Boron carbide

Boron carbide ceramics;
Boron carbide ceramics are a class of ceramics with Boron carbide as the main chemical component. Boron carbide has the chemical formula B4C, belongs to the hexagonal rhombic crystal system, and has 12 boron atoms in its unit cell, with lattice parameters co = 1.212 nm and ao = 0.56 nm. The crystal structure can accommodate atoms with a diameter up to 0.18 nm, thus allowing lithium or helium atoms to be retained within the crystal structure. Boron carbide powder is mainly synthesized using the carbothermic reduction method. Besides direct reduction with boron anhydride, it can also be prepared by reducing boron anhydride with Mg in the presence of carbon (C). The reaction formula is: 2B2O3 + 6Mg + C → B4C + 6MgO, with a reaction temperature of 1000–1200℃. This reaction is strongly exothermic, and the final product needs to be acid-washed with H2SO4 or HCl, followed by washing with hot water to obtain relatively pure Boron carbide powder with a fine particle size (0.1–5 μm) and free of carbon. Boron carbide ceramics are primarily produced through hot pressing, but hot isostatic pressing and pressureless sintering are also possible. Hot pressing sintering temperatures range from 2000 to 2100℃, typically requiring the addition of metals such as Mg, Al, Cr, Si, and Ti, or oxides like Al₂O₃ and MgO, or glass as sintering aids. Boron carbide has a melting point of 2450℃, a theoretical density of 2.519 g/cm³, an elastic modulus of 360–460 GPa, a coefficient of thermal expansion of 5.73 × 10⁻⁶/K (300–1970 K), a thermal conductivity of 24 W/(m·K) at 200℃, and a microhardness of 4950 kg/mm², second only to diamond and cubic boron nitride, exhibiting a large thermal neutron trapping cross-section. It can be used to process gemstones, ceramics, molds, lathe tools, and bearings. It can also be used in sandblasting nozzles, bulletproof materials, and as a neutron absorber in nuclear reactors.

Applications:
The powdered form is used as an abrasive; molded products can be used as anti-wear materials; it is also used in nuclear reactors.

Applications:
Used for grinding, lapping, drilling, and polishing hard materials such as cemented carbide and gemstones; manufacturing of metal borides; smelting boron steel and boron alloys; and special welding.

Applications:
Manufacturing chemical-resistant ceramics and wear-resistant tools.