Flame and furnace synthesis of single-walled and multi-walled carbon nanotubes and nanofibers

Results are presented for flame synthesis of metal-catalyzed carbon nanotubes. A thermal evaporation technique is used to create the catalyst nanoparticles of Fe or Ni through gas condensation followed by entrainment into the flame. Results are compared with those using a high-temperature tube furnace to provide the reactive environment. Each system yields consistent results, with CO/H2 mixtures generally yielding single-walled nanotubes (SWNTs) with Fe while C2H2/H2 mixtures usually produce multiwalled nanotubes (MWNTs) with Ni. A ternary gas mixture of CO/C2/H2 produces a better yield of nanofibers than either a CO/H2 or C2H2/H2 mixture at 700 °C with Ni catalyst. Our results reflect a combination or possibly a synergy between thermal-plus adsorbate-induced restructuring and adsorbate-particle steric factors affecting particle structure and reactivity.