The carbon fiber is a kind of high-strength, high-modulus fiber made of polypropylene rayon fiber, viscose fiber, or pitch fiber, which is prepared by heating out all other elements except carbon. It has good chemical stability and high temperature resistance and is an excellent structural material in high performance reinforced composites.
According to the carbonization temperature, carbon fibers can be divided into three types.
(1) Ordinary type (A type) carbon fiber: carbon fiber obtained by carbonization at 900 to 1200°C. This carbon fiber has a low strength and elastic modulus, generally less than 11 cN/dtex, and a modulus less than 1346 cN/dtex.
(2) High-strength (Type II or Type C) carbon fibers: carbon fibers obtained by carbonization at 1300 to 1700°C. This carbon fiber has a high strength of 14 to 17 cN/dtex and a modulus of 1384 to 1661 c/dtex.
(3) High-modulus (I- or B-type) carbon fibers, also known as graphite fibers: refers to carbon fibers obtained after carbonization and high temperature graphitization above 2500°C. This kind of carbon fiber has high strength, about 9.8~12.2cN/dtex, high modulus, generally up to 1711cN/dtex or even up to 3178cN/dtex.
Carbon fiber performance characteristics
Carbon fibers are made up of many microcrystals. The thickness of microcrystals is 4~10nm and the length is 10~25nm. It consists of about 12~30 layers.
The spacing between the measured layers of carbon fiber is approximately (3.39-3.42) × 10 -1 nm, which is slightly larger than that of graphite microcrystals. In addition, each carbon atom between the parallel planes is not as regular as graphite.
Physical and mechanical properties
The binding force between carbon fiber shafts is stronger than that of graphite, so its axial strength and modulus are much higher than that of graphite. However, radial strength and modulus are similar to those of graphite and are relatively low. Therefore, carbon fiber should avoid radial forces. Low knot strength.
2. Heat resistance
Carbon fiber has good heat resistance and high temperature resistance. Sublimation temperature of carbon fiber is as high as about 3650°C. The temperature of the carbon fiber is rapidly changed, the coefficient of thermal expansion is small, and it is corrosion-resistant and conductive.
3. Chemical properties
The chemical properties of carbon fiber are very similar to that of carbon. When the temperature is higher than 400°C in the air, it will obviously oxidize. The carbon dioxide and carbon monoxide will dissipate on the surface of the fiber. Therefore, the use temperature of carbon fiber in the air should not be too high, generally Below 360°C. In the case of oxygen barrier, the use temperature can be significantly increased, generally up to 1500 ~ 2000 °C, and the higher the temperature, the greater the strength of the fiber.
In addition to being a strong oxidant, carbon fibers generally have no effect on it. The carbon fiber has a self-lubricant. After 25% of the carbon fiber is mixed in the copper, the wear rate of the composite material can be greatly reduced.
Although the density of carbon fibers is larger than that of ordinary fibers, it is much smaller than ordinary metals. Usually, its density depends on the pyrolysis process and the nature of the raw silk used. For example, a carbon fiber made of viscose fiber as a raw yarn has a density of 15 to 17 g/cm 3 , and polypropylene fiber is used as the carbon fiber produced by the original fiber, and the density is about 1.7 to 2.0 g/cm 3 .
The use of carbon fiber
Carbon fiber is not used alone. It is generally added to a matrix such as resin, metal, or ceramic as a skeleton material of a composite material. The composite material thus constructed is a very useful structural material. It is not only lightweight, high temperature resistant, but also has high tensile strength and elastic modulus. It is indispensable for manufacturing spacecraft, rockets, missiles, high-speed aircraft, and large passenger aircraft. Missing ingredients.
Carbon fiber is used in addition to the structural material of the aircraft. Its composite materials are also widely used in the fields of atomic energy, electromechanical, chemical, metallurgy, transportation and other industries as well as containers and sporting goods (such as tennis rackets, ice rackets, golf rackets, skis, regattas, and sailing boats).
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