Home >
A Light, Durable and Innovative Material
What is Carbon Fiber?
Carbon fiber consists of extremely fine filaments, between 5 and 7 microns in diameter. More than 90% of these carbon filaments are composed of carbon atoms, the rest being mainly nitrogen atoms. Carbon atoms form graphitic planes organised in crystals.
How is Torayca® Carbon Fiber Manufactured?
Torayca® Carbon Fiber is produced from polyacrylonitrile (PAN) fiber. These PAN fibers are obtained by polymerising, spinning and then stretching the polymer. The resulting polymeric chains are aligned in the filament axis’s direction. This is essential to obtain the characteristic properties of carbon fiber.
- The PAN fiber is then transformed into carbon fiber by undergoing the process of carbonisation. The first step, called oxidation, is carried out to make the polyacrylonitrile fiber non-flammable. Oxidation occurs between 200 and 300 °C. During this step, tension is applied to the fiber filament to ensure the polymeric chains remain correctly aligned.
- In the next step, called carbonisation, heat is applied to the fiber to remove non-carbon atoms and retain only carbon atoms. At temperatures of around 1,500 °C, oxidised polyacrylonitrile fiber reacts under an inert atmosphere to form the characteristic graphitic planes of carbon fiber.
- Carbon fiber may undergo a second heat treatment at temperatures above 2,000 °C. Under the effect of heat, the carbon fiber’s crystalline structure transforms itself into high-modulus carbon fibers.
- Carbon fiber then undergoes a surface treatment: chemical electrolysis. It allows the grafting of oxygen groups on the surface of the filaments. These oxygen groups prepare the fiber for the final part of the carbonisation process: the application of a sizing treatment. Sizing is used to facilitate the bonding between the fiber and the polymer matrix of the composite material. This optimises the subsequent processing of the carbon fiber.
What are the Properties of Carbon Fiber?
Lightweight Properties
Carbon fiber is light because carbon atoms have a low atomic mass. In addition, the chemical structure composed of graphitic planes organised in crystal alignments induces larger spacing between carbon atoms.
Mechanical Properties
Carbon fiber is extremely robust and rigid (high modulus). Covalent bonds bind carbon atoms in the graphitic planes. These chemical bonds are highly stable: as the carbon atoms share electrons, a great deal of energy is required to break a covalent bond.
The structure of the carbon filaments also plays an important role in the material’s strength and resistance.
As a result, carbon composites offer unrivalled tensile strength, modulus and resistance to fatigue.
Thermal Properties
Carbon fiber is heat-resistant. When used at high operating temperatures, carbon fiber does not degrade or expand.
To make full use of its thermal properties, carbon fiber is sometimes combined with a ceramic matrix, to create a ceramic matrix composites material (CMCs). Carbon can thus be considered ceramic material. Consequently, CMCs retain carbon properties up to temperatures above 2,000 °C.
Conductivity and Electrical Resistance
Carbon fiber is electrically conductive. Under electric current, carbon fiber generates Joule heat. Thanks to its electrical conductivity and excellent thermal resistance, it offers an excellent heating solution. Carbon composites can also be used to shield electronic equipment from radio or electromagnetic interference. Carbon composites, therefore, act as a Faraday cage.
X-Ray Permeability
Carbon fiber is composed of lightweight elements: 95% of carbon atoms and 5% nitrogen. It absorbs very few X-rays making it ideally suited for use in medical imaging.
Non-flammable
Carbon fiber has an extremely orderly structure that induces many strong bonds between carbon atoms. As a result, the oxidation reaction produced in a fire cannot self-feed, giving this material its non-flammable characteristic.
What are the Applications of Carbon Fiber?
Light, durable and resistant, carbon fiber is a cutting-edge material. It is most notably used to reinforce composite materials. The main applications are found in the:
- Aerospace Industry;
- Sports and Leisure Industry (golf clubs, fishing rods, bicycle frames);
- Automotive Industry;
- Marine Industry;
- Civil Engineering;
- Energy Industry.
Carbon fiber is regularly used to reduce the weight of vehicles, aeroplanes and other forms of public transport. An aeroplane with a fuselage made of carbon composites is 20% lighter than one made using traditional materials. Over the life cycle of the plane, this 20% reduction in weight enables CO2 emissions to be reduced by 400 tons.
Automotive Industry: the Hydrogen Solution
Hydrogen vehicles now have higher battery life than electric battery vehicles (> 500 km). This performance is possible thanks to the storage of compressed hydrogen in a carbon fiber pressure tank. Thanks to its unique properties, carbon fiber is the only material capable of providing the necessary strength, light ness and long-term performance for these tanks.
Toray’s innovative Carbon Paper, is also the solution used to produce the key component of PEM fuel cells: gas diffusion membranes.
