Nano particle size is small, high surface energy, reunited with spontaneous tendency, and the existence of the reunion will greatly influencing the full play of the advantages of nano powder, so how to improve the dispersion and stability of nano powder in liquid medium is an important research subject.
Particle dispersion is a new frontier subject developed in recent years. Particle dispersion refers to the separation of powder particles in a liquid medium and spread out evenly distributed throughout the liquid phase project, mainly including wetting, reunion and stabilization of dispersed particle three phase. Wetting is the process by which the air or other impurities on the surface of the powder are replaced by the liquid. The solution of agglomeration refers to the dispersing of larger particle size into smaller particles by means of mechanical or superorganism. Stabilization is to ensure that the powder particles are evenly dispersed in the liquid for a long time. According to the dispersion method, it can be divided into physical dispersion and chemical dispersion. Ultrasonic dispersion is one of the physical dispersion methods.
Ultrasonic dispersion method: the ultrasonic wave has the characteristics of short wavelength, near-linear transmission and easy concentration of energy. Ultrasonic wave can improve chemical reaction rate, shorten reaction time and improve the selectivity of reaction. It can also stimulate chemical reactions that do not occur when there is no ultrasound. Ultrasonic dispersion is a kind of dispersing method with high intensity, which can be treated by ultrasonic wave with appropriate frequency and power. The mechanism of ultrasonic dispersion is generally believed to be related to cavitation. The propagation of ultrasonic waves is carried by the medium, and there is an alternating period of positive and negative pressure in the propagation of ultrasonic waves in the medium. The medium is squeezed and pulled by alternating positive and negative pressure. When using large amplitude of the ultrasonic enough to work on liquid medium critical molecules remain the same distance, liquid medium fracture occurs, the formation of foam, foam further grow up to become a cavitation bubbles. These bubbles can be redissolved in the liquid medium, and may float and disappear. It may also be isolated from the resonance phase of the ultrasonic field. It is proved by practice that there is the optimum frequency for the dispersion of suspended solids, and its value is determined by the particle size of the suspended particles. For this reason, it is better to stop a certain amount of time after a certain period of time, and then continue to overlive, to avoid overheating. It is also a good method to use air or water for cooling.