Reduction of cathode carbon deposit by buffer gas outflow

Abstract

The problem of the cathode carbon deposit arising from the carbon vapor developed by conventional arc discharge plasma during fullerene synthesis is addressed. This carbon deposit significantly reduces fullerene productivity, wastes valuable energy and graphite material, and presents a major obstacle in achieving desirable productivity and scalability. A study of the deposit microstructure and its mechanical and physical properties revealed that the deposit is of a three-dimensional fractal structure having a rigid and microporous structure. Analysis reveals that the graphite evaporation rate determines carbon deposit formation, soot content, fullerene yield, and vapor quality, as well as defines the deposit formation. The buffer gas outflow approach utilizes the injection of a buffer gas into the hot plasma zone, provides quick evacuation of the produced carbon vapor away from the plasma zone, allows usage of large currents and bigger electrodes without a significant reduction of fullerene yield, and reduces the carbon deposit by more then 99%. Based on this work, the elimination of the cathode deposit is a major step in the development of efficient, productive and scalable fullerene and nanotube technology.