Authors: S. Danczyk and B. Chehroudi
Affilation: ERC/ Air Force Research Laboratory, United States
Pages: 226 - 229
Keywords: ignition, fuel, SWCNT, nanoparticles
It was reported in the literature that as-produced single-walled carbon nanotubes (SWCNTs) ignited when accidentally subjected to a common photographic flash at a close range. This effect was observed for dry and “fluffy” SWCNTs but diminished somewhat for compacted material. Ignition did not occur for similar materials such as multiwalled carbon nanotubes, graphite powder, fluffy carbon soot, and C60. Structural changes in the SWCNTs during the ignition process indicated that a temperature in excess of 1500oC was attained. It was then concluded that the ignition occurred due to a heat pulse created through light absorption by the nanotubes. We have used this phenomenon to develop an ignition method that is capable of igniting liquid fuels, such as RP-1 and methanol, and solids, such as perclorate(?) and wax paper with SWCNTs and a simple camera flash. Although the exact mechanism which causes the nanotubes to be damaged by the flash of light is unknown, there is evidence that the nanosized metal catalyst particles, specifically iron which is used in the formation process, oxidize and are responsible for igniting the fuels. We have found that the SWCNTs were able to ignite the fuels only when the they were in contact with the air or immersed in an oxygen environment. The SWCNTs did not ignite the fuels if they were completely submerged in the fuel. Therefore, we have concluded that oxygen plays an important role in the ignition process of these nanotubes and the absorption of light is not the only factor contributing to the process. Nanosized iron particles are considered as pyrophoric materials. Therefore, the carbon nanotubes, which surround the iron particles, have a stabilizing effect on the nanosized iron particles. We believe that the flash of light damages the structure of theses nanotubes in such a way to expose the iron nanoparticles to oxygen. The iron then ignites and the heat produced can be used to ignite other fuels. If the SWCNTs are purified to have less than approximately 1% of iron nanoparticles by weight, the nanotubes can not be ignited even in an oxygen-rich environment with a camera flash. We have observed that as the concentration of the iron nanoparticles is increased, the easier the nanotubes are ignited. Nanotubes with 3% iron nanoparticles by weight are only reliably ignited in an oxygen-rich environment. As the concentration of these nanoparticles is increase to 30% by weight, the nanotubes ignite very reliably in atmospheric air. We have also demonstrated the ability to ignite a single droplet of fuel (RP-1) with SWCNTs and a camera flash. This ignition method has the potential to be developed into a low-power distributed ignition method.