Ultrasound has become an important synthetic tool in liquid-solid chemical reactions, but the origins of the observed enhancements remained unknown. The effects of high-intensity ultrasound on solid-liquid slurries were examined. Turbulent flow and shock waves produced by acoustic cavitation were found to drive metal particles together at sufficiently high velocities to induce melting upon collision. A series of transition-metal powders were used to probe the maximum temperatures and speeds reached during such interparticle collisions. Metal particles that were irradiated in hydrocarbon liquids with ultrasound underwent collisions at roughly half the speed of sound and generated localized effective temperatures between 2600 degrees C and 3400 degrees C at the point of impact for particles with an average diameter of approximately 10 microns.

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Examination, by optical microscopy, of the matrix/analyte morphology of a sample prepared from a droplet in matrix-assisted UV laser-desorption mass spectrometry (MUVLDMS) reveals that the matrix crystallizes to a large extent, thus altering the concentration of the material in regions on the surface from that of the bulk applied solution. Microscopy reveals that vanillic acid and to a lesser extent nicotinic acid matrices form prominent crystalline rings around the dried sample spot while sinapic acid forms a more uniform dispersion of the crystallized matrix. Insulin analyte investigated in this report tends to form a thin isotropic phase in the center of the drops. The first reported use of a KrF excimer laser (249 nm) in MUVLDMS is also discussed.

High-intensity ultrasound can enhance both homogeneous and heterogeneous reactions.1"13 It has found an important niche in

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