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Spontaneous combustion in nanobubbles inspires compact ultrasonic loudspeaker

Date:
September 29, 2011
Source:
University of Twente
Summary:
Nanometer-sized bubbles containing the gases hydrogen and oxygen can apparently combust spontaneously, although nothing happens in larger bubbles. For the first time, researchers have demonstrated this spontaneous combustion. They intend to use the phenomenon to construct a compact ultrasonic loudspeaker.

Formation of bubbles at the electrodes during electrolysis (can be seen in a and b). Situations c, d, and e show the formation of both hydrogen and oxygen on the left, hydrogen alone in the middle and oxygen alone on the right. Situation e shows combustion taking place on the left. No bubbles can be seen on the electrodes.
Credit: Image courtesy of University of Twente

Nanometre-sized bubbles containing the gases hydrogen and oxygen can apparently combust spontaneously, although nothing happens in larger bubbles. For the first time, researchers at the University of Twente's MESA+ Institute for Nanotechnology have demonstrated this spontaneous combustion in a publication in Physical Review E. They intend to use the phenomenon to construct a compact ultrasonic loudspeaker.

The fact that a violent reaction takes place is already evident from the damage incurred by the electrodes with which the reaction is initiated. These electrodes are used to make hydrogen and oxygen by electrolysis, in the usual manner, in an ultra-small reaction chamber. If the plus and minus poles are continually alternated, tiny bubbles containing both gases arise.

The frequency with which the poles are alternated determines the size of the bubbles: the higher the frequency, the smaller the bubbles. Combustion only takes place in bubbles that are smaller than 150 nanometres (a nanometre is a millionth of a millimetre); nothing happens in larger bubbles. Early experiments in microreactors also showed that nothing happened in larger bubbles; the heat can dissipate to the larger internal surface.

Metres per second

Researcher Vitaly Svetovoy was working on the construction of an actuator for rapidly building pressure when he came across this phenomenon. Such actuators are, for example, used in loudspeakers for ultrasonic frequencies undetectable by the human ear in the medical world. None of the mechanical techniques currently available are suitable for making a very compact loudspeaker of this kind and still achieving a 'deflection' of metres per second on this scale. Svetovoy thought, however, that it might be possible by building up pressure with bubbles. The problem was that the bubbles could be made very rapidly but that they did not disappear quickly enough. The combustion reaction that has now been demonstrated might solve this problem. But it causes other problems too, such as the damage to the electrodes. "That is what we now have to look at," Svetovoy said.


Story Source:

The above story is based on materials provided by University of Twente. Note: Materials may be edited for content and length.


Journal Reference:

  1. Vitaly Svetovoy, Remko Sanders, Theo Lammerink, Miko Elwenspoek. Combustion of hydrogen-oxygen mixture in electrochemically generated nanobubbles. Physical Review E, 2011; 84 (3) DOI: 10.1103/PhysRevE.84.035302

Cite This Page:

University of Twente. "Spontaneous combustion in nanobubbles inspires compact ultrasonic loudspeaker." ScienceDaily. ScienceDaily, 29 September 2011. <www.sciencedaily.com/releases/2011/09/110928185909.htm>.
University of Twente. (2011, September 29). Spontaneous combustion in nanobubbles inspires compact ultrasonic loudspeaker. ScienceDaily. Retrieved October 21, 2014 from www.sciencedaily.com/releases/2011/09/110928185909.htm
University of Twente. "Spontaneous combustion in nanobubbles inspires compact ultrasonic loudspeaker." ScienceDaily. www.sciencedaily.com/releases/2011/09/110928185909.htm (accessed October 21, 2014).

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