Large-scale production of single-walled carbon nanotubes by induction thermal plasma

High quality single-walled carbon nanotubes (SWNT) have been synthesized at large scales by the method of direct evaporation of carbon black and metallic catalyst mixtures, using induction thermal plasma technology. The processing system consists mainly of an RF plasma torch, which generates a plasma jet of extremely high temperature (∼15 000 K), with a high energy density and abundance of reactive species (ions and neutrals). With the present reactor system, it has been demonstrated that carbon soot product which contains approximately 40 wt% of SWNT can be continuously synthesized at the high production rate of ∼100 g h−1. The processing parameters involved have been examined closely in order to evaluate their individual influences on SWNT synthesis. The results have shown that the quality and purity of the SWNT produced are critically affected by the grade of carbon black, the plasma gas composition and the metallic catalyst employed. Theoretical calculations, including thermodynamic and two-dimensional thermal flow analyses, have also been performed to determine the optimal process environment most suitable for SWNT synthesis and to obtain a better understanding of the effects of process parameters. Finally, product comparisons have been made against other reference materials using Raman spectroscopy, which has shown that the quality of thermal plasma-grown SWNT is superior to that of arc discharge-grown SWNT and approaches the quality of laser-grown SWNT. This result confirms that the induction thermal plasma technology developed in this work is one of the most promising methods for the production of high quality SWNT at large scales for commercial uses.