Overview of Carbon Carbon Composite Materials

Definition of C/C Composite Materials

Carbon carbon composite material (referred to as "C/C composite", the same below) is a type of carbon fiber composite material, which uses carbon fiber as the reinforcing material and deposited carbon as the matrix material. Carbon fiber composite materials are a general term for composite materials formed by reinforcing carbon fibers with resin, carbon, metal, ceramics and other matrices. According to the different matrix materials, they are mainly divided into carbon fiber reinforced resin based composite materials, carbon carbon composite materials, carbon fiber reinforced metal based composite materials, etc. The common carbon fiber composite materials are resin based carbon fibers with resin as the matrix, such as wind turbine blades, rackets, etc. The matrix of C/C composites is carbon, which is almost entirely composed of elemental carbon and has excellent high temperature resistance. At the same time, it inherits the strong mechanical properties of carbon fibers and has been industrialized earlier in the field of national defense.

Market demand for C/C composite materials

Application Fields

C/C composites are located in the midstream of the industry chain, with upstream applications including carbon fiber and prefabricated manufacturing, and downstream applications being more extensive. C/C composites are mainly used as heat-resistant materials, friction materials, and high mechanical performance materials, and are applied in aerospace (rocket nozzle throat liners, thermal protection materials, and engine thermal structural components), brake materials (high-speed trains, aircraft brake discs), photovoltaic thermal fields (insulation barrels, crucibles, flow tubes, and other components), biological organisms (artificial bones), and other fields. C/C composites are located in the middle of the industry chain, with upstream coverage of carbon fiber and carbon fiber preform production. Currently, domestic C/C composite enterprises mainly focus on a single link of composite materials and extend towards upstream preforms.

C/C composites have excellent comprehensive properties, including low density, high specific strength, high specific modulus, high thermal conductivity, low thermal expansion coefficient, good fracture toughness, wear resistance, and erosion resistance. Especially unlike other materials, the strength of C/C composites not only does not decrease but may also increase with increasing temperature, making it an excellent heat-resistant material. Therefore, it was the first to achieve industrial application in rocket throat liners.

C/C composite, as a composite material of graphite and carbon fiber, inherits the excellent mechanical and processing properties of carbon fiber, while also possessing the heat resistance and corrosion resistance of graphite. It has become a strong competitor to graphite products. Especially in the application field with high strength requirements - photovoltaic thermal field, the cost-effectiveness and safety of C/C composites have become increasingly prominent under the large-scale silicon wafer, and have become a necessity. On the contrary, graphite has become a supplement to C/C composites due to limited supply capacity.

Technology:

1. Process accumulation: Two process routes, pure chemical gas phase and gas-liquid mixture, have been formed in China. The cost difference between different processes is significant, and the composite of carbon fiber and matrix carbon is the densification process. The higher the degree of densification, the better the mechanical properties of the material. The formed prefabricated body contains many pores and has a low density, which cannot be directly applied. Carbon needs to be deposited on the prefabricated body to become a truly dense and high-performance C/C composite material. The mainstream production processes in China include two types: liquid immersion thermal decomposition method and chemical vapor deposition method (also known as CVD).

(1) Chemical vapor deposition: using pyrolytic carbon as the carbon source, the main steps include pyrolytic carbon, vapor deposition, mechanical processing, and heat treatment. Due to the formation of a coating hard shell on the surface of the billet during the densification process, which leads to the closure of channels inside the embryo, repeated machining and heat treatment are required to remove the surface hard shell layer and open closed pores. The preparation cycle is quite long.

(2) Liquid phase impregnation: Using resin or asphalt as a carbon source, immerse the prefabricated body into it and heat treat it under an inert atmosphere to convert the resin or asphalt into the matrix carbon. This process is relatively simple, the raw materials are cheap, and the impregnation method has better penetration effect, but it has certain damage to the fibers.

Comparing the two processes, the advantage of CVD is that the densification process does not lose fibers, making it suitable for producing C/C composites with higher mechanical properties. However, its disadvantage is that the gradual diffusion of gas leads to concentration differences inside the preform, resulting in uneven material density distribution.