The Introduction of Carbon Fibers

Carbon fibers are very thin filaments, having diameters between 5 and 10 micrometer and consisting of 99.9% chemically pure carbon. They are not chemical compounds or alloys like many conventional structural materials such as alumunium or steel, which are invariably associated with small quantities of other alloying elements. Carbon fibers were discovered during the utilizing of these fibers as filament in lamps. These early carbon fibers were prepared by the carbonisation of bamboo and rayon. Soon after the development of tungsten filaments, this use of carbon fiber was abandoned and they were almost forgotten.

The present breed of high performance carbon fibers was first prepared from rayon at the Wright Patterson Air Force Base for the aerospace industry to provide lightweight and more fuel-efficient aircraft capable of high speeds. Union Carbide developed the process and commercialized the product as Thornel. At about the same time, Shindo in Japan and Watt and coworkers in the United Kingdom, working independently, successfully prepared carbon fibers from polyacrylonitrile (PAN). The pitch-based carbon fibers were developed by Otani, who used polyvinylchloride (PVC) pitch as a raw material, while mesophase pitch fibers were introduced by Singer at Union Carbide in the United States.

Carbon fibers exhibit both a high specific strength and a high specific modulus. Moreover, carbon fibers are available in a wide range of strength and modulus. Polyacrylonitrile-based carbon fibers form the most important group, with high strength and high modulus, while the mesophase-pitch-based fibers provide an ultra-high modulus type although with lower strengths. Isotropic pitch fibers have both a low modulus and low strength and can be used as general purpose carbon fibers.

In addition to strength and stiffness, carbon fibers are elastic to failure at normal temperature, which makes them creep-resistant and susceptible to fatigue. They have exceptional thermophysical and excellent damping characteristics. They are electrically conductive, and their conductivity can be enhanced by intercalation. They are chemically inert except in strongly oxidizing environments or when in contact with certain molten metals.