About Nanotubes

Nanotubes, discovered in 1991, are a new form of carbon. With four electrons available for bonding, the carbon atom can combine with others in a number ways and produce many useful materials. For instance, diamond, as shown in the diagram, has each carbon atom bonded to four neighbors in three dimensions, making diamond by far the hardest natural substance found on Earth.

Arrangements of carbon atoms...

in diamond

in graphite

in a buckyball

(images courtesy of
Institut Laue-Langevin, Grenoble)

A much more common form of carbon—graphite—is what we call “lead” in our pencils. Unlike diamond’s three-dimensional structure, the carbon atoms in graphite bind to three others in hexagonal two-dimensional sheets, which slip past each other easily, so the graphite slides off the pencil point and onto the paper. See the diagram for the structure of graphite.

An unexpected new form of carbon, the buckyball, was discovered in 1987, in the soot left behind when a high electric current makes an arc between carbon electrodes. Buckyballs are closed three-dimensional structures, and they are very strong. The diagram shows the simplest buckyball structure, C⁶⁰.

This same soot from carbon arcs can yield another new form of carbon, the nanotube. As their name suggests, nanotubes are quite small—their diameter is only a few nanometers, less than one ten-thousandth the diameter of a human hair. (More information about the Nanoscale) Nanotubes have been grown up to a millimeter long.

To picture a nanotube, imagine rolling up a sheet of graphite to make a narrow cylinder, as shown in the diagram. Each carbon atom is still bonded to its three nearest neighbors, and this array of bonds makes nanotubes 100 times stronger than steel at only about one sixth the density. Moreover, nanotubes have useful electrical properties that may lead to all sorts of applications.

Side view of nanotube showing network of interlocked carbon atoms (Copyright V. H. Crespi. Distributed under the Open Content License.)