Frequency and power dependence of the sonochemical reaction.

The dependence of the sonochemical reaction on ultrasonic intensity was studied over a wide frequency range of 22-1960 kHz and sample volume range of 25-200 mL. The effect of a stainless steel reflector set on the water surface was also considered. Experiments were carried out by direct ultrasonic irradiation of a sample in a vessel. The potassium iodide (KI) method was used to evaluate the sonochemical reaction in terms of efficiency and reaction rate, and calorimetry was used to determine ultrasonic power. A quenching phenomenon, where the reaction rate decreased despite an increasing ultrasonic power, was observed at all frequencies and sample volumes, which indicated the existence of a maximum reaction rate. The maximum reaction rate increased with the frequency, except at 1960 kHz, and with the sample volume. The ultrasonic power at which quenching occurred increased with the frequency and sample volume. Sudden quenching occurred without the reflector, whereas gradual quenching occurred with the reflector. Based on the results, ultrasonic power density (i.e., ultrasonic power divided by the sample volume) can be used to estimate the ultrasonic power at which quenching occurs for various sample volumes.