Introduction and application of boron carbide

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History of boron carbide: it was discovered in the 19th century as a byproduct of the study of metal borides, and was not scientifically studied until the 1930s. It is the fifth hardest material known after boron nitride, diamond, fullerene compound and diamond whole fiber tube.

Boron carbide
English Name: bolon carbide
Alias: b4-c, B4C, black diamond, tetraboron carbide
CAS No.: 12069-32-8
Binecs No.: 235-111-5
RTECS No.: ed7420000
MSDS: external MSDS
Chemical formula: B4C
Relative molecular weight: 55.26
Appearance: black powder
Density: 2.52g/cm3 (solid)
Melting point: 2450 ℃
Boiling point: 3500 ℃
Crystal structure: rhombic hexahedron
Mohs hardness: 9.36
Microhardness: 4950kgf / mm2
Water solubility: insoluble

Physical properties and physicochemical constants of boron carbide:
Boron carbide is produced by smelting boric acid and carbon materials at high temperature in an electric furnace. Its theoretical density is 2.52g/cm3, melting point is 2450 ℃, microhardness is 4950kgf / mm2, and Mohs hardness is 9.3. Its hardness is second only to diamond and CBN. It has the characteristics of high temperature resistance, acid and alkali corrosion resistance, high strength, good chemical stability and light specific gravity. It has been widely used in many new material fields. Extensive application.

Main application fields and characteristics of boron carbide:
For defense industry:
Make bulletproof materials, such as bulletproof plates in bulletproof vests, ceramic bulletproof tiles in the cockpit of military aircraft pilots, and ceramic bulletproof plates of modern armored personnel carriers and tanks. It can be used as a nozzle for making guns and guns in the arms industry. At present, Al2O3 based bulletproof ceramics have been used in “502 project” and “212 project”, but when Al2O3 based ceramic composite armor is used in the side of chariot body and other parts, its weight reduction effect is not obvious, while the weight of the same thickness high-performance boron carbide ceramic composite armor is 15% ~ 20% less than Al2O3 based bulletproof ceramics, and the bulletproof performance is further improved. Therefore, the key equipment engineering ceramic composite armor development project puts forward an urgent demand for high-performance and low-cost boron carbide bulletproof ceramics. Therefore, the development and application of high-performance and low-cost boron carbide bulletproof ceramic materials can greatly improve the performance of related weapons and equipment, with significant military and economic benefits. The application direction of boron carbide bulletproof ceramic materials is as follows: key equipment engineering, future main battle tank, infantry fighting vehicle, airborne vehicle and other light armored vehicles, as well as armor protection for the web of armed helicopter and superstructure of ship boat.

For nuclear industry:
Boron carbide is used to make control rod, regulating rod, accident rod, safety rod and shielding rod of nuclear reactor, boron carbide tile, plate or neutron absorber for radiation protection (made of powder with high B10 content), or mix with cement to make shielding layer of nuclear reactor, which is the important functional element next to nuclear fuel element. Characteristics: boron carbide can absorb a large number of neutrons without forming any radioisotopes, so it is an ideal neutron absorber and core assembly of nuclear reactor in the nuclear power plant. The neutron absorber mainly controls the rate of nuclear fission, but it is made into powder to increase the surface area. Boron carbide has high neutron absorption cross section, wide absorption energy spectrum, low price, abundant raw materials, no strong λ ray secondary radiation after absorbing neutrons, so the waste is easy to be treated, so boron carbide is an important neutron absorption material.

For refractories:
Boron carbide is used as antioxidant additive in low carbon magnesia carbon brick and castable. It is used in the key parts of high temperature and erosion resistance in iron and steel industry. Such as ladle, tap (nozzle), slide plate, plug bar, etc. With the energy saving and consumption reduction of iron and steel industry and the need of smelting low carbon steel and ultra-low carbon steel, the research and development of low carbon magnesia carbon brick (carbon content is generally less than 8%) with excellent performance is increasingly concerned by the industry at home and abroad. At present, the performance of low-carbon magnesia carbon brick is generally improved by improving the carbon structure, optimizing the matrix structure of magnesia carbon brick, and increasing high-efficiency antioxidants. Among them, the graphitized carbon black composite powder composed of industrial grade B4C and some graphitized carbon black is used as carbon source and antioxidants for low-carbon magnesia carbon brick, which has achieved good results. The low carbon magnesia carbon brick with B4C has good conventional physical properties, oxidation resistance and thermal shock stability.

Characteristics: boron carbide plays an anti-oxidation role in carbon containing refractories, which can densify the products and prevent the oxidation of carbon in carbon containing refractories. At the same time, it reacts at 1000 ℃ ~ 1250 ℃, forming (9 Al2O3 · 2b2o3) columnar crystals which are distributed in the matrix and gap of refractories, thus reducing the porosity, increasing the medium temperature strength, forming crystal volume expansion, healing volume contraction and reducing Few cracks.

For other engineering ceramic materials:
Boron carbide for sandblasting machine nozzle, high-pressure water cutting machine nozzle, seal ring, ceramic mold and so on. Features: boron carbide nozzle with wear-resistant and high hardness will gradually replace the known hard alloy (tungsten steel) and silicon carbide, silicon nitride, alumina, zirconia and other materials sandblasting nozzle. In addition, the application of boron carbide in the field of composite ceramics: boron carbide is a compound with strong covalent bond, and the plasticity of boron carbide is very poor, and the resistance of grain boundary movement is very large, so it is difficult to obtain compact sintered body. In addition to some special occasions, such as microcrystalline boron carbide gas dynamic bearing material, boron carbide block used as neutron absorption material in atomic energy reactor, it is usually added sintering. The sintering behavior of boron carbide can be improved by the method of auxiliary agent, and more cheap and practical boron carbide products can be obtained. In addition, adding a large amount of silicon carbide to boron carbide to make composite materials is an effective way to improve the sintering density. Silicon carbide itself has good mechanical and physical properties, including high specific strength, specific modulus, good corrosion resistance and thermal shock resistance, low density and thermal expansion coefficient, etc. Meanwhile, in the periodic table of elements, the position of Si is adjacent to B and C, so the properties are very similar. According to the similar compatibility principle, the existence of SiC can improve the sintering diffusion and promote the sintering of boron carbide. In the study of SiC ceramic sintering, scientists found that adding proper amount of boron carbide to SiC can obtain more compact sintering body. It can be seen that boron carbide and silicon carbide can promote the densification process mutually. What’s more, B4C SiC composite ceramics can keep the excellent physical and mechanical properties of boron carbide ceramics while reducing the sintering conditions. B4C SiC ceramic is considered to be a kind of high temperature corrosion-resistant and wear-resistant material with wide application prospect, which has been applied in the fields of industrial nozzle, pump sealing and hot extrusion die.

In recent decades, due to the rapid development of science and technology, especially the rapid development of electronic technology, space technology and computer technology, materials with special properties are urgently needed. Special ceramics with abundant reserves, cheap price, easy preparation and many unique properties came into being. Wearing the laurel of “omnipotent ceramics”, they have become one of the most promising materials in the 21st century. Boron carbide has become an important member of special ceramics family because of its many excellent properties. At present, many problems about the preparation of boron carbide powder and sintering of boron carbide ceramic materials have been solved. In the future, boron carbide will play an important role because of its excellent properties.

For general industry:
Boron carbide is used to make high-grade wear-resistant electrode to enhance the wear-resistant strength of welding surface; it is used as grinding and polishing materials, abrasive for water cutting and diamond abrasive correction materials; it is used for high-precision polishing and grinding in jewelry industry. Properties: boron carbide is a solid harder than silicon carbide or tungsten carbide. It was used as a kind of coarse sand grinding material a long time ago. Because of its high melting point, it is not easy to cast into artificial products, but through high temperature melting powder, it can be processed into a simple shape, used for grinding, grinding, drilling and polishing of cemented carbide, gem, etc.

Application of electrical properties of boron carbide:
Boron carbide graphite thermocouple consists of graphite tube, boron carbide rod and boron nitride bush between them. In inert gas and vacuum, the service temperature is up to 2200 ℃. The linear relationship between electric potential difference and temperature is good between 600 ℃ and 2200 ℃.
Application of boron carbide as chemical raw material:
Boron carbide powder is activated by halogen and can be used as boronizing agent of steel and other alloys to Boronize on the steel surface, so as to generate the strength and wear resistance of the thin layer reinforced material of iron borate. Boron carbide can also be used as a non-metallic additive for some metal based friction materials. When boride powder is prepared by reduction synthesis method, boron carbide can be used as boron source to prepare TiB2, ZrB2, CrB2 and other powders, which are called “boron carbide method” for powder preparation.

Application of boron carbide in sapphire chip (LED):
In recent years, the country’s strong support and promotion of LED industry has made the development of LED industry better, which has brought great business opportunities to the enterprises that produce and process sapphire crystal. Because of the high strength and hardness of sapphire crystal (Mohs 9), it is very difficult for processing enterprises. From the point of view of materials and grinding academia, the best materials for processing and grinding sapphire crystal are synthetic diamond, boron carbide and silicon dioxide. Because the hardness of synthetic diamond is too high (Mohs hardness 10), it will scratch the surface of sapphire wafer when it is grinded, which will affect the transparency of the wafer, and the price is expensive. However, the hardness of silica is not enough (Mohs 7), and the grinding force difference is time-consuming and labor-consuming in grinding engineering. Therefore, boron carbide abrasive (Mohs 9.3) becomes the most ideal material to process and grind sapphire crystal. Boron carbide abrasives have outstanding performance in both sides grinding of sapphire wafer and back thinning and polishing of sapphire based LED epitaxial wafer. Some national key universities also have major research on the grinding of sapphire crystal with boron carbide. In short, with the rapid development of LED industry, boron carbide will also rise rapidly

In short, with the development of society and science and technology, the application field of boron carbide will be found and expanded continuously, and the market application prospect will be more broad.

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