The chemical effects of ultrasound have significance in the areas of bulk liquid processing, in technologies related to emulsification (e.g. pharmaceuticals and cosmetics), in processes for solvent degassing, and solid dispersion (e.g. fume scrubbers). Although the chemical effects of ultrasound have been recognized for more than 50 years, understanding of the nature and range of sonochemistry remains quite limited. The principal mechanism involves acoustic cavitation: the creation, expansion, and implosive collapse of small vapor vacuoles in the liquid. The rapid compression in this cycle proces intense local heating and thus creates high energy chemistry in a cold, condensed medium. By using comparative rate thermometry, it has recently been determined that the effective temperature reached during cavitational collapse is 5200 Kelvin with heating and cooling rates of two billion degrees per second| The proposed research will deal with the chemical effects of ultrasound on both homogeneous liquids and on heteerogeneous (liquid-solid) systems. In the homogeneous area, special emphasis will be placed on sonoluminescence of non-aqueous liquids and on organometallic systems. Examples of homogeneous sonocatalysis with rate enhancements of one million have been developed and will continue; as well as developing further analogies to bomb reactions and metal vapor chemistry. In heterogeneous systems, the effect of cavitation near surfaces on particle morphology, surface structure, and both stoichiometric and catalytic reactivity will be explored. Already, a 100,000 enhancement of catalytic activity of Ni due to the removal of a passivating oxide coating has been discovered. A wide range of surface analysis techniques, especially SEM and Auger electron spectroscopy, will be used in this work.
