Arc Process Parameters for Single-Walled Carbon Nanotube Growth and Production: Experiments and Modeling

Collarets rich in single-walled carbon nanotubes (SWCNTs) have been grown using a direct current arc method. Arc process parameters such as current, pressure, and anode to cathode distance were varied experimentally and by modeling to provide an optimal working window. The best collaret yields were obtained when helium was used as a buffer gas. Mixing helium with argon in the buffer permits controlling nanotube diameters. In addition to an experimental study, a modeling approach was developed assuming local thermal equilibrium and homogenous and heterogeneous neutral chemistry. The gas-phase chemical model involves 81 neutral carbon species (C₁, C₂,..., C₇₉, C_60F, C_70F) and 554 reactions with rates taken from data of Krestinin and Moravsky. Axial profiles of temperature, C atom, C₂ radical, and fullerene distributions in the reactor are predicted as a function of process parameters. Carbon nanotube growth is considered by a set of surface reactions simulating open nanotube growth. Because nanotube surface chemistry is controlled by the local terminated bond and not by the bulk nanotube bond, a mechanistic approach based on the formal resemblance between the bonding and the structure of open nanotube and other carbon surfaces is proposed to explain nanotube growth. Predicted growth rates are in the range of 100 to 1000 m/min.