Reinforced carbon–carbon
Carbon fibre-reinforced carbon (aka carbon–carbon, abbreviated C/C) is a composite material consisting of carbon fibre reinforcement in a matrix of graphite. It was developed for the nose cones of intercontinental ballistic missiles, and is most widely known as the material for the nose cone and wing leading edges of the Space Shuttle orbiter. It has been used in the brake systems of Formula One racing cars since 1976; carbon–carbon brake discs and pads are a standard component of Formula One brake systems.
Carbon–carbon is well-suited to structural applications at high temperatures, or where thermal shock resistance and/or a low coefficient of thermal expansion is needed. While it is less brittle than many other ceramics, it lacks impact resistance; Space Shuttle Columbia was destroyed after one of its RCC panels was broken by the impact of a piece of foam insulation from the Space Shuttle External Tank. This catastrophic failure was due in part to original shuttle design requirements which did not consider the likelihood of such violent impacts.
Production
The material is made in three stages:
First, material is laid up in its intended final shape, with carbon filament and/or cloth surrounded by an organic binder such as plastic or pitch. Often, coke or some other fine carbon aggregate is added to the binder mixture.
Second, the lay-up is heated, so that pyrolysis transforms the binder to relatively pure carbon. The binder loses volume in the process, so that voids form; the addition of aggregate reduces this problem, but does not eliminate it.
Third, the voids are gradually filled by forcing a carbon-forming gas such as acetylene through the material at a high temperature, over the course of several days. This long heat treatment process also allows the carbon to form into larger graphite crystals, and is the major reason for the material's high cost, exceeding $100,000 per panel.
C/C is a generally hard material that can be made highly resistant to thermal expansion, temperature gradients, and thermal cycling, depending on how the fibre scaffold is laid up and the quality/density of the matrix filler.
Mechanical properties
The strength of carbon–carbon with unidirectional reinforcement fibres is up to 700 MPa. Carbon–carbon materials retain their properties above 2000 °C.[1] This temperature may be exceeded with the help of protective coatings to prevent oxidation.[2]
Similar products
Carbon fibre-reinforced silicon carbide (C/SiC) is a development of pure carbon–carbon, and can be used in automotive applications, such as components of brake systems on high performance road cars, namely the brake disc and brake pads. C/SiC utilises silicon carbide with carbon fibre, and this compound is thought to be more durable than pure carbon–carbon.
Applications initially included the Mercedes-Benz C215 Coupe F1 edition,[3] and are standard fitment on the Bugatti Veyron and certain current Bentleys, Ferraris, Porsches and Lamborghinis. They are also offered as an "optional upgrade" on certain high performance Audi cars, including the D3 S8, B7 RS4, C6 S6 and RS6, and the R8.
Carbon brakes became widely available for commercial airplanes in the 1980s.[4]