11-09 :: September 2011

nanotimes News in Brief

Nanometre-sized bubbles con- taining 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 sponta- neous combustion in a publica- tion in Physical Review E. They intend to use the phenomenon to construct a compact ultra- sonic 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 elec- trodes are used to make hydro- gen and oxygen by electrolysis, in the usual manner, in an ultra-small reaction chamber. If the plus and minus poles are continu- ally 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 150nm; 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. Researcher Vitaly Svetovoy was working on the construction of an actuator for rapidly building pressure when he

45

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. © Vitaly Svetovoy