Boron nitride is a crystal composed of nitrogen and boron atoms. The chemical composition is 43.6% boron and 56.4% nitrogen, with four different variants: HBN, RBN, CBN, and WBN. CBN is usually a black, brown, or dark red crystal with a sphalerite structure and good thermal conductivity. Hardness is second only to diamond and is a superhard material commonly used as tool materials and abrasives. BN is resistant to chemical attack and is not eroded by inorganic acids and water. The boron nitrogen bond is broken in hot concentrated alkali. Oxidation begins in the air at 1200 ℃. Decomposition starts at about 2700 ℃ in a vacuum. Slightly soluble in burning acid, insoluble in cold water, relative density 2.29. The compressive strength is 170Mpa. The maximum operating temperature is 900 ℃ in an oxidizing atmosphere and 2800 ℃ in an inactive reducing atmosphere, but the lubricating performance is poor at room temperature. Most properties of BN are better than carbon materials. For HBN: low friction coefficient, good high-temperature stability, good heat shock resistance, high strength, high thermal conductivity, low expansion coefficient, high resistivity, corrosion resistance, microwave or infrared transmission.
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Chemical Formula |
BN |
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Exact Mass |
25 |
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Molecular Weight |
25 |
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m/z |
25 (100.0%), 24 (24.8%) |
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Elemental Analysis |
B, 43.56; N, 56.44 |
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Material characteristics
CBN is usually a black, brown, or dark red crystal with a sphalerite structure and good thermal conductivity. Hardness second only to diamond, it is a superhard material commonly used as a tool material and abrasive.
Boron nitride has chemical resistance and is not corroded by inorganic acids and water. The boron nitrogen bond is broken in hot concentrated alkali. Oxidation begins in the air above 1200 ℃. Decomposition begins at around 2700 ℃ under vacuum. Slightly soluble in hot acid, insoluble in cold water, with a relative density of 2.29. When boiled with water, hydrolysis is very slow, producing a small amount of boric acid and ammonia. It does not react with weak acids and strong bases at room temperature and is slightly soluble in hot acids. It can only decompose when treated with molten potassium hydroxide, and chlorine can only react with it under red hot conditions.
The compressive strength is 170MPa. The maximum operating temperature under oxidizing atmosphere is 900 ℃, while it can reach 2800 ℃ under non reactive reducing atmosphere, but the lubrication performance is poor at room temperature. Most of the properties of BN are superior to carbon materials. For HBN: low friction coefficient, good high-temperature stability, good thermal shock resistance, high strength, high thermal conductivity, low expansion coefficient, high electrical resistivity, corrosion resistance, microwave or infrared transparency.
Material structure
BN hexagonal crystal system, most commonly graphite lattice, also has amorphous variants. In addition to the hexagonal crystal form, BN has other crystal forms, including r-BN, c-BN and w-BN. People have even discovered two-dimensional BN crystals that resemble graphite thin.
The commonly produced boron nitride has a graphite type structure, commonly known as white graphite. Another type is diamond type, which is similar to the principle of graphite transforming into diamond. Graphite type BN can be transformed into diamond type BN at high temperature (1800 ℃) and high pressure (8000Mpa) [5-18GPa]. It is a new type of high-temperature resistant superhard material used for making drill bits, grinding tools, and cutting tools.
Preparation method
In 1957, Wentorf first synthesized cubic BN artificially. When the temperature approaches or exceeds 1700 ℃ and the minimum pressure is 11-12GPa, pure HBN directly transforms into CBN. Subsequently, it was discovered that the use of catalysts can significantly reduce the transition temperature and pressure. The commonly used catalysts include alkali and alkaline earth metals, alkali and alkaline earth nitrides, alkaline earth fluoronitrides, ammonium borate salts, and inorganic fluorides. The temperature and pressure required for using ammonium borate as a catalyst are the lowest, with a pressure of 5GPa at 1500 ℃ and a temperature range of 600-700 ℃ at 6GPa. From this, it can be seen that although adding catalysts can greatly reduce the transformation temperature and pressure, the required temperature and pressure are still relatively high. Therefore, the equipment for its preparation is complex, the cost is high, and its industrial application is limited.
In 1979, Sokolowski successfully prepared CBN films using pulsed plasma technology at low temperature and low pressure. The equipment used is simple and the process is easy to implement, which has led to rapid development. Multiple methods of vapor deposition have emerged. Traditionally, it mainly refers to thermochemical vapor deposition. The experimental setup generally consists of heat-resistant quartz tubes and heating devices. The substrate can be heated by either a heating furnace (hot wall CVD) or high-frequency induction heating (cold wall CVD). The reaction gas decomposes on the surface of the high-temperature substrate and undergoes a chemical reaction to deposit a film. The reaction gas is a mixture of BCl3 or B2H6 and NH3.
This method uses water as the reaction medium in a high-temperature and high-pressure reaction environment inside an autoclave, allowing substances that are usually insoluble or difficult to dissolve to dissolve. The reaction can also undergo recrystallization. Hydrothermal technology has two characteristics: first, it has a relatively low temperature, and second, it is carried out in a closed container to avoid component volatilization. As a low-temperature and low-pressure synthesis method, it is used to synthesize cubic BN at low temperatures.
As a recently emerging method for synthesizing low-temperature nanomaterials, benzene thermal synthesis has received widespread attention. Due to its stable conjugated structure, benzene is an excellent solvent for solvothermal synthesis and has recently been successfully developed into a benzene thermal synthesis technique, as shown in the reaction equation:
BCl3 + Li3N → BN + 3LiCl
Or BBr3+Li3N → BN+3LiBr
The reaction temperature is only 450 ℃, and the benzene thermal synthesis technology can prepare a metastable phase that can only exist under extreme conditions and ultra-high pressure at relatively low temperatures and pressures. This method enables the low-temperature and low-pressure preparation of cubic boron nitride. However, this method is still in the experimental research stage and is a synthetic method with great potential for application.
Self propagating technology
By utilizing external energy to induce highly exothermic chemical reactions, the system undergoes localized reactions to form a chemical reaction front (combustion wave). The chemical reaction rapidly proceeds with the support of its own heat release, and the combustion wave spreads throughout the entire system. Although this method is a traditional inorganic synthesis method, it has only been reported in recent years for the synthesis of BN.
Ion beam sputtering technology
Using particle beam sputtering deposition technology, a mixed product of cubic BN and hexagonal BN is obtained. Although this method has fewer impurities, the morphology of the product is difficult to control due to the difficulty in controlling the reaction conditions. There is still great potential for the development of research on this method.
Carbon thermal synthesis technology
This method uses boric acid as the raw material, carbon as the reducing agent, and ammonia gas to nitride BN on the surface of silicon carbide. The resulting product has high purity and great application value for the preparation of composite materials.
Laser-induced reduction method
Using laser as an external energy source to induce redox reactions between reaction precursors and combine B and N to generate BN, but this method also produces a mixed phase.
1. Mold release agents for metal forming and lubricants for metal drawing.
2. Special electrolytic and resistive materials in high temperature conditions.
3. High temperature solid lubricants, extrusion anti-wear additives, additives for producing ceramic composite materials, refractory materials and antioxidant additives, especially for applications that resist molten metal corrosion, thermal enhancement additives, and high-temperature resistant insulation materials.
4. Heat sealing desiccants for transistors and additives for polymers such as plastic resins.
5. Pressed into various shapes of BN products, which can be used as high-temperature, high-voltage, insulation, and heat dissipation components.
6. Thermal shielding materials in aerospace.
7. With the participation of a catalyst, it can be converted into cubic BN that is as hard as diamond through high-temperature and high-pressure treatment.
8. Structural materials of atomic reactors.
9. Jet nozzles for aircraft and rocket engines.
10. Insulators for high-voltage, high-frequency electrical and plasma arcs.
11. Packaging materials that prevent neutron radiation.
12. A superhard material processed from BN, which can be used to make high-speed cutting tools and drill bits for geological exploration and oil drilling.
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13. Separation rings used in metallurgy for continuous cast steel, flow slots for amorphous iron, and release agents for continuous cast aluminum (various optical glass release agents).
14. Make evaporation boats for various capacitor film aluminum plating, cathode ray tube aluminum plating, display aluminum plating, etc.
15. Various fresh-keeping aluminum plated packaging bags, etc.
16. Various laser anti-counterfeiting aluminum plating, trademark hot stamping materials, various cigarette labels, beer labels, packaging boxes, cigarette packaging boxes aluminum plating, and so on.
17. Cosmetics are used as fillers for lipstick, which are non-toxic, lubricating, and glossy.
Boron nitride was introduced over 100 years ago, with its earliest application being hexagonal BN as a high-temperature lubricant. Its structure and properties are very similar to graphite, and it is also pure white, hence it is commonly known as "white graphite".
BN ceramics were discovered as early as 1842. Extensive research on BN materials has been conducted abroad since World War II, and it was not until 1955 that the BN hot pressing method was developed. The American Diamond Company and United Carbon Company were the first to enter production, producing over 10 tons by 1960.
In 1957, R.H. Wentrof was the first to successfully develop CBN. In 1969, General Electric sold it as Borazon, and in 1973, the United States announced the production of CBN cutting tools.
In 1975, Japan imported technology from the United States and also prepared CBN cutting tools.
In 1979, pulsed plasma technology was successfully used for the first time to prepare collapsed c-BN thin films at low temperature and low pressure.
In the late 1990s, people were able to prepare c-BN thin films using various physical vapor deposition (PVD) and chemical vapor deposition (CVD) methods.
From a domestic perspective in China, development has made rapid progress. Research on BN powder began in 1963, was successfully developed in 1966, and was put into production and applied in China's industry and cutting-edge technology in 1967.
Everything You Need to Know
What is boron nitride used for?
Boron Nitride products are widely used across industries such as: Steel and foundry production. High-temperature furnace manufacturing. Microelectronics and semiconductor industries.
Is boron nitride good for skin?
As a synthetic product, it is chemically stable and known to be safe and gentle for the skin. Due to a strictly controlled manufacturing process, Tokuyama h-BN is extremely pure, with very little soluble boron. Conforming to 2021 Japanese Standards of Quasi-Drug Ingredients.
Is boron nitride food safe?
Boron Nitride is a real and healthy alternative (NSF food contact safe certified) to PTFE or Teflon, which can also be used as a filler in polymers due to its excellent lubrication properties.
Is boron nitride stronger than diamond?
It has been reported to be 18% stronger than diamond. Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Because of excellent thermal and chemical stability, boron nitride ceramics are used in high-temperature equipment and metal casting.
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