Nanoparticles have small particle size, high surface energy, and have a tendency to spontaneously agglomerate, and the presence of agglomeration will greatly affect the superiority of nanopowders. Therefore, it is very important to improve the dispersion and stability of nanopowders in liquid media. Research topics.
Dispersion of particles is an emerging edge discipline that has developed in recent years. The so-called particle dispersion refers to a process in which powder particles are separated and dispersed in a liquid medium and uniformly distributed throughout the liquid phase, and mainly include three stages of wetting, deagglomeration, and stabilization of dispersed particles. Wetting refers to a process in which a powder is slowly added to a vortex formed in a mixed system to allow air or other impurities adsorbed on the surface of the powder to be replaced by the liquid. Deagglomeration refers to the dispersal of larger particle size aggregates into smaller particles by mechanical or ultrasonic methods. Stabilization refers to ensuring uniform dispersion of the powder particles in the liquid over a long period of time. According to the different methods of dispersion, physical dispersion and chemical dispersion can be divided. Ultrasonic dispersion is one of the physical dispersion methods.
Ultrasonic dispersion method: Ultrasonic waves have the characteristics of short wavelength, nearly straight line propagation, and easy energy concentration. Ultrasound can increase the rate of chemical reaction, shorten the reaction time, increase the selectivity of the reaction; and it can also stimulate chemical reactions that cannot occur in the absence of ultrasound. Ultrasonic dispersion is to place the particle suspension to be processed directly in the supergeneous field, and it is treated with ultrasonic waves of the appropriate frequency and power, which is a very high intensity dispersion method. The mechanism of ultrasonic dispersion is currently widely believed to be related to cavitation. Ultrasonic wave propagation is based on medium. There is an alternating period of positive and negative pressure in the process of ultrasonic wave propagation in the medium. The media is squeezed and pulled under alternate positive and negative pressures. When a sufficiently large amplitude ultrasonic wave is applied to a critical molecular distance where the liquid medium remains constant, the liquid medium will break, forming microbubbles, and the microbubbles will further grow into cavitation bubbles. On the one hand, these bubbles can be redissolved in the liquid medium, and they may also float and disappear; they may also collapse from the resonant phase of the ultrasonic field. Practice has proved that there is an optimal frequency for the dispersion of the suspension, and its value depends on the particle size of the suspended particles. For this reason, it is best to stop for a while after a certain period of time has passed, and continue to surpass it to prevent overheating. Cooling with air or water is also a good method for supernaturalization.