Bacon’s breakthrough

The modern era of carbon fibers began in 1956, when Union Carbide opened its Parma Technical Center just outside Cleveland. The complex was one of the major laboratories of Union Carbide’s basic research program, modeled after the university-style corporate labs that became popular in the late 40s and 50s. They gathered young, bright scientists from a variety of backgrounds and let them loose on their favorite projects, giving them an extraordinary degree of autonomy.

With a freshly minted Ph.D. in physics, Roger Bacon joined the Parma staff in 1956. “I got into carbon arc work, studying the melting of graphite under high temperature and pressures,” Bacon recalls. “I took on the job of trying to determine the triple point of graphite. That’s where the liquid, solid, and gas are all in thermal equilibrium.” The equipment was akin to the early carbon arc streetlamps, only operating at much higher pressures. Small amounts of vaporized carbon would travel across the arc and then deposit as liquid. As Bacon decreased the pressure in the arc, he noticed that the carbon would go straight from the vapor phase to the solid phase, forming a stalagmite-like deposit on the lower electrode. “I would examine these deposits, and when I broke one open to look at the structure, I found all these whiskers,” he says. “They were imbedded like straws in brick. They were up to an inch long, and they had amazing properties. They were only a tenth of the diameter of a human hair, but you could bend them and kink them and they weren’t brittle. They were long filaments of perfect graphite.”

The year was 1958, and Bacon had demonstrated the first high performance carbon fibers. In fibrous forms, carbon and graphite are the strongest and stiffest materials for their weight that have ever been produced. Bacon demonstrated fibers with a tensile strength of 20 Gigapascals (GPa) and Young’s modulus of 700 GPa. Tensile strength measures the amount of force with which a fiber can be pulled before it breaks; Young’s modulus is a measure of a material’s stiffness, or its ability to resist elongation under load. For comparison, steel commonly has a tensile strength of 1-2 GPa and Young’s modulus of 200 GPa.

Carbon fibers are polymers of graphite, a pure form of carbon where the atoms are arranged in big sheets of hexagonal rings that look like chicken wire. Bacon’s graphite whiskers were sheets of graphite rolled into scrolls, with the graphite sheets continuous over the entire length of the filament.

“After studying the heck out of these things, I finally published a paper in the Journal of Applied Physics in 1960,” Bacon says. The paper has since become a milestone, partially because some have claimed that Bacon may have been the first person to produce carbon nanotubes — hollow cylinders of graphite with diameters on the order of single molecules. Their incredible properties have made nanotubes one of the hottest areas of research in recent years, promising to revolutionize just about every area of science. Sumio Iijima published a paper in 1991 that is often regarded as the first discovery of carbon nanotubes; it reported on a method that produced both tubes and scrolls. The process is similar to Bacon’s, suggesting that he too may have prepared nanotubes along with his whiskers, although he didn’t know it at the time. “I may have made nanotubes, but I didn’t discover them,” he says.

By producing his high strength and high modulus whiskers, Bacon had demonstrated experimentally something that theoreticians had proposed long ago. But the fibers were still just a laboratory phenomenon, not a practical development. “I estimated the cost of what it took to make them, and it was $10 million per pound,” he says. To tap their full potential, manufacturers needed a cheap and efficient way to produce the fibers. Much of the research in the ensuing decades was dedicated to exactly that.

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