Carbon nanotube

Carbon nanotubes are tubular carbon molecules that have properties that make them potentially useful in nanotechnology. They exhibit unusual strength and unique electrical properties, and are extremely efficient conductors of heat.

A nanotube is a structure similar to a fullerene, only the carbon atoms are rolled into a cylinder instead of a sphere; each end is capped with half a fullerene molecule. They are only one nanometer wide (on the order of one ten-thousandth the width of a human hair), and their length can be millions of times greater than their width.

In 1889, two British men received a US patent on producing "hair-like carbon filaments" from methane. In the 1960s and 1970s, groups at the National Carbon company in Parma, Ohio, United States and the University of Canterbury in Christchurch, New Zealand, produced and identified the tubes.

Nanotubes were rediscovered in 1991 by Sumio Iijima. It has since been discovered how nanotubes can be produced in large quantities. The price of nanotubes are still in the $100 dollar per gram range which prohibits any large scale use of them; when large-scale nanotube production is implemented, however, it is assumed that prices would be far lower, to around five cents per gram or so.

Although it was not known until after the discovery of carbon nanotubes in the lab, carbon nanotubes are naturally found in candle flames and some forest fires, although they break down when the flames go out.

Nanotubes can be opened and filled with materials such as biological molecules, raising the possibility of applications in biotechnology. They can be used to dissipate heat from tiny computer chips. The strength and flexibility of carbon nanotubes makes them of potential use in controlling other nanoscale structures, which suggests they will have an important role in nanotechnology engineering. Though it is debatable if nanotube materials can ever be made with a tensile strength approaching that of individual tubes, composites may still yield incredible strengths potentially sufficient to allow the building of such things as space elevators, extremely deep bunker buster bombs and more.

One use for nanotubes that has already been developed is as extremely fine electron guns, which could be used as miniature cathode ray tubes in thin high-brightness low-energy low-weight displays. In this type of display, a group of many tiny CRTs would provide the electrons to hit the phosphors of one pixel, instead of having one giant CRT whose electrons are aimed using electric and magnetic fields. These diplays are known as Field Emission Displays (FEDs) A nanotube formed by joining nanotubes of two different diameters end to end can act as a diode, suggesting the possibility of constructing electronic computer circuits entirely out of nanotubes. Nanotubes have been shown to be superconducting at low temperatures.

Current Progress

In April of 2001, IBM announced it had developed a technique for automatically developing pure semiconductor surfaces from nanotubes.

Other applications for nanotubes that are currently being researched include high tensile strength fibers. Two methods are currently being tested for the manufacture of such fibers. A French team developed a liquid spun system that involves pulling a fiber of nanotubes from a bath which yields a product that is approximately 60% nanotubes. The other method, which is simpler but produces weaker fibers uses traditional melt-drawn polymer fiber techniques with nanotubes mixed in the polymer. After drawing, the fibers can have the polymer burned out of them to make them purely nanotube or they can be left as they are. These technologies are currently being developed by Alexander Lobovsky with Advanced Fiber Engineering, LLC and the University of Texas NanoTech Institute

High purity (80%) nanotubes with metallic properties can be extracted with electrophoretic techniques. See: Krupke and Hennrich

These take advantage of the incredible aspect ratio and strength of nanotubes. Computer storage devices using nanotubes are currently in the prototype stages. Both high speed non-volatile memory which can be used to replace nearly all solid state memory in computers today, and high density storage that may replace hard drives, are being devoloped. Major limiting factors in development include orienting the nanotubes, which tend to tangle because of their length, and their price.

Nanotubes are already replacing fiberglass in production car bumpers because of their high strength and the electrical conductivity they lend to the product.

Political Implications

The large number of potential applications for carbon nanotubes has caused some controversy in the political world. Some people believe that carbon nanotubes could be used in military technology, such as missiles, which could eventually lead to an arms race or similar conflict. Some even believe in the possibility of self-replicating "nanobots," which could be used by the military to kill entire populations. A few people believe that if such bots got out of hand, they could wipe out the human race. However, claims regarding such bots are dismissed by many leading scientists, including Nobel Prize winner Richard Smalley, of Rice University. In addition, MIT is working on military jackets utilizing carbon nanotubes for ultrastrong fibers and for monitoring a soldier's conditions.

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