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Application and production method of boron carbide

wallpapers News 2021-05-14
Boron carbide overview
Boron carbide is a metallic black crystal, second only to diamond in hardness and higher than silicon carbide, with a Mos hardness of 9.3. Stable chemical properties, can not react with acid and base solution, molecular formula is B4C, relative density 2.52, melting point 2350℃, boiling point is higher than 3500℃. Molten boron carbide can dissolve large amounts of graphite carbon. Boron carbide is stable in dilute acid solution and can be decomposed by a mixture of sulfuric acid and hydrofluoric acid or a mixture of sulfuric acid and nitric acid. Slowly chemically oxidized to carbon dioxide and boron trioxide in oxygen heated to 1000℃. Boron carbide has high thermal neutron capture ability, wear resistance and semiconductor conductivity. In most cases, boron carbide (B4C) as the control material can meet the requirements of high temperature reactor. The control efficiency of boron materials can be improved by increasing the concentration of B10 element in boron carbide. The density of boron carbide is 2.51×103kg/m3, the melting point is 2450℃, and the thermal expansion coefficient (20 ~ 800℃) is 4.5×10-6/℃.
Method for preparation of boron carbide for industrial use
The main production method of industrial boron carbide is to melt boron anhydride in an electric arc furnace and make it react with carbon. In addition, it can be obtained by carbon magnesium reduction method or carbon hydrogen reduction method. Boron carbide is mainly used as an abrasive for grinding and polishing industry. Boron carbide is usually prepared from boron oxide and carbon heated at high temperature in an electric furnace. The reaction formula is as follows: 2B2O3+7C→B4C+6CO. The general quality requirement of the product is that the abrasive type contains not less than 94% B4C, and the abrasive type contains not less than 90% B4C. Carbon Chemicalbook boron is mainly used for grinding, grinding, drilling and polishing of hard materials such as cemented carbide and gemstone. The molded products can be used as wear-resistant materials and refractory materials, used to make hard corrosion-resistant ceramics and water-resistant bearings, used as neutron control rods in nuclear reactors, and also used for smelting boron steel, boron alloy and special welding. Alloys of boron carbide and aluminum (containing up to 50% B4C) are used for neutron shielding, reactor screen shielding, etc. Boron carbide is packed in plastic bags and stored in dry, clean warehouses.
Application of boron carbide ceramics
Boron carbide ceramics is a kind of ceramics with boron carbide as the main chemical composition. The chemical formula of boron carbide is B4C, belongs to hexagonal rhomboid crystal system, there are 12 boron atoms in the crystal cell, lattice parameters Co = 1.212nm, Ao = 0.56nm. The presence of atoms up to 0.18nm in diameter in the crystal structure allows the retention of lithium or helium atoms within the crystal structure. In addition to the direct reduction of boron anhydride, boron anhydride can also be prepared with Mg in the presence of carbon (C). The reaction formula is: 2B2O3+6Mg+C→B4C+6MgO. The reaction temperature is 1000 ~ 1200℃. This reaction is highly exothermic. The final product is pickled with H2SO4 or HCl and then washed in hot water to obtain a relatively pure, fine-grained (0.1 ~ 5μm) Chemicalbook boron carbide powder without C. Boron carbide ceramics are mainly sintering by hot pressing, hot isostatic pressing and no pressure sintering can also be used. The temperature of hot pressing sintering is 2000 ~ 2100℃. Generally, metals such as Mg, Al, Cr, Si, Ti or oxides such as Al2O3, MgO or glass are added as sintering additives. The melting point of boron carbide is 2450℃, the theoretical density is 2.519g/cm3, the elastic modulus is 360 ~ 460GPa, the thermal expansion coefficient is 5.73×10-6/K(300 ~ 1970K), the thermal conductivity is 24W/(m·K) and the microhardness is 4950kg/mm2 at 200℃. It is only lower than diamond and cubic boron nitride and has a large thermal neutron capture cross section. It can be used to process gems, ceramics, moulds, turning tools and bearings, etc. It can also be used as sandblasting nozzle, bulletproof material and neutron absorber for atomic reactors.
Application and production method of boron carbide
Powdered materials are used as grinding materials, molded products can be used as anti-wear materials, but also used in nuclear reactors for hard alloy, gem and other hard materials grinding, grinding, drilling and polishing, metal boride manufacturing and smelting boron steel, boron alloy and special welding. Use for anti - chemical lu pottery, wear - resistant tools manufacturing.
Production method: Carbothermal reduction method: After the graphite and coal are crushed, they are fully mixed with boric acid in a ball mill at a ratio of 0.5:0.5:3, and then placed in a single-phase bipolar horizontal electric arc furnace for carbonization reaction at 1700 ~ 2300℃. After the reaction is completed, the material is released, cooled, crushed, selected, washed in hot water, and then coarse-crushing, grinding, pickling (temperature is not less than 80℃, 12h), washed with water to neutral, and then sedimentation and series washing method selection, drying, screening, boron carbide finished products. Its 4 h3bo3 + 7 c - B4C co write + 6 + 6 h2o.

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