Single-walled carbon nanotube formation on iron oxide catalysts in diffusion flames
- 224 Downloads
Single-walled carbon nanotubes (SWCNTs) are shown to grow rapidly on iron oxide catalysts on the fuel side of an inverse ethylene diffusion flame. The pathway of carbon in the flame is controlled by the flame structure, leading to formation of SWCNTs free of polycyclic aromatic hydrocarbons (PAH) or soot. By using a combination of oxygen-enrichment and fuel dilution, fuel oxidation is favored over pyrolysis, PAH growth, and subsequent soot formation. The inverse configuration of the flame prevents burnout of the SWCNTs while providing a long carbon-rich region for nanotube formation. Furthermore, flame structure is used to control oxidation of the catalyst particles. Iron sub-oxide catalysts are highly active toward SWCNT formation while Fe and Fe2O3 catalysts are less active. This can be understood by considering the effects of particle oxidation on the dissociative adsorption of gas-phase hydrocarbons. The optimum catalyst particle composition and flame conditions were determined in near real-time using a scanning mobility particle sizer (SMPS) to measure the catalyst and SWCNT size distributions. In addition, SMPS results were combined with flame velocity measurement to measure SWCNT growth rates. SWCNTs were found to grow at rates of over 100 μm/s.
KeywordsSingle-wall carbon nanotubes Diffusion flames Differential mobility analyzer Iron oxide catalyst Oxy-fuel combustion
The authors thank Xiaofeng Zhang for his efforts in collecting TEM data and Dr. John Gleaves for his helpful discussions. This research was funded by the Center for Materials Innovation at Washington University and NASA.
- de Heer WA (2004) Nanotubes and the pursuit of applications. MRS Bulletin, Pittsburgh, pp 281–285Google Scholar
- Donnet J-B, Bansal RC, Wang M-J (eds) (1993) Carbon black science and technology. Marcel Dekker, Inc., New YorkGoogle Scholar
- Du J, Axelbaum RL (1996) The effects of flame structure on extinction of CH4–O2–N2 diffusion flames. Proc Combust Inst 26:1137–1142Google Scholar
- Kumfer BM, Skeen SA and Axelbaum RL (2008) Soot inception limits in laminar diffusion flames with application to oxy-fuel combustion. Combust Flame 154:546–556Google Scholar
- Unrau CJ, Axelbaum RL, Biswas P, Fraundorf P (2007a) Online size characterization of nanofibers and nanotubes. Mansoori GA, George TF, Assoufid L, Zhang G (eds) Molecular building blocks for nanotechnology: from diamondoids to nanoscale materials and applications, vol 109. Springer, New York, pp 212–245Google Scholar