The Chemical Consequences of Cavitation
K.S.Suslick (School of Chemical Sciences, University of Illinois at Urbana-Champaign, Urbana, IL, USA)
Fundamentally, chemistry is the interaction of energy and matter. Surprisingly, there are relatively few ways of putting energy into molecules. High intensity ultrasound has found new applications in driving chemical reactions and in the preparation of unusual materials. The chemical effects of ultrasound originate from acoustic cavitation: the formation, growth, and implosive collapse of bubbles in a liquid. From sonoluminescence spectroscopy, we have established that cavitation produces local conditions inside the bubbles of about 5000 K and 1000 atmospheres, but on a nanosecond timescale. In otherwise cold liquids, ultrasound is able to drive reactions that normally occur only under extreme conditions. The sonochemical syntheses of nanostructured metals, alloys, metal carbides, supported heterogeneous catalysts, and nano-colloids derives from the sonochemical decomposition of volatile organometallic precursors during cavitation, which produces clusters a few nm in diameter. Such nanostructured solids are active heterogeneous catalysts for various reactions. Even single cavitating bubbles drive sonochemical reactions, which limits the extent of heating due to compression. Quantitative confirmation of the reactions of N2 and O2 in single bubble sonoluminescence in water has been recently achieved.
Section : 11