Published November 2003
Carbon nanotubes were discovered by Dr. Sumio Iijima of NEC Corp. (Japan) in the course of his research on fullerenes in 1991. Carbon nanotubes are ultra thin straw-shaped molecules of carbon with diameters of 1-20 nm and lengths of up to 0.1 mm (10,000 nm). Carbon nanotubes (CNTs) are characterized by their surprising strength, which is 5-200 times greater than that of steel at a density just 1/6 that of steel. CNTs can form the world's strongest fiber; their electrical conductivity is higher than that of copper and heat conductivity is higher than that of diamond. Moreover, they are resistant to extreme heat and are lighter than aluminum. Carbon nanotubes also possess superior field emitting properties.
CNTs look promising for use in a variety of applications, including semiconductor and other electronic devices, field emission display (FED) devices, fuel cells, batteries, sensors, catalysts, and composites. In mid-2003, over 25 companies worldwide were already committed to CNT production, and early-stage products incorporating CNTs were already being test marketed. The main drawback to CNTs presently is their high unit production cost. Prices for CNTs have been dropping quickly as process and catalyst technologies advance and scale of production increases, and are expected to continue dropping rapidly for at least another several years.
Most CNTs are produced by one of three processes: arc discharge, laser ablation, or catalytic chemical vapor deposition (CVD). Arc discharge and laser ablation are being used mainly to produce multi-wall CNTs, or MWCNTs for research applications, and laser ablation is being used to produce research quality single-wall CNTs, or SWCNTs. All of the commercial production of MWCNTs is based on the catalytic CVD process. Recently, CNRI of Japan introduced an alcohol-based catalytic CVD process (ACCVD) for more cost-effective production of SWCNTs from a CVD-based process. And laser ablation was adapted to produce a carbon nanohorn product.
Japan has played a key role in the R&D and early commercialization of CNTs during the last decade. This Review brings readers up-to-date on new CNT synthesis, applications, and process commercialization efforts in Japan since 2000, and provides process diagrams and photographs for three new projects to produce SWCNTs more economically. The Review is based in large part on work done by Techno Alliance Corporation (TAC) of Tokyo, Japan as part of a Nanomaterials Report from TAC's program on Advances in Materials Science in Japan.