Parabolic Equations in Biology

Abstract

Single-walled carbon nanotubes (SWCNTs) are shown to grow rapidlyon iron oxide catalysts on the fuel side of an inverse ethylene diffusionflame. The pathway of carbon in the flame is controlled by the flamestructure, leading to formation of SWCNTs free of polycyclic aromatichydrocarbons (PAH) or soot. By using a combination of oxygen-enrichmentand fuel dilution, fuel oxidation is favored over pyrolysis, PAHgrowth, and subsequent soot formation. The inverse configurationof the flame prevents burnout of the SWCNTs while providing a longcarbon-rich region for nanotube formation. Furthermore, flame structureis used to control oxidation of the catalyst particles. Iron sub-oxidecatalysts are highly active toward SWCNT formation while Fe and Fe2O3catalysts are less active. This can be understood by consideringthe effects of particle oxidation on the dissociative adsorptionof gas-phase hydrocarbons. The optimum catalyst particle compositionand flame conditions were determined in near real-time using a scanningmobility particle sizer (SMPS) to measure the catalyst and SWCNTsize distributions. In addition, SMPS results were combined withflame velocity measurement to measure SWCNT growth rates. SWCNTswere found to grow at rates of over 100 mu m/s.