Carbon nanotube synthesis on catalytic metal alloys in methane/air counterflow diffusion flames

Various morphologies of multi-walled carbon nanotubes (MWNTs) are grown catalytically on metal-alloy probes in counterflow diffusion flames using methane as fuel. Carbon nanotube (CNT) properties and morphologies are investigated as functions of local gas-phase temperatures, C-related species concentrations (e.g. C₂H₂, CO), sampling positions, C₂H₂ adding to the fuel, and metal-alloy compositions (i.e., Fe, Fe/Cr, Ni/Cu, Ni/Ti, Ni/Cr, Ni/Cr/Fe). MWNTs grow optimally in non-sooty regions of the flames. C₂H₂ addition is found to promote direct synthesis of vertically well-aligned MWNTs with uniform diameters from Ni/Cr/Fe and Ni/Ti alloys.