Wrapping carbon into superstrong tubes.What could one do with an ultrastrong tube only a few nanometers wide but hundreds of kilometers long? In his 1978 novel The Fountains of Paradise, Arthur C. Clarke Sir Arthur Charles Clarke, CBE (born 16 December 1917) is a British science-fiction author and inventor, most famous for his novel , and for collaborating with director Stanley Kubrick on the . imagined using such "hyperfilaments" to construct an elevator to a tethered Attached to a data or power source by wire or fiber. Contrast with untethered. space station in synchronous orbit synchronous orbit
A geostationary orbit.
An orbit of a satellite around a rotating body, such that one orbit is completed in the time it takes for the body to make one revolution on its around Earth.
Although Clarke's space elevator A space elevator is a proposed megastructure designed to transport material from a celestial body's surface into space, first conceived by Konstantin Tsiolkovsky. Many different types of space elevators have been suggested. remains firmly embedded in the realm of science fiction, his notion of fabricating extremely tough, microscopically thin, flawless fibers from carbon gained credibility with the discovery that sheets of carbon atoms can wrap themselves into microscopic tubes (SN: 11/16/91, p. 310). Produced in a high-voltage electric arc, the resulting nanotubes appear to have perfectly formed structures, consisting of networks of carbon atoms arranged in a hexagonal hex·ag·o·nal
1. Having six sides.
2. Containing a hexagon or shaped like one.
3. Mineralogy pattern.
"This is a new kind of crystal;' says chemist Richard E. Sinalley of Rice University in Houston. If it were possible to manufacture such tubes in meter lengths, "they would be the strongest fibers that we could ever make from anything."
Nanotubes normally form as a thick black deposit on the end of a carbon electrode. Close examination of this deposit reveals a fibrous interior and a hard outer shell of fused carbon.
The entire structure seems organized as a hierarchy of tubes, says Thomas W. Ebbesen of the NEC (NEC Corporation, Tokyo, www.nec.com, www.necus.com) An electronics conglomerate known in the U.S. for its monitors. In Japan, it had the lion's share of the PC market until the late 1990s (see PC 98).
NEC was founded in Tokyo in 1899 as Nippon Electric Company, Ltd. Fundamental Research Laboratories in Tsukuba, Japan. The visible fibers consist of bundles, which themselves consist of smaller bundles, and so on, down to the carbon nanotubes. Each nanotube A carbon molecule that resembles a cylinder made out of chicken wire one to two nanometers in diameter by any number of millimeters in length. Accidentally discovered by a Japanese researcher at NEC in 1990 while making Buckyballs, they have potential use in many applications. , in turn, typically consists of two or more tubules nested within one another to form a layered assemblage. These multilayered tubes range from 1 to 20 nanometers wide and up to 3 microns long.
Smalley and his co-workers have now taken a tentative step toward growing such tubes as continuous fibers. Basing their approach on the assumption that high electric fields are largely responsible for keeping nanotubes growing in an orderly fashion, the researchers create a high voltage The term high voltage characterizes electrical circuits, in which the voltage used is the cause of particular safety concerns and insulation requirements. High voltage is used in electrical power distribution, in cathode ray tubes, to generate X-rays and particle beams, to between a carbon electrode and a sharp, needle-like electrode. Then they introduce benzene vapor, or some other hydrocarbon, into the narrow gap between the electrodes.
Using a laser to heat the hydrocarbon molecules and gradually increasing the separation between the electrodes, the researchers create a carbon fiber just 50 nanometers wide and up to a centimeter long. The product, however, lacks the perfection of true nanotubes. Smaller structures branch off from the main fiber at various places along its length. Only tiny portions actually appear tubular.
"We're beginning, but it's still very crude;' Smalley says. "It's not the fullerene fullerene, any of a class of carbon molecules in which the carbon atoms are arranged into 12 pentagonal faces and 2 or more hexagonal faces to form a hollow sphere, cylinder, or similar figure. fiber of our dreams."
The presence of hydrogen from the hydrocarbons may account for some of the defects, but there's no guarantee that this particular approach will ultimately lead anywhere, Smalley admits. He described this work at last week's American Physical Society The American Physical Society was founded in 1899 and is the world's second largest organization of physicists. The Society publishes more than a dozen science journals, including the world renowned Physical Review and Physical Review Letters, and organizes more than twenty science meeting, held in Seattle.
Meanwhile, Ebbesen and his colleagues are exploring ways of stuffing carbon nanotubes with metal atoms to create microscopically thin wires. In earlier work, NEC researchers had managed to introduce lead into nanotubes (SN: 1/30/93, p.69). Because nanotubes normally form with capped ends, lead atoms had somehow broken the seals and entered the tubes.
"We [now] know how to open nanotubes in large quantities in a very simple way," Ebbesen reports. That makes it possible to fill tubes with metals other than lead.