Graphite Classifications and Applications
Graphite resources are abundant and widely distributed, but many of them are small and medium-sized minerals. Many private graphite mines have appeared, and the added value of graphite mineral products is extremely low. After the reorganization of mineral enterprises and the continuous improvement of graphite utilization, the graphite resources have been more effectively used. Now the graphite industry has developed high-purity graphite, Isostatic graphite, expanded graphite, fluorinated graphite, colloidal graphite, graphene and other high-performance graphite products.
1. High purity graphite
High-purity graphite (carbon content >99.99%) is used in military industry fireworks material stabilizers, metallurgical industry advanced refractory materials and high-grade refractory materials due to its complete crystalline flakes, thin flakes, good thermal conductivity, high temperature resistance and corrosion resistance. Chemical fertilizer industry catalysts, additives, etc.
2. Isostatic graphite
Isostatic graphite is pressed from high-purity graphite. It has the characteristics of low thermal expansion coefficient, good heat resistance, chemical resistance, and good thermal and electrical conductivity. Isostatic graphite is a new product developed in the past 50 years in the world. It not only has great achievements in civil use, but also occupies an important position in the cutting-edge of national defense. It is a new type of material and is eye-catching. Mainly used in the following aspects.
(1) Heater for polysilicon ingot furnace.
In recent years, with the global warming, humans’ awareness of protecting the earth has gradually increased, and more and more people have begun to favor natural energy sources that do not emit carbon dioxide. Under this general trend, solar cells have become the "darling" of the new era. The ingot furnace heater used in the manufacturing process needs to be made of isostatic graphite.
(2) High temperature gas-cooled reactor (nuclear fission reactor).
Since graphite used as a moderator in high-temperature gas-cooled reactors must have radiation creep and strong resistance to the radiation stress caused by deformation, a modular high-temperature gas-cooled reactor was proposed. Contemporary new ultra-high temperature nuclear reactors have the characteristics of high power density and high temperature, which puts forward higher requirements for the new generation of graphite materials: high quality and low price, ultra-high radiation damage tolerance, product homogenization, etc.
(3) Nuclear fusion reactor.
Graphite also plays an important role in nuclear fusion reactors due to its special properties. It can reduce the metal impurities in the material plasma to a large extent, so it plays a huge role in improving the energy confinement of the material plasma. With the gradual enlargement of nuclear fusion devices, graphite materials with good thermal conductivity and high mechanical strength stand out as the first wall material facing the plasma, and they exhibit a good discharge pulse effect during application. In addition, because graphite has the characteristics of low atomic number and low radiation loss, it can keep high-temperature plasma stable even if it is mixed into plasma.
(4) Electric discharge machining electrode.
Graphite electrodes have many advantages in the electrodes for electrical discharge machining: ①The quality is lighter than similar electrodes, and it is easy to handle; ②Easy to process; ③Not easy to produce stress and deformation during cutting; ④Under extremely high temperature, the thermal expansion coefficient is small, so Graphite electrodes are rarely deformed by the heat generated by electrical discharge machining. However, graphite electrodes also have some shortcomings, such as dust and wear during cutting.
3. Expandable graphite
Expandable graphite is made of high-quality natural flake graphite, an interlayer compound treated with acidic oxidants (sulfuric acid, nitric acid and hydrogen peroxide, potassium permanganate), also known as acidified graphite. Expanded graphite has many advantages such as high temperature resistance, high pressure resistance, good sealing performance and corrosion resistance of various media. It is a new type of advanced sealing material. It is mainly used in the following areas.
(1) The field of environmental protection.
The lipophilicity and hydrophobicity of expanded graphite can make it selectively remove non-aqueous solution in water. This feature is widely used to remove slick oil on the sea surface. Because of its special molecular structure, it shows a large amount of adsorption. After the oil, it can be aggregated into blocks, float on the sea, and can be recycled and reused without causing secondary pollution. In addition to selective adsorption in the liquid phase, expanded graphite also has an inhibitory effect on air pollution, such as the adsorption of carbon dioxide gas.
(2) Sealing material.
Expanded graphite can be processed into flexible graphite (small thermal expansion coefficient, no brittleness, no cracking at low temperature, no softening and no creep at high temperature) used as a sealing material, so it is known as the "sealing king".
4. Graphite fluoride
Graphite fluoride is one of the research hotspots of high-tech, high-performance and high-efficiency new carbon and graphite materials in the world. It has excellent performance and unique quality and is widely used in functional materials.
(1) Used as a release agent.
Graphite fluoride has the characteristics of low surface energy and is mainly used as a release agent for metal molds such as powder molding, die casting, and plywood molding.
(2) Solid lubricants.
Because fluorinated graphite has low interlayer energy, low surface energy, good chemical properties and thermal stability, it has outstanding lubricating properties and is suitable for use under harsh conditions such as high temperature, high pressure, corrosive media and high load, such as high temperature Lubricants for bearings, aircraft and automobile engines, etc.
(3) Battery raw materials.
Although batteries composed of fluorine-lithium have high energy, fluorine gas is poisonous, and it is extremely difficult to use fluorine as the anode active material. However, graphite fluoride has excellent electrochemical properties in organic electrolytes, so it is widely used in integrated circuit memories of computers, watches, and cameras.
5. Colloidal graphite
Colloidal graphite mainly has: ①Lubricity. Applying colloidal graphite in some machines with high friction strength will form a lubricating film on the surface of the friction machine, thereby reducing the friction resistance and the temperature generated by friction, avoiding the machine from burning out, jamming, and extending the working life; ② heat insulation | Because the colloidal graphite film has heat insulation in the vertical direction, it is widely used in hot steam cylinders and turbine propellers; ③The film is evenly formed, and has excellent electrical and thermal conductivity. It is used in the electronics industry to prevent reflections and suppress The second reflection of electrons eliminates static electricity.
6. Graphene
Graphene is a hexagonal honeycomb lattice composed of carbon atoms and sp2 hybrid orbitals. It is a two-dimensional material with the thickness of only one carbon atom. It is the nanomaterial with the highest hardness and toughness found so far.
Because of the characteristics of its special atomic arrangement structure, it has been widely used.
(1) According to the ultra-thin graphene (single-layer graphene is almost transparent, its molecules are tightly arranged, even the smallest helium atoms cannot pass through), and the strength is super-strong, which can be used to make ultra-light body armor, ultra-thin and ultra-light aircraft, etc. .
(2) Because its conductive electrons can not only move without obstacles in the crystal lattice, but also have a very fast speed, which far exceeds the moving speed of electrons in metal conductors or semiconductors. It is made into graphene conductive agent.
(3) Its thermal conductivity surpasses all existing known substances, and the rapid movement of its conductive electrons enables it to be researched and applied instead of silicon in future curved mobile phones, photon sensors and supercomputers.
(4) Other applications: Researchers have found that bacterial cells cannot grow on graphene, but human cells are not damaged. Take advantage of this; graphene can be used for bandages, food packaging, etc.
