What is carbon fiber?

Carbon fiber (abbreviated as CF), often referred to as the “king of new materials,” plays a pivotal role in modern industry, aerospace, new energy, and high-end manufacturing worldwide.

1. The Nature and Core Properties of Carbon Fiber Carbon fiber refers to high-strength, high-modulus fibers with a carbon content of 90% or higher. It is produced by carbonizing and graphitizing organic fibers (such as polyacrylonitrile and pitch) at high temperatures. Its core physical advantages can be summarized in one sentence: “As light as a feather, as strong as steel.” ” Ultra-high specific strength and specific modulus: Its density is only about $1/4$ that of steel (approximately $1.5 - 2.0 \text{g/cm}^3$), yet its tensile strength is 7 to 9 times that of steel. Excellent corrosion resistance and fatigue resistance: It exhibits extremely high stability against common acids and alkalis and is resistant to metal fatigue under long-term alternating loads. Extremely low coefficient of thermal expansion: It exhibits virtually no dimensional change under extreme temperature fluctuations, making it the material of choice for precision optical instruments and spacecraft. Excellent electrical and thermal conductivity: It inherits the electrical and thermal properties of carbon.

2. In practical industrial applications, carbon fibers are typically classified based on the type of precursor and mechanical properties (grade):

   1. Classification by Precursor
   PAN-based carbon fibers (polyacrylonitrile-based): The absolute mainstream. More than 90% of the world’s carbon fibers fall into this category; they offer good overall performance and a relatively mature production process.

   Asphalt-based carbon fiber: Primarily used in specialized aerospace and electronic heat dissipation components that require extremely high thermal conductivity, high stiffness, or a zero coefficient of thermal expansion; it is expensive.

   Viscose-based carbon fiber: Produced in relatively small quantities, it is mainly used in ablation-resistant and thermal insulation materials.

3. Classification by Mechanical Properties (Using Toray Industries, Inc. Standards as an Example)
   The “T Series” (emphasizing strength) and “M Series” (emphasizing stiffness), commonly heard in the market, are internationally recognized references:
   
   
   High-Strength Type (T Series): e.g., T300, T700, T800, T1000, T1100, T1200. The higher the number, the greater the tensile strength.
   
   
   Applications: T300 and T700 are primarily used in sporting goods, automobiles, and wind turbine blades; T800 and higher grades are strictly prohibited from being exported without authorization and are mainly used in commercial aircraft cabins, military applications, and aerospace.
   
   
   High-Modulus Type (M Series): e.g., M40, M50, M60. These primarily aim for high modulus (i.e., extremely resistant to stretching or bending, with exceptional rigidity).
   
   
   Applications: Satellite antenna mounts, spacecraft docking mechanisms.
   
   
4. Classification by Tow Size
   Small tows (1K–24K): Each carbon fiber tow contains 1,000 to 24,000 individual filaments. These offer excellent performance but are expensive, and are primarily used in aerospace and high-end sports equipment.
   
   
   Large-tow (48K and above): Primarily used in civilian industries, such as wind turbine blades, building reinforcement, and hydrogen storage tanks, with a focus on low cost and large-scale production.