Mechanism for ultrasonic pitting of starch particles

In this study, the ultrasonic pitting of microscopic particles is investigated using ultrasound with frequencies from 26 kHz to 3.6 MHz. With increasing ultrasonic frequency, the number of pits formed on the surfaces of the microscopic particles increases initially but then decreases, and these changes in the number of pits are attributed to the relationship between the cavitation bubbles and the size of the object, and to the stress generated. Also confirmed is that adding a surfactant affects the ultrasonic pitting, with that effect differing with the surfactant concentration and the ultrasonic frequency. The results suggest that the number of pits depends on the size distribution of the cavitation bubbles and the distance between the bubble and the object. Overall, it is concluded that the important parameters in ultrasonic pitting are (i) the size relationship between the cavitation bubble and the object, (ii) the physical characteristics of the object, and (iii) the distance between the bubble and the object.