Multi‐walled carbon nanotubes with ppm level of impurities

Abstract

Abstract Here multi‐walled carbon nanotubes (MWNT) of different average diameters with ppm level purity were produced by a low temperature C 2 H 4 pyrolysis on Fe‐Co type catalysts combined with forthcoming graphitization at 2200–2800 °C in argon flow. Annealed nanotubes were characterized with X‐ray fluorescent analysis, BET surface measurements, HR TEM, X‐ray diffraction, DTA analysis, and measurements of temperature and magnetic field dependences of conductivity. The graphitization of MWNT results in removal of residual catalyst metal impurities, reduction of the wall defects, and closure of nanotube tips. It was found that extent of these effects depends on MWNT diameters. It was proposed that the graphitization is caused by a significant thermal displacement and diffusion of carbon atoms at temperatures higher the Debye temperature.