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Apr 1991

Volume 89, Issue 4B, pp. 1851-2015

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back to top Session 3PA: Physical Acoustics: Sonochemistry and Acoustic Cavitation
Invited Papers
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The past, present, and future of acoustic cavitation nucleation (A)

Anthony A. Atchley

J. Acoust. Soc. Am. Volume 89, Issue 4B, pp. 1884-1884 (1991); (1 page)

Online Publication Date: 14 Aug 2005

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Those familiar with the field do not need to be reminded that acoustic cavitation is the cornerstone of sonoluminescence and sonochemistry. However, an equally important and often overlooked statement is that nucleation is the cornerstone of acoustic cavitation. So critical is the nature of the nucleus to the cavitation process that the acoustic cavitation threshold in water can be varied from a few atmospheres to a few hundred atmospheres just by altering the distribution and properties of the nuclei. (The acoustic cavitation threshold is the maximum acoustic pressure amplitude to which a liquid can be exposed before cavitation inception.) The fundamentals of acoustic cavitation nucleation will be presented in this paper, which is intended to be tutorial in nature. Topics include homogeneous and heterogeneous nucleation, stabilization mechanisms, models of heterogeneous cavitation nuclei, and the dependence of the cavitation threshold on the properties of the nucleus. [Work supported by ONR and the NPS Res. Program]
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Gas temperatures in bubble oscillations (A)

A. Prosperetti and V. Kamath

J. Acoust. Soc. Am. Volume 89, Issue 4B, pp. 1884-1884 (1991); (1 page)

Online Publication Date: 14 Aug 2005

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Sonolumineseenec effects are critically dependent on the temperature field of the gas contained in oscillating bubbles. Polytropic models of the gas pressure‐volume relationship are totally inadequate for an accurate determination of the temperature. A better model based on the conservation equations of continuum mechanics is described and its predictions illustrated with a number of examples. The influence of the computed temperature field on a model dissociation reaction is illustrated. [Work supported by NSF.]
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Experimental aspects of sonoluminescence (A)

Ronald A. Roy and D. Felipe Gaitan

J. Acoust. Soc. Am. Volume 89, Issue 4B, pp. 1885-1885 (1991); (1 page)

Online Publication Date: 14 Aug 2005

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It is well known that acoustically driven gas bubbles can generate light through a process known as sonoluminescence. Although readily observed, this phenomenon has, until recently, been poorly understood. in the past, the existence of competing models (i.e., hot spots, electrical microdischarge, etc.) inspired several “definitive” experiments, many of which led to ambiguous or erroneous conclusions. Since then, improvements in our ability to detect photons as well as monitor and manipulate bubble oscillations have resulted in a significant enhancement of our understanding of the sonoluminescence process. This talk will begin with a brief review of the early theories and experiments, to be followed by a detailed description of recent experiments involving acoustically levitated, light‐emitting bubbles. At issue is the timing of light output vis á vis the bubble collapse, the role played by the equilibrium size of the bubble and the acoustic pressure amplitude, the estimated collapse temperatures, and the contribution of various cyclic cavitation processes to the dynamics of single and multiple‐bubble cavitation fields. [Work supported by ONR.]
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Shape oscillations of bubbles driven by modulated ultrasonic radiation pressure: Experiments (A)

Philip L. Marston, Thomas J. Asaki, and Eugene H. Trinh

J. Acoust. Soc. Am. Volume 89, Issue 4B, pp. 1885-1885 (1991); (1 page)

Online Publication Date: 14 Aug 2005

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The shape of a bubble in water should change in response to the radiation pressure of an ultrasonic wave. Furthermore, modulation of the radiation pressure at the resonance frequencies for shape oscillations should facilitate the stable excitation of such modes [P. L. Marston, J. Acoust. Soc. Am. 67, 15–26 (1980)]. Recently this method of driving oscillations has been demonstrated by employing a novel ultrasonic levitator developed at Jet Propulsion Laboratory which traps bubbles in the size range of 1‐ to 5‐mm diameter. The quadrupole mode was observed with resonance frequencies in the range from 400 to 40 Hz. Oscillations were detected with the unaided eye and with television and laser light scattering methods. These experiments suggest methods for investigating the nonlinear dynamics of bubbles, effects of surfactants, and the dynamics of bubbles in low gravity. Some comparisons with the dynamics of drops will be noted. [Research supported by ONR and NASA.]
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Sonoluminescence (A)

Brad Barber, Ritva Löfstedt, and Seth Putterman

J. Acoust. Soc. Am. Volume 89, Issue 4B, pp. 1885-1885 (1991); (1 page)

Online Publication Date: 14 Aug 2005

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Sonoluminescence (SL) is an extraordinary phenomenon in that a standing wave sound field with an energy of 10−12 eV per atom can focus to such an extent that photons are emitted with energies that can be greater than 1 eV. The phenomenon has been known for over 50 years and the long held picture that it is due to acoustic cavitation has been demonstrated beyond a shadow of a doubt by the recent work of Gaitan and Crum [J. Acoust. Soc. Am. Suppl. 1 87, S141 (1990)]. They measured the dynamic radius, light emission, and sound field of a single bubble. Here, their pioneering work is extended to determine the details of the individual photon bursts and it is found that they last less than 2 ns and incude about a million photons. From a more general perspective the issue is raised of: Do cooperative optical processes affect the bursts and what are the limits of amplification that can be achieved via the self‐focusing effects which lead to SL? Calculations suggest that our current acousto‐optic conversion efficiency of 10−5 can be increased by at least 3 orders of magnitude. [Work supported by the Dept. of Energy, Office of Basic Energy Sci.]
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The sonochemical hot spot (A)

Kenneth S. Suslick

J. Acoust. Soc. Am. Volume 89, Issue 4B, pp. 1885-1886 (1991); (2 pages)

Online Publication Date: 14 Aug 2005

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The origin of “sonochemistry” is acoustic cavitation: the formation, expansion, and implosive collapse of bubbles in liquids irradiated with ultrasound. The compression of such bubbles generates intense local heating, which has been quantified recently from both chemical kinetic thermometry and from high‐resolution sonoluminescence spectra. The temperatures reached during cavitation are ≈5000 K, but have an effective lifetime of only a few microseconds. Consistent with this, the sonoluminescence that accompanies sonochemistry closely resembles flame emission! The chemistry generated by these hot spots is different than either ordinary thermal or photochemical processes and sonochemistry represents a fundamentally unique interaction of energy and matter. [For recent reviews see K. S. Suslick, Sci. Am. 260, 80 (Feb. 1989) and Science 247, 1439 (1990).] Recently, the use of ultrasound in liquid‐powder slurries to enhance dramatically their chemical reactivity has been explored. For example, heterogeneous catalysis can be induced in normally nonreactive metals and the catalytic activity of Ni has been enhanced by 105. Using a variety of surface science techniques, it was shown that ultrasound removed the passivating oxide coating normally found on Ni and other metal surfaces, thus increasing their activity. The origin of these effects comes from extremely high‐speed interparticle collisions which occur during ultrasonic irradiation of liquid‐solid slurries. Turbulent flow and shockwaves produced by acoustic cavitation can drive metal particles together at sufficiently high velocities to induce melting upon collision. A series of transition metal powders have been used to probe the maximum temperatures and speeds reached during such interparticle collisions. Metal particles that are irradiated in hydrocarbon liquids with ultrasound undergo collisions at roughly half the speed of sound and generate localized effective temperatures between 2600°C and 3400°C at the point of impact. [Work supported by NSF and the UIUC Materials Res. Lab.]
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Sonochemistry of volatile and nonvolatile solutes in aqueous solutions: A spin trapping study (A)

Peter Riesz

J. Acoust. Soc. Am. Volume 89, Issue 4B, pp. 1886-1886 (1991); (1 page)

Online Publication Date: 14 Aug 2005

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The very high temperatures and pressures induced by acoustic cavitation in collapsing gas bubbles in aqueous solutions exposed to ultrasound lead to the thermal dissociation of water vapor into H atoms and OH radicals. Their formation has been confirmed by spin trapping for continuous wave and pulsed ultrasound. Sonochemical reactions occur in the gas‐phase (pyrolysis reactions), in the gas‐liquid interface, and in the bulk of the solution (radiation‐chemistry reactions). The high‐temperature gradients in the interfacial regions lead to pyrolysis products from nonvolatile solutes present at sufficiently high concentrations. The sonochemically generated radicals from carboxylic acids, amino acids, dipeptides, sugars, pyrimidine bases, nucleosides, and nucleotides were identified by spin trapping with a nonvolatile nitroso spin trap. At low concentrations of nonvolatile solutes, the spin trapped radicals produced by sonolysis are due to H atom and OH radical reactions. At higher concentrations of these nonvolatile solutes, sonolysis leads to the formation of additional reactions due to pyrolysis processes (typically methyl radicals). A preferred localization of nonvolatile surfactants at the gas‐liquid interface was demonstrated. The volatile solutes methanol, ethanol, acetone, and acetonitrile were studied over the complete range of solvent composition. By the use of rare gases with different thermal conductivities, the contributions of individual reaction steps with widely different energies of activation can be evaluated.
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Industrial applications of high‐intensity ultrasound (A)

Raymond L. Hunicke

J. Acoust. Soc. Am. Volume 89, Issue 4B, pp. 1886-1886 (1991); (1 page)

Online Publication Date: 14 Aug 2005

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With the increased laboratory investigations of sonochemistry, large‐scale industrial applications can be expected in the near future. The ultrasonic manufacturing industry can provide large scale equipment with power ratings in the tens of kW and with flow rates of thousands of gallons per hour. For these scales, magnetostrictive transducers have strong relative advantages over piezoelectric transducers. Prior commercial applications of ultrasound to large‐scale cleaning, aluminum soldering, and coal and ore benefication are discussed.
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