Carbon fibre can refer to carbon filament thread, or to felt or woven cloth made from those carbon filaments. By extension, it is also used informally to mean any composite material made with carbon filament. It is a strong and very expensive material.
Each carbon filament is made out of long, thin sheets of carbon similar to graphite. A common method of making carbon filaments is the oxidation and thermal pyrolysis of polyacrylonitrile (PAN), a polymer used in the creation of many synthetic materials. Like all polymers, polyacrylonitrile molecules are long chains, which are aligned in the process of drawing fibres. When heated in the correct fashion, these chains bond side-to-side, forming narrow graphene sheets which eventually merge to form a single, jelly roll-shaped filament. The result is usually 93-95% carbon. Lower-quality fibre can be manufactured using pitch or rayon as the precursor instead of PAN. The carbon can become further enhanced, as high modulus, or high strength carbon, by heat treatment processes. Carbon heated in the range of 1500-2000°C (carburizing) exhibits the highest tensile strength (820,000 Psi or 5,650 N/mm²), while carbon fibre heated from 2500-3000°C (graphitizing) exhibits a higher modulus of elasticity (77,000,000 Psi or 531 kN/mm²).
These filaments are stranded into a thread. Carbon fibre thread is rated by the number of filaments per thread, in thousands. For example, 3K (3,000 filament) carbon fibre is 3 times as strong as 1K carbon fibre, but is also 3 times as heavy. This thread can then be used to weave a carbon fibre cloth. The appearance of this cloth generally depends on the size of thread and the weave chosen. Carbon fibre is naturally a glossy black but recently colored carbon fibre has become available.
Carbon fibre is most notably used to reinforce composite materials, particularly the class of materials known as graphite reinforced plastic. This class of materials is used in high-performance vehicles, sporting equipment, and other demanding mechanical applications; a more thorough discussion of these uses, including composite lay-up techniques, can be found in the carbon fibre composite article.
Non-polymer materials can also be used as the matrix for carbon fibres. Due to the formation of metal carbides (i.e., water-soluble AlC) and corrosion considerations, carbon has seen limited success in metal matrix composite applications. Reinforced carbon-carbon (RCC) consists of carbon fibre-reinforced graphite, and is used structurally in high-temperature applications, such as the nose cone and leading edges of the space shuttle.
The fibre also finds use in filtration of high-temperature gases, as an electrode with high surface area and impeccable corrosion resistance, and as an anti-static component in high-performance clothing.
Some string instruments, such as violins and cellos, use carbon fibre reinforced composite bows. This is an alternative to the more common wooden bows.
Many high end frames for road bikes and mountain bikes are made of carbon fibre reinforced composite. Also, many road bikes made of aluminum have carbon fibre reinforced composite seat posts, handlebars and forks for reduced weight.
Carbon nanotubes are currently being investigated as possible improvements on the traditional carbon fibre material. While the nanotechnology field isn't advanced enough to create long-enough fibres made entirely of carbon nanotubes, research has shown that even as little as 5% (by weight) carbon nanotube constituents within the carbon fibres will dramatically improve properties. Andrews et. al. reported that tensile strength increased by 90%, modulus increased by 150%, and electrical conductivity increased by 340%. This was in a pitch composite fibre with 5% (by weight) loading of purified single walled nanotubes (as compared to the corresponding values in unmodified isotropic pitch fibres). Further research is still needed to resolve issues such as nanotube dispersion and alignment, as well as interfacial bonding; however, this approach holds great promise for improving both the mechanical and electrical properties of carbon fibre composites.
Use of the material has been more readily adopted by low-volume manufacturers like TVR who use it primarily for creating body-panels for some of their high-end cars due to its increased strength and decreased weight compared with the glass-reinforced plastic they use for the majority of their products.