The use and classification of graphite

What is graphite?

Graphite is generally iron-black, and the monomer forms are mostly needle-pointed, fine-fibrous, and scale-like, and a small amount is leaf-like. The aggregate form is mostly powder, earthy, cryptocrystalline, and non-glossy; semi-metallic luster, Cryptocrystalline ones are dim, hardness 1~2, specific gravity 2.21~2.26g/cm3, melting point 3652℃, boiling point 4827℃, insoluble in water, flexible flakes, slippery, easy to dirty hands, good conductivity.

There is no pure graphite in nature, which often contains impurities such as SiO2, Al2O3, FeO, CaO, P2O5, and CuO.

Therefore, it is necessary to purify graphite before using graphite for the deep processing industry. Graphite purification is a complex physical and chemical process. The purification methods mainly include the flotation method, alkaline acid method, hydrofluoric acid method, chlorination roasting method, and high temperature method.

Graphite applications

The purified graphite can be used in the production of refractory materials, conductive materials, wear-resistant lubricating materials, petrochemicals, hydrometallurgy, acid-base production, synthetic fibers, papermaking, etc.; in addition, graphite is also used in casting, sand-finding, and compression molding. And high-temperature metallurgical materials, the atomic energy industry and national defense industry, and electrodes. In addition, graphite is also a polishing agent and anti-rust agent for glass and paper in the light industry, and is an indispensable raw material for the manufacture of pencils, ink, black paint, ink, synthetic diamonds, and diamonds.

Refractory

Graphite and its products have the properties of high temperature resistance and high strength. It is mainly used in the metallurgical industry to make graphite crucibles. In steelmaking, graphite is often used as a protective agent for steel ingots and as a lining for metallurgical furnaces.

Conductive materials, electrodes

Used in the electrical industry to manufacture graphite electrodes, brushes, graphitecarbon block, carbon tubes, positive electrodes of mercury positive current devices, graphite washers, telephone parts, coatings for television picture tubes, etc.

Wear-resistant lubricating material

Graphite is often used as a lubricant in the machinery industry. Lubricating oil is often not used under high-speed, high-temperature, and high-pressure conditions, while graphite wear-resistant materials can work at high sliding speeds at a temperature of 200 to 2000 ℃ without lubricating oil. Many types of equipment that transports corrosive media widely use graphite materials to make piston cups, seals, and bearings. They do not need to add lubricating oil when they are running. Graphite emulsion is also a good lubricant for many metal processing (wire drawing, pipe drawing).

Used as casting, sand-finding, pressing mold, and high temperature metallurgical materials

Because graphite has a small thermal expansion coefficient and can withstand rapid cold and rapid heat changes, it can be used as a glass mold. After graphite is used, ferrous metals can obtain castings with precise dimensions, high surface finish, and high yield, and can be used without processing or a little processing. Save a lot of metal. The production of cemented carbide and other powder metallurgy processes usually uses graphite materials to make porcelain boats for pressing and sintering. Single crystal silicon crystal growth crucibles, regional refining vessels, support fixtures, induction heaters, etc. are all made of high-purity graphite. In addition, graphite can also be used for vacuum smelting graphite heat insulation boards and bases, high-temperature resistance furnace tubes, rods, plates, grid sheds, and other components.

Used in the atomic energy industry and defense industry

Graphite has a good neutron moderator used in atomic reactors, and the uranium-graphite reactor is one of the most used atomic reactors. The deceleration material in the nuclear reactor used as power should have a high melting point, stability, and corrosion resistance. Graphite can fully meet the above requirements. The purity of graphite used in atomic reactors is very high, and the impurity content should not exceed dozens of PPM. Especially the boron content should be less than 0.5PPM. In the defense industry, graphite is also used to make solid-fuel rocket nozzles, missile nose cones, parts of aerospace equipment, heat insulation materials, and radiation protection materials.

Light industry applications

Graphite is a polishing agent and anti-rust agent for glass and papermaking in the light industry. It is an indispensable raw material for making pencils, ink, black lacquer, ink, artificial diamonds, and diamonds. It is a very good energy-saving and environmentally friendly material, and the United States has used it like a car battery. With the development of modern science and technology and industry, the application field of graphite is still expanding, and it has become an important raw material for new composite materials in the high-tech field, and it plays an important role in the national economy.

Special properties of graphite

High temperature resistance

The melting point of graphite is 3850±50°C. Even if it is burned by ultra-high temperature arc, the weight loss is very small, and the thermal expansion coefficient is also very small. The strength of graphite increases with the increase in temperature. 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. The thermal conductivity exceeds that of metal materials such as steel, iron, and lead. Thermal conductivity decreases with increasing temperature, even at extremely high temperatures, graphite becomes an insulator. Graphite can 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 transfer charge.

Lubricity

The lubricating performance of graphite depends on the size of the graphite flakes. The larger the flakes, the smaller the friction coefficient and the better the lubricating performance.

Chemical stability

Graphite has good chemical stability at room temperature and is resistant to 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 being damaged when used at room temperature. When the temperature changes suddenly, the volume of graphite will not change much and no cracks will occur.

Graphite can be divided into two categories: natural graphite and artificial graphite

Natural graphite comes from graphite deposits, and natural graphite can also be divided into flake graphite, earthy graphite and block graphite. The graphite obtained from natural mining contains a lot of impurities, so it needs beneficiation to reduce its impurity content before it can be used. The main purpose of natural graphite is to produce refractory materials, electric brushes, flexible graphite products, lubricants, lithium-ion battery anode materials, etc. Some carbon products sometimes add a certain amount of natural graphite.

There are many types of artificial graphite, such as single crystal graphite, polycrystalline graphite, pyrolytic graphite, highly oriented pyrolytic graphite, polyimide synthetic graphite, graphite fiber, etc. Most artificial graphite products belong to the category of polycrystalline graphite. The main products of artificial graphite are graphite electrodes used in electric arc steelmaking furnaces and submerged electric furnaces. Graphite electrodes are a high-temperature and corrosion-resistant conductive material.

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