Nanoparticles have small particle size, high surface energy and the tendency of spontaneous agglomeration. The existence of agglomeration will greatly affect the advantages of nano powders. Therefore, how to improve the dispersion and stability of nano powders in liquid medium is a very important research topic.

Particle dispersion is a new frontier discipline developed in recent years. The so-called particle dispersion refers to the project in which the powder particles are separated and dispersed in the liquid medium and uniformly distributed in the entire liquid phase, mainly including three stages: wetting, disaggregation and stabilization of dispersed particles. Wetting refers to the process of slowly adding the powder into the eddy current formed in the mixing system, so that the air or other impurities adsorbed on the surface of the powder are replaced by liquid. Disaggregation refers to making aggregates with larger particle size disperse into smaller particles by mechanical or super generation methods. Stabilization means to ensure that the powder particles can be uniformly dispersed in the liquid for a long time. According to different dispersion methods, it can be divided into physical dispersion and chemical dispersion. Ultrasonic dispersion is one of the physical dispersion methods.

Ultrasonic dispersion method: ultrasonic has the characteristics of wave length, approximate straight line propagation, easy energy concentration, etc. Ultrasound can improve the chemical reaction rate, shorten the reaction time and improve the selectivity of the reaction; It can also stimulate chemical reactions that cannot occur in the absence of ultrasound. Ultrasonic dispersion is to directly place the suspended particles to be treated in the super growth field and treat them with ultrasonic waves of appropriate frequency and power, which is a highly intensive dispersion method. At present, the mechanism of ultrasonic dispersion is generally believed to be related to cavitation. The propagation of ultrasonic wave is carried by the medium, and there is an alternating period of positive and negative pressure in the propagation process of ultrasonic wave in the medium. The medium is squeezed and pulled under alternating positive and negative pressures. When the ultrasonic wave with enough amplitude acts on the critical molecular distance of the liquid medium to keep constant, the liquid medium will break and form microbubbles, which will further grow into cavitation bubbles. On the one hand, these bubbles can be re dissolved in the liquid medium, and may also float and disappear; It may also collapse away from the resonance phase of the ultrasonic field. Practice has proved that there is an appropriate supergeneration frequency for the dispersion of suspension, and its value depends on the particle size of suspended particles. For this reason, it is good to stop for a certain period of time after the super birth and continue the super birth to avoid overheating. It is also a good method to use air or water for cooling during the super birth.