Pitch-based carbon fiber is a synthetic fiber based on pitch, which has high temperature resistance, ablation resistance, impact resistance, and high modulus. Alfa Chemistry provides pitch-based carbon fibers to meet your lightweight structural composite needs.
Introduction
When the fibers are heat-treated at high temperatures and the proportion of graphite in the fibers varies from 0% to 100%, they are called carbon fibers. Various carbon fiber precursor materials have thus been derived, such as polyacrylonitrile (PAN), viscose rayon and petroleum pitch. Among them, pitch-based carbon fiber refers to a type of carbon fiber prepared from materials rich in polycyclic aromatic hydrocarbons such as pitch, through polymerization, spinning, non-melting, and carbonization.
Properties
The strength and modulus of general-purpose pitch carbon fiber are much worse than that of PAN-based carbon fiber. However, high-performance pitch carbon fiber has ultra-high mechanical properties (especially high modulus) compared with PAN carbon fiber, and has sufficient raw materials, excellent impact resistance, excellent heat transfer, electrical conductivity and extremely low thermal expansion coefficient. In terms of application fields, the aerospace field is the largest demand side for pitch-based carbon fibers. [1]
Pitch Precursor
Pitch, a low molecular (compared to synthetic base) by-product of the coal or petroleum industry, was chosen as one of the early candidates for carbon fiber precursors due to its high carbon yield (85%). The main advantage of using pitch as a precursor is the production of ultra-high modulus carbon fibers due to the significantly increased graphite crystallite size. Isotropic pitch precursors and mesophase pitch precursors can be used to prepare general-purpose pitch carbon fiber (also known as isotropic pitch carbon fiber, IPCF) and high-performance pitch carbon fiber (also known as mesophase pitch carbon fiber, MPCF), respectively.
The pitch precursors are derived from pure chemicals (aromatics and polymers), petroleum and coal processing by-products consisting of various polycyclic aromatic hydrocarbons. However, impurities in raw materials (coke, inorganics, ash, etc.) and special compounds (heavy components, quinoline insolubles, etc.) have a negative impact on the properties of pitch precursors. Therefore, various pretreatments, such as heat treatment, are required to obtain pitch precursors with good spinnability.
Manufacturing Process
Carbon fiber production is a complex process, including raw material pretreatment, pitch preparation, melt spinning, stabilization, carbonization, and graphitization. Each step has a significant impact on the properties and performance of the final carbon fiber product. In particular, the temperature during carbonization and graphitization has a significant effect on the microstructure of carbon fibers, as shown in the figure below. Carbonization and graphitization of pitch-based carbon fibers generally include the following steps:
- Stage 1 - Stable in air at 250 - 350°C.
- Stage 2 - Pre-carburization at 700 - 900°C in an inert medium (such as N2).
- Stage 3 - Carbonization in N2 at 1500 - 1800°C.
- Stage 4 - Graphitization (to obtain very high modulus fibers) to 3000°C.
Microstructural changes during carbonization and graphitization with increasing temperature.[2]
References
- Rahul D. Sandhanshiv, et al. IOP Conf. Ser.: Mater. Sci. Eng. 2020, 810 012014.
- Jinchang Liu, et al. Energy Sources, Part A: Recovery, Utilization, and Environmental Effects, 2020.
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