Talking about Carbon Fiber: Different Carbon Fiber, Counting the Functional Applications of Carbon Fiber

 

It has been a long time since I updated the article “Talking about Carbon Fiber”. Su Ge Lawei has been busy with the mid-term assessment of his postdoctoral project recently. It is really time-sensitive and the task is heavy. Please understand that I will continue to write original articles. This article mainly discusses some cases of carbon fiber non-structural material applications. If you have any suggestions, please add Su Ge Lawei WeChat to discuss: zahawe.

 

The biggest feature of carbon fiber is its high specific strength, that is, light weight and high strength. Most carbon fiber composites use this property of carbon fiber. In composite materials, carbon fiber is composited with plastics, ceramics, metals and even carbon matrices. The matrix material plays the role of transferring loads in composite materials, and it transfers external forces to carbon fibers.

 

Carbon fiber plays the role of bearing loads in composite materials, so the destruction of composite materials must first break the carbon fiber. This is our common carbon fiber composite material. In addition to high specific strength, carbon fiber also has high temperature resistance, corrosion resistance, soft and easy to weave, small thermal expansion coefficient, and easy conductivity. Although the application of these properties of carbon fiber is not as good as as a structural material, it has also formed certain special products. This article is a simple introduction to this type of application.

 

As a Thermal Insulation Material

 

Isn’t carbon fiber high in thermal conductivity? How can it be used as a thermal insulation material? This starts with the way heat is transferred. There are three ways of heat transfer: heat transfer, convection, and thermal radiation.

 

Heat transfer is the contact between objects of different temperatures, and heat is transferred from the high-temperature object to the low-temperature object. Convection is the transfer of heat through fluid flow. Thermal radiation is the transfer of heat to another object in the form of radiation waves. Carbon fiber is needled into felt, which becomes a loose and porous carbon fiber polymer. The shape of the felt is maintained by friction between the fibers. The fibers are overlapped together, which is a point contact, which greatly reduces the heat transferred through the solid heat transfer path.

 

Above 800℃, as the radiation intensity increases, thermal radiation becomes the main form of heat transfer. The radiation wave is constantly reflected between the fibers and dissipated inside the felt, thereby achieving the effect of heat insulation.

 

Currently, carbon fibers used as insulation materials are also divided into three types: viscose-based, polyacrylonitrile-based, and asphalt-based. Polyacrylonitrile-based raw materials are cheap and the production process is simple. Many domestic companies are using this type of carbon felt. However, after high-temperature treatment, the fibers of this type of carbon felt are brittle and prone to broken fiber scraps, which is harmful to the furnace environment and human health. Therefore, foreign companies rarely use polyacrylonitrile-based carbon felt.

 

Viscose-based carbon fiber is not easy to graphitize during high-temperature treatment, so the heat transferred through the solid is very small. Under the same conditions, the thermal insulation effect is also the best of the three materials. However, the carbon yield in the production process of viscose-based carbon fiber is relatively low. Even 10 kg of raw silk can produce 1 kg of viscose-based carbon fiber, so additives are needed to increase the carbon yield, which will produce residues of other elements. However, many companies can now achieve high purity. Asphalt-based carbon fiber is easy to graphitize, so the purity can be improved very well.

 

Activated Carbon Fiber

 

Write down the title, careful friends may see a “typo”, in fact, it is mainly distinguished from the difference between carbon and charcoal, which will be discussed later.

 

As we all know, activated carbon mainly uses the principle of solid surface adsorption. Why does the solid surface have an adsorption effect? This is because there are other atoms around the atoms inside the solid, so it is in a state of equilibrium, but there are no atoms on the surface atoms, so the surface atoms are in a non-equilibrium state, so it has a tendency to adsorb other atoms to reach a state of equilibrium.

 

The larger the specific surface area of ​​activated carbon, the more atoms are on the surface, and the higher the adsorption rate. However, there is also an adsorption efficiency issue. If impurities are to be adsorbed on the surface of solid activated carbon, they need to diffuse, and the micropores on the surface of activated carbon can promote the migration of adsorbed atoms.

 

Activated carbon fiber is fibrous activated carbon. Its characteristic is that there are many micropores on the fiber surface, which can drive the adsorbed atoms to diffuse to the solid surface of activated carbon. The pore structure of traditional activated carbon is mainly composed of macropores, mesopores, and micropores. Most of the micropores are in mesopores and macropores, which increases the adsorption path, making the adsorption efficiency not as good as that of activated carbon fiber.

 

Activated carbon fiber has been used in many applications, such as air purifier filters, mask filters, gas masks, medical excipients, etc., and has applications in many aspects such as precious metal extraction, organic solvent recovery, water pollution treatment, and air pollution treatment. As the national environmental protection policy is further implemented, this type of carbon fiber application will become more and more common.

 

Carbon Fiber Sealing Material

 

The packing is usually woven from softer threads, usually with a square or rectangular or round cross-sectional area, and filled in the sealing cavity to achieve sealing. In some corrosive or high-temperature environments, carbon fiber packing has its own advantages. It mainly uses carbon fiber for no creep, good fatigue resistance, small thermal expansion coefficient, good corrosion resistance, and good thermal conductivity. It is mainly used in high temperature, high pressure and wear-resistant working conditions.

 

Carbon Fiber Heating Material

 

I remember when I first arrived at the Carbon Fiber Center, both air conditioners broke down in winter. The instructor temporarily took a few carbon fiber heating tubes and connected them online. The room suddenly became much warmer and very comfortable. Carbon fiber heating materials use the electrical conductivity and thermal radiation properties of carbon fiber.

 

At present, the floor heating and bathroom heaters with the concept of carbon fiber are very popular, and it is also a hot spot for the use of carbon fiber. Carbon fiber heating materials have the advantages of long life, high thermal efficiency, and good radiation waves for the body.

 

The most important thing is that the heat radiation waves emitted by carbon fiber will not cause the skin to lose moisture while heating the body, and there is no dry feeling on the skin after using the traditional bathroom heater.

 

Carbon Fiber Powder Conductive Material

 

This type of material is widely used, but the characteristic is to use the conductive properties of carbon fiber. The equal-length cylindrical particles obtained by cutting and grinding carbon fiber retain many excellent properties of carbon fiber, and are small in shape, pure in surface, large in specific surface area, easy to be wetted by resin and dispersed. It has been widely used in conductive additives for positive and negative electrode materials of nickel-hydrogen and nickel-cadmium batteries, electronic chips, conductive plates, conductive floors, electronic machinery, anti-static industry (paint, floor, paint, ink), anti-static filter element, national defense and military industry, building insulation, chemical food coarse-effect filtration, motorcycle muffler, paint drying room air filtration, polytetrafluoroethylene and other fields.

 

The above is written in a hurry, and there are some application fields that have not been explained in detail, which will be supplemented slowly in the future. In any case, carbon fiber has been recognized by all parties for its excellent performance and has been continuously used in new products and new industries. This is the charm of carbon fiber. I hope that with everyone’s efforts, we can jointly promote the application of carbon fiber.