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Nanotubes go flash bang wallop
19:00 25 April 02 NewScientist.com news service

Taking a snapshot of carbon nanotubes using an ordinary camera flash can cause them to emit a loud pop and then suddenly burst into flame.

Scientists say this unique explosive phenomenon may lead to new means of manufacturing nanoscale carbon materials and even remote-control devices for small explosive charges.

Pulickel Ajayan and his team at Rensselaer Polytechnic Institute, New York, have been at work since one of his students accidentally sparked a tiny explosion by photographing a bundle of single-walled carbon nanotubes. "It was a complete accident," Ajayan told New Scientist.

Researchers around the world are exploring the potential that carbon nanotubes could have for a wide range of super-strong materials and nanoscale circuits. Ganapathiraman Ramanath, also at Rensselaer Polytechnic, says that the latest discovery "will serve as a starting point for developing nanotube-based actuators and sensors that rely on remote activation and triggering."


Ultra-absorbent

Ajayan says the explosion occurs because the black carbon nanotubes absorb light so efficiently that, when it is converted into heat, the heat cannot dissipate quickly enough across bunched-up tubes. However, only the single-walled variety of nanotubes catch fire. Those with multiple walls do not explode - the researchers are unsure why.

Video of flashlit nanotube explosion (5.2MB, Hosted at Rensselaer Polytechnic Institute)

The initial popping noise is generated by the heating of the oxygen inside and between the tubes, which causes a shock wave. And when the temperature of carbon reaches between 600њC and 700њC it oxidises sparking combustion.

When the researchers tried the experiment in the absence of oxygen they found that the tubes were transformed into different nanoscopic shapes, some reminiscent of cone-shaped "nanohorns".

"It's a very nice surprise," says Angel Rubio, an expert in carbon nanotubes at the University of the Basque Country in Spain. "Because it's the only carbon material that exhibits this ignition property."

Journal Reference: Science (vol 296, p 705)
 

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