Introduction and application of boron carbide

Physical properties and physicochemical constants of boron carbide:

Boron carbide is made of boric acid and carbon materials smelted at high temperature in an electric furnace, with a theoretical density of 2.52 g/cm³, a melting point of 2450 °C, a microhardness of 4950 kgf/mm², and a hardness of 9.3 on the Mohs scale, which is second only to diamond and cubic boron nitride, and has the characteristics of high temperature resistance, acid resistance, alkali corrosion resistance, high strength and good chemical stability. New materials in many fields, such as high temperature resistance, acid resistance, alkali corrosion resistance, high strength, chemical stability, light weight, etc. It is widely used in many fields of new materials.

(1) For the defense industry:

Production of bulletproof materials such as bulletproof plates in bulletproof vests, bulletproof ceramic tiles and bulletproof ceramic plates in the cockpit of military aircraft, modern armored personnel carriers and tanks. They can also be used as nozzles for the arms industry to produce guns and cannons. At present, Al2O3-based bulletproof ceramics are used in "Project 502" and "Project 212", but in the side hull of the tank with Al2O3-based ceramic composite armor, its weight reduction effect is not obvious, and high-performance boron carbide ceramics, such as thick ceramics, should be used. Thick ceramic. Composite armor is 15%-20% less mass than Al2O3-based ballistic ceramics, while ballistic performance is further improved. Therefore, the high-performance and low-cost boron carbide bulletproof ceramics advocated by the ceramic composite armor development project of important equipment engineering are imminent. Therefore, the development and application of high-performance and low-cost boron carbide bulletproof ceramic materials can significantly improve the performance of related weapons and equipment, and bring important military and economic benefits. The application direction of boron carbide bulletproof ceramic materials: major equipment projects, light armored vehicles such as future main battle tanks, infantry fighting vehicles, and airborne aircraft, as well as the armor protection of the web of the helicopter gunship and the superstructure of the ship.

(2) For the nuclear industry:

The production of boron carbide is used in the production of nuclear reactor control rods, regulating rods, accident rods, safety rods, shielding rods, radiation protection tiles, plates and neutron absorbers (made with powders with a high B10 content), or in the production of reactor shielding and mixed cement, and is an important functional component second only to nuclear fuel elements. Features: Boron carbide is an ideal neutron absorber for nuclear power plant and reactor core components because it can absorb large amounts of neutrons without forming radioactive isotopes. Neutron absorbers are mainly used to control the rate of fission, but are powdered to increase their surface area. Boron carbide is an important neutron absorber because of its high neutron absorption cross-section, wide absorption spectrum, low price, abundant raw materials, and no strong secondary radiation of lambda rays after neutron absorption, which is easy to dispose of waste.

(3) Used in the field of refractory materials:

Boron carbide can be used as an antioxidant additive for low-carbon magnesia-carbon bricks and castables. In the steel industry, it is used for key components that are resistant to high temperatures and wear and tear. Ladle, tap hole (water outlet), slide plate, plug bar, etc. With the demand of the iron and steel industry for energy-saving low-carbon steel smelting and ultra-low-carbon steel, the research and development of low-carbon magnesia-carbon bricks with excellent performance (carbon content is generally <8%) has attracted more and more attention from the industry at home and abroad. At present, the performance of low-carbon magnesia carbon bricks is generally improved by improving the composite carbon structure, optimizing the matrix structure of magnesia carbon bricks and adding high-efficiency antioxidants. Low-carbon magnesia-carbon bricks containing B4C have good conventional properties, oxidation resistance, and thermal shock stability.

Features: The antioxidant effect of boron carbide in carbonaceous refractories is to prevent carbon oxidation in carbonaceous refractories, and at the same time as the reaction occurs from 1000 °C to 1250 °C, the product is densified and (9 Al2O3-2B2O3) columnar crystals are distributed in the refractory matrix and pores, thereby reducing porosity, improving the strength at medium temperature, crystal volume generation and expansion, volume contraction can be healed, and cracking can be reduced.

(4) Used in other engineering ceramic materials:

Production of boron carbide sandblasting machine nozzles, high-pressure water cutting machine nozzles, sealing rings, ceramic molds, etc.

Features: Boron carbide nozzles have high wear hardness and will gradually replace other materials such as known carbide (tungsten steel), silicon carbide, silicon nitride, alumina, zirconia and sandblasting machine nozzles. There is also the application of boron carbide in the field of composite ceramics: boron carbide is a very covalent compound, the plasticity of boron carbide is very poor, the migration resistance of grain boundaries is very large, and it is in addition to the gas dynamic bearing material of some special occasions such as microcrystalline boron carbide, it is more difficult to obtain a dense sintered body, and the boron carbide block is used as a neutron absorbing material for sintering in the reaction furnace, and the boron carbide is usually sintered by adding sintering additives. The addition of sintering additives to boron carbide is usually done to improve the sintering properties of boron carbide and obtain a cheaper and more practical product. Adding a large amount of silicon carbide to boron carbide to make composites is also an effective way to increase the sintering density. Silicon carbide itself has very good mechanical and physical properties, such as high specific strength and specific modulus, excellent corrosion resistance and thermal shock resistance, low density and thermal expansion coefficient, etc. According to the principle of similarity and compatibility, the presence of silicon carbide can improve the diffusion of sinter and promote the sintering of boron carbide. Scientists who study the sintering of silicon carbide ceramics have found that adding the right amount of boron carbide to silicon carbide can produce a denser sintered body. During the sintering process, boron carbide and silicon carbide can mutually promote the densification process. More notably, while reducing the sintering conditions of boron carbide ceramics, B4C-SiC composite ceramics can better maintain the excellent physical and mechanical properties of boron carbide ceramics. They are used in areas such as hot extrusion dies.

In recent decades, with the rapid development of science and technology, especially the development of electronics, aerospace and computer technology, there is an urgent demand for materials with special properties. Abundant reserves, low cost, simple preparation methods and many unique properties have made special ceramics wear the laurel of "universal ceramics" and become one of the most promising and important materials in the 21st century. Boron carbide has many excellent properties and has become an important member of the specialty ceramics family. At present, many problems such as the preparation of boron carbide powder and the sintering of boron carbide ceramic materials have been solved. In the field of materials in the future, boron carbide will definitely occupy an important position with its excellent performance.

(5) Application in general industry.

Boron carbide can be used in the manufacture of high-grade wear-resistant welding rods to improve the wear strength of welded surfaces, as well as in the manufacture of grinding and polishing materials, abrasive grains for waterjets, diamond abrasive compounds, and high-precision grinding and polishing in the jewelry industry.

Features: Boron carbide is a harder solid than silicon carbide or tungsten carbide and has been used as a coarse sand abrasive material for a decade. Due to its high melting point, it is not easy to cast into artificial products, but by melting the powder at high temperatures, it can be processed into simple shapes such as grinding, grinding, drilling, and polishing cemented carbide and jewelry.

(6) Application of boron carbide electrical properties:

Boron carbide graphite thermocouples consist of graphite tubes, boron carbide rods, and boron nitride bushings between them. In inert gases or vacuums, they can be used at temperatures up to 2200°C. At 600-2200°C, the potential difference has a good linear relationship with temperature.

(7) Application of boron carbide as chemical raw material:

Boron carbide powder can be used as a boriding agent for steel and other alloys after halogen activation, and boron infiltration on the steel surface produces a thin layer of iron boride to increase the strength and wear resistance of the material. Boron carbide can also be used as a non-metallic additive for metal-based friction materials. Boron carbide produces boride powder by reduction-chemical method, and boron carbide can be used as a boron source to produce TiB2, ZrB2, CrB2 and other powders, which is called the "boron carbide method" of powder production.

(8) Application of boron carbide in sapphire chip (LED):

Synthetic diamond is too hard (10 on the Mohs scale) to cause surface scratches when grinding sapphire wafers, affecting the light transmittance of the wafers, and is expensive. The hardness of silica is not enough (Mohs scale 7), the grinding process is time-consuming, labor-intensive, and the grinding capacity is poor. Therefore, boron carbide abrasives (9.3 on the Mohs scale) are the most ideal materials for machining and grinding sapphire crystals. Boron carbide abrasives excel in double-sided grinding of sapphire wafers and backside grinding of sapphire-based LED epitaxial wafers. Several leading national universities are also conducting significant research on the application of boron carbide in sapphire crystal polishing. 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 increase, and the market application prospect will be broader.

In recent years, the state's support and promotion of the LED industry, the development situation of the LED industry tends to improve, which has brought huge business opportunities to the production and processing industry of sapphire crystals. The high strength and hardness of sapphire crystals (9 on the Mohs scale) pose great difficulties for processing companies. From the perspective of the materials and abrasive industry, the best materials for processing and grinding sapphire crystals are synthetic diamond, boron carbide, and silicon dioxide.