Over the past few years, carbon nanotubes have developed into a major object of research in nanotechnology, materials science and electronics. Because of their outstanding mechanical stability and electric transport properties, they have become one of the most popular pure carbon materials.
Carbon nanotubes are cylindrical tubes made of carbon atoms with an inner diameter > 0.9 nm. They are used, for example, to produce field emitters with high angular current emission, fillers in composite fabrication or nanoscale bearings.
For the heat treatment of carbon nanotubes, high temperatures over 2000°C are required to remove structural defects, like metallic impurities and vacancies. High temperatures are also required to change the structure of the tubes themselves from a single-walled carbon nanotube (SWNT) to a double-walled carbon nanotube (DWNT) or even to a multi-walled carbon nanotube (MWNT).
Both DWNTs and MWNTs are much more stable compared to their single-walled equivalents. The structural changes to create DWNTs and MWNTs occur at a temperature between 2000°C and 2800°C in an Argon atmosphere.