Manager Hao (pre oxygenation thread): 13831164999
Manager Shi (pre oxygenation wire): 17332928150
Manager Gu (Pre oxygenation Silk): 13833138900
Manager Zhao (woven fabric, pre impregnated fabric, prefabricated body): 15028196018
Manager Zhang (woven fabric, axial fabric): 13703314888
Manager Zhao (Composite Products): 13944687090
Manager Steve Duan:15704489366
Address: 226 Shifu East Road, Gaocheng District, Shijiazhuang City, Hebei Province
The carbonization process is the core link that determines the basic structure and core mechanical properties of carbon fiber—it transforms the thermoset pre-oxidized fiber into a carbon-rich crystalline structure, directly affecting the strength, modulus, density, and chemical stability of the final carbon fiber. Below is a detailed analysis of its effects, tailored for industrial B2B scenarios:
Pre-oxidized fiber has a three-dimensional cross-linked structure containing a large number of non-carbon elements (O, H, N, etc.). The carbonization process (400–1500°C, inert atmosphere) removes these non-carbon elements through pyrolysis reactions (dehydration, deamination, decarboxylation), and rearranges the remaining carbon atoms into a turbostratic graphite-like structure (disordered stacked graphite microcrystals).
Key structural changes:
Non-carbon elements are removed in the form of small molecules (H₂O, NH₃, CO₂), and the carbon content of the fiber increases from ~60% (pre-oxidized fiber) to 90–95% (carbonized fiber).
Carbon atoms form planar hexagonal rings, which are stacked loosely and disorderly (unlike the highly ordered structure of natural graphite). This turbostratic structure is the basis of carbon fiber’s high strength and modulus.
Impact on subsequent processes: A complete carbonization reaction lays the foundation for the ordered arrangement of graphite microcrystals in the subsequent graphitization stage. Incomplete carbonization will leave residual non-carbon elements, which will cause defects in the graphite structure during graphitization.
The temperature, heating rate, and tension control in the carbonization process directly affect the density of the carbon fiber structure and the orientation of microcrystals, thereby determining the core mechanical properties.
Tensile strength:
Positive effect: Slow heating (1–3°C/min) allows small molecules to escape gradually, avoiding the formation of internal bubbles or microcracks; appropriate tension (0.5–1.0 cN/dtex) reduces structural shrinkage and improves the compactness of the fiber. Under optimized parameters, the tensile strength of PAN-based carbon fiber can reach 3–7 GPa.
Negative effect: Too fast heating will cause rapid escape of small molecules, forming porous defects inside the fiber, which reduces the tensile strength by 20–30%; excessive tension will cause fiber breakage, while insufficient tension will lead to loose structure and low strength.
Elastic modulus:
Carbonization mainly lays the foundation for the modulus—the modulus of carbonized fiber is 150–200 GPa (for PAN-based). The high modulus of carbon fiber (250–800 GPa) is further improved by the graphitization process, but the ordered arrangement of microcrystals in graphitization depends on the complete carbonization of the fiber.
If carbonization is incomplete, residual non-carbon elements will hinder the orientation of graphite microcrystals during graphitization, making it impossible to achieve high modulus even with high-temperature treatment.
The carbonization process significantly increases the density of the fiber by removing low-density non-carbon elements and improving structural compactness.
Density change: The density of pre-oxidized fiber is ~1.3–1.4 g/cm³, and after carbonization, it increases to 1.7–1.8 g/cm³ (PAN-based). Higher density means a more compact structure and fewer internal defects.
Porosity control: The heating rate is the key factor affecting porosity. Slow heating ensures that small molecules escape through the fiber surface without forming internal pores; fast heating will trap small molecules inside the fiber, forming a porous structure (porosity >5%), which drastically reduces the mechanical properties of carbon fiber.
After carbonization, the fiber has a high carbon content and a stable carbon structure, which significantly improves its chemical stability.
Corrosion resistance: Carbonized fiber is inert to most acids, alkalis, and organic solvents (except strong oxidizing acids at high temperatures), which is much better than pre-oxidized fiber (prone to hydrolysis due to surface oxygen-containing groups).
High-temperature resistance: In an inert atmosphere, carbonized fiber can withstand high temperatures of 1500°C without decomposition; in an oxidizing atmosphere, it begins to oxidize at ~400°C (this oxidation resistance can be further improved by coating in subsequent processes).
Color change: Pre-oxidized fiber is yellowish-brown, and after carbonization, it turns into black, glossy carbon fiber due to the formation of a carbon-rich structure.
Dimensional shrinkage: During carbonization, the fiber undergoes axial shrinkage (5–10%) and radial shrinkage (10–15%) due to the removal of non-carbon elements and the rearrangement of carbon atoms. Tension control during carbonization can reduce axial shrinkage—higher tension leads to smaller shrinkage and better dimensional stability of the fiber.
The carbonization process is not only a process of removing non-carbon elements but also a process of constructing the basic structure of carbon fiber. Only by strictly controlling the temperature gradient, heating rate, inert atmosphere purity, and tension can we obtain carbon fiber with high strength, low porosity, and stable structure. Incomplete carbonization or improper parameter control will lead to permanent defects in the fiber, which cannot be compensated by subsequent graphitization or surface treatment.
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Ltd. All rights reserved.
Manager Hao (Pre-oxidized Fiber): 13831164999,hjh@hbtangu.com
Manager Shi (Pre-oxidized Fiber): 17332928150,sj@hbtangu.com
Manager Gu (Pre-oxidized Fiber): 13833138900
Manager Zhao (Woven Cloth, Prepreg Cloth, Preform): 15028196018,zb@hbtangu.com
Manager Zhang (Woven Cloth, Axial Cloth): 13703314888
Manager Zhao (Composite Products): 13944687090, zqy@hbtangu.com
Manager Steve Duan:15704489366,245140980@qq.com
Email: 245140980@qq.com
Address: No. 226, East Shifu Road, Gaocheng District, Shijiazhuang City, Hebei Province
