultra-fine powder is often a combination of physical and chemical methods, that is, the materials in the liquid phase are dispersed by physical methods, and then the materials are stably dispersed by chemical methods for a long time.

I Guiding principles for dispersion performance evaluation

There are two guiding principles for evaluating the stability of ultrafine powder particles in the liquid phase:

1、 If the settling speed of ultrafine powder particles in the liquid phase is slow, it is considered that the suspension time of particles in the system is long and the dispersion stability is good; 　

2. If the particle size of ultrafine powder in the liquid phase does not increase with time, it is considered that the stability of the dispersion system is good. 　

2、 Decentralization evaluation index

According to the above two guiding principles, a series of methods for evaluating the dispersion stability of ultrafine powder particles in the liquid phase have been studied and developed by relevant scholars in recent years. 　

Three elements of dispersion technology: dispersion medium, dispersant and dispersion equipment

1. Dispersion medium

(1) According to different viscosities, dispersion media are divided into high viscosity, medium viscosity and low viscosity. In low viscosity media, such as water and agricultural production system solvents, nano powder tubes are easy to disperse. Medium viscosity media such as liquid epoxy resin, liquid silicone rubber, etc., and high viscosity media such as molten plastic

(2) The nano powder tube dispersion technology introduced in this PPT document is aimed at medium and low viscosity dispersion media

2. Dispersant

(1) The selection of dispersant is closely related to the structure, polarity and solubility parameters of the dispersion medium

(2) The dosage of dispersant is related to the specific surface area of nano powder and the functional group modified by covalent bond

(3) It is recommended to use in water-based medium. In strong polar agricultural production system solvents, such as alcohol, DMF, NMP, TNADIS is recommended. Medium polarity agricultural production system solvents such as esters, liquid epoxy resin, liquid silicone rubber, TNEDIS is recommended

3. Decentralized equipment

(1) Ultrasonic dispersion equipment: it is very suitable for laboratory scale, low viscosity medium dispersion, and will be limited when used for medium and high viscosity medium

(2) Grinding and dispersion equipment: suitable for large-scale dispersion of carbon nanotubes, medium viscosity medium dispersion powder

(3) The combination method of "grinding dispersion first, then ultrasonic dispersion" can be used to disperse the powder efficiently and stably