Effects of Sound Field and Acoustic Streaming on Nanometer Sized Diamond Particles Dispersion System using Ultrasound

We reported the improvement of dispersion of nanometer sized diamond particles using shock wave and active oxygen species by acoustic cavitation at 155 kHz in 2004 IEEE International UFFC Joint 50(th) Anniversary Conference in Montreal. Average sound pressure calculated from sound pressure distribution in horizontal plane at distance of 10 rum from a stainless steel vibrating disk in water tank was used as acoustic index for improvement of dispersion of the diamond particles. The measured horizontal plane was on the loop of the standing wave acoustic field. However, improvement of dispersion characteristics of the particles was performed in whole water in the water tank. Therefore, each sound pressure distribution in horizontal plane at the distances of 10 mm to 95 mm from the stainless steel vibrating disk was measured by hydrophone. Sound pressure distribution all over water in the water tank was observed three dimensionally. The generation of active oxygen species in the water tank was estimated by observation of sonochemical luminescence. As the results, higher sound pressure than 100 kPa was measured in central region lower than height of 55 mm from the stainless steel vibrating disk in the water tank. Sonochemical luminescence could not be observed in above region in the water tank. They were contradictory results. We guess that the acoustic streaming prevents from trapping cavitation bubble at the loop of standing wave sound field. We think that the acoustic streaming is one cause of the contradictory results. Homogenous sound pressure distribution is required improvement of dispersion characteristics of nanometer sized diamond particles by ultrasound exposure.