Acoustic cavitation, and sonochemistry

Since the early 1980s, sonochemistry has become a well-defined technique for both mechanistic and synthetic studies. The general details of the process of acoustic cavitation and the high-energy... 

Ionic liquids have favorable intrinsic properties that make them of interest as solvents for various chemical reactions. The same properties that make the liquids effective solvents also make them interesting liquids for studies involving sonochemistry, acoustic cavitation, and sonoluminescence (Suslick et al., 1991, Suslick, 1988). Recent interest in using ultrasound to accelerate chemical reactions conducted in ionic liquids necessitates an understanding of the effects of acoustic cavitation on these solvents (Flannigan et al., 2005). 

Fig. 1. Transient acoustic cavitation the origin of sonochemistry and sonoluminescence.

The phenomenon of acoustic cavitation results in an enormous concentration of energy. If one considers the energy density in an acoustic field that produces cavitation and that in the coUapsed cavitation bubble, there is an amplification factor of over eleven orders of magnitude. The enormous local temperatures and pressures so created result in phenomena such as sonochemistry and sonoluminescence and provide a unique means for fundamental studies of chemistry and physics under extreme conditions. A diverse set of apphcations of ultrasound to enhancing chemical reactivity has been explored, with important apphcations in mixed-phase synthesis, materials chemistry, and biomedical uses. 

Sonochemistry started in 1927 when Richards and Loomis [173] first described chemical reactions brought about by ultrasonic waves, but rapid development of ultrasound in chemistry really only began in the 1980s. Over the past decades there has been a remarkable expansion in the use of ultrasound as an energy source to produce bond scission and to promote or modify chemical reactivity. Although acoustic cavitation plays... 

Abstract Acoustic cavitation is the formation and collapse of bubbles in liquid irradiated by intense ultrasound. The speed of the bubble collapse sometimes reaches the sound velocity in the liquid. Accordingly, the bubble collapse becomes a quasi-adiabatic process. The temperature and pressure inside a bubble increase to thousands of Kelvin and thousands of bars, respectively. As a result, water vapor and oxygen, if present, are dissociated inside a bubble and oxidants such as OH, O, and H2O2 are produced, which is called sonochemical reactions. The pulsation of active bubbles is intrinsically nonlinear. In the present review, fundamentals of acoustic cavitation, sonochemistry, and acoustic fields in sonochemical reactors have been discussed. 

Fig. 1.1 The regions for transient cavitation bubbles and stable cavitation bubbles when they are defined by the shape stability of bubbles in the parameter space of ambient bubble radius (R0) and the acoustic amplitude (p ). The ultrasonic frequency is 515 kHz. The thickest line is the border between the region for stable cavitation bubbles and that for transient ones. The type of bubble pulsation has been indicated by the frequency spectrum of acoustic cavitation noise such as nf0 (periodic pulsation with the acoustic period), nfo/2 (doubled acoustic period), nf0/4 (quadrupled acoustic period), and chaotic (non-periodic pulsation). Any transient cavitation bubbles result in the broad-band noise due to the temporal fluctuation in the number of bubbles. Reprinted from Ultrasonics Sonochemistry, vol. 17, K.Yasui, T.Tuziuti, J. Lee, T.Kozuka, A.Towata, and Y. Iida, Numerical simulations of acoustic cavitation noise with the temporal fluctuation in the number of bubbles, pp. 460-472, Copyright (2010), with permission from Elsevier...

Segebarth N, Eulaerts O, Reisse J, Crum LA, Matula TJ (2002) Correlation between acoustic cavitation noise, bubble population, and sonochemistry. J Phys Chem B 106 9181-9190... 

Physical Chemist who specializes in Sonochemistry, teaches undergraduate and postgraduate Chemistry and is a senior academic staff member of the School of Chemistry, University of Melbourne. Ashok is a renowned sono-chemist who has developed a number of novel techniques to characterize acoustic cavitation bubbles and has made major contributions of applied sonochemistry to the Food and Dairy industry. His research team has developed a novel ultrasonic processing technology for improving the functional properties of dairy ingredients. Recent research also involves the ultrasonic synthesis of functional... 

In 1981, we first reported on the sonochemistry of discrete organometallic complexes and demonstrated the effects of ultrasound on metal carbonyls in alkane solutions (J 8). The transition metal carbonyls were chosen for these initial studies because their thermal and photochemical reactivities have been well-characterized. The comparison among the thermal, photochemical, and sonochemical reactions of Fe(C0)5 provides an excellent example of the unique chemistry which acoustic cavitation can induce, and (because of space limitations in this review) we will focus upon it as an archetype. 

G.L Eskin, Degassing, filtration, and grain refinement processes of light alloys in a field of acoustic cavitation. Advances in Sonochemistry, T.J. Mason (ed.), JAI Press, London, 1996, 4, 101-159. 

Sonochemical destruction is a process for the destruction of volatile organic compounds (VOCs) in water using ultrasound. The technique is being researched for the treatment of contaminated ground and process water. Sonochemistry in liquids is the inducement of chemical reactions by the application of ultrasound energy acoustic cavitation results in the formation of hot spots of intense temperature and pressure that cause the destruction of VOCs. 

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