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What are Nanotubes?
A nanotube is a cylinder made up of atomic particles and whose diameter is around one to a few billionths of a meter. They can be made from a variety of materials.
Nanotubes vary by the number of cylinders; there are nanotubes made up of a single cylindrical layer but there are also reinforced nanotubes comprised of two or more cylindrical layers (one nanotube cylinder completely encloses another). Wall thickness also differs; some nanotubes are thicker than others. Since nanotubes vary by wall thickness and number of cylinders, the radius of nanotubes is also variable. Moreover, the length of nanotubes is also not universal. Finally, nanotubes can be organic or inorganic, depending on the particles used in nanotube construction.
Carbon Nanotubes
A carbon nanotube (which is the most popular type of nanotube at the moment) is a cylinder which has a wall of single graphite atoms. Its diameter is exactly one nanometer.
A carbon nanotube has exceptional endurance due to its unique sp2 bonding structure. However, at a certain degree of pressure, the nature of the atomic bonding changes and this allows multiple nanotubes to link together and form a longer carbon nanotube chain. Nanotubes of this type are therefore exceedingly strong yet still flexible.
Nanotubes made of graphite atoms also have distinctive electrical properties so they can become conductors or semi-conductors in turn. They can be used in the manufacture of capacitors; by using multiple layers, nanotubes become capable of holding electrical charge. They can also be used in the manufacture of resistors and transistors.
Multiple cylinders of a single nanotube have been found to work well together. The inner cylinder can actually rotate or move inside the outer cylinder without much resistance from the latter. This characteristic can be applied to make special microscopic rotors.
Nanotubes have an amazing potential in a wide variety of fields such as electronics engineering (especially in the manufacture of microscopic chips), optical technologies, nanotechnology, and materials engineering.
Manufacturing Nanotubes
There are several approaches to the commercial manufacture of carbon nanotubes. They include the arc discharge method, the laser-aided vaporization method and the chemical vapor deposition (CVD) method.
The arc discharge method has been accidentally discovered in 1991 when carbon nanotubes were found in the residue of an electrical arc discharge. The laser-aided vaporization method (commonly known as the laser ablation method) involves a graphite board that's enclosed within a high-temperature reactor chamber. A laser is then activated and the graphite board is consequently vaporized. All the while, a non-reactive gas is allowed to escape into the reactor chamber. The vapor inside the chamber is then allowed to cool and carbon nanotubes are formed in result.
The CVD method involves a substrate layer on which surface lie catalytic metal particles. The substrate is placed inside the reactor and heated while two types of gas are fed into the reactor. As the carbon-containing gas passes over the heated metal particles, pure carbon is separated from its base compound and carbon nanotubes are formed.
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