Nanoparticles have small particle size, high surface energy and spontaneous agglomeration, and the presence of agglomeration will greatly affect the advantages of nanopowders. Therefore, how to improve the dispersion and stability of nanopowders in liquid media is very important. Research topics.
Particle dispersion is an emerging edge discipline that has developed in recent years. The so-called particle dispersion refers to the process in which the powder particles are separated and dispersed in the liquid medium and uniformly distributed throughout the liquid phase, and mainly includes three stages of wetting, deagglomeration and stabilization of the dispersed particles. Wetting refers to the process of slowly adding the powder to the vortex formed in the mixing system to replace the air or other impurities adsorbed on the surface of the powder with the liquid. Deagglomeration refers to dispersing larger particle size aggregates into smaller particles by mechanical or ultrasonic methods. Stabilization refers to ensuring that the powder particles remain uniformly dispersed for a long period of time in the liquid. According to the 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 waves have the characteristics of short wavelength, approximate linear propagation, and easy energy concentration. Ultrasonic waves can increase the rate of chemical reactions, shorten the reaction time, increase the selectivity of the reaction, and also stimulate chemical reactions that cannot occur in the absence of ultrasonic waves. Ultrasonic dispersion is a high-strength dispersion method by directly placing the suspension of particles to be treated in an ultrasonic field and treating it with ultrasonic waves of appropriate frequency and power. The mechanism of action of ultrasonic dispersion is currently considered to be related to cavitation. The propagation of ultrasonic waves is based on the medium. There is an alternating period of positive and negative pressure during the propagation of ultrasonic waves in the medium. The medium is squeezed and pulled under alternating positive and negative pressures. When ultrasonic waves of sufficient amplitude are used to act on the critical molecular distance at which the liquid medium remains constant, the liquid medium breaks, forming microbubbles, and the microbubbles further grow into cavitation bubbles. On the one hand, these bubbles can be redissolved in the liquid medium, or they may float and disappear; they may also collapse out of the resonance phase of the ultrasonic field. Practice has shown that there is an optimum ultrasonic frequency for the dispersion of the suspension, and its value depends on the particle size of the suspended particles. For this reason, it is preferable to stop the ultrasound for a certain period of time after a period of time, and then continue the ultrasound to avoid overheating. It is also a good method to cool the air with air or water.