Growth of metal catalyst nanoparticles in hydrocarbon-rich atmosphere of arc discharge for synthesis of carbon nanotubes

A direct current (DC) arc discharge is a widely used method for industrial-scale production of single-walled carbon nanotubes (SWCNT). A high-selectivity synthesis of SWCNT requires ultra-fine, typically a few nanometers in diameter, catalyst particles, which is challenging to achieve in harsh arc environments involving high temperatures, ablation of electrode materials, convection, and instabilities. Here, we explore how the size of metal catalyst nanoparticles is affected by a hydrocarbon-rich atmosphere of the DC arc. In this arc, iron nanoparticles are produced by the evaporation of an anode, made from low-carbon steel. Methane admixture into argon gas serves as a carbon source. Electron microscopy and elemental analysis suggest that hydrocarbons decompose on iron clusters forming a carbon shell, which limits further iron particle growth. Experimental observations are explained using an aerosol growth model. The results demonstrate the potential to manipulate the catalyst particle size in hydrocarbon arc environments.