Ultrasound-related variables and their effects on chemical reactions

Ultrasound-related variables and their effects on chemical reactions 

As shown in the previous sections, most analytical applications of US-assisted reactions have been developed without optimizing US variables such a simple sentence as ultrasound is applied for x min has been the only detail given in most cases. Past experience with US-assisted reactions makes it advisable to consider the following variables in developing new analytical applications. 

It has been widely demonstrated that low frequencies, close to 20 kHz, enhance cavitation, which is the source of the dramatic effect of ultrasonic power on chemical reactivity. However, higher frequencies are advantageous when radical formation is the key to facilitating, accelerating or making possible a given reaction. 

Application of an external pressure to a reaotion system, which increases the hydrostatic pressure of the liquid, increases the energy required to initiate cavitation. In praotioal terms, if such a threshold energy can be exceeded with the available irradiation souroe, then raising the hydrostatic pressure will increase the sonochemical effect as the maximum temperatures and pressures experienced during bubble collapse will be higher under these conditions. 

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