Carbon fiber products are widely distributed in our lives. Carbon fiber is a good material for making many daily necessities. So, what is carbon fiber? What are the characteristics of carbon fiber? What are the advantages of carbon fiber compared with other ordinary materials?
In fact, there are many types of carbon fiber. So, what are the categories of carbon fiber? What are the advantages and characteristics of various categories?
What is carbon fiber?
Carbon fiber (CF for short) is a new type of fiber material with high strength and high modulus fiber with a carbon content of more than 95%. It is a microcrystalline graphite material obtained by carbonizing and graphitizing organic fibers such as flake graphite microcrystals stacked along the axial direction of the fiber. Carbon fiber is "soft outside and hard inside". It is lighter than metal aluminum, but its strength is higher than steel. It has the characteristics of corrosion resistance and high modulus. It is an important material in national defense, military industry and civilian use. It not only has the inherent intrinsic characteristics of carbon materials, but also has the softness and processability of textile fibers. It is a new generation of reinforcing fiber.
Carbon fiber has many excellent properties. Carbon fiber has high axial strength and modulus, low density, high specific performance, no creep, ultra-high temperature resistance in non-oxidizing environment, good fatigue resistance, specific heat and conductivity between non-metal and metal, small thermal expansion coefficient and anisotropy, good corrosion resistance and good X-ray transmittance. Good electrical and thermal conductivity, good electromagnetic shielding, etc. Compared with traditional glass fiber, carbon fiber has a Young's modulus of more than 3 times that of traditional glass fiber, and compared with Kevlar fiber, its Young's modulus is about 2 times that of traditional glass fiber. It is insoluble and non-swelling in organic solvents, acids and alkalis, and has outstanding corrosion resistance. What are the categories of carbon fiber? Carbon fiber can be divided into polyacrylonitrile-based carbon fiber, 1K carbon fiber-made tube asphalt-based carbon fiber, viscose-based carbon fiber, phenolic-based carbon fiber, and vapor-grown carbon fiber according to the source of raw materials. It can be divided into general-purpose, high-strength, medium-modulus high-strength, high-model and ultra-high-model carbon fiber according to performance, and divided into filament, short fiber and short-cut fiber according to state. According to mechanical properties, it can be divided into general-purpose and high-performance types. The strength of general-purpose carbon fiber is 1000 MPa and the modulus is about 100 GPa. High-performance carbon fiber is divided into high-strength type (strength 2000 MPa, modulus 250 GPa) and high type (modulus 300 GPa or more). Strength greater than 4000 MPa is also called ultra-high strength type; modulus greater than 450 GPa is called ultra-high model.
With the development of aerospace and aviation industries, high-strength and high-strength carbon fiber has also appeared, with an elongation greater than 2%. The most used is polyacrylonitrile PAN-based carbon fiber.
More than 90% of carbon fibers on the market are mainly PAN-based carbon fibers.
Because the mysterious veil of carbon fiber has not been completely unveiled, people cannot directly use carbon or graphite to make it. They can only use some carbon-containing organic fibers (such as nylon, acrylic, rayon, etc.) as raw materials, and combine organic fibers with plastic resins to carbonize and make carbon fibers.
PAN-based carbon fiber
The production process of PAN-based carbon fiber mainly includes two processes: precursor production and precursor carbonization: first, through a series of processes such as acrylonitrile polymerization and spinning, it is processed into polyacrylonitrile fiber or precursor called "mother", and these precursors are placed in an oxidation furnace for oxidation at 200 to 300 ° C, and then in a carbonization furnace, carbonization and other processes are performed at a temperature of 1000 to 2000 ° C to make carbon fiber.
Asphalt-based carbon fiber
The United States invented the base metal mesophase asphalt containing the textile asphalt-based carbon fiber. After the precursor is stabilized and carbonized, the tensile strength of the carbon fiber is 3.5G Pa and the modulus is 252G Pa; France has developed heat-resistant and highly conductive mesophase asphalt-based carbon fiber, and Poland has developed a new method for metal-coated carbon fiber. For example, copper-coated asphalt-based carbon fiber is made by a mixing method. First, copper salt is mixed with isotropic coal tar, centrifugal spinning is performed, stabilized in air and treated in high-temperature hydrogen to obtain alloy copper carbon fiber. The world's production capacity of asphalt-based carbon fiber is relatively small. Domestic research and development of asphalt-based carbon fiber started earlier, but there is a big gap in development, production and application compared with foreign countries.
Carbon fiber is divided into two categories according to different product specifications: aerospace grade and industrial grade, also known as small tow and large tow. Carbon fiber above 48K is usually called large tow carbon fiber, including 360K and 480K. Aerospace-grade carbon fiber was mainly 3K in the early stage, and gradually developed into 12K and 24K. It is mainly used in national defense and military industry and high technology, as well as sports and leisure products, such as aircraft, missiles, rockets, satellites, fishing rods, clubs and rackets. Industrial-grade carbon fiber is used in different civilian industries, including: textiles, medicine and health, electromechanical, civil engineering, transportation and energy.
,
