Synthesis and Research of Carbon Fiber

1What is carbon fiber?

Carbon fiber is a carbon content in95%The above high strength, high modulus fiber of the new fiber material. It is a microcrystalline graphite material obtained by carbonization and graphitization treatment by stacking organic fibers such as flake graphite crystallites along the axial direction of the fiber. carbon fiber"Soft outside and rigid inside"It is lighter than metal aluminum, but its strength is higher than that of steel, and it has the characteristics of corrosion resistance and high modulus. It is an important material in national defense and civilian use. It not only has the inherent characteristics of carbon materials, but also has the softness of textile fibers.MachinabilityIt is a new generation of reinforcing fibers.

2Physical and Chemical Properties

Carbon fiber is a new material with excellent mechanical properties. The tensile strength is approximately2To7GPaand the tensile modulus is approximately200To700GPa. The density is about1.5To2.0Gram per cubic centimeter, which in addition to the original silk structure, mainly depends on the temperature of carbonization treatment. Generally through high temperature3000 ℃Graphitization treatment, density up2.0grams per cubic centimeter. In addition, its weight is very light, and its specific gravity is lighter than that of aluminum, less than that of steel.1/4The specific strength is iron.20Times.

The thermal expansion coefficient of carbon fiber is different from other fibers, and it has anisotropic characteristics. carbon fiberspecific heat capacityGenerally7.12. The thermal conductivity decreases with increasing temperature. It is negative parallel to the fiber direction.(0.72To0.90)while perpendicular to the fiber direction is positive(32To22).

carbon fiberspecific resistancerelated to the type of fiber, in25 ℃When the high modulus is775High strength carbon fiber per centimeter1500. This results in carbon fibers having the highest specific strength and specific modulus of all high performance fibers.

Compared with titanium, steel, aluminum and other metal materials, carbon fiber has the characteristics of high strength, high modulus, low density and small linear expansion coefficient in physical properties, which can be called the king of new materials.

The tensile strength of carbon fiber resin composites is generally3500Above megapascals, it is steel7To9times, the tensile modulus of elasticity is230To430GPa is also higher than steel;ThereforeCFRPThe specific strength of the material is the ratio of the strength of the material to its density.2000above MPa, whileA3SteelThe specific intensity of is only59MPa or so, its specific modulus is also higher than steel.

Compared with conventional glass fiber, Young's modulus(A physical quantity that characterizes the tensile or compressive strength of a material within the elastic limit.)It's fiberglass3More than twice;Compared with Kevlar fiber, not only Young's modulus is its2Times or so. Tests on carbon fiber epoxy laminates show that both strength and modulus decrease with increasing porosity. The effect of porosity on the interlaminar shear strength, bending strength and bending modulus is very large.;Tensile strength decreases relatively slowly with the increase of porosity;Tensile modulus is less affected by porosity.

Carbon fiber also has excellent denier(One of the representations of the titer is9000grams of rice long fiber), generally only about19grams, pulling force up300Kilogram per micron. Few other materials have as many excellent series of properties as carbon fiber, so there are strict requirements in the fields of degree, stiffness, weight, fatigue characteristics, etc.

In the absence of contact with air and oxidants, the carbon fiber can withstand3000Compared with other materials, the temperature of carbon fiber is higher than that of other materials.1500 ℃The strength began to decline, and the higher the temperature, the greater the decline in fiber strength. The radial strength of carbon fiber is not as good as the axial strength, so carbon fiber should avoid radial strength.(That is, you cannot tie a knot.)The whisker properties of other materials have also been greatly reduced. In addition, carbon fiber also has good low temperature resistance, such as in liquid nitrogen temperature is not brittle.

The chemical properties of carbon fiber and carbon know, it can be strong oxidant oxidation, the general alkaline is inert. In the air the temperature is higher400 ℃When there is obvious oxidation, the formationCOwithCO2. Carbon fiber has good corrosion resistance to general organic solvents, acids and alkalis, insoluble and non-swelling, excellent corrosion resistance, and there is no rust problem at all. There are scholars in1981years willPANBase carbon fiber soaked in strong alkali sodium hydroxide solution, time has passed30For many years, it still maintains its fibrous form. However, its impact resistance is poor, easy to damage, oxidation occurs under the action of strong acid, the electromotive force of carbon fiber is positive, while the electromotive force of aluminum alloy is negative. Carbonization, carburization and electrochemical corrosion occur when carbon fiber composites are used in combination with aluminum alloys. Therefore, the carbon fiber must be surface treated before use. Carbon fiber also has the characteristics of oil resistance, radiation resistance, radiation resistance, absorption of toxic gases and deceleration neutrons. .

3Preparation method

Carbon fibers can be made from polyacrylonitrile fibers, pitch fibers, viscose fibers or phenolic fibers by carbonization, respectively. The more commonly used carbon fibers are mainly polyacrylonitrile carbon fibers and pitch carbon fibers. The manufacture of carbon fibers includes fiber spinning, thermal stabilization(pre-oxidation)Carbonization, graphitization, etc.4process. The accompanying chemical changes include dehydrogenation, cyclization, pre-oxidation, oxidation and deoxidation.

From viscose fiber to produce high mechanical properties of carbon fiber must be high-temperature stretching graphite, low carbonization yield, technical difficulties, complex equipment, products are mainly used for ablation-resistant materials and insulation materials.;Carbon fiber from pitch is rich in raw materials and has a high carbonization yield, but it has not been developed on a large scale due to complex raw material modulation and low product performance.;High-performance carbon fiber can be produced from polyacrylonitrile fiber precursor, and its production process is simpler than other methods with excellent mechanical properties.20Century60After the years, the carbon fiber industry developed well.

To get good quality carbon fiber, you need to pay attention to the technical points:

(1)The primary task of preparing high-performance carbon fiber is to achieve high purification, high strengthening, densification and smooth surface. The carbon fiber system engineering needs to start from the polymerized monomer of the precursor yarn. The quality of the precursor not only determines the nature of the carbon fiber, but also restricts its production cost. QualityPANPrecursor is the primary prerequisite for the manufacture of high-performance carbon fibers.

(2)The minimization of impurity defects is the fundamental measure to improve the tensile strength of carbon fiber, and it is also a hot topic for scientific and technological workers. In a sense, the process of improving strength is essentially a process of reducing and reducing defects.

(3)In the pre-oxidation process, under the premise of ensuring homogenization, the pre-oxidation time is shortened as much as possible. This is a directional issue to reduce the production cost.

(4)Research on high-temperature technology and high-temperature equipment and related important components. High temperature carbonization temperature is generally1300To1800 ℃, graphitization is generally in2500To3000 ℃. Operating at such a high temperature requires continuous operation and increasing the service life of the equipment, so it is particularly important to study a new generation of high-temperature technology and high-temperature equipment. Such as inert gas protection, oxygen-free microwave, plasma and induction heating technology.

4, prospect

World carbon fiber production reaches annual4More than 10,000 tons, the whole carbon fiber production line in the world is mainly Japan, the United States, Germany and South Korea and a few other countries have mastered the core technology of carbon fiber production, and have large-scale production.

At present, the global carbon fiber core technology is firmly in the hands of a few developed countries. On the one hand, the developed countries led by the United States and Japan have always maintained a strict technical blockade of China's carbon fiber industry.;On the other hand, foreign carbon fiber industry leaders began to enter the Chinese market, China's local carbon fiber enterprises increased pressure. Although China has increased the guidance and support for the carbon fiber industry, the breakthrough of domestic carbon fiber is still bumpy under the large technology gap.

References

[1]Yan Ying,Chen Yan.Development Trend and Application of Carbon Fiber Technology[J].Aging and Application of Synthetic Materials,2018,47(05):134-138.

[2]Zhang deposit.Industrial Development and Application of Carbon Fiber Composites[J].Jiangsu Building Materials,2018(05):13-16.

[3]Huang Fangfang.carbon fiber40Year:Difficult Tackling under the International Blockade[J].Economy,2018(16):24-28.    

Author: Tong Yongzhong

Reviewer: Qiu Zhenduo Zhu Xinguo Chen Jiawei Zeng Zhihong

Source:Polymer Physics;Carbon Fiber Workshop Finishing

Hunan Enruiprofessional productioncarbon fiber continuous carbonization furnace, high temperaturecontinuous graphitization furnace.