Nanotubes for the Mass Market
Jun 17, 1998
The remarkable properties of carbon nanotubes could lead to a wide range of applications ranging from smog composite materials to flat panel displays. However, research into the properties of carbon nanotubes has been limited by the cost of the materials - $5, 000 a gram - and a complex manufacturing process. Charles Howard Olk from General Motors ( Patent 5753088) has now simplified part of the production process, which could lead to the development of a large-scale manufacturing plants.
Carbon nanotubes - which can be thought of as a rolled-up graphite sheet - were discovered in 1991. One way to produce large quantities of nanotubes is to place two water-cooled carbon electrodes 1mm apart in a vacuum chamber filled with an inert gas such as argon. A high-current arc between the electrodes creates nanotubes on the negative electrode while removing carbon from the positive electode. A scraper then pushes the nanotubes to the floor of the chamber at regular intervals. As the positive electrode is 'eaten' away by the process, one of the electrodes has to be moved towards the other to retain the 1 mm gap. However, the need for these moving parts inside the vacuum chamber increases the complexity of the manufacturing process. Olk overcomes this problem by submerging the electrodes in a tank filled with liquid nitrogen or argon, avoiding the need for a vacuum chamber. Mechanisms for moving the electrodes can be positioned above the tank in the open air, simplifying the equipment and the production process.