Carbon felt and graphite felt is non-metallic mineral fiber products with excellent thermal conductivity and electrical properties. They are widely used in vacuum heat treatment, electric furnaces, chemical equipment, aerospace, and other fields. Carbon felt can be classified into soft and hard carbon felt (also known as cured felt, which is soft carbon felt solidified with glue). Depending on the temperature during the production process, it is divided into carbon felt (typically processed at around 900 degrees Celsius domestically) and graphite felt (typically processed at around 1700 degrees Celsius domestically). The main base materials for carbon felt include polyacrylonitrile (PAN)–based carbon felt, viscose-based carbon felt, and pitch-based carbon felt. Carbon felt is a cost-effective substitute for graphite felt, suitable for applications where chemical purity is not critically important.
Differences between Carbon Felt and Graphite Felt
Temperature Resistance
The carbonization temperature of carbon fiber is around 1000 degrees Celsius, and after being made into carbon fiber felt, the carbon content is about 90%, with a usage temperature of around 1000 degrees Celsius. When carbon fiber felt is heated above 2000 degrees Celsius in an oxygen-free environment, it becomes graphite fiber. After being made into graphite fiber felt, the carbon content can exceed 99%, and the usage temperature can reach 2000 degrees Celsius. If carbon fiber felt is used in insulation environments above 2000 degrees Celsius, further reactions will occur.
Composition and Structure
Carbon felt is primarily made from carbon fiber and is a black fiber felt with good thermal conductivity and electrical properties. The main material of carbon felt is carbon fiber or bonded carbon fiber felt, where carbon fiber gradually crystallizes and becomes graphitized at high temperatures. Carbon fiber and graphitized carbon fiber are bonded by resin adhesives.
Graphite felt, on the other hand, is a porous material made by mixing natural graphite or artificial graphite micro powder with kerosene and then adding resin as a binder. This mixture is then subjected to high pressure, dried, and baked. Its structure is relatively loose, and soft, and has good lubricity and chemical stability.
Graphite felt has a higher carbon content than carbon felt, reaching over 99%.
Manufacturing Process
Both carbon felt and graphite felt are made from precursor fibers through processes such as weaving, needling, low-temperature carbonization, and high-temperature carbonization. Their initial processes are similar, with the main difference being that graphite felt undergoes further high-temperature carbonization. In the manufacturing process of graphite felt, carbon fibers are first cut into short fibers, mixed with a binder, and then formed, cured, carbonized, and graphitized to produce graphite felt.
Carbon felt is mainly prepared through steps such as vapor deposition, carbonization, and high-temperature heat treatment, where the carbonization process generally involves chemical reactions like vapor cracking. For graphite felt, its preparation involves the exfoliation and compaction of graphene. Specifically, large-scale production of graphite felt can be achieved through mechanical exfoliation, chemical exfoliation, and physical exfoliation methods.
Applications
Carbon felt is mainly used for insulation, protection, and conductivity in high-temperature environments, such as in aerospace manufacturing, nuclear engineering, solar panels, and thermal conductive plates. Graphite felts main use is as an insulation material in single-crystal silicon smelting furnaces. In the chemical industry, it can be used as a filtration material for high-purity corrosive chemical reagents. Under non-oxidizing atmospheres, the usage temperature of graphite felt can reach around 3000 degrees Celsius.
Vacuum Furnaces: The heating elements used in vacuum furnaces require good thermal conductivity and electrical properties. Both carbon felt and graphite felt can be used as heating elements. Graphite felt, due to its lower strength, usually needs support materials for fixation.
Chemical Industry: Graphite felt has better chemical stability and lubricity, making it more suitable for use in reaction vessels requiring stirring.
Aerospace: In the aerospace field, heating elements need good radiation resistance and high-temperature stability, making carbon felt more suitable for such applications.
Physical and Chemical Properties
Physical Properties
- Density: The density of carbon felt is generally higher than that of graphite felt, typically ranging from 1.7 to 2.0 g/cm³, while the density of graphite felt ranges from 1.5 to 1.8 g/cm³.
- Thermal Conductivity: Both carbon felt and graphite felt have good thermal conductivity, but the thermal conductivity of graphite felt is slightly higher than that of carbon felt.
- Electrical Properties: Both carbon felt and graphite felt exhibit excellent electrical properties, especially at high frequencies and high temperatures.
- Strength: Carbon felt has higher strength than graphite felt, but graphite felt is more flexible.
Chemical Properties
- Stability: Graphite felt has better chemical stability, maintaining stability in high-temperature and corrosive environments, whereas carbon felt is more susceptible to oxidation and corrosion.
- Radiation Resistance: Carbon felt has good radiation resistance, making it suitable for nuclear industry applications, whereas graphite felt has relatively poor radiation resistance.
Choosing Carbon Felt or Graphite Felt?
When purchasing, it is important to consider the specific application’s requirements, including the operating environment’s temperature, chemical properties, and physical form needs (such as whether folding or cutting is required). Additionally, cost-effectiveness should be taken into account, as although graphite is felt to have superior performance, it may be more expensive. If the application does not require particularly high-temperature resistance or other extreme performance, choosing carbon felt may be more economical.
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