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This paper reviews the processing, properties, and structure of carbon fibers. Carbon fibers are derived from several precursors, with polyacrylonitrile being the predominant precursor used today. Carbon fibers have high strength (3-7 GPa), high modulus (200-500 GPa), compressive strength (1-3 GPa), shear modulus (10-15 GPa), and low density (1.75-2.00 g/cm^sup 3^). Carbon fibers made from pitch can have modulus, thermal, and electrical conductivities as high as 900 GPa, 1,000 W/mK, and 10^sup 6^ S/m, respectively. These fibers have become a dominant material in the aerospace industry and their use in the automotive and other industries is growing as their cost continues to come down.
INTRODUCTION
Carbon fibers contain at least 90% carbon by weight obtained by pyrolysis of an appropriate precursor fiber.1 Graphite is one form of carbon. In graphite, the sp2 hybridized carbon atoms are arranged in two-dimensional hexagonal planes.1 These graphitic planes are highly anisotropic due to the difference between in-plane and out-of-plane bonding of carbon atoms. The elastic modulus is much higher in the plane than it is perpendicular to the plane. The bonding between graphitic planes is van der Waals bonding so the planes can slide with respect to each another. Alignment of the graphitic planes parallel to the fiber axis leads to high tensile modulus and electrical and thermal conductivity parallel to the fiber axis.2
Polymeric materials, which leave a carbon residue and do not melt upon pyrolysis in an inert atmosphere, are generally considered candidates for carbon-fiber production.3 The historical development of carbon fiber has been traced extensively.4 The first carbon fibers were produced by T. Edison in the United States and J.W. Swan in England from a cellulose precursor for light-bulb filaments.5 Modern carbon fibers were developed in the late 1950s and early 1960s by W. Watt in England,6 A. Shindo in Japan,7 and R. Bacon in the United States.8 Though cellulose was the early precursor used for carbon fibers, today polyacrylonitrile (PAN) is the predominant carbon-fiber precursor, followed by petroleum pitch. Carbon fibers are also produced by decomposing gaseous hydrocarbons at high temperatures. The first account of vapor-grown carbon fiber (VGCF) production was in 1890.9
PROCESSING OF CARBON FIBERS
PAN-Based Carbon Fibers
Polyacrylonitrile is favored as a carbon-fiber precursor due to its combination of tensile and...