Graphite is an allotrope of elemental carbon, and each carbon atom is surrounded by three other carbon atoms (multiple hexagons arranged in the form of a honeycomb) bound by covalent bonds to form a covalent molecule. Since each carbon atom emits an electron that can move freely, graphite is a conductor. Graphite is one of the soft minerals whose uses include the manufacture of pencil leads and lubricants.
Graphite due to its special structure, and has the following special properties:
High temperature resistance: graphite melting point of 3850±50 °C, boiling point of 4250 °C, even after arc burning, the loss of weight is very small, the coefficient of thermal expansion is also very small. The strength of graphite increases with increasing temperature, and at 2000 ° C, the strength of graphite doubles.
Electrical and thermal conductivity: The conductivity of graphite is one hundred times higher than that of general non-metallic minerals. Thermal conductivity exceeds that of steel, iron, lead and other metal materials. Thermal conductivity decreases with increasing temperature. Graphite is able to conduct electricity because each carbon atom in graphite forms only 3 covalent bonds with other carbon atoms, and each carbon atom still retains 1 free electron to transmit charge.
Lubricity: The lubricating properties of graphite depend on the size of the graphite scales, the larger the scales, the smaller the coefficient of friction, and the better the lubrication properties.
Chemical stability: Graphite has good chemical stability at room temperature, and can resist acid, alkali and organic solvent corrosion.
Plasticity: Graphite has good toughness and can be crushed into very thin flakes.
Thermal shock resistance: graphite can withstand drastic changes in temperature without destruction when used at room temperature, and when the temperature suddenly changes, the volume of graphite does not change much, and cracks will not occur.
1.as refractory materials: graphite and its products have high temperature resistance, high strength properties, in the metallurgical industry is mainly used to manufacture graphite crucibles, in steelmaking commonly used graphite as a protective agent for steel ingots, metallurgical furnace lining.
2. As a conductive material: used in the electrical industry as a positive electrode for manufacturing electrodes, brushes, carbon rods, carbon tubes, mercury current flow devices, graphite gaskets, telephone parts, TV picture tube coatings, etc.
3. As a wear-resistant lubrication material: Graphite is often used as a lubricant in the machinery industry. Lubricating oil is often not used under high-speed, high-temperature, high-pressure conditions, and graphite wear-resistant materials can be used at a high sliding speed at a temperature of 200 ~ 2000 °C, without lubricating oil. Many equipment for conveying corrosive media, widely using graphite materials to make piston cups, seals and bearings, do not need to add lubricating oil when they run. Graphite milk is also a good lubricant for many metal processing (wire drawing, pipe drawing).
4. Graphite has good chemical stability. Specially processed graphite, with corrosion resistance, good thermal conductivity, low permeability and other characteristics, is used to make heat exchangers, reaction tanks, condensers, combustion towers, absorption towers, coolers, heaters, filters, pump equipment. Widely used in petrochemical, hydrometallurgy, acid and alkali production, synthetic fiber, paper and other industrial sectors, can save metal materials.
5. Casting, sand turning, stamping and high temperature metallurgical materials: Due to the small coefficient of thermal expansion of graphite, and can withstand the change of rapid cold and heat, it can be used as a casting mold of glassware, and the ferrous metal obtains accurate casting size after the use of graphite, the surface finish rate is high, and it can be used without processing or slight processing, thus saving metal. The production of powder metallurgy processes such as cemented carbide, usually made of graphite materials into porcelain boats for stamping and sintering. Crystal growth crucibles, regional refining vessels, bracket fixtures, induction heaters, etc. of monocrystalline silicon are all processed with high-purity graphite. In addition, graphite can also be used as a graphite insulation plate and base for vacuum smelting, high-temperature resistance furnace tube, rods, plates, lattice sheds and other components.
6. used in the atomic energy industry and national defense industry: graphite has a good neutron reducer for atomic reactors, uranium-graphite reactor is currently more used in an atomic reactor. As a powered atomic energy reactor in the deceleration material should have a high melting point, stability, corrosion resistance performance, graphite can fully meet the above requirements. The purity of graphite used as an atomic reactor is very high, and the impurity content should not exceed dozens of PPM. In particular, the boron content should be less than 0.5PPM. Graphite is also used in the defense industry to make nozzles for solid-fuel rockets, nose cones for missiles, parts for space navigation equipment, thermal insulation materials, and ray-proof materials.
7. Graphite can also prevent boiler scaling, the relevant unit test shows that adding a certain amount of graphite powder in the water (about 4 to 5 grams per ton of water) can prevent the boiler surface from scaling. In addition, graphite applied to metal chimneys, roofs, bridges, pipes can be anti-corrosion and rust-proof.
8. Graphite can be used as pencil refill, pigment, polishing agent. After special processing, graphite can be made into various special materials for use in the relevant industrial sectors.
Flexible graphite products. Flexible graphite, also known as expanded graphite, is a new graphite product. The United States successfully researched flexible graphite sealing materials to solve the problem of leakage of atomic energy valves, and then Germany, Japan and France also began to develop and produce. In addition to the properties of natural graphite, this product also has special flexibility and elasticity. Therefore, it is a sealing material. Used in petrochemical, atomic energy and other industrial fields. The market demand is increasing year by year. Light industrial applications. In addition, graphite is also a polishing agent and rust inhibitor for glass and paper in light industry, and is an indispensable raw material for the manufacture of pencils, inks, black paints, inks, synthetic diamonds and diamonds. With the development of modern science and technology and industry, the application field of graphite is still expanding, and has become an important raw material for new composite materials in the field of high technology, and plays an important role in the national economy.
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