All About Carbon Nanotubes

Scientists don't know everything about carbon nanotubes or CNTs for short, but they do know that they are very thin lightweight hollow tubes made up of carbon atoms. A carbon nanotube is like a sheet of graphite that is rolled into a cylinder, with distinctive hexagonal latticework making up the sheet. Carbon nanotubes are extremely small; the diameter of one carbon nanotube is one nanometer, which is one ten-thousandth (1/10,000) the diameter of a human hair. Carbon nanotubes can be produced to varying lengths.

Carbon nanotubes are classified according to their structures: single-wall nanotubes (SWNTs), double-wall nanotubes (DWNTs), and multi-wall nanotubes (MWNTs). The different structures have individual properties that make the nanotubes appropriate for different applications.

Because of their unique mechanical, electrical, and thermal properties, carbon nanotubes present exciting opportunities for scientific research and industrial and commercial applications. There is much potential for CNTs in the composites industry.

How Are Carbon Nanotubes Made?

Candle flames form carbon nanotubes naturally. In order to use carbon nanotubes in research and in the development of manufactured goods, however, scientists developed more reliable methods of production. While a number of production methods are in use, chemical vapor deposition, arc discharge, and laser ablation are the three most common methods of producing carbon nanotubes.

In chemical vapor deposition, carbon nanotubes are grown from metal nanoparticle seeds sprinkled on a substrate and heated to 700 degrees Celsius (1292 degrees Fahrenheit). Two gases introduced into the process start the formation of the nanotubes. (Because of reactivity between the metals and electric circuitry, zirconium oxide is sometimes used in place of metal for the nanoparticle seeds.) Chemical vapor deposition is the most popular method for commercial production.

Arc discharge was the first method used for synthesizing carbon nanotubes. Two carbon rods placed end-to-end are arc vaporized to form the carbon nanotubes. While this is a simple method, the carbon nanotubes must be further separated from the vapor and soot.

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Laser ablation pairs a pulsing laser and an inert gas at high temperatures. The pulsed laser vaporizes the graphite, forming carbon nanotubes from the vapors. Like with the arc discharge method, the carbon nanotubes have to be further purified.

Advantages of Carbon Nanotubes

Carbon nanotubes have a number of valuable and unique properties, including:

• High thermal and electrical conductivity
• Optical properties
• Flexibility
• Increased Stiffness
• High tensile strength (100 times stronger than steel per unit of weight)
• Lightweight
• Range of electro-conductivity
• Ability to be manipulated yet remain strong

When applied to products, these properties provide tremendous advantages. For example, when used in polymers, bulk carbon nanotubes can improve the electrical, thermal, and electrical properties of the products.

Applications and Uses

Today, carbon nanotubes find application in many different products, and researchers continue to explore creative new applications.

Current applications include:

• Bicycle components
• Wind turbines
• Flat panel displays
• Scanning probe microscopes
• Sensing devices
• Marine paints
• Sports equipment, such as skis, baseball bats, hockey sticks, archery arrows, and surfboards
• Electrical circuitry
• Batteries with longer lifetime
• Electronics

Future uses of carbon nanotubes may include:

• Clothing (stab-proof and bulletproof)
• Semiconductor materials
• Spacecraft
• Space elevators
• Solar panels
• Cancer treatment
• Touch screens
• Energy storage
• Optics
• Radar
• Biofuel
• LCDs
• Submicroscopic test tubes

While high production costs currently limit commercial applications, the possibilities for new production methods and applications are encouraging. As understanding of carbon nanotubes expands, so will their uses. Because of their unique combination of important properties, carbon nanotubes have the potential for revolutionizing not only daily life but also scientific exploration and healthcare.

Possible Health Risks of Carbon Nanotubes

CNTs are a very new material with little long term history. Although none have yet fallen ill as a result of nanotubes, scientists are preaching caution when handling nano particles. Humans have cells that can process out toxic and foreign particles such as smoke particles. However, if a certain foreign particle is either too big or too small, the body might not be able to capture and process out that particle. This was the case with asbestos.

The potential health risks are not cause for alarm, however, people handling and working with carbon nanotubes should take the necessary precautions to avoid exposure.