Combustion synthesis of fullerenes and fullerenic nanostructures

Samples of condensable material collected from low-pressure premixed and diffusion benzene/oxygen/argon flames were analyzed chemically to determine fullerene yield and by high-resolution transmission electron microscopy to characterize the fullerenic material on and within the soot particles. Results show that fullerene formation is sensitive to changes in operating conditions, such as fuel/oxygen ratio, chamber pressure, and inert gas dilution, and that the formation of amorphous and fullerenic carbon occurs early in the flame, with the structures becoming more curved with greater residence time. All flames exhibit a fullerene maximum with the premixed flame showing two distinct regions of formation. Additionally, the fullerene maximum in the diffusion flames is always just above the stoichiometric flame surface and a maximum is observed with increasing dilution due to competing dilution effects. Image analysis data show that the curvatures and diameters of the structures are consistent with the chemical analysis and that nanostructures, found at greater residence times than fullerenes, are formed directly from curved structures in the soot. These data complement previous fullerene studies and shed light on several proposed mechanisms for fullerene formation in combustion. (C) 2002 Elsevier Science Ltd. All rights reserved.