Ultrasonic dispersion is a high-strength dispersion method by directly placing the suspension of particles to be treated in a super-skin 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 proved that there is an optimum super-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 certain period of time after a period of super-life, and then continue to survive, to avoid overheating, and it is also a good method to cool with air or water in the super-life.
What is the difference between ultrasonic dispersion and conventional mechanical dispersion?
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.
Mechanical dispersion methods can be divided into:
Grinding, ordinary ball milling, vibrating ball milling, colloid milling, air milling, mechanical agitation, etc.
The mechanical dispersion method has many steps and requires a lot of equipment, and the ultrasonic dispersion only needs one power supply and one vibration rod.
Mechanical crushing limit problem:
In the nano-crushing, the fine particles have a large interfacial energy, and the Van der Waals force between the particles is strong. As the particle size decreases, the tendency of self-aggregation between the particles becomes larger, the dispersion and aggregation are balanced, and the particle size does not change.
Therefore, the pulverization to a certain extent, the particle size is no longer reduced or the rate of decrease is rather slow, which is the mechanical pulverization limit of the material. Therefore, the mechanical dispersion method cannot restore the true particle size of the nanomaterial, and the effect is far less than that of the ultrasonic dispersion method.
Article source: Ultrasonic dispersion