1. What material is carbon fiber?
Fiber material is a structured material formed by fibrous substances through textile processing technology. There are many materials that can be used to make fiber materials, such as common glass fiber, asbestos fiber, polyester fiber, etc. Carbon fiber is also a kind of fiber material.
Carbon fiber is a special fiber composed of carbon elements. Its carbon content is more than 90%. It is a high-strength, high-modulus fiber. It is made of acrylic fiber and viscose fiber and is oxidized and carbonized at high temperature. Compared with other fiber materials, the density of carbon fiber is small, so the specific strength and specific modulus are high, and it has the characteristics of high temperature resistance, friction resistance, electrical conductivity, thermal conductivity and corrosion resistance.
2. How is carbon fiber made?
Carbon fiber is mainly composed of carbon, but it is not directly made of carbon or graphite, but some organic fiber raw materials containing carbon are used to combine organic fiber and plastic resin to carbonize to obtain carbon fiber. The specific production process is :
1). Choose organic fibers
The organic fibers selected to prepare carbon fibers mainly include: polyacrylonitrile fibers, pitch fibers, viscose filaments or phenolic fibers, etc. Among them, polyacrylonitrile carbon fibers and pitch carbon fibers are the most commonly used. Selecting different organic fibers as raw materials will have different requirements for specific process parameters, and the properties of the prepared carbon fibers will also have certain differences.
2). Fiber spinning
Take polyacrylonitrile carbon fiber as an example, polyacrylonitrile is made of 15% spinning solution with water solvent, the water solvent is generally sodium thiocyanate or nitric acid, dimethyl sulfite, etc. The raw silk can be obtained by spinning processes such as silk; the obtained raw silk is woven into a cloth in a weft loom, and then sent to a pre-oxidation processor for pre-oxidation treatment.
3). Pre-oxidation treatment
The pre-oxidation treatment is carried out in two stages. The polyacrylonitrile fiber cloth is first oxidized with air (or oxidation) for 10-30min in the presence of a catalyst at 200-220°C and under tension conditions, and then at 220-330°C under tension conditions. Continue the oxidation treatment for 30-100min, so that the color of the fiber gradually changes from white to yellow, and finally becomes copper-brown. The exhaust gas generated in the pre-oxidation treatment is discharged from the treatment device, and the treated fibers are sent to the carbonization processor for carbonization treatment.
4). Carbonization
The carbonization process is carried out under the protection of pure nitrogen flow (or vacuum), and is converted into carbon fibers with a turbostratic structure through low-temperature carbonization (300-1000 °C) and high-temperature carbonization (1000-1800 °C). The nitrogen-hydrogen decomposition gas and the carbonized decomposition gas generated in the carbonization process are discharged from the carbonization treatment device successively.
After the above steps, the carbon fiber is produced. If it needs to be made into graphite fiber, the carbon fiber can be sent to the graphite processor for processing.