Fabrication of Carbon Nanotubes

The most common method used to fabricate carbon nanotubes is electric-arc discharge. An electric arc is an electrical breakdown of a gas which produces an ongoing plasma discharge, similar to the instant spark, resulting from a current flowing through normally nonconductive material such as air. The arc occurs in the gas-filled space between two conductive electrodes (often made of carbon) and it results in a very high temperature, capable of melting or vaporizing just about anything. So this process takes place like this: 1) a current is run through an anode, or a positively charged piece of carbon, 2) then this current jumps through a certain type of plasma material to a cathode, or a negatively charged piece of carbon, where there is an evaporation and deposition of carbon particles in through the plasma, 3) finally an outer hard-shell region made of decomposed graphite is formed and an inner core region with loosely packed columns which consist of straight, stiff multishell carbon nanotubes and closed polyhedral particles (also known as carbon nanoparticles). These columns grow at a rate of approximately 1mm per minute on the cathode surface. The best result of carbon nanotubes and nanoparticles from the anode that can be obtained is about 25%. The average temperature in the plasma where the nanotubes are formed is very high at 4000 K (about 6740 degrees F).