Response of Fe powder, purified and as-produced HiPco single-walled carbon nanotubes to flash exposure

An Innovative Ignition Method Using SWCNTs and a Camera Flash

“…The iron oxide particles that remained after our combustion were much larger than any particles that were in the initial mixture. This reinforces the observation by Smits et al [4] that the Fe particles melted and coalesced as the oxidation continued. Since the nanosized Fe particles are pyrophoric, it is believed that the SWCNTs must stabilize the Fe particles as mentioned before.…”

“…Ignition did not occur if the pile of SWCNTs were compacted before being exposed to a flash light. There is no reason to believe that the metal oxides which remained in our tests are any different than what Brady et al [3] and Smits et al [4] described. The orangecolored material is most likely iron oxides Fe 2 O 3 and Fe 2 O 4 .…”

“…Both morphology types were considerably larger than the nanoparticles of Fe in the pristine SWCNTs, which were 1-5 nm in diameter. Smits et al [4] conducted experiments to determine the cause for ignition of the SWCNTs. They tested three different samples: (a) as-produced SWCNTs synthesized by the HiPco process (from Carbon Nanotechnologies Inc.), (b) the same material obtained but after a purification process, and (c) 99.5% pure, 6 -10 µm diameter Fe powder.…”

“…The remaining Fe nanoparticles left after the purification process are less likely to oxidize during flash exposure. Smits et al [4] found that the exothermic oxidation of Fe released sufficient heat to cause melting, coalescence and oxidation of nanoparticles, which caused aggregation into clusters of large particles. The heat released during the oxidation is sufficient to promote transformations within the adjacent SWCNTs, including fusing some SWCNTs into larger tubes.…”

“…These may have condensed on the surface of the Fe 2 O 3 particles during cooling of the oxide particles. Smits et al [4] believe that the flash ignition of SWCNTs should be attributed to the pyrophoric nature of fine Fe particles within the nanotube bundles, rather than to any property of the SWCNTs themselves. However, the SWCNTs are providing a medium to stabilize these nanoparticles so that they will not spontaneously initiate ignition until they are exposed to an appropriate stimulus such as energy from an ordinary camera flash.…”