内容
Quality indicators of carbon materials
Carbon materials are widely used in various fields such as aerospace, electronic industry, and communications technology. Carbon materials have the characteristics of light weight, high strength, good electrical conductivity and thermal conductivity, and outstanding energy absorption performance. Carbon materials are mainly divided into graphite and carbon fiber reinforced composite materials. Carbon materials can be divided into two categories according to the shape of carbon materials: one is when the basic form of carbon materials is plate, such as graphite plate, carbon plate and carbon film; the other is when the basic form of carbon materials is fibrous material, such as carbon fiber and high-strength carbon fiber. The quality indicators of carbon materials mainly focus on the following aspects:
1. Density. Density is an important indicator of the quality of carbon materials. The relative density of graphite and activated carbon is between 1.8-2.0g/cm3, and the relative density of carbon fiber and its composite material is mainly 0.16-0.5g/cm3.
2. Strength. There are two kinds of strength indicators for carbon materials: flexural strength and compressive strength. Flexural strength refers to the strength of a material to resist bending force, while compressive strength refers to the strength of a material to resist compression force. The main testing method of in-plane strength is three-point bending test or four-point bending test, among which the three-point bending test is more commonly used. Generally, the in-plane flexural strength of ordinary graphite board is 2 to 4 times higher than that of ordinary resin board.
3. Porosity. Porosity refers to the ratio of volume of voids to the total volume of carbon materials. For graphite materials, its porosity is very important for the determination of its temperature resistance, electrical insulation and so on. For carbonized fiber materials, the porosity of carbonized fiber products mainly depends on the degree of control during the sintering process.
4. Thermal properties. Thermal properties refer to the physical properties which characterize the materials response to temperature changes. Generally, the thermal conductivity of graphite and carbon materials is several times that of ordinary resin, and the thermal expansion coefficient of graphite is much lower than that of ordinary resin, which is beneficial to reduce the thermal expansion and contraction of components.
5. Electrical properties. Electrical properties refer to the ability to conduct or insulate electricity of specific electrical materials. According to the electrical properties, there are three types of graphite materials: insulating graphite materials, semiconducting graphite materials and conductive graphite materials. Different types of graphite materials have different electrical properties. Generally, the electrical resistivity of graphite materials increases with the increase of temperature.
6. Chemical properties. The chemical properties of carbon materials include corrosion resistance, oxidation resistance, acid and alkali resistance, etc. Generally, graphite has good oxidation resistance, acid and alkali resistance, and has excellent corrosion resistance to some non-oxidizing acids.
As a kind of important material for the development of aeronautics and astronautics industry, civil light industry, electronics industry and other high-tech fields, carbon materials have unique mechanical, electric, thermal and chemical properties. The quality of carbon materials mainly depends on the quality indicators of carbon materials. In order to make the product performance up to the required level, people must pay attention to the quality indicators of carbon materials and take corresponding measures in the production process to ensure the quality of the product.
