The sonocrystallisation of ice in sucrose solutions: primary and secondary nucleation

Two investigations of the sonocrystallisation of ice are reported for solutions in the concentration range of 0-45 wt.% sucrose. The first, carried out at 20 kHz using a commercial sonicator shows clear evidence of the stimulation of primary nucleation, by increasing the temperature at which nucleation takes place. The nucleation temperature is also increased as the ultrasonic power output level or duty cycles are increased. The second uses a novel measurement cell which permits the direct visualisation of the crystallisation and cavitation with a light microscope while different levels of alternating pressures at a frequency of 67 kHz are applied to the sample, whose heating and cooling is carefully controlled and monitored. This provides confirmation of the fragmentation of ice dendrites growing in a sucrose solution to produce smaller new ice crystals (secondary nucleation). These observations show that the primary and secondary nucleation of ice are both possible during the sonocrystallisation of ice.