The much-heralded and wondrous carbon nanotubes were discovered in 1991. Since then, many new applications have been reported by scientists who are attracted by the potentials of these very miniscule cylinders. Their potential to become the twenty-first century wonder materials has driven an entire industry with big budgets hoping to invent the next super product.

Carbon nanotubes are generally produced by three main techniques: Arc discharge, laser ablation and chemical vapor deposition. New methods being researched right now promise far more economic ways to produce nano particles.

In arc discharge, two carbon electrodes with a catalyst create an arc vapor discharge, and nanotubes grow outward from that carbon vapor. In laser ablation technology, a high-powered laser beam heats a volume of carbon in a methane or carbon monoxide gas. Chemical vapor deposition uses special gasses in plasma-like conditions to deposit carbon tubes directly to a surface. Laser ablation typically produces a smaller amount of cleaner nanotubes, whereas arc discharge methods generally produce large quantities of impure varying types of material. All methods are expensive to set up and run, producing only small amounts of carbon tubes at monumental prices.  

The typical production batch of carbon nanotubes will have a quantity of low-conductivity particles as well as semi-conductive tubes and a small portion of highly conductive particles. The trick is to refine the production process to produce the highest percentage of the type of tube you require.

Carbon tubes are arranged into basic groups according to their wall characteristics: single-walled nanotubes (SWNTs), double-walled nanotubes (DWNTs) and multi-walled nanotubes (MWNTs). There are also subcategories that describe the size of the tube as well as extra features, such as bumps as well as the description of the type of fiber.

Carbon nanotubes of both single-walled and multi-walled varieties combine ultra-iniaturization with exceptionally high structural strength. Carbon tubes have very high surface areas (hundreds of square feet per gram), high melting temperatures (3,500°C) and high Young's modulus strength (1,000 gpa), for a strength 10,000 times that of steel. Some carbon tubes also feature high electrical conductivity of 1,000 s/cm, which is 20 times greater than copper, with corresponding very high thermal conductivity of 3,000 W/m°C or 10 times that of copper. All are highly desired properties.

It really is a matter of size; carbon nanotubes are 1 atom-thick sheets of graphite 125,000 times smaller than a human hair. The typical nano particle is a mere 25 hydrogen atoms wide--compare that to the dime in your pocket at 12,500,000 nanometers. Nanotubes range in diameter from less than one nanometer to about 40 nanometers.  

Separating DWNTs from the SWNTs and MWNTs is the big trick. The problem lies with  firing a metal in a hot gas to manufacture carbon tubes--you also make everything from carbon black (soot) to bucky balls and four to five different carbon tubes and every combination in between. A water bath can be used to separate the different tubes; each one with a different density. By varying the surface tension and density of the water bath, specific tube types will individually float up to be collected.

The carbon nanotube and its super properties are very desirable, but it also shows its bad side by being problematic for integration into our big world.

Carbon tubes tend to conduct only in one direction, and they don't mix well with metals or glues because of the non-wetting surface of the carbon. Carbon tubes do not conduct electrically well when combined in strings with other carbon nanotubes.