Boron nitride is a crystal composed of nitrogen atoms and boron atoms. The chemical composition is 43.6% boron and 56.4% nitrogen with four different variants: hexagonal boron nitride (HBN), rhombic boron nitride (RBN), cubic boron nitride (CBN) and wurtzite nitrogen Boronide (WBN).
Boron nitride came out more than 100 years ago. The earliest application was hexagonal boron nitride as a high-temperature lubricant [abbreviation: h-BN, or a-BN, or g-BN (that is, graphite boron nitride)], h- BN has not only its structure but also its performance is very similar to graphite. It's own white, so commonly known as white graphite.
Boron nitride (BN) ceramics were discovered as early as 1842. A lot of research work on BN materials has been carried out abroad since the Second World War, and it was not developed until the BN hot pressing method was solved in 1955. The American Diamond Company and United Carbon Company were first put into production. In 1960, they produced more than 10 tons.
In 1957, R·H·Wentrof took the lead in successfully trial-manufacturing CBN. In 1969, General Electric Company of the United States sold it as a product Borazon. In 1973, the United States announced that it made CBN tools.
In 1975, Japan introduced technology from the United States and prepared CBN tools.
In 1979, Sokolowski successfully used pulsed plasma technology to prepare c-BN thin films at low temperature and low pressure.
In the late 1990s, people have been able to use a variety of physical vapor deposition (PVD) and chemical vapor deposition (CVD) methods to prepare c-BN thin films.
CBN is usually black, brown, or dark red crystals, sphalerite structure, has good thermal conductivity. Hardness is second only to diamond, and it is a super hard material, often used as tool material and abrasive.
Boron nitride is resistant to chemical attack and is not attacked by inorganic acids and water. The boron-nitrogen bond is broken in hot, concentrated alkali. Above 1200 ℃ began to oxidize in the air. The melting point is 3000℃, and it begins to sublimate when it is slightly lower than 3000℃. It occurs to decompose at about 2700°C under vacuum. Slightly soluble in hot acid, insoluble in cold water, relative density 2.25. The compressive strength is 170MPa. The maximum operating temperature is 900°C in an oxidizing atmosphere, and up to 2800°C in an inactive reducing atmosphere, but the lubrication performance is mediocre at an average temperature. Most properties of boron carbide are better than carbon materials. For hexagonal boron nitride: low coefficient of friction, excellent stability at high temperature, good thermal shock resistance, high strength, high thermal conductivity, small expansion coefficient, large resistivity, corrosion resistance, microwave penetration or Through infrared.
Boron nitride hexagonal crystals, most commonly graphite lattices, and amorphous variants. In addition to hexagonal crystal forms, boron carbide has other crystal forms, including rhombohedral boron nitride (abbreviation: r-BN, or Said: Trigonal boron nitride, whose structure is similar to h-BN, will be produced during the conversion of h-BN to c-BN), cubic boron nitride [abbreviation: c-BN, or | 3-BN, or z -BN (that is sphalerite type boron nitride), the texture is tough], wurtzite type boron nitride (abbreviation: w-BN, a hard state under h-BN high pressure). People even found two-dimensional boron nitride crystals like graphite dilute (similar to MoS: two-dimensional crystals).
High temperature and high-pressure synthesis
In 1957, Wentorf co-founded BN for the first time. When the temperature is close to or higher than 1700℃ and the minimum pressure is 11-12GPa, it is directly transformed from pure hexagonal boron nitride (HBN) to cubic boron nitride (CBN). Subsequently, it was found that the use of catalysts can significantly reduce the transition temperature and pressure. Commonly used enzymes are alkali and alkaline earth metals, alkali and alkaline earth nitrides, alkaline earth fluoronitrides, ammonium borate, and inorganic fluorides. Among them, the temperature and pressure required to use ammonium borate as the catalyst are the lowest. The required pressure is 5GPa at 1500°C, and the temperature range is 600-700°C when the pressure is 6GPa. It can be seen that although the addition of catalysts can significantly reduce the transition temperature and pressure, the required temperature and pressure are still relatively high. Therefore, the equipment for its preparation is complicated, and the cost is high, and its industrial application is limited.
Chemical vapor synthesis
In 1979, Sokolowski successfully used pulsed plasma technology to produce cubic boron nitride (CBN) films at low temperature and low pressure. The equipment used is simple, and the process is easy to implement, so it has developed rapidly. Various vapor deposition methods have emerged. Traditionally, it mainly refers to thermal chemical vapor deposition. The experimental device is generally composed of a heat-resistant quartz tube and a heating device. The substrate can be heated either by a heating furnace (hot-wall CVD) or by high-frequency induction heating (cold wall CVD). The reaction gas decomposes on the surface of the high-temperature substrate, and at the same time, the chemical reaction deposits and forms a film. The reaction gas is a mixed gas of BCl3 or B2H4 and NH3.
In this method, water is used as the reaction medium in the high-temperature and high-pressure reaction environment in the autoclave, so that ordinarily insoluble or insoluble substances are dissolved, and the reaction can also be recrystallized. Hydrothermal technology has two characteristics: its relatively low temperature and the other is that it is carried out in a closed container to avoid the volatilization of components. As a low temperature and low-pressure synthesis method, it is used to synthesize cubic boron nitride at low temperatures.
As a low-temperature nanomaterial synthesis method emerging in recent years, benzene thermal synthesis has received widespread attention. Because of its stable conjugated structure, benzene is an excellent solvent for solvothermal synthesis. Recently, benzene has been successfully developed into benzene thermal synthesis technology, such as the reaction formula:
The reaction temperature of BCl3+Li3N→BN+3LiCl or BBr3+Li3N→BN+3LiBr is only 450 ℃, benzene thermal synthesis technology can be prepared at relatively low heat, and pressure, which can usually be ready under extreme conditions, under ultra-high pressure Can exist in the metastable phase. This method realizes the preparation of cubic boron nitride at low temperatures and low weight. However, this method is still in the experimental research stage and is a synthetic method with high application potential.
Using externally provided necessary energy to induce a highly exothermic chemical reaction, the system reacts locally to form a chemical reaction frontier (combustion wave). The chemical reaction proceeds quickly with the support of its heat release, and the combustion wave spreads throughout the system. Although this method is a traditional inorganic synthesis method, it has only been reported in recent years for boron nitride synthesis.
Carbothermal synthesis technology
The method uses boric acid as the raw material on the surface of silicon carbide, carbon as the reducing agent, and ammonia nitriding to obtain boron nitride. The resulting product has high purity and has excellent application value for the preparation of composite materials.
Ion beam sputtering technology
Using the particle beam sputtering deposition technique, a mixed product of cubic boron nitride and hexagonal boron nitride is obtained. Although this method has fewer impurities, it is difficult to control the reaction conditions, so the product's form is difficult to control. There is still great potential for the development of this method.
Using a laser as an external energy source induces a redox reaction between the reaction precursors, and combines B and N to generate boron nitride. Still, this method also obtains a mixed phase.
Trunnano is one of the world's largest nitride manufacturers. Boron nitride is one of the leading products. If you are interested in boron nitride, please contact Dr. Leo, email: firstname.lastname@example.org.
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