Carbon fiber is a filamentous carbon material obtained from organic fibers through carbonization processes. It has a diameter of 5-10 microns and is the fiber with the highest specific strength and specific modulus among mass-produced high-performance fibers. It is widely used in aerospace, rail transit, ships and vehicles, new energy, and other fields.
What Is Carbon Fiber?
Carbon fiber (CF) is an inorganic fiber with a carbon main chain structure containing more than 90% carbon, formed by pyrolysis and carbonization of organic fibers such as polyacrylonitrile (or pitch, viscose) in a high-temperature environment.
Carbon fiber possesses excellent physical and chemical properties, including low density, high strength, high-temperature resistance, high chemical stability, fatigue resistance, and friction resistance.
Advanced composite materials reinforced with carbon fiber, such as CFRP, exhibit excellent properties such as high specific strength, high specific modulus, high-temperature resistance, corrosion resistance, fatigue resistance, and low thermal expansion coefficient.
Structure of Carbon Fiber
Its structure depends on the precursor structure and carbonization process. Regardless of the material used, carbon atoms in carbon fiber are always oriented parallel to the fiber axis.
The basic element of this structure is the hexagonal carbon atom layer lattice, forming layer planes. Within the layer plane, carbon atoms are connected by strong covalent bonds with a bond length of 0.1421nm. The layer planes are connected by weak van der Waals forces, with an interlayer spacing between 0.3360-0.3440 nm. Carbon atoms between layers have no regular fixed positions.
During the process of production, due to the large amount of elements and various gases (such as CO, CO2, H2O, NH3, H2, N2) escaping during the carbonization process of the precursor, various small defects and voids will form on its surface and interior. These defects and voids will greatly impact the strength, with the vast majority of fiber breakages occurring at defects or cracks.
Kinds of Carbon Fiber
By Raw Materials
It can mainly be divided into three categories: polyacrylonitrile (PAN) based carbon fiber, pitch-based carbon fiber, and rayon-based carbon fiber. Among them, PAN-based carbon fiber is the mainstream, accounting for more than 90% of global production.
| Polyacrylonitrile (PAN) based carbon fiber is formed through the spinning, pre-oxidation, and carbonization stages of polyacrylonitrile. It has high strength, high stiffness, lightweight, high-temperature resistance, corrosion resistance, excellent electrical properties, and very strong compression and bending resistance. Currently, PAN-based carbon fiber is still the mainstream in the global market.
| Pitch-based carbon fiber is made from petroleum pitch or coal pitch through pitch refinement, spinning, pre-oxidation, carbonization, or graphitization. The raw material cost of pitch-based carbon fiber is lower than that of PAN-based carbon fiber, but due to the complex production process, its production cost is greatly increased.
In addition, it has relatively low compressive strength, and its post-processing performance is not as good as PAN-based carbon fiber, so its production scale and application areas are somewhat limited. However, due to its excellent heat transfer, electrical conductivity, and extremely low thermal expansion coefficient, the pitch-based material still plays a unique role in military and aerospace fields where these properties are required.
| Rayon-based carbon fiber is derived from viscose fiber, which is mainly composed of cellulose, through dehydration, pyrolysis, and then carbonization. Rayon-based carbon fiber has an underdeveloped three-dimensional graphite structure and small thermal conductivity. At the same time, it is derived from natural cellulose wood or cotton lint, which has excellent biocompatibility and can also be used as a good environmental protection and medical hygiene material.
However, the production process is longer, the process conditions are strict, and it is not suitable for large-scale production, resulting in higher costs. In addition, the overall performance indicators of rayon-based carbon fiber are worse than those of PAN-based carbon fiber, and its comprehensive performance-price ratio is at a disadvantage in competition. Currently, it accounts for less than 1% of the world’s carbon fiber production.
By Tow Size
PAN-based carbon fiber can be divided into small tow and large tow categories based on the bundle specifications:
| Small tow: Carbon fiber bundle specifications are below 24K, with the number of single fibers in the bundle between 1,000 and 24,000. Small tow carbon fiber has strict process control requirements, high equipment costs for carbonization, etc., and higher production costs. It is mainly used in high-tech fields such as national defense and military, as well as aircraft, missiles, rockets, satellites, and other areas.
| Large tow: The bundle specifications reach or exceed 48K, with the number of single fibers in the bundle exceeding 48,000, including 48K, 60K, 80K, etc. Large tow products have relatively lower performance and lower production costs, mainly used in industrial applications, including textiles, transportation, energy, and other fields.
the number of single fibers in the bundle exceeds 48000.
By Carbon Fiber Performance Characteristics
It can usually be divided into three categories: high-strength series characterized by high strength, high-modulus characterized by high modulus, and high-modulus high-strength series with both high modulus and high strength.
Characteristics of Carbon Fiber
| Low density and lightweight, with a density of 1.5-2 g/cm³, equivalent to 1/4 of steel density and 1/2 of aluminum alloy density.
| High strength and elastic modulus, with strength 4-5 times that of steel and 100% elastic recovery;
| Low thermal expansion coefficient, the thermal conductivity decreases with increasing temperature, resistant to sudden cooling and heating, and will not crack even when suddenly cooled from several thousand degrees Celsius to room temperature;
| Good electrical conductivity, with a specific resistance of 775μΨ/cm for high-modulus series and 1500μΨ/cm for high-strength series at 25°C;
| Good resistance to high and low temperatures, not melting or softening in non-oxidizing atmospheres at 3000°C, and remaining flexible without embrittlement at liquid nitrogen temperatures;
| Good acid resistance, inert to acids, and resistant to concentrated hydrochloric acid, phosphoric acid, sulfuric acid, etc. In addition, it also has characteristics such as oil resistance, radiation resistance, absorption of toxic gases, and neutron moderation.
The Grades of Carbon Fiber
The naming of carbon fiber grades contains key information about its performance and applications. There are numerous carbon fiber grades, each with its unique performance characteristics and application scenarios.
T series, such as T300, etc. “T” usually stands for “tensile strength”.
| T300 carbon fiber, where “300” in this grade is not just a simple number, but represents a specific performance level. T300 has medium strength and modulus, and its naming reflects its relative positioning in the development history of carbon fiber. Due to its relatively balanced performance and moderate cost, it is widely used in industrial fields. In general mechanical parts and sports equipment such as low-end bicycle frames, it can meet basic strength and performance requirements, providing a certain lightweight advantage for products.
| T700 carbon fiber has achieved a significant leap in performance. The number “700” suggests a significant increase in strength compared to T300. This enhancement in strength has enabled T700 to find wide applications in the automotive industry. Today, as cars pursue lightweight design to improve fuel efficiency and performance, car parts made of T700, such as some frame structures and engine components, can significantly reduce weight while withstanding complex working stresses, greatly improving the overall performance and reliability of cars.
| T800 carbon fiber, as a representative of high performance, clearly indicates its excellent performance in terms of strength with “800”. In the aerospace field, where material requirements are almost demanding, T800 has become an ideal choice for manufacturing key structural components of aircraft, such as the main load-bearing parts of wings and structural components of spacecraft, thanks to its ultra-high strength, excellent modulus, and good thermal stability. Its naming accurately conveys its high-end positioning among high-strength carbon fibers.
M series, such as M40, M55, etc. “M” usually stands for “modulus”.
| M40 carbon fiber, where “40” reflects its modulus level. The high modulus characteristic makes it play an important role in fields that require extremely high dimensional stability and precision. For example, in satellite antenna structures and support components of high-end optical instruments, M40 can ensure precise shape and position maintenance in complex environments, ensuring normal equipment operation.
| M55 carbon fiber, where “55” in its naming further reflects a higher modulus level. At the same time, M55 also has excellent high-temperature resistance. This makes it perform well in some high-temperature, high-precision industrial applications, such as some key components of aircraft engines, where M55 can maintain good performance and dimensional stability under extreme conditions.
How to Choose Appropriate Carbon Fiber?
In practical applications, choosing the appropriate carbonaceous fiber is crucial. This requires comprehensive consideration of factors such as the product’s use environment, performance requirements, cost budget, and more.
For example, in the field of sports equipment, if pursuing high performance and high-end quality, T800 or M series carbon fibers might be chosen to manufacture top-level competition bicycles or golf clubs to meet athletes’ ultimate demands for lightweight and high-strength equipment. For some mass-produced consumer products, such as ordinary bicycles or general sports equipment, the T300 or T700 may achieve a better balance between performance and cost.
Applications of Carbon Fiber
| Aerospace: In the manufacture of aircraft engines, the application of titanium alloys has greatly reduced the weight of engines, but as a metal, there is a serious problem of fatigue. If the metal is subjected to sufficiently large forces for a long time, microcracks will occur, which can develop into safety hazards when the entire material cracks. Compared to metal materials, the carbon composite does not have the concept of fatigue strength, and it also has the characteristics of low density, high strength, and strong fatigue resistance. It is used to manufacture rocket fuel storage tanks, aircraft shells, etc. In the manufacture of advanced civil aircraft, the proportion of carbon fiber use has exceeded 50%.
| Automotive: It has wide applications in the new energy field. Reducing the weight of cars can reduce carbon dioxide emissions, so car lightweight is an important energy-saving method. Battery boxes can effectively reduce weight by nearly 40% compared to traditional battery boxes.
Many racing cars and high-performance cars use carbon fiber car seats, which have advantages such as impact resistance, corrosion resistance, high strength, and good shock absorption performance.
| Sports: They have many advantages when used in sports equipment, such as lightweight and good mechanical properties. Lightweight sports equipment helps users perform better, such as tennis rackets, golf clubs, bicycles, skis, etc. In addition, some equipment that moves with power other than human power, such as racing cars and boats, are also easier to control when lighter.
FAQ
What’s The Meaning of a Specific Modulus?
Specific modulus is the elastic modulus per unit density. It is an important indicator of a material’s load-bearing capacity. The higher the specific modulus, the greater the rigidity of the part.
What’s The Meaning of a Specific Strength?
Specific strength is the ratio of a material’s strength to its apparent density. The higher the specific strength, the lighter the material used to achieve the corresponding strength. High-quality structural materials should have a relatively high specific strength to meet strength requirements.
With the continuous advancement of technology and the increasing diversity of application needs, the research and development of carbon fiber are constantly innovating, carbon fiber performance is continuously improving, and application areas are expanding.
From traditional fields such as aerospace, automotive, and sports to emerging industries such as energy, medical care, and electronics, it is changing our lives with its unique performance advantages.
Carbon Fiber Provider: Tengye
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Image Source: Adesivisicurezza & BMW & Gminsights & M-chemical & Precedenceresearch & Velocite-bikes & Gdwise
