Making the Most of Carbon Nanotubes
The Miracle Material of the 21st Century?
Authored by Ottilia Saxl.
What are carbon nanotubes?
Fullerenes (a form of carbon) were first identified in 1985 as products of experiments in which graphite was vaporized using a laser. The decipherment of the structure of the soccerball-shaped carbon C60 molecule led to the award of the Nobel Prize in 1996 to three researchers, Robert Curl, Sir Harold Kroto, and Richard Smalley.
These C60 molecules were given the quixotic name Buckminster Fullerenes (colloquially now termed ‘bucky balls’) after the architect R Buckminster Fuller, famous for his design of geodesic dome structures. The geodesic design he invented enabled architectural structures possessing great strength to be built of lightweight materials. Similarly, the arrangement of carbon atoms imparts great strength to the C60 buckyballs, and to carbon nanotubes, its cylindrical form, which also boasts many other remarkable properties.
Carbon nanotubes consist of long, thin cylinders of carbon whose diameter is very small (usually only a few nanometres) but whose length can be of the order of a millimeter or more, giving a truly astonishing length-to-width ratio. Apart from Single Walled Nano Tubes (SWNTs), carbon nanotubes can exist as Multiple Walled Nano Tubes (MWNTs) – which are cylinders inside other cylinders, and exhibit further extraordinary properties.
What are the properties of carbon nanotubes?
The wide range of electronic, thermal, and structural properties of carbon nanotubes vary according to the different diameter, length, and direction of ‘twist’ of the nanotube. Many applications arise from the surprising and desirable properties they exhibit, some of which are already being used in new and improved products. For example, carbon nanotubes are highly conductive both to electricity and heat - they exhibit an electrical conductivity as high as copper, and thermal conductivity as great as diamond.
Nanotubes can be either metallic or semiconducting, leading to the potential for developing nanowires, nanoscale electrical components and nanoelectromechanical systems. They therefore offer amazing possibilities for creating future nanoelectronic devices, circuits and computers. Carbon nanotubes also have extraordinary mechanical properties - they are 100 times stronger than steel, while only one sixth of the weight. These mechanical properties offer huge possibilities - for example, in creating nanocomposites for a variety of application scenarios ranging from military to aerospace to medicine.
Applications of carbon nanotubes
Many potential applications have been proposed for carbon nanotubes, including:
- nanometer-sized semiconductor devices, probes and interconnects
- conductive and high-strength specialist composites
- devices for energy storage and energy conversion
- field emission displays and radiation sources
- hydrogen storage media
Research is expected to lead to new materials, lubricants, coatings, catalysts, electro-optical devices, and medical applications.
The cost, purification, separation of nanotube type (SWNTs from MWNTs), constraints in processing and scaling up, and assembly methods are still hurdles for some applications which are in the process of being overcome. However, some applications are already manifest in products in the market place, others are under development. For example, tennis racquets containing carbon nanotubes are already on the market. The nanotubes are used to re inforce the frame and improve the racquet's ability to absorb shocks. Re inforced tennis racquets are only one of many potential applications. Some Carbon nanotubes can be mixed with many different materials such as plastics and textiles for lightweight bullet-proof vests.
According to engineers at the Fraunhofer Technology Development Group TEG in Stuttgart the greatest potential for creating new products at the present time lies in harnessing the electrical properties of light and robust nanotubes to generate heat. Potential applications range from electric blankets and heatable aircraft wings that no longer ice up, through to wallpaper heating for cold walls.
Not to be outdone by their nanotube cousins, the bucky ball, the only molecule composed of a single element, forms a hollow spheroid which is already a focus of attention by medical researchers for its potential for in novel drug delivery systems.
Carbon nanotubes sound like a product designer’s dream. But like many technologies that offer benefits, there are risks which have to be addressed sensibly in order that the full benefits can be realized. We have all learned how to handle electricity, gas, steam and even cars and aeroplanes in a safe manner because we need their benefits. The same goes for carbon nanotubes. Mostly they will be perfectly safe, embedded within other materials, such as polymers.
There is some possibility that free carbon nanotubes of a specific length scales may pose health threats if inhaled, particularly at the manufacturing stage. Industry is very conscious of this possibility, and is endeavouring to ensure that any potential hazard is minimised, so that we can all reap the benefits and promise of this new wonder material.