carbon fibres abbr., CF otherwise carbon filaments (rus. волокна, углеродные otherwise углеволокна) — family of structural fibres composed of carbon, differing in methods of production, microstructure, mechanical properties and applications.

Description

The foundation of the modern carbon fibre industry was laid by Watt, Johnson and Phillips who created the first carbon fibres in England in the early 1960s. These were, apparently, the first nanostructured objects, designed as a structural material. The typical dimensions of the carbon fibre structure are in the range of tens and hundreds of nanometres, which determines the high mechanical properties of such fibres.

Most carbon fibres are obtained from three types of precursors: polyacrylonitrile (PAN), mesophase pitch and cellulose. The process of fibre manufacture from these precursors includes the following main steps: obtaining the precursor fibre, stabilisation of the precursor at a relatively low temperature, carbonisation (at 1,000-2,000°C) and graphitisation (at 2,400-3,000°C).

By their mechanical properties carbon fibres are conventionally divided into high-strength fibres (with the strength of 4.0-4.4 GPa or higher), high-modulus fibres (with the modulus of above 400 GPa) and fibres with a moderately high modulus (250-400 GPa). One of the important operations in the production of carbon fibres is the drawing, as a result of which the planes of the crystallites get oriented along the fibre axis; this provides for production of high-modulus fibres. Depending on the fibre type the drawing is performed at different stages of the process: for the PAN fibres, during preparation of the fibres; for other types, during carbonisation and graphitisation.

Carbon fibres are produced and used in the following forms:

- continuous fibres, grouped into thin (up to 24 K) or thick (up to 320 K) strands;

- carbon fibre fabric;

- paper or mats made of short fibres.

Carbon fibres are primarily used in reinforced plastics, where their mechanical properties are best demonstrated. Carbon fibre reinforced plastics are used in structural elements of aircrafts and space vehicles, in sports goods, the structures of bridges and other areas where high strength and elasticity modulus and low density are of greatest importance. The second important application for such fibres is the carbon-carbon composites used in rocket technology (nozzle elements of solid-propellant engines, thermal protection of warheads and most heated elements of space shuttles, braking devices that absorb large amounts of kinetic energy in their operation).

In addition to their high mechanical characteristics, carbon fibres have valuable physical and chemical properties. They are characterised by their high thermal and chemical stability: during thermal exposure up to 1,600-2,000°C in the absence of oxygen the mechanical characteristics of the fibres remain practically unchanged, which enables them to be used as a component of heat-shielding composite materials. The chemical stability of carbon fibres makes them suitable for use in such applications as filtration of aggressive media, gas purification and manufacturing of protective clothing. By changing the conditions of heat treatment, it is possible to obtain carbon fibres with different physical properties (specific volume electrical resistance from 10-3 to 106 ohm·cm) and use them as electrical heating elements intended for various purposes (clothing, space heating, heating of pipelines). Treatment of carbonised carbon fibres with water steam at high temperatures enabpes the production of materials with a large active surface (up to 1,000 m2/g) that act as effective sorbents. The application of catalysts to the carbon fibres allows one to create effective catalytic systems with a developed surface.

Authors

  • Mileiko Sergey T.
  • Nazarov Victor G.

Sources

  1. Kelli A. Triumph of carbon fiber (in Russian) // Kompozity i Nanostruktury. 2009. No 1. p. 38–49.
  2. Chawla K. K. Fibrous Materials. — Cambridge University Press, 1998. — 309 p.

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