| Budget Amount *help |
¥15,500,000 (Direct Cost: ¥15,500,000)
Fiscal Year 2005: ¥10,600,000 (Direct Cost: ¥10,600,000)
Fiscal Year 2004: ¥4,900,000 (Direct Cost: ¥4,900,000)
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| Research Abstract |
Liquids irradiated with high intensity ultrasound undergo the acoustic cavitations ; the formation of the cracks of the liquid, which will be embryos of the cavitation bubbles. The formed bubbles undergo the growth and the implosive collapse cycles during the rarefaction and the compression phase of the acoustic field, respectively. In the violent collapsing, the energy charged in the growth cycle is released as acoustic noise, shock wave, chemical reaction and light emission. A hot spot is formed at the center of the collapsing bubble. In last decade, a solitary bubble without any disturbance from other bubbles is spatially trapped at the antinode of the acoustic field. The light emission from this single bubble is the single bubble sono-luminescence (SBSL). The repeated collapses of the bubble decompose poly-atomic molecules contained inside leaving sono-chemical products. Since the bubble as a tiny chemical reactor is open for the exchange of energy and substances, a specific dissip
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ation structure was expected and calculated by Storey and Szeri. Different molecular species segregate spatially inside the collapsing bubble and the lighter species stay at the center. Here we report the experimental proof of this structure by observing the emission spectra of SBSL in an aqueous solution containing n-butanoic acid as a function of pH with different seeding mono-atomic noble gases ; He, Ar and Xe. The segregation will shed light on designing the sono-chemical reaction with more than couple of species involved that are required to be in the hot spot at the same time.
Recently, observing SBSL in sulfuric acid, Flannigan and Suslick found discrete spectral lines not seen in water. Their experiment demonstrates that there exist the plasma at the hot spot and the sound estimate of the temperature of the spot that rises above 15,000K. This is hot enough to initiate the plasma reaction. But, for the reaction, the reactant molecules must be in the hot-spot, which requires the specific spatio-temporal structure in the bubble. The spatial segregation reported here has important consequences of not only the sono-luminescence but also the sono-chemistry. In considering the Ar rectification under normal sono-chemical conditions ; in water open to the air, the efficient reactions can be expected with molecules whose molecular weights are lighter than that of Ar, 40. Less
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