| Co-Investigator(Kenkyū-buntansha) |
WAKAKO Hiraoka Meiji University, Dept. of Physics, Associate Professor, 理工学部, 准教授 (00212168)
SHIGEMI Saito Tokai University, Dept. of Environ. Information Engineering, Professor, 海洋学部, 教授 (50091690)
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| Budget Amount *help |
¥3,100,000 (Direct Cost: ¥3,100,000)
Fiscal Year 2006: ¥700,000 (Direct Cost: ¥700,000)
Fiscal Year 2005: ¥800,000 (Direct Cost: ¥800,000)
Fiscal Year 2004: ¥1,600,000 (Direct Cost: ¥1,600,000)
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| Research Abstract |
We investigated the process of bubble collapse in ultrasonic cavitation through sonoluminescence study and vibratiional spectroscopic study. High-intensity ultrasound irradiated in liquids such as water causes cavitation, that is, the formation, growth and implosive collapse of bubbles. The energy stored in bubbles is released when bubble violently collapses in the compression phase of the ultrasound as acoustic noise, shock waves, chemical reactions, and the emission of light. The violent collapse is predicted to generate a hot spot of thousands of Kelvin with in bubbles. Water molecules in bubbles are dissociated to make H and OH radicals. To monitor the process of bubble collapse, we measured vibrational spectrum of OH-stretching mode using time-resolved Raman scattering. We observed a slight difference in the spectrum at 3500 cm-1 under cavitation and no-ultrasound. However, we obtained no clear evidence that the difference is due to the OH radicals produced in cavitation. Therefor
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e, we changed the plan to study the sonoluminescence from water, ethanol solutions and NaCl solutions.
Spectra of multi-bubble sonoluminescence (MBSL) were measured in argon-saturated water and ethanol solutions in the concentration range 2-100 mM at the frequencies of 116 kHz and 1.0 MHz. The spectral peaks from OH-radical emission near 310 nm were observed at relatively low ultrasonic power at both frequencies. The sub-peaks at 290 and 340 nm were also observed, which are attributed to OH-radical vibronic transition. The MBSL spectra from ethanol solutions indicated that the quenching of OH-radical emission was more efficient than that of underlying continuous spectrum. The continuous spectrum suggested the decrease in temperature with increasing ethanol concentration. The concentration dependence of spectrum quenching showed no frequency dependence. A new peak was observed at 385 nm only at small ethanol concentrations and at the frequency of 1.0 MHz, which attributed to CH or CN molecule emission.
We have measured the spectra of multi-bubble sonoluminescence from Ar-saturated NaCl solutions at the frequencies of 108 kHz and 1.0 MHz. The intensity of sodium-atom emission observed takes a maximum at the concentration of 2 M, which corresponds to the formation of OH radicals measured using KI colorimetric method. High-resolution spectroscopic study was made on sodium D lines for various ultrasonic powers. The effects of ethanol on the sodium D line-width were also investigated. The line-width showed asymmetric broadening toward red region, and depended on the ultrasonic power. The addition of ethanol in the range of 0.5-2 mM caused sudden quenching and broadening of sodium D lines. The results indicate that collisions between excited sodium atoms and foreign atoms, that is, argon gas and molecules decomposed from ethanol are responsible for the observed line broadening. This clearly demonstrates that the sodium-atom emission occurs within bubbles. The electronic exciting process of sodium atom is discussed in terms of chemical excitation by OH radicals or H radicals. Less
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