Sonofragmentation: Effect of Ultrasound Frequency and Power on Particle Breakage

This paper investigates, for the first time, the breaking mechanism of particles exposed to implosions of stable and transient cavitation bubbles via Kapur function analysis. The effect of ultrasonic frequencies of 30-1140 kHz and powers of 4-200 W on particle breakage of paracetamol crystals was studied. The dominant cavitation bubble type was defined via sonoluminescence measurements. The breakage rate of seed crystals with a median size of 75 mu m was found to be independent of the applied power when ultrasonically generated stable cavitation bubbles were generated. Furthermore, a particle size threshold of ca. 35 mu m was observed. The particle size could not be reduced below this size regardless of the applied power or frequency. For transient bubbles, in contrast, higher powers lead to considerably smaller particles, with no threshold size within the investigated power range. The Kapur function analysis suggests that stable bubbles are more efficient than transient bubbles to break coarse particles with sizes above 40 mu m . Finally, cumulative breakage functions were calculated, and it was observed that transient bubbles generate more abrasion than stable bubbles.