The Chemical Effect of Ultrasonic Wave
Ultrasonic waves interact with the media in the process of propagation, and the phase and amplitude of the media change, which can make the state, composition, structure, function and property of the media change.Such changes are called ultrasonic effects.The interaction between ultrasonic wave and media can be divided into thermal mechanism, mechanical mechanism and cavitation mechanism.In a chemical reaction system promoted by ultrasound, the above mechanisms, either alone or in coordination, catalyze the reaction:
1. Thermal mechanism: when ultrasonic waves travel in the medium, their vibration energy is constantly absorbed by the medium and converted into heat, which increases the temperature of the medium.This effect of increasing the temperature of media is called the thermal mechanism of ultrasonic.
2. Mechanical mechanics mechanism: when the frequency is low, the absorption coefficient is small, and the ultrasonic action time is very short, the ultrasonic effect is not accompanied by obvious thermal effect.At this time, the ultrasonic effect can be attributed to the mechanical mechanics mechanism, that is, the ultrasonic effect comes from the contribution of representing the sound field mechanical quantity.Ultrasonic wave is also a form of transmission of mechanical energy. The ultrasonic effect can be expressed by the mechanical parameters such as origin displacement, vibration velocity, acceleration and sound pressure in the process of fluctuation.
3. Cavitation mechanism: one of the main mechanisms of ultrasonic acoustic-chemical effect is acoustic cavitation (including the formation, growth and disintegration of bubbles).The phenomenon includes two aspects, that is, the strong ultrasonic produces bubbles in the liquid and the special movement of bubbles under the strong ultrasonic action.
Ultrasonic wave is a kind of high frequency mechanical wave, with the characteristics of energy concentration, strong penetrating power and so on.Ultrasonic waves are composed of a series of denser and denser longitudinal waves that travel around through a liquid medium.When the sound energy is high enough, the attraction between molecules in the liquid phase is broken down to form a cavitation nucleus during the loose half period.Cavitation nucleus of about 0.1 mu s life, it is at the instant of the explosion can produce about 4000-6000 K and the local environment of high temperature and high pressure of 100 mpa, and generate speed of about 110 m/s has strong impact of the micro jet, this phenomenon is called ultrasonic cavitation.Ultrasonic chemical reaction mainly originates from the acoustic cavitation mechanism, which is the main power of the acoustic chemical reaction.These conditions to make organic chemical bond fracture happens within the cavitation bubbles, water phase combustion (aqueous combustion), high temperature decomposition (pyrolysis) or free radical reaction, etc.
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