Influence of the fuel structure on the flame synthesis of carbon nanomaterials

Carbon nanomaterials (CNMs) were grown on nickel-coated stainless-steel mesh grids using a combustion synthesis method. Three fuel feedstocks of dissimilar chemical structures, ethylene, ethyl benzene and ethyl alcohol, were burned at fuel-rich equivalence ratios to generate disparate combustion products. The chemical compositions of these products were assessed to identify and contrast the species that contribute to the growth of CNMs. The generated CNMs were characterized using SEM and TEM. Each set of conditions produced a distinct distribution (bi-modal or mono-modal) of CNMs, including carbon nanotubes and carbon nanofibers, both of varying diameters and lengths. The effects of combustion-generated light aliphatic hydrocarbons and light aromatic hydrocarbons on CNM growth and structure were ascertained. It was found that ethylene and ethyl alcohol generated tubular CNMs under all tested conditions, whereas ethyl benzene generated only small amounts of CNMs and under much more limited conditions. It was also determined that concentrations of aliphatic species, notably methane and acetylene, at mole fractions as low as 500 ppm have a thickening effect on the resulting CNMs. Linear correlations were found between the concentrations of these species and the mean diameter of the CNMs. (C) 2011 Elsevier Ltd. All rights reserved.