First direct measurement of the temperature of a cavitation bubble

Sonoluminescence - the phenomenon by which air bubbles in a liquid emit a flash of light under the action of acoustic waves - has been described by scientists for a long time. But its mechanisms are still poorly known.

David Flannigan and Kenneth Suslick of the University of Illinois at Urbana Champaign have taken a new step in understanding the process by creating a unique argon bubble in a sulfuric acid solution. Under the action of sound waves with frequencies above 18000 cycles per second, the bubble first dilated before reaching its limits and then quickly collapsed. It is during this last stage that we observe the emission of light. Thanks to their work, the two researchers managed to obtain a spectrum 3000 times brighter than the previous experiments. This allowed them to do a more detailed analysis of the event. According to their measurements, the local temperature reached the 15000 Kelvin, which is several times the temperature on the surface of the Sun. But the most remarkable is the detection of highly energetic ionized argon and oxygen atoms during the experiment.

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A result that traditional chemical and thermal reactions do not suffice to explain and that the authors of the research thus attribute to the collision of atoms with electrons and ions of very high energies in the form of very hot plasma formed in the nucleus of the bubble. If these data were confirmed, they would be the first direct detection of a plasma associated with sonoluminescence.

NYT 15 / 03 / 04 (Tiny bubbles implode with
the heat of a star) http://www.nytimes.com/2005/03/15/science/15soni.html

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