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Expandable graphite was first discovered by the German Schaufautl. In 1841, Schaufautl immersed natural graphite in a mixture of concentrated HNO3 and H2SO4, took it out and dried it for several hours, and found that graphite had expanded.
United Carbide Company first applied for an expandable graphite manufacturing technology patent in 1963 and industrialized production in 1968
1. Sealing material The raw material high-carbon graphite is mixed with concentrated sulfuric acid and concentrated nitric acid for acidification treatment, followed by heat treatment and compression molding. The prepared flexible graphite is a new type of high-performance sealing material, which is a nano material grown in situ. Compared with traditional sealing materials such as asbestos rubber, it has excellent properties such as good compressibility, resilience, self-adhesion, and low density, and can be used for a long time under severe working conditions such as high temperature and high corrosion. The graphite plates and sealing elements made with it are widely used in aerospace, machinery, electronics, nuclear energy, petrochemical, power, shipbuilding, smelting and other industries. Because of its light weight, electrical conductivity, thermal conductivity, high temperature resistance, acid and alkali corrosion resistance, good resilience, lubricity, plasticity and chemical stability and other excellent characteristics, it is known as the "King of Seals" in the world.
2. Environmental protection Expandable graphite obtained by high temperature expansion has a rich pore structure and therefore has excellent adsorption performance, so it has a wide range of uses in environmental protection and biomedicine. The pore structure of expandable graphite includes open pores and closed pores. The pore volume accounts for about 98%, and the pores are mainly large pores. The pore size distribution ranges from 1 to 10.3 nm. Because it is mainly macroporous and mesoporous, it has different adsorption characteristics from microporous materials such as activated carbon. It is suitable for liquid phase adsorption, but not for gas phase adsorption. It is lipophilic and hydrophobic in liquid phase adsorption. 1 g of expandable graphite can absorb more than 80 g of heavy oil, so it is a promising environmentally friendly material for removing oil pollution on the water surface. In the wastewater treatment of chemical companies, microbial (bacterial) treatment is often used. Expandable graphite is a good microbial carrier, especially in water treatment of oily organic macromolecules. Recycling and multiplexing have good application prospects.
3. Medicine Due to the adsorption characteristics of expandable graphite to organic and biological macromolecules, it has a wide range of applications in biomedical materials.
4. High-energy battery material As a battery material, expandable graphite uses the free energy change of the expandable graphite layer reaction to transform into electrical energy. Generally, expandable graphite is used as the cathode, lithium is used as the anode, or expandable graphite composite silver oxide is used as the cathode, and zinc is used as the anode. Expandable graphites such as fluorinated graphite, graphic acid, and metal halides such as AuCl3 and TiF4 have been used in batteries.
5. Flame retardant and fireproof
Fireproof sealing strips Due to the expandability and high temperature resistance of expandable graphite, expandable graphite has become an excellent sealing material and is widely used in fireproof sealing strips. There are two main forms: the first is to mix, vulcanize, and mold the expandable graphite material with rubber materials, inorganic flame retardants, accelerators, vulcanizing agents, reinforcing agents, fillers, etc. to make various specifications of expansion Sealing strips are mainly used in fire doors, fire windows, etc. This kind of expansion sealing strip can play a role in blocking the flow of smoke in normal temperature and fire. The other is based on glass fiber ribbon, which is used to bond expandable graphite to the carrier with a certain kind of adhesive. The shear resistance provided by the carbide formed by this adhesive at high temperature can effectively prevent the graphite slide. It is mainly used for fire doors, but it cannot effectively block the flow of cold smoke at room temperature or low temperature, so it must be used in conjunction with a room temperature sealant.
Flame retardancy of plastic materials Expandable graphite is a good flame retardant for plastic materials. It is non-toxic and non-polluting. It can achieve the ideal flame retardant effect when used alone or mixed with other flame retardants. When the expandable graphite achieves the same flame retardant effect, the amount is far less than that of ordinary flame retardants. Its working principle is: at high temperature, expandable graphite expands sharply, suffocating the flame, and at the same time, the graphite expanded material it covers covers the surface of the substrate, which isolates the contact between thermal energy radiation and oxygen; the acid radicals inside its sandwich are expanding The release also promotes the carbonization of the substrate, thereby achieving good results through a variety of flame retardant methods.
Fireproof bag, plastic fireproof material, fireproof ring Because expandable graphite has anti-destructive ability at high temperature and has a high expansion rate, it can be used as an effective component of fireproof bag, plastic fireproof material and fireproof ring. Intumescent flame retardant materials, used for fire blocking in buildings (for example: sealing construction pipes, cables, wires, gas, gas pipes, holes through which air pipes pass, etc.).
Applications on coatings Fine particles of expandable graphite are added to ordinary coatings, which can produce better flame retardant antistatic coatings and improve their high temperature resistance and fire resistance. The large amount of light non-combustible carbon layer formed in the fire can effectively block the radiation of heat insulation amount to the substrate and effectively protect the substrate. In addition, because graphite is a good electrical conductor, the prepared coating can prevent the accumulation of electrostatic charges and is used in petroleum storage tanks to achieve the dual effects of fire prevention and antistatic.
Fireproof board, fireproof paper Anti-corrosion and high-temperature resistant board: The metal base layer is lined with an expandable graphite layer, there is a carbonized cement layer between the expandable graphite layer and the metal base layer, and the expandable graphite layer is covered with a carbonized protective layer. With anti-corrosion, high temperature and high pressure resistance. At the same time, it can withstand thermal shock and can be used normally at low temperature. It is not afraid of rapid cooling and rapid heating, and has excellent thermal conductivity. The operating temperature is -100 ～ 2 000 ℃. Wide application range, easy manufacture and low cost. In addition, graphite paper, which is expanded after high-temperature expansion of expanded graphite, is also used in fire-proof and heat-preservation places.
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