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October 20, 2003
Volume 81, Number 42
CENEAR 81 42 pp. 31
ISSN 0009-2347


CHEMICAL LANDMARK

CARBON FIBER RESEARCH HONORED

Site of breakthrough development in Parma, Ohio, is designated a chemical landmark

AALOK MEHTA, C&EN WASHINGTON

In 1979, Arthur C. Clarke's novel "The Fountains of Paradise" popularized the concept of a space elevator--one end planted on the equator, the other tethered 40,000 km above Earth to a satellite in geosynchronous orbit--as an efficient way to shuttle material and people back and forth from space. His fictional engineer solves the structural problems associated with building such an enormous structure by using an ultrahigh-strength monofilament carbon fiber.

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RECOGNITION McClelland (right) presents a plaque honoring the discovery of high-performance carbon fibers to GrafTech's Batty. PHOTO BY JUDAH GINSBERG
The space elevator itself remains the stuff of dreams, but high-performance carbon fibers have made it to the final frontier: In addition to uses in aircraft brakes and bodies, lithium batteries, sports equipment, and construction materials, such fibers are also vital components of space structures and the wingtips of the space shuttle. The American Chemical Society designated a key facility in the development of these fibers, the Union Carbide (now GrafTech International) research center in Parma, Ohio, as a National Historic Chemical Landmark on Sept. 17.

Nina I. McClelland, chair of the ACS Board of Directors, presented a plaque to Lionel Batty, director of corporate research and development at GrafTech, at the event.

"The men and women who have worked at the Parma Technical Center of Union Carbide transformed our vision of what's possible for more than two amazingly productive decades," McClelland said. Dan D. Edie, Dow Chemical Professor of Chemical Engineering and director of the Center for Advanced Engineering Fibers & Films, also spoke.

The plaque reads: "Scientists at the Parma Technical Center of Union Carbide Corporation (now GrafTech International) performed pioneering research on carbon fibers, for their weight the strongest and stiffest material known at the present time. In 1958, Roger Bacon demonstrated the ultrahigh strength of graphite in filamentary form. Seven years later continuously processed high performance carbon yarn, from a rayon precursor, was commercialized. In 1970, Leonard Singer produced truly graphitic fibers, leading to the commercialization of carbon yarn derived from liquid crystalline pitch. Carbon fibers are used in aerospace and sports applications."

THE RESEARCH CENTER in Parma is the 47th site that ACS has designated a National Historic Chemical Landmark since 1992. The landmarks recognize important places, discoveries, and achievements in the history of chemistry. Prior landmarks have included Joseph Priestley's Pennsylvania home, the discovery of penicillin, and the National Institute of Standards & Technology.

Carbon fibers are the artificial equivalent of spider silk, possessing high stiffnesses and tensile strengths that belie their low weight. Their discovery is attributed in large part to Bacon, who arrived at Parma in 1956 and began carbon arc research, studying the melting of graphite under high temperatures and pressures.

Bacon was meticulous: Though he had produced the first carbon fibers (as graphite whiskers) in 1958, he didn't publish a paper in the Journal of Applied Physics until two years later, after thoroughly studying his find. In the process, some scientists suggest that Bacon may even have produced the first carbon nanotubes without realizing it.

The fibers that Bacon discovered possessed an unusually high tensile strength (a measure of the amount of force with which a fiber can be pulled before it breaks) and Young's modulus (a measure of a material's stiffness--its ability to resist elongation under load). Steel has a tensile strength of 1–2 gigapascals (GPa) and a Young's modulus of 200 GPa; Bacon's fibers were measured at 20 GPa and 700 GPa, respectively. But they were also expensive to make, and even commercial versions of carbon fibers are haunted to this day by high prices.

The first commercial high-performance carbon fibers were available by 1963, based on a process discovered at Parma for heat-treating rayon. High-modulus fibers became available within a few more years, when Bacon and Wesley Schalamon used a "hot-stretching" process to stretch carbon yarn during heat-up, not afterward.

In 1970, Singer made progress on another kind of carbon fiber at Parma while studying pitch, a tarlike mixture of hundreds of branched compounds with differing molecular weights formed by heating petroleum or coal. He used a "taffy-pulling" apparatus to align molecules in pitch's mesophase (its liquid-crystal state) and then heated the resulting mixture to produce a highly oriented carbon fiber.

These graphitized mesophase-pitch fibers had an even higher Young's modulus than Bacon's fibers (approaching 1,000 GPa) and showed high thermal conductivity, making them ideal for applications such as brakes and electronic circuits.

"The Parma Technical Center made it possible for scientists like Roger Bacon and Leonard Singer to explore the odd, 'funny' results of laboratory experiments," McClelland said. "And the center provided researchers the resources they needed to keep moving forward until they reached those groundbreaking eureka moments."

Research into carbon fibers continues to drop their price, opening up new applications. Currently used only in small amounts in the automotive industry, less expensive fibers could become the material of choice for manufacturing entire body panels; they could also be used in earthquake-proof homes and bridges. And someday they might even have a more permanent place in space, linking Earth to the heavens in the form of a space elevator.



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