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Approaching Boron Nitride

wallpapers News 2021-03-25
Overview of Boron Nitride
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), rhombohedral boron nitride (RBN), cubic boron nitride (CBN) and wurtzite nitrogen Boron (WBN).
The development history of boron nitride
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-type boron nitride)], h- BN not only its structure but also its performance is very similar to graphite, and its own whiteness, so it is commonly called: white graphite.
Boron nitride (BN) ceramics is a compound discovered as early as 1842. A lot of research work has been done on BN materials 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 Union Carbon Company first started production, and in 1960 they had produced more than 10 tons.
In 1957, R·H·Wentrof was the first to successfully trial-produce CBN. In 1969, General Electric Company sold the product as Borazon. In 1973, the United States announced the production of CBN tools.
In 1975, Japan imported technology from the United States and also produced CBN tools.
In 1979, Sokolowski successfully used pulsed plasma technology to prepare c-BN films at low temperature and low pressure for the first time.
At the end of the 1990s, people have been able to use a variety of physical vapor deposition (PVD) and chemical vapor deposition (CVD) methods to prepare c-BN films.
From the perspective of China, the development is advancing by leaps and bounds. The research on BN powder began in 1963, successfully developed in 1966, and was put into production in 1967 and used in my country's industry and cutting-edge technology.
The physical properties of boron nitride
CBN is usually black, brown or dark red crystals with a zinc blende structure with good thermal conductivity. Hardness is second only to diamond, it is a super hard material, often used as tool materials and abrasives.
Boron nitride has chemical resistance properties and is not corroded by inorganic acids and water. The boron-nitrogen bond is broken in the hot concentrated alkali. Above 1200°C, it starts to oxidize in the air. The melting point is 3000°C, and it begins to sublimate when it is slightly lower than 3000°C. It begins 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, while it can reach 2800°C in an inactive reducing atmosphere, but the lubrication performance is poor at room temperature. Most of the properties of boron carbide are better than carbon materials. For hexagonal boron nitride: 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 transparent Infrared.
The physical structure of boron nitride
The hexagonal crystal of boron nitride is the most common graphite lattice, and there are also amorphous variants. In addition to the hexagonal crystal form, boron carbide has other crystal forms, including: rhombohedral boron nitride (abbreviation: r-BN, or Name: trigonal boron nitride, its structure is similar to h-BN, it will be produced in the process of converting h-BN to c-BN), cubic boron nitride [abbreviation: c-BN, or |3-BN, or z -BN (namely sphalerite type boron nitride), very hard texture], wurtzite type boron nitride (abbreviation: w-BN, h-BN is a hard state under high pressure). People even found two-dimensional boron nitride crystals like graphene (similar to MoS: two-dimensional crystals).
Manufacturing process of boron nitride
The boron nitride usually produced has a graphite-type structure, commonly known as white graphite. The other is diamond type, similar to the principle of converting graphite to diamond, graphite type boron nitride can be converted into diamond type boron nitride under high temperature (1800℃) and high pressure (8000Mpa) [5~18GPa]. It is a new type of high-temperature-resistant superhard material used to make drill bits, abrasive tools and cutting tools.
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