Monday, 18 October 2004 - 9:50 AM
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This presentation is part of: PHYS: General Papers II

Single Bubble Cavitation in Concentrated Sulfuric Acid

David J. Flannigan and Kenneth S. Suslick. University of Illinois at Urbana-Champaign, Urbana, IL

For the first time, we have observed strong atomic emission and extensive molecular vibronic progressions within single-bubble sonoluminescence (SBSL) spectra obtained from concentrated sulfuric acid (H2SO4). The atomic emission lines, arising from neutral Ar atoms, and extensive vibronic progressions, arising from diatomic sulfur monoxide (SO) molecules, are well resolved and easily lend themselves to accurate quantitative temperature determinations, another very important first for SBSL. Of very special note, the atomic Ar excited states being populated are extremely high in energy (>13 eV) and cannot be thermally populated at the Ar temperatures we calculate (15,000 K). This is, therefore, the first experimental evidence for the existence of a hot, optically-opaque plasma core. The Ar excitation occurs via high-energy particle impact (e.g. electron impact). The observed molecular and atomic emission occur from an emissive shell surrounding the much hotter plasma core. In addition to the atomic and molecular emission lines contained in the spectra, we have observed an extraordinary increase in the SBSL intensity. The overall SBSL intensity observed from concentrated H2SO4(aq) solutions is well over two orders of magnitude greater than SBSL observed from any other fluid, and is well over three orders of magnitude greater than SBSL from pure water at comparable solution temperatures. This is due, in part, to the very low vapor pressures of concentrated H2SO4(aq) solutions (30 mTorr at 295 K in 85 wt% H2SO4(aq)). Also, the parameter space that supports SBSL in H2SO4(aq) is much larger than in water, with SBSL observable over an acoustic pressure range of 1.3 to >6 bar. For comparison, SBSL in water is not observed above ~1.5 bar. Because of the wealth of information contained in the spectra, this work has greatly advanced the understanding of the physical conditions and chemical processes occurring during single bubble cavitation.

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