High-temperature resistant carbon felt used for heat treatment furnaces and single crystal silicon smelting furnaces

Carbon felt is a soft, porous, felt-like pure carbon material composed of randomly interwoven carbon fibers. It is made through fiber stacking and needling processes, followed by high-temperature pyrolysis treatment, making its main element carbon. Essentially, it is an aggregate of carbon fibers rather than a solid block of carbon, which gives it unique comprehensive properties: it possesses the high-temperature resistance and chemical stability of carbon materials, as well as the flexibility of fiber materials and the excellent insulation of porous materials.
 

In the industrial field, carbon felt is often distinguished from graphite felt. The main difference between the two lies in the heat treatment temperature:

Carbon felt: typically carbonized at temperatures between 1000°C and 1500°C, its carbon atoms form a turbostratic structure, microscopically classified as non-graphitized carbon.

Graphite felt: obtained by graphitizing carbon felt at high temperatures between 2200°C and 3000°C. This process transforms the turbostratic structure into an ordered three-dimensional graphite crystal structure.

Therefore, graphite felt has a higher degree of graphitization, better thermal/electrical conductivity, higher purity, and greater rigidity, but it is also more expensive. Carbon felt, on the other hand, emphasizes excellent insulation and cost-effectiveness.

Characteristics of Carbon Felt

1. High Temperature Resistance

In an inert atmosphere: Under vacuum or inert gas protection (such as argon), carbon felt can withstand temperatures up to 3000°C without melting (carbon sublimates at about 3600°C), making it one of the most heat-resistant materials known.

Poor oxidation resistance: In air, carbon begins to oxidize and burn when the temperature exceeds 400°C. Therefore, in practical high-temperature applications, it must be used in conjunction with vacuum or inert atmospheres or coated with an anti-oxidation layer on its surface.

2. Excellent Thermal Insulation (Low Thermal Conductivity)

Carbon felt is composed of a large number of disordered carbon fibers with many pores between the fibers. These pores effectively block heat conduction and convection, making it an excellent high-temperature insulation material. Its insulation performance far surpasses that of traditional ceramic fibers.

3. Low Heat Capacity and Thermal Inertia

Carbon felt itself is very lightweight with low density (about 0.1-0.2 g/cm³), resulting in a very small heat capacity. This means it absorbs and stores very little heat, allowing for very rapid heating and cooling, which is beneficial for energy saving and improving temperature control efficiency in industrial furnaces.

4. Good Chemical Stability

Except for being eroded by strong oxidizers (such as oxygen) at high temperatures, carbon felt exhibits excellent corrosion resistance to most acids, alkalis, salt solutions, and organic solvents. It also does not react with most molten metals at high temperatures.

5. Flexibility and Processability

Unlike traditional hard graphite felts or graphite plates, carbon felt is soft in texture, easy to cut, bend, and wrap into various complex shapes, making installation very convenient.

6. Electrical Conductivity

Carbon is a good conductor, so carbon felt also has electrical conductivity. This property allows it to be used directly as a heating element (generating high temperatures through its electrical resistance when powered), which is central to many vacuum furnace designs.

Applications of Carbon Felt

1. Core Material for High-Temperature Vacuum/Atmosphere Furnaces

Insulation screens/thermal insulation layers: In vacuum sintering furnaces, brazing furnaces, carburizing furnaces, and heat treatment furnaces, carbon felt is made into insulation covers to isolate the high-temperature zone from the furnace walls, greatly reducing heat loss and improving energy efficiency.

Heating elements: Carbon felt is processed into specific shapes (such as rods or plates) and directly supplied with low-pressure high current; its own resistance generates high temperatures, serving as the heating source of the furnace.

2. Crystal Growth Field

In the crystal growth process of single crystal silicon (the basic material for photovoltaics and semiconductors) and sapphire (LED substrates), a Czochralski (CZ) furnace is used. Carbon felt, as a key component of the thermal field system (insulation cages, heaters, crucible supports, etc.), provides a uniform, stable, and pure high-temperature environment for crystal growth.

3. Aerospace Field

Used as insulation layers for rocket engine nozzles and nose cones to withstand high-temperature gas flows.

Used in thermal protection systems (TPS) for hypersonic vehicles as one of the materials for heat shields, resisting extreme aerodynamic heating during atmospheric re-entry.

4. New Energy and Energy Storage Field

Fuel cells: Used as gas diffusion layers (GDL), conducting electrons, diffusing reactive gases, removing reaction product water, and supporting the catalyst layer.

Flow batteries: Used as electrode materials, utilizing its large specific surface area and excellent conductivity for electrochemical reactions.

5. Other Industrial Applications

Aluminum industry: Used for filtering molten aluminum to remove impurities.

Sintering trays: Used in the powder metallurgy industry to support parts during high-temperature sintering without reacting with the parts.

High-purity graphite preparation: Carbon felt itself is a soft felt; after high-temperature graphitization treatment, it can be transformed into a denser structured, higher-performance graphite hard felt.

E-mail:
gdkaidun@163.com

Phone/WeChat:
86-131-3828-6677

Address:
Room 401, Building 21, No. 1, Keqing Road, Yundonghai Street, Sanshui District, Foshan City, Guangdong Province