ROLE OF FREQUENCY IN THE ULTRASONIC ACTIVATION OF CHEMICAL-REACTIONS

The effects of ultrasonic irradiation at different frequencies, i.e. 20, 40, 60 and 80 kHz, on the activation of a model chemical reaction (iodide to iodine oxidation) has been investigated. All other parameters being kept constant, it has been ascertained that an appropriate frequency value of ultrasound can be selected, capable of driving a sonochemical reaction to its maximum yield. A straightforward interpretation of the fundamental role played by ultrasound frequency indicates that such an effect occurs when bubbles, with a radius value at the centre of a statistical distribution curve, are excited. Such an event is also made possible by driving the bubbles' field from its equilibrium distribution state to a different one suitable for transient cavitation to take place. In addition, experimental evidence suggests that a Gaussian-like distribution of gas bubble radii is to be expected in a real liquid, when an external gas atmosphere is present.