KSEF R&D Excellence: Counter-Flow Flame Synthesis of Multi-Walled Carbon Nanotubes

A study of synthesis mechanism of multi-walled carbon nanotubes (MWCNTs) is proposed, motivated by the need to understand interactions of flame structure, metal catalyst and pyrolyzed hydrocarbons in the growth of carbon nanotubes (CNTs). The experiments will involve a laminar counter-flow diffusion flame, to improve sampling possibilities and to compare with our current work on the synthesis of MWCNTs using candle-like, co-flow diffusion flames, at conditions where CNTs synthesize on a metal catalyst substrate. A laminar counter-flow diffusion flame will be applied because this flame configuration provides experimentally and computationally tractable models for processes including pyrolysis of carbon source, formation of catalyst particles, adsorption of catalyst surface, precipitation of carbon precursor, and growth of CNTs. Laminar diffusion flame is appropriate for this purpose because our current work has bcen very successful on synthesis of high-purity, high-quality MWCNTs by co-flow diffusion flamcs. The importance of the catalytic substrate positioning in the flame and the effect of flame temperature are emphasized by the co-flow studies. However, the influence of these factors has not been adequately studied due to the small flame volume. Use of laminar counter-flow di ffusion flame configuration can provide better sampling possibilities and measurements. Additionally, it was shown that the counter-flow diffusion flame has a strong potential for nanotube growth, producing high temperature and high radical concentrations. Two kinds of experiments are planned: (I) detailed measurements of flame structure (velocity, temperature, stable species concentrations, and some radicals (pyrolyzed unsaturated Cz, C3 and C4) species concentrations) from which a critical condition where MWCNTs can be grown will result; and (2) applications of different hydrocarbon fuels for the nanotube synthesis including straight chain hydrocarbons with single C-C bonds (methane and ethane), double C=C bonds (ethylene), and triple C =C bonds (acetylene), and aromatic hydrocarbons (benzene and toluene). The counterflow diffusion flame will also be numerically simulated to help in interpreting the experimental results and to provide capability to extend consideration to immeasurable pyrolyzed species. The analysis equipment of gas chromatogram (GC), scanning electron microscopy (SEM), transmission electron microscopy (TEM) are available at UK's laboratories and will be used to analyze sampled species and synthesized products.