Carbon has a wide range of macroscopic forms—coal, ash, graphite, diamond. A relatively new form of carbon, nanotubes, is becoming a revolutionary material in many ways. Carbon nanotubes (CNTs), or buckytubes, are microscopic cylindrical cages of carbon atoms. Each nanotube is essentially a giant molecule with a diameter of about one nanometer and usual length of several millimeters. Multi-walled CNTs (which consist of nanotubes inside larger ones) have very little friction between layers. Individually a CNT has a greater strength to weight ratio than steel and can conduct heat and electricity better than copper.
So far the main use for CNTs has been to improve other materials. Adding them to mixture-based materials improves strength and durability, such as making crack-resistant concrete. On their own, however, carbon nanotubes can be much more impressive. Imagine a cable made of carbon nanotubes that extends many miles from the ground to a space station in geosynchronous orbit. Such a lengthy cable made of any other material would break from its own weight if not the tension of securing the space station. The incredible tensile strength of CNTs might make a cable of that magnitude possible. The cable would allow a “space elevator” to climb up into the heavens without need of rockets. Wouldn't it be incredible to ascend into outer space without the huge rocket engines but with a hi-tech elevator?
The electrical properties of CNTs make them attractive for improving electronic products. Recent research indicates that nanotubes could be used to speed up DNA sequencing. Chinese researchers have discovered that a sheet of CNTs can be used as a speaker. When a varying electrical current is applied, the CNTs heat up nearby air accordingly. The changing temperature causes rapid changes in pressure which we hear as sound. Normal speakers use vibration to produce changes in air pressure, and they can be rigid, fragile, and bulky. This new speaker, however, is as thin as paper, flexible as fabric, and turns transparent when stretched. Stretching, bending, and even cutting the CNT sheet into different shapes will not significantly affect sound quality.
Solar panels made with carbon nanotubes are also thin, flexible, and lightweight. These unique properties may one day lead to the replacement of today's thick, heavy, and fragile silicon solar panels. CNTs can not only improve how we obtain energy, but they can help us store it. Paper embedded with CNTs constitutes a “paper battery”. It looks and feels like black paper, but it can store electricity and function at greater temperature extremes than many conventional batteries. Medical researchers are interested in this technology because paper batteries can be powered by blood or urine. Imagine a pacemaker that is charged by blood passing through the heart.
While CNTs have astounding properties, there are some major hurdles in the way of success. The extraordinary capabilities are undermined by defects which can be difficult to prevent at the nano-scale. Over the last ten years the cost (per gram) has gone from $500+ to $50. This decreasing trend is promising, but for now it is still too expensive to produce CNTs in large quantities. About large quantities: it is still very difficult to make nanotubes longer than a few centimeters.
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