1. What's carbon fiber?
Carbon fiber, alternatively graphite fiber, carbon graphite or CF,
is a material consisting of fibers about 5–10 μm in diameter and composed mostly of carbon atoms.
The carbon atoms are bonded together in crystals that are more or less aligned parallel to the long axis of the fiber. The crystal alignment gives the fiber high strength to-volume ratio (makes it strong for its size).
Several thousand carbon fibers are bundled together to form a tow, which may be used by itself or woven into a fabric.
2.The properties of carbon fibers
High stiffness, high tensile strength, low weight, high chemical resistance, high temperature tolerance and low thermal expansion
3.Structure and properties of Carbon fibers
Each carbon filament thread is a bundle of many thousand carbon filaments.
A single such filament is a thin tube with a diameter of 5–8 micrometers and consists almost exclusively of carbon.
The earliest generation of carbon fibers (e.g. T300, and AS4) had diameters of 7-8 micrometers. Later fibers (e.g. IM6) have diameters that are approximately 5 micrometers.
The atomic structure of carbon fiber is similar to that of graphite,
consisting of sheets of carbon atoms (graohene sheets) arranged in a regularh exagonal pattern.
The difference lies in the way these sheets interlock.
Graphite is a crystalline material in which the sheets are stacked parallel to one another in regular fashion.
The intermolecular forces between the sheets are relatively weak van der Waals firces, giving graphite its soft and brittle characteristics.
Depending upon the precursor to make the fiber, carbon fiber may be turbostratic or graphitic,
or have a hybrid structure with both graphitic and turbostratic parts present.
In turbostratic carbon fiber the sheets of carbon atoms are haphazardly folded, or crumpled, together.
Carbon fibers derived from Polyacrylonitrile(PAN) are turbostratic,
whereas carbon fibers derived from mesophase pitch are graphitic after heat treatment at temperatures exceeding 2200 C.
Turbostratic carbon fibers tend to have high tensile strength, whereas heat-treated mesophase-pitch-derived
carbon fibers have high Young's modulus (i.e., high stiffness or resistance to extension under load) and high thernal conductivity.
4. Applications of carbon fibers
Carbon fiber is most notably used to reinforce composite materials,
particularly the class of materials known as carbon fiber or graphite reiinforced polymers.
Non-polymer materials can also be used as the matrix for carbon fibers.
Due to the formation of metal carvudes and corrosion considerations, carbon has seen limited success inmetal matrix composite applications.
Reubforce carbon-carbon (RCC) consists of carbon fiber-reinforced graphite, and is used structurally in high-temperature applications.
The fiber 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.
Molding a thin layer of carbon fibers significantly improves fire resistance of polymers or thermoset composites because a dense,
compact layer of carbon fibers efficiently reflects heat.
Strongest demands come from aircraft & aerospace, wind energy, as well as the automotive and Carbon bicycle industry.