Plasma torch production of macroscopic carbon nanotube structures

Analysis of the many studies of carbon nanotube formation in high-temperature ovens clearly indicates the key requirements of nanotube formation are an 'atomic' carbon source and a source of nanometal particles. We adapted this formulation to the high temperature (>3000 K) environment found in a low-power (<1000 W) atmospheric pressure, microwave plasma torch, by simultaneously feeding carbon monoxide (carbon source), and (presumably) iron carbonyl (source of metal catalyst particles) through an argon stabilized plasma flame. This technique led to the relatively rapid (25 mg/h) formation of carbon nanotubes of a unique form: macro-sized 'woven' threads. Scanning electron microscopy and high-resolution transmission electron microscopy studies revealed that the woven threads consist entirely of carbon nanotubes (primarily carbon single-wall nanotube) and associated nano-iron particles. The structures appear 'fractal' in that each woven thread appears to be constructed of smaller threads that in turn are formed of yet smaller woven threads. Simple mechanical tests show the threads can be bent without breaking, and the thread will spring to its original shape when the force holding it is released. Threads of the size produced can be woven together to form actual cloth or ropes and thus this result represents a step toward the ultimate application of carbon nanotubes for super strong/light structures. (C) 2003 Elsevier Ltd. All rights reserved.