Most manufacturing methods, which use a metal catalyst to form the tubes, have several drawbacks that have impeded development of SWCNTs’ numerous applications. NASA researchers have discovered a simple, safe, and inexpensive method to create SWCNTs without the use of a metal catalyst.
Traditional catalytic arc discharge methods produce an “as prepared” sample with a 30% to 50% SWCNT yield. NASA’s method produces SWCNTs at an average yield of 70%.
Because NASA’s process does not use a metal catalyst, no metal particles need to be removed from the final product. Eliminating the presence of metallic impurities results in the SWCNTs exhibiting higher degradation temperatures (650 °C rather than 500 °C) and eliminates damage to the SWCNTs by the purification process.
Researchers used a helium arc welding process to vaporize an amorphous carbon rod and then form nanotubes by depositing the vapor onto a watercooled carbon cathode. Analysis showed that this process yields bundles, or “ropes,” of single-walled nanotubes at a rate of 2 grams per hour using a single setup.
This process received a Nanotech Briefs Nano 50 award
Hat tip to Roland Piquepaille's Technology Trends which also has other links on this topic