Cavitation chemistry

Henglein A (1993) Contributions to various aspects of cavitation chemistry. In Mason TJ (ed) Advances in Sonochemistry, vol. 3 17-83, JAI Press, London... 

If, however, the effect is truly based on the cavitation chemistry, then cavitation must be provided during the transformation itself either operated in continuous manner or in suitable pulsed operation. The scientific database from the laboratory... 

Cravatto G, Cintas P (2006) Power ultrasound in organic synthesis Moving cavitational chemistry from academia to innovative and large-scale applications. Chem Soc Rev 35 180-196... 

Cavitation chemistry encompasses complex pathways involving numerous reactive intermediates, and identification of these intermediates is crucial for elucidating the mechanism... 

Zhang, G. andHua, I. Cavitation Chemistry of Polychlorinated Biphenyls Detection of Reactive Intermediates and By-Products and the Impact of Ultrasonic Frequency,... 

Zhang, G. and Hua, I. Cavitation chemistry of polychlorinated biphenyls decomposition mechanisms and rates. Environ. Sci. Technol, 34(8) 1529-1534, 2000. 

As was already outlined, the experimental conditions for sonochemistry must be carefully considered when a process is designed, and these conditions must be carefully controlled during operation. Here is a brief account of the main parameters influencing cavitation chemistry. 

Moser, W. R., Giang, T., Nguyen, S., and Kozyuk, O. V., A new route to cavitational chemistry and chemical processing by controlled flow cavitation, in Process Intensification for the Chemical Industry, 3rd International Conference (A. Green, Ed.), pp. 38, 173, BHR Group, London (1999). 

A. Helglein, Contributions to Various Aspects of Cavitation Chemistry, in T.J. Mason (Ed.), Advances in Sonochemistry, JAI Press, London, 1993, p. 17. 

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. 

Whenever corrosion resistance results from the formation of layers of insoluble corrosion products on the metallic surface, the effect of high velocity may be to prevent their normal formation, to remove them after they have been formed, and/or to preclude their reformation. All metals that are protected by a film are sensitive to what is referred to as its critical velocity i.e., the velocity at which those conditions occur is referred to as the critical velocity of that chemistry/temperature/veloc-ity environmental corrosion mechanism. When the critical velocity of that specific system is exceeded, that effect allows corrosion to proceed unhindered. This occurs frequently in small-diameter tubes or pipes through which corrosive liquids may be circulated at high velocities (e.g., condenser and evaporator tubes), in the vicinity of bends in pipelines, and on propellers, agitators, and centrifugal pumps. Similar effects are associated with cavitation and mechanical erosion. 

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... 

Suslick KS, Mdleleni MM, Reis JT (1997) Chemistry Induced by Hydrodynamic Cavitation. J Am Chem Soc 119 9303-9304... 

Pradhan AA, Gogate PR (2009) Degradation of p-nitrophenol Using Acoustic Cavitation and Fenton Chemistry. J Haz Mat 173 517-522... 

We sincerely hope that this book is immensely beneficial to graduate students and researchers to learn the fundamental aspects of cavitation and to launch new research activities in the sonochemistry research field. The readers will also realize that sonochemistry is not just limited to chemistry but has the potential to incorporate in other areas including physics, engineering, biochemistry and medicine. 

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... 

Thus, the parameters of acoustic intensity, temperature, ambient gas, and solvent choice have strong influences on sonochemical reactions. It is clear that one can fine tune the energetics of cavitation by the use of these variables and hence exercise control on the rates and reaction pathways followed by the associated chemistry. Specific examples will be discussed shortly. Clearly, the thermal conductivity of the ambient gas (e.g., a variable He/Ar atmosphere) and the overall solvent vapor pressure provides easy mechanisms for experimental control of the peak temperatures generated during the cavitational collapse. 

It is now clearly demonstrated through the use of free radical traps that all organic liquids will undergo cavitation and generate bond homolysis, if the ambient temperature is sufficiently low (i.e., in order to reduce the solvent system s vapor pressure) (89,90,161,162). The sonolysis of alkanes is quite similar to very high temperature pyrolysis, yielding the products expected (H2, CH4, 1-alkenes, and acetylene) from the well-understood Rice radical chain mechanism (89). Other recent reports compare the sonolysis and pyrolysis of biacetyl (which gives primarily acetone) (163) and the sonolysis and radiolysis of menthone (164). Nonaqueous chemistry can be complex, however, as in the tarry polymerization of several substituted benzenes (165). 

In 1981, the first report on the sonochemistry of discrete organometallic complexes demonstrated the effect of ultrasound on iron carbonyls in alkane solutions (174). 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(CO)5 provides an excellent example of the unique chemistry which homogeneous cavitation can... 

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