What Is Boron Carbide?
Boron carbide, a compound of boron and carbon with the chemical formula B4C, is a grayish-black powder known for its exceptional hardness—second only to diamond on the modified Mohs scale—and excellent wear resistance. This material is notable for its chemical stability, being resistant to attack by both acids and alkalis.
Uses of Boron Carbide
Due to its superior hardness and wear resistance, boron carbide is utilized in various applications requiring durability. It is commonly found in cutting tools, abrasives, cermets, mortars, and bulletproof materials. Its high electrical insulation and thermal conductivity make it suitable for use in high-temperature industrial environments, including in electronic components and hard disk heads. Additionally, its high neutron absorption capacity, thanks to the natural abundance of boron-10, allows its use in nuclear reactors for fission reaction control and neutron shielding.
Properties of Boron Carbide
With a molecular weight of 55.25, a density of 2.51, and a melting point of 2350℃, boron carbide boasts a high melting point, low specific gravity, and remarkable heat and chemical resistance. It begins to oxidize at 570℃ and reacts with chlorine at high temperatures to form boron trichloride, although it is generally resistant to acids and alkalis except when exposed to alkali fusion or hydrofluoric acid.
Structure of Boron Carbide
The rhombohedral crystal structure of boron carbide features three carbon atoms on the diagonal of a unit lattice, with boron atoms forming an icosahedron at each vertex. This structure allows for the substitution of carbon with boron, affecting the material’s properties minimally due to the unchanged crystal backbone.
Types of Boron Carbide
Available in both bulk and powder forms, boron carbide is processed into various ceramic products such as plates, nozzles, and seals, utilized in bulletproofing, sandblasting, and mechanical sealing. Its particulate form serves as an abrasive, antioxidant for refractory materials, and a sintering aid for silicon carbide, with applications determined by particle size uniformity.
Other Information on Boron Carbide
How Boron Carbide Is Produced
Industrially, boron carbide is synthesized by heating a mixture of boron oxide and carbon in an electric furnace. This thermal carbon reduction method uses boric acid or boron oxide and activated carbon or petroleum coke, offering a cost-effective and safe mass synthesis approach. Alternative methods include direct boron and carbon reaction, synthesis from composite carbides using TiO2-SiO2-B2O3 glass, and a low-temperature synthesis involving boric anhydride or borax, magnesium, and carbon.