Introduction and Application of Boron Carbide
English name: Boron Carbide
Synonyms: B4-C, B4C, black diamond, tetraboron carbide
CAS Number: 12069-32-8
BINECS number: 235-111-5
RTECS number: ED7420000
MSDS : External MSDS
Chemical formula: B4C
Relative molecular weight: 55.26
Appearance: Black powder
Density: 2.52g/cm3 (solid)
Melting point: 2450°C
Boiling point: 3500°C
Crystal structure: rhomboid hexahedron
Mohs hardness: 9.36
Microhardness: 4950kgf/mm2
Water solubility: insoluble
Physical Properties and Physico-Chemical Constants of Boron Carbide: Boron carbide is produced by the high-temperature smelting of boric acid and carbon materials in an electric furnace. It has a theoretical density of 2.52 g/cm³, a melting point of 2450°C, a microhardness of 4950 kgf/mm², and a Mohs hardness of 9.3. Its hardness is only surpassed by diamond and cubic boron nitride. Boron carbide possesses characteristics such as high temperature resistance, acid and alkali corrosion resistance, high strength, good chemical stability, and low specific gravity, leading to its widespread applications in many new materials fields.
Main Application Fields and Characteristics of Boron Carbide:(1) Application in the Defense Industry:Boron carbide is used to manufacture ballistic materials, such as bulletproof plates in bulletproof vests, Ceramic Ballistic tiles in pilot cockpits of military aircraft, and ceramic ballistic plates in modern armored personnel carriers and tanks. In the arms industry, it can be utilized to manufacture nozzles for guns and cannons. Currently, Al2O3-based anti-ballistic ceramics have been applied in the '502 Project' and '212 Project'. However, when using Al2O3-based ceramic composite armor on the sides of armored vehicles, the weight reduction effect is not significant. In contrast, using high-performance boron Carbide Ceramic composite armor of the same thickness can reduce the weight by 15% to 20% while further enhancing ballistic performance. Therefore, there is an urgent demand for high-performance, low-cost boron carbide anti-ballistic ceramics in the development of key equipment engineering ceramic composite armor. The development and application of high-performance, low-cost boron carbide ballistic ceramic materials can significantly improve the operational performance of related weaponry and offers substantial military and economic benefits. The application direction for boron carbide ballistic ceramic materials includes: key equipment engineering, future main battle tanks, infantry fighting vehicles, airdrop vehicles, and other light armored vehicles, as well as armor protection for the belly panels of armed helicopters and the upper structures of boats.
(2) Application in the Nuclear Industry:Boron carbide is used to make control rods, regulating rods, accident rods, safety rods, and shielding rods for nuclear reactors. It is also used in the production of boron carbide tiles, plates, or neutron absorbers (made with high B10 content powder) for radiation protection, and can be mixed with cement for the construction of reactor shielding layers. It is an essential functional component, second only to nuclear fuel elements. Characteristics: Boron carbide can absorb a large number of neutrons without forming any radioactive isotopes, making it an ideal neutron absorber as well as a core component of nuclear reactors in the field of nuclear energy generation. Neutron absorbers primarily control the rate of nuclear fission, and to increase surface area, they are produced in powder form. Boron carbide has a high neutron absorption cross-section, a broad absorption energy spectrum, a low price, abundant raw material sources, and minimal strong λ-ray secondary radiation after neutron absorption, making waste disposal easier. Consequently, boron carbide represents an important neutron absorption material.
(3) Used in the field of refractory materials:Boron carbide is used as an antioxidant additive in low-carbon magnesium-carbon bricks and castables. In the steel industry, it is employed in critical areas that require high temperature resistance and erosion resistance, such as ladles, tapping outlets (tundishes), sliding plates, and stopper rods. With the energy-saving and consumption-reducing demands of the steel industry and the need for smelting low-carbon steel and ultra-low-carbon steel, there is increasing attention from both domestic and international industries on research and development of high-performance low-carbon magnesium-carbon bricks (with carbon content generally < 8%). Currently, the usage performance of low-carbon magnesium-carbon bricks is improved mainly by enhancing the bonding carbon structure, optimizing the matrix structure of magnesium-carbon bricks, and adding efficient antioxidants. Among these measures, using industrial-grade B4C combined with partially graphitized carbon black to form a graphitized carbon black composite powder as both a carbon source and antioxidant in low-carbon magnesium-carbon bricks has shown very good results. Low-carbon magnesium-carbon bricks with added B4C exhibit excellent conventional physical properties, oxidation resistance, and thermal shock stability.
Characteristics: Boron carbide acts as an antioxidant in carbon-containing refractory materials, which can densify the product and prevent the oxidation of carbon within the carbon-containing refractory materials. Simultaneously, reactions occur at temperatures ranging from 1000°C to 1250°C, generating columnar crystal structures of (9 Al2O3•2B2O3) that are distributed within the matrix and gaps of the refractory materials. This process reduces porosity, enhances medium-temperature strength, and the generated crystal volume expands, healing volume shrinkage and reducing cracks.
(4) For other engineering ceramic materials:Boron carbide is used to manufacture nozzles for sandblasting machines, high-pressure water cutting machine nozzles, sealing rings, ceramic molds, and other applications. Characteristics: Boron carbide nozzles have high hardness and wear resistance, which will gradually replace known hard alloys (tungsten steel) as well as materials like silicon carbide, silicon nitride, aluminum oxide, and zirconium oxide. Additionally, the application of boron carbide in composite ceramics: Boron carbide is a compound with very strong covalent bonds and poor plasticity, and it has significant resistance to grain boundary movement, making it challenging to obtain dense sintered bodies. Aside from some special cases, such as micromorph boron carbide gas dynamic bearing materials and boron carbide blocks used as neutron absorbents in atomic reactors, the issue of boron carbide's sintering behavior is generally improved by adding sintering aids to achieve more cost-effective and practical boron carbide products. Furthermore, adding a significant amount of silicon carbide to boron carbide to create composite materials is an effective way to enhance the sintering density. Silicon carbide itself possesses excellent mechanical and physical properties, including high specific strength, specific modulus, good corrosion resistance, thermal shock resistance, low density, and low thermal expansion coefficient.
Moreover, in the periodic table, Si is adjacent to B and C, making their performances quite similar. According to the principle of similar compatibility, the presence of SiC improves sintering diffusion and promotes the sintering of boron carbide. Scientists studying the sintering of silicon carbide ceramics have found that adding an appropriate amount of boron carbide to silicon carbide results in a denser sintered body. Thus, it is evident that boron carbide and silicon carbide can mutually enhance the densification process during sintering. Notably, B4C-SiC composite ceramics can lower the sintering conditions of boron carbide ceramics while maintaining the excellent physical and mechanical properties of boron carbide ceramics. B4C-SiC ceramics are considered to be high-temperature corrosion and wear-resistant materials with broad application prospects, having already found use in industrial nozzles, pump seals, and hot extrusion molds.In recent decades, due to the rapid development of science and technology, especially in electronic technology, space technology, and computer technology, there has been an urgent need for materials with special properties. Special ceramics, which are abundant in resources, inexpensive to produce, easy to fabricate, and possess many unique properties, have emerged, earning the title of "universal ceramics" and becoming one of the most promising materials of the 21st century. Boron carbide has become an important member of the special ceramics family due to its many excellent properties. Currently, many of the challenges concerning the preparation of boron carbide powder and the sintering of boron carbide ceramic materials have been successfully addressed. In the future material field, boron carbide will undoubtedly occupy an important position due to its outstanding properties.
(5) Used in general industrial fields:
Boron carbide is made of high-grade wear-resistant welding rods to enhance the wear strength of the welding surface; It is used as a grinding and polishing material, an abrasive for water cutting and a diamond abrasive correction material; High-precision polishing and grinding in the jewelry industry. Properties: Boron carbide is a solid harder than silicon carbide or tungsten carbide, and it was used as a coarse sand abrasive material a long time ago. Due to its high melting point, it is not easy to cast into artifacts, but by melting powder at high temperatures, it can be processed into simple shapes and used for grinding, grinding, drilling and polishing carbide, gemstones, etc.
(6) Electrical properties of boron carbide applications:
The boron carbide-graphite thermocouple consists of a graphite tube, a boron carbide rod, and a boron nitride bushing between the two. In inert gas and vacuum, use temperatures up to 2200°C. Between 600~2200°C, the potential difference has a good linear relationship with temperature.
(7) Application of boron carbide as a chemical raw material:
Boron carbide powder is activated by halogens and can be used as a boronizing agent for steel and other alloys to infiltrate boron on the surface of steel to generate the strength and wear resistance of thin layers of iron boride reinforcement. Boron carbide can also be used as a non-metallic additive for some metal-based friction materials. When boride powder is prepared by the reduction-chemical method, boron carbide can be used as a boron source to produce TiB2, ZrB2, CrB2 and other powders, which is called the "boron carbide method" for powder preparation.
(8) Boron carbide in sapphire wafers (LEDs):
In recent years, the country's strong support and promotion of the LED industry has made the development situation of the LED industry better, thus bringing great business opportunities to enterprises that produce and process sapphire crystals. Due to the high strength and hardness of sapphire crystal (Mohs hardness 9), it brings great difficulties to processing enterprises. From the perspective of materials and grinding science, the best materials for processing and grinding sapphire crystals are artificial diamond, boron carbide, silica. Because the hardness of artificial diamond is too high (Mohs hardness 10), it will scratch the surface when grinding sapphire wafers, affect the light transmission of the wafers, and is expensive. However, the hardness of silica is not enough (Mohs hardness 7) and the grinding force is poor in the grinding process. Therefore, boron carbide abrasives (Mohs hardness 9.3) are the most ideal material for processing and grinding sapphire crystals. Boron carbide abrasives have excellent performance in double-sided grinding of sapphire wafers and thinning and polishing of sapphire-based LED epitaxial wafers. Some key universities in the country also have major research on boron carbide in grinding sapphire crystals. In short, with the rapid development of the LED industry, boron carbide will also rise rapidly
In short, with the development of society and science and technology, the application fields of boron carbide will continue to be discovered and expanded, and the market application prospects will be broader.