Fraunhofer IWS Dresden has developed a process suitable especially for the mass production of single-walled carbon nanotubes. The single-walled carbon nanotubes are produced inside a reactor during a pulsed arc evaporation of carbon.
The diameters of the produced carbon nanotubes are between 1.0 and 1.6 nm. This corresponds to about 1 / 10 000 of the human hair. After the production the tube length lies in the range of several micrometers. Carbon nanotubes then show a metallic conductivity or semiconductivity depending on their diameter. The proportion of semiconducting to metallic conducting carbon nanotubes is in general between two thirds and one third. This proportion, however, can be specifically varied with the process developed at the Fraunhofer IWS and is yet another characteristic feature of the process. Moreover, the carbon nanotubes have a very low defect density. So there are hardly any defects with the hexagonal arrangement of the atoms.
The Fraunhofer IWS is currently one of the few institutes worldwide which is able to produce the single-walled carbon nanotubes on a kg-scale. The process seems to be very promising for the industrial mass production. It allows for the development of attractive applications based on the excellent electrical, thermal and mechanical properties of the single-walled carbon tubes.
SWCNT synthesis is possible via physical vapor deposition (PVD) processes. In contrast to the commonly used continuous arc process, IWS engineers use a unique pulsed arc process. A pilot line was set up, which includes numerous in-house developments.
The manufacturing process is continuous and shows the greatest potential for SWCNT mass production compared to alternative approaches (PVD: continuous arc process, laser ablation and chemical vapor deposition (CVD): thermal CVD, high pressure carbon monoxide (HiPCO)-process).
Principle design of the IWS SWCNT manufacturing line based on pulsed arc technology. Right: synthesis reactor with anode and cathode, left: second part of the reactor for functionalization processes.