TEXAS - TUBULAR BALLS
"Carbon Chemistry: Tubular Balls," Science and Technology column of The Economist, 3 August 1996, p 70.
Nanotubes (or buckytubes as they are sometimes known) are related to the buckyball (Buckminsterfullerene) which was discovered in 1985 by Dr. Richard Smalley (a chemist at Rice University, Houston, Texas) and Harold Kroto (University of Sussex, Britain). The buckyball consists of 60 carbon atoms at the vertices of a shape known as a truncated icosahedron, in which each carbon atom is linked to three of its neighbors.
Nanotubes are similar in concept, each carbon atom also has three links. But the models of this molecule look more like cylinders made of chicken wire instead of soccer balls. Over the past few years, chemists have created quite a collection of various shapes, but they have not yet made anything practical. "Many uses have been proposed for the original 60-carbon fullerenes lubricants, catalysts, superconductors and even anti-viral agents. But the only industry the buckyball has really revolutionized is the generation of scientific papers."
Buckytubes, the optimists hope, may change that. Recent research has confirmed that they are the strongest fibers known. Researchers also found that they can conduct electricity, like metals. And if nanotechnology is destined to be more than science fiction, then buckytubes seem to be the right components to build with.
Carbon atoms bonding with each other cling very tightly hence the hardness of diamonds, a form of carbon in which each atom is linked to four neighbors. Carbon fibers used as reinforcement have long exploited this fact both strongly and lightly, in uses ranging from tennis rackets to aeroplanes. But these carbon fibers are rather crude, patchwork strips of graphite "pasted" into columns.
The strongest carbon fiber, in theory, should be a seamless cylinder of mutually binding carbon atoms - a nanotube.
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Measuring this strength is challenging since nanotubes are 1,000 times skinnier than most carbon fibers. In June Michael Treacy and Thomas Ebbesen, at the NEC Research Institute in Princeton, New Jersey, announced that they had managed to measure a tube's strength indirectly. Dr. Treacy, trying to look at individual nanotubes through an electron microscope, found that he could not bring them into focus, and realized that this was because they were vibrating. He and Dr. Ebbesen then realized that, by applying standard engineering theory to the vibrations, they should be able to calculate a tubes stiffness from the rate at which its vibrations grew as its temperature rose. Buckytubes, they discovered once they had done the relevant measurements, are stronger than steel, carbon fibers and even diamonds.
Unlike diamonds, buckytubes can sometimes conduct electricity. This has been suspected since 1991, but it had not, until recently, been put rigorously to the test. A few months ago Dr. Ebbesen decided do so. He worked with Henrik Lezec at Micrion Europe GmbH, a firm in Munich. Together they were able to attach four tiny electrical leads to nanotubes, using a technique similar to that with which electrical circuits are laid down on silicon chips. They announced their results in July. Some tubes, they discovered, conduct as well as metals that is, very well indeed. Others, whose carbon atoms are arranged differently, are superb insulators only one millionth as willing as their conductive cousins to pass electrons between their atoms.
To make such a discovery useful, buckytubes must be able to be manufactured reasonably easily. Dr. Smalley thinks he can do that now. Instead of making nanotubes with an electric arc using graphite electrodes, which produced nested concentric tubes, Smalley is vaporizing graphite with laser beams. This produces bundles of single nanotubes, most having the same diameter and the correct geometry to conduct electricity. This is a distinct advantage to researchers. But, at one gram of nanotubes per day, production won't be big business quite yet.
Summary by D. Torres
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Oct. 23, 1996.