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Buckyballs' supercool spring surprise.

Buckyballs' Supercool Spring Surprise

For sports fans spring brings on baseball mania; for scientists this year, it's the season of the buckyball. Doped, bounced, enlarged, decorated, modified, even chilled, this 60-atom member of the fullerene family of all-carbon molecules shows promise as a chemical All-Star.

At the American Chemical Society meeting in Atlanta this week, researchers fueled the Fullerene fever with reports that the soccerball-shaped [C.sub.60] becomes superconducting when chilled and that the fullerences are so hospitable to chemical substitutions and additions that they could lead to a entirely new class of materials. Scientists also described a more efficient way to make fullerences and detected a family member with 200 carbon atoms.

"It's the biggest, cheapest hollow molecule we've ever seen," Richard E. Smalley of Rice University in Houston told SCIENCE NEWS. "We're going to be making fullerenes in truckload quantities for a few dollars a pound, and that will make all sorts of things possible."

Physicist Arthur F. Hebard of AT&T Bell Laboratories in Murray Hill, N.J., surprised scientists at the meeting with evidence that [C.sub.60] films "doped" with potassium become superconductors when chilled to 18 kelvins -- a much higher temperature than he and his colleagues expected, he says. Graphite, another carbon material, needs much colder conditions to lose all electrical resistance. Hebard and others speculate that the fullerene film's three-dimensional structure enhances its superconductivity. However, "there's not much incentive to think about [practical] applications," notes Arthur W. Sleight of Oregon State University in Corvallis. Ceramics have already shown superconductivity atw higher temperatures, and potassium is so reactive that the doped from cannot be exposed to air.

Doping is the process of adding impurities to an otherwise homogeneous material. The Bell Labs researchers, who detail their experiments in the April 18 NATURE, added potassium to [C.sub.60] molecules in thin films, creating mixtures in which the potassium atoms settled in the spaces between the buckyballs.

Using a different kind of doping, Smalley has succeeded in replacing some carbon atoms with impurities in the soccerball structure itself without destroying the integrity of the molecule. He calls the results "dopyballs." So far, the says, he has managed to tuck three, and perhaps four, boron atoms and a few nitrogen atoms into the molecule. This impurity-inserting process makes silicon a semiconductor, and it could do the same for fullerene crystals, Smalley says.

After observing half a dozen reactions between fullerenes and other chemicals, organic chemist Fred Wudl of the University of California, Santa Barbara, reports that fullerenes "love electrons" and bond easily with substances that readily give them up. "The bottom line is you can attach [a fullerene] to anything," he says. "It's a new starting material for making a whole new family of organic compounds."

Wudl says he plans to publish blue-prints for a simplified, benchtop fullerene reactor assembled in less than a week with store-bought equipment and about $60 worth of laboratory glassware. "Any chemist can do it," he says.

Other advances have yielded larger molecules and improved the efficiency of fullerene production. At the University of California, Los Angeles, physical chemist Robert L. Whetten uses an apparatus that resembles a lightbulb with a graphite filament. When heated by electrical current, the filament gives off a soot containing about 40 percent fullerene--up from about 15 percent in earlier techniques. About half of these fullerenes contain more than 60 carbons, he says.

By dissolving the soot in solvents with ever-higher boiling points, Whetten has extracted ever-larger fullerenes -- up to 200 carbon atoms. His spectroscopic studies confirm that these molecules, which vary in color from golden to red, are related to the magenta [C.sub.60].

In other work, Whetten accelerated fullerene molecules to about 15,000 miles per hour and crashed them against stainless steel barriers, only to find that the molecular balls simply bounced back. These tests show that charged fullerenes are rugged enough to stay intact if used as propellants in space vehicles. "It's resilient beyond any particle that's been known," Whetten says.
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Title Annotation:chilling buckminsterfullerene molecules makes them superconducting and hospitable to chemical substitutions
Author:Pennisi, Elizabeth
Publication:Science News
Date:Apr 20, 1991
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