The terms graphite and carbon fiber have become interchangeable to some extent. However, graphite in lead pencils and graphite in a tennis racket are obviously not the same material. The material that makes a strong racket is actually made of carbon fibers. Both graphite and carbon fibers are carbon-based; the differences lie in the process that produces the end product.
According to an article by the Department of Polymer Science at the University of Southern Mississippi, graphite is pure carbon with its atoms arranged in big sheets of hexagonal rings. The article compares them to chicken wire. Carbon fibers differ in that they are a polymer which is a type of graphite. A polymer is a chain of carbon atoms that are connected to one another. The polymer must undergo a process to become carbon fiber that makes it different than graphite.
Converting that long chain of carbon atoms into carbon fibers involves stretching the polymer. An oxidation treatment at 200 to 300 degrees centigrade starts the process from polymer to carbon fiber. The polymer is then heated to temperatures ranging from 1,000 to 2,500 degrees centigrade. The exact amount of heat depends upon the use for the specific fibers. During the heating process, the fibers are reduced to a substance that is approximately 92 percent carbon. The polymer becomes very thin as a result of the heat, at which point it becomes carbon fiber. If the process continues and the heat rises above 2,500 degrees centigrade, the polymer will turn into graphite instead of carbon fiber.
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According to the University of Bristol, carbon fibers are very strong, despite their lack of density. Both graphite and carbon fibers are inert and unreactive; this explains why graphite in lead pencils does not react with paper, and the carbon fibers in tennis rackets do not interact with the other components of the racket. As the University of Wisconsin's Department of Chemistry points out, carbon fibers make the right material for ligament replacements.
The main difference between graphite and carbon fiber is the fact that graphite breaks apart easily while carbon fiber is strong. This difference explains why graphite works well in a pencil and carbon fiber works well in sports equipment, airplanes and the space shuttle.