MECHANISM OF CARBON FILAMENTS AND NANOTUBES FORMATION ON METAL CATALYSTS

摘要

The consideration of the formation mechanisms of carbon deposits on surface metal catalysts led us to conclusion that the majority of these mechanisms include some common steps. The most important of which are the formation of metal or metal carbide particle oversaturated with carbon atoms and the nucleation of carbon deposits on the metal surface. A thermodynamic analysis of the carbon nucleation on the metal surface was performed. The master equation for the dependence of critical radius of the carbon nucleus on the reaction parameters, such as the reaction temperature, the catalyst nature, the supersaturation degree of catalyst particle by carbon was obtained. This equation and the phase diagram approach were used for a discussion of the different scenarios of carbon deposit formation, namely, encapsulated metal particles, carbon fibers and filaments, bamboo-like nanotubes, multi-wall and single-wall carbon nanotubes.