집속초음파를 이용한 비접촉식 미립자 분산장치에 관한 연구

Abstract

Abstract In the past several years there has been increasing interest in dispersion methods using ultrasound power for minute particles, such as cosmetics, medicine, catalyst, pigments, toner and ink. However, for nano-sized particles, the conventional ultrasound homogenizer, which is using a Langevin-type transducer with low resonant frequency of about 20 kHz, is not appropriated to disperse. Not only the wavelength but also the pulse width of the shock wave caused by the ultrasonic cavitation is too long to disperse the nano particles by such low frequency. Moreover, the acoustic field distribution is not uniform in the liquid because of the limited container size. The acoustic waves are radiated from the horn of the conventional ultrasound homogenizer, and they are reflected from the wall of the water tank. In this study, a new dispersion system using focused ultrasound field is suggested for pure minute particle dispersion of the particles. Prior to the experiment, the frequency spectrum of the pulse from collapsing cavitation is analyzed theoretically. The spectrum shows that the acoustic energy is distributed in high frequency range over than 10 MHz. The effects of ultrasound radiation on aqueous suspension of titanium dioxide (TiO2), two polystyrene standard particle and alumina (Al2O3) minute particles were investigated under various exposure conditions experimentally. The optimum condition for the dispersion was investigated when the ultrasound exposure time and the acoustic power were varied in different samples. Futhermore the effects of focused ultrasound field on the residual particle distribution in the deionized and the distilled water were investigated. The particle size distributions were measured for various exposure time of ultrasound radiation. It is confirmed that the number of residual particles were increased as the exposure time of the ultrasound increased.