Tiny bangs triggered by camera flashes

TROY, N.Y., April 25 (UPI) -- Just as disgruntled actors tend to react explosively when camera bulbs flash in their faces, scientists have found carbon nanotubes that can actually burst into flames under bright light, reaching temperatures hot enough to melt steel at a scorching 2,732 degrees Fahrenheit.

An international team, led by investigators at Rensselaer Polytechnic Institute, said the microscopic nanotubes -- only nanometers or billionths of a meter wide -- could be used in novel, light-triggered fuses or even rocket fuel additives.

"This is the first known instance where a simple flash of normal, visible light created ignition of a material," said researcher Pulickel Ajayan, a materials scientist at RPI.

Carbon nanotubes interest scientists intensely because they are extraordinarily strong, light and good at conducting heat and electricity. Their surprising new capacity to burst into flame is mercifully confined only to single-walled carbon nanotubes, however. Other forms of carbon, such as diamonds, graphite, so-called buckyballs and multi-walled carbon nanotubes cannot be ignited by flashes of light.

The discovery was made by accident, the scientists said. A student ignited the nanotubes by taking photos of them in the lab using a flash bulb. The nanotubes emitted a bright red flame and, according to Rensselaer researcher Ganapathiraman Ramanath, "a loudly audible pop."

When a flash of light hits a knot of nanotubes, the resulting heat that would normally be conducted evenly throughout the tubes is trapped in the jumble, igniting the carbon. Evenly spaced nanotube arrays -- the ones desired for most practical or technological applications -- avoid this fiery fate.

"I would not have expected that so much energy would be released," commented nanotechnologist David Carroll of Clemson University in Pendleton, S.C. "The most exciting thing about this is the potential use in solid propellants, like a space shuttle's solid rocket motors."

Carroll added, "Nanotubes are quite expensive at this point. But one can imagine that when price permits, these might make important additives to solid fuels, allowing tailored or controllable release of energy, higher efficiency and greater propellant velocities."

Scientists also have discovered when the nanotubes are not exposed to oxygen -- but are instead, say, immersed in helium or argon, or placed in a vacuum -- bright flashes seem to restructure the hollow carbon strands, transforming them into cones.

"While the initial surprise is that the nanotubes will ignite upon exposure to a camera flash, perhaps most exciting is the fact that the nanotubes are transformed into new carbon structures in the absence of oxygen," researcher Thomas Ebbesen, of Louis Pasteur University in Strasbourg, France, told United Press International.

The scientists describe their findings in the April 26 issue of the journal Science.