Influence of acid concentration on cavitation intensity in ultrasonic cleaning in aqueous solutions of acids

It is known from the practice of ultrasonic cleaning that in most cases the increase in concentration of an alkaline solution used for ultrasonic cleaning leads to lower cavitation intensity, a primary causative agent of efficient ultrasonic cleaning. On the other hand, there is no information as regards cavitation intensity trends with increasing concentration of acid solutions. In order to check the influence of concentration (from 1 to 7% w/w) on cavitation intensity, the maximum cavitation of three acids (orthophosphoric, tartaric and citric) was measured under the same conditions at 50 and 60 degrees C in ultrasonic cleaners operating at 34, 35.5, 36.7, 40 and 44 kHz. The resulting data did not confirm, unlike most alkaline cleaning solutions, that increasing the concentration of acid solutions above 3% w/w, the concentration most frequently used, reduced cavitation intensity. An exception was the operation of tartaric acid at 40 kHz.