Brief Description of the Production Process of Carbon Fiber Felt and the Principle of Carbonization Activation

 

Carbon Fiber Felt has good electrical conductivity and can withstand temperatures up to 1300°C. It is often used in long-term high-temperature environments, such as single crystal ingot furnaces, to provide insulation and heat preservation. The production process of carbon fiber felt mainly consists of the following four steps:

 

1. Carbon Felt Impregnation and Drying Process: After the raw material viscose fiber cloth is screened and inspected, it enters the 1% diammonium phosphate aqueous solution prepared in the impregnation tank and is immersed in it for 1 hour. After being fished out, it enters the continuous extrusion equipment for extrusion, and the extruded diammonium hydrogen phosphate solution flows back to the impregnation tank. After using natural light energy, it is placed on a drying rack to dry or dried in a dryer.

 

2. Carbon Felt Carbonization Process: The dried viscose fiber cloth enters the carbonization furnace and is heated to 300°C. The temperature rises slowly at first and then quickly. There are nitrogen pipes at the bottom of the furnace, and nitrogen is introduced into the furnace as a protective gas for product carbonization. Carbonization is the process of removing volatile non-carbon components in the fiber, increasing the carbon content and purity of the product, and forming carbonized fibers with a graphite-like microcrystalline structure.

 

 

3. Carbon Felt Activation Process: The carbonized viscose fiber cloth is heated to about 1400℃ (furnace temperature) for activation, and the activated carbon fiber felt is the crude product. At the same time, steam is passed, and the fiber felt cloth is perforated with a high-temperature resistant tube to increase the surface area and obtain the finished carbon fiber felt. The so-called activation process is to add a catalyst (such as nitrogen) to increase the number of activated molecules in the entire reaction, making the properties of carbon molecules and atoms more active and energetic.

 

4. Slitting and Rolling: After the carbon fiber felt after the perforation is naturally cooled, it is cut into corresponding sizes according to the sales needs using a slitting machine, a cutting machine, and a rolling machine, and then cut and rolled and temporarily stored for sale.

 

Since 90% of the carbon felt is void, its thermal insulation performance in a vacuum or inert atmosphere is very superior, especially stable under high temperature conditions. Many people know a lot about the production process of carbon felt, but know little about the carbonization activation principle of carbon felt.

 

Carbonization and activation of carbon felt are important process flows in the production of carbon fiber felt, and are also the key to determining the void structure and performance of the product. After impregnation, the viscose fiber does not melt or burn at high temperatures, and maintains the fiber shape.

 

Cellulose fiber is carbonized and cracked at high temperatures, and other non-carbon substances are cracked into small molecules or other gaseous forms and escape. After pyrolysis, non-carbon atoms escape and undergo polycondensation to form a turbostratic graphite structure. Viscose fiber will remove physically adsorbed water at room temperature to 130°C, and the main chain of the macromolecule will break while dehydrating at 270-400°C (temperature in the carbonization furnace).

 

 

8%-10% of CO2 and H2O small molecules bound in the raw fiber of carbon felt escape and release NH3. Carbonization occurs in a stable thermal state, driving away non-carbon atoms, and turns black with high temperature oxidation. During the carbonization and activation process, the nitrogen, oxygen, and hydrogen elements contained in the fiber are released in the form of H2O, CO2, NH3, and N2 to become carbon fiber. The reaction formula is:

 

 

Carbon Felt Carbonization and activation are complex physical changes and structural transformation processes, which are thermal decomposition and thermal polymerization processes under the protection of inert gas (N2) in the furnace. The final result is that the trapezoidal structure formed by the oxidation process is transformed into a carbon fiber turbostratic graphite structure. This process includes the breaking of carbon-carbon bonds and the polymerization between functional groups. The gases generated are mainly CO2 and H2O.

 

Low-temperature carbonization gradually enriches carbon elements, and activation occurs when the temperature rises, so that the carbon structure is gradually fixed. Carbon felt is light in weight, small in specific heat capacity, soft in texture, good in insulation, and easy to operate. It is particularly suitable for intermittent high-temperature vacuum furnaces, which can save a lot of energy and is an excellent thermal insulation material for vacuum metallurgical industrial furnace equipment.