Carbon fiber is a material composed of extremely thin, strong, crystalline filaments made primarily of carbon atoms. These filaments are bonded together in long chains, resulting in a material known for its exceptional strength-to-weight ratio and stiffness. These properties make carbon fiber valuable in demanding applications.
The Raw Materials
The journey of carbon fiber begins with precursor materials, from which the carbon filaments are derived. The most common precursor, polyacrylonitrile (PAN), accounts for approximately 90% of global production. PAN’s long, chain-like molecules are well-suited for forming the continuous fibers.
Its high carbon content and thermal stability make PAN a suitable starting material. While PAN is predominant, other less common precursors like rayon or petroleum pitch can also be used. Precursor selection and quality significantly influence the final product’s characteristics.
Core Manufacturing Steps
Transforming precursor fibers into carbon fiber involves precise thermal processing steps. Stabilization, the first stage, prepares PAN fibers for subsequent high-temperature treatments. This involves heating fibers in an oxygen-rich environment, usually air, at 200°C to 300°C.
During stabilization, PAN fibers undergo a chemical rearrangement, forming a more thermally stable, ladder-like structure. This controlled oxidation and cyclization prevents the fibers from melting or degrading at the much higher temperatures of the next stage.
Following stabilization, fibers proceed to carbonization, converting them into nearly pure carbon. This involves heating stabilized fibers to 1000°C and 3000°C in an inert atmosphere, such as nitrogen or argon, to prevent burning. During carbonization, non-carbon elements like hydrogen, nitrogen, and oxygen are driven out of the fibers. This high-temperature treatment leaves a material predominantly carbon (>90% purity), with a graphite-like crystalline structure. The specific temperature used during carbonization influences the final properties of the carbon fiber, with higher temperatures generally leading to increased stiffness. This stage imparts carbon fiber with its remarkable strength and rigidity.
Post-Production Treatments
After carbonization, carbon fibers undergo further treatments to enhance performance and compatibility. Surface treatment modifies the fiber’s outermost layer. This is often achieved through oxidation, exposing fibers to gases or chemical solutions like nitric acid.
Surface treatment improves carbon fiber’s bonding with resin matrices in composite materials. This process creates a slightly rougher surface and introduces active chemical groups, allowing the resin to adhere more effectively. Enhanced bonding is essential for the composite product’s strength and durability.
Following surface treatment, sizing, a protective layer, is applied to the fibers. This coating protects delicate carbon fibers from damage during handling, winding, and weaving. Sizing agents also improve compatibility between carbon fibers and resins used to create composite parts. This ensures better integration and load transfer within the composite, contributing to its mechanical properties.
Key Characteristics and Uses
The manufacturing process yields carbon fibers with unique properties, highly sought after in many industries. Carbon fiber exhibits an exceptional strength-to-weight ratio, being incredibly strong for its low mass. It also possesses high stiffness, providing rigidity to structures. Beyond mechanical strength, carbon fiber offers corrosion resistance and high temperature tolerance, contributing to durability in harsh environments. These properties allow carbon fiber use where performance and weight savings are crucial.
Carbon fiber is widely used across various sectors, including aerospace, where it is found in aircraft fuselages and wings to reduce weight and improve fuel efficiency. The automotive industry utilizes carbon fiber in high-performance vehicles and racing cars for enhanced strength and reduced mass. In sporting goods, it is integral to equipment like tennis rackets, golf clubs, bicycles, and skis, providing improved performance. Carbon fiber also plays a role in large structures like wind turbine blades, where its strength and lightness are beneficial.