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Boron nitride-A material harder than diamond

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Update time : 2019-08-26 11:35:53
Boron nitride is a double compound composed of the same number of nitrogen atoms and boron atoms, so its experimental formula is BN. Boron nitride and carbon are isoelectronic, and like carbon, boron nitride has a variety of isomorphs. The cubic boron nitride structure is similar to diamond, and its hardness is only lower than that of diamond, but the high temperature resistance is better than diamond. The hexagonal boron nitride structure is similar to graphite and is a very practical lubricant.
 
Characteristic
 
Boron nitride is a crystal composed of a nitrogen atom and a boron atom, and the crystal structure is divided into: hexagonal boron nitride (HBN), close packed hexagonal boron nitride (WBN), and cubic boron nitride, wherein hexagonal boron nitride crystals The structure has a similar graphite layer structure, and presents a white powder which is loose, lubricated, easy to absorb moisture, and light in weight, so it is also called "white graphite".

Boron nitride is made up of nitrogen and boron atoms in the crystal, the crystal structure can be divided into: hexagonal boron nitride (HBN), dense rows of hexagonal boron nitride (WBN) and cubic boron nitride, the crystal structure of hexagonal boron nitride have similar graphite layer structure, loose, lubrication, easy absorption of moisture, light and other traits of white powder, so it is also called “white graphite”.

1. The hexagonal boron nitride structure is similar to graphite, also known as h-BN, α-BN or g-BN (graphitic BN), sometimes referred to as "white graphite", which is the most commonly used form of boron nitride. Similar to graphite, the hexagonal form is composed of many hexagons. These sheets have different registrations from the layers, but as seen from the arrangement pattern of graphite, this is because the boron atoms make the boron nitride atoms elliptical above the nitrogen atoms. Such a structure reflects the polarity of the boron-nitrogen chain. The lower covalent nature of boron nitride makes it a lower semi-metal with respect to graphite, which circulates in the network of pi-chains in its hexagonal flakes. The lack of color of hexagonal boron nitride shows a lower electron delocalization, indicating a larger energy gap.

Hexagonal boron nitride is a very good lubricant at very low and very high (900 °C) temperatures and even oxygen, and is particularly useful when graphite conductivity and chemical reactions with other materials cause difficulties. Since its lubrication mechanism does not involve water molecules between the layers, boron nitride lubricants can also be used under vacuum, such as when working in space.

Hexagonal boron nitride is still stable in air up to 1000 ° C, 1400 ° C in vacuum and 2800 ° C in inert gas, and is one of the best thermal conductivity insulators. It does not chemically react to most substances and is not wetted by many molten substances (eg aluminum, copper, zinc, iron and steel, chromium, silicon, boron, cryolite, glass and halogenated salts.)

2. The cubic boron nitride structure is similar to diamonds and is extremely hard. The microhardness is HV72000~98000Mpa, and the hardness is only lower than that of diamond. Similar to diamonds, cubic boron nitride is an insulator but an excellent thermal conductor. Also known as c-BN, β-BN, or z-BN (named after the crystal structure of Zinc Blende), it is a widely used industrial drilling tool.
 
Because it is insoluble in iron, nickel and other superalloys, CBN is suitable for processing ferrous metals such as iron and nickel, and diamonds chemically react with these materials to cause rapid wear of the cutting tools. Polycrystalline c-BN drilling tools are mostly used in mechanical steel, while diamond drilling tools are mostly used in aluminum alloys, pottery and glass. Like diamonds, cubic boron nitride has high heat transfer due to phonons. In contact with oxygen at high temperatures, boron nitride forms a passivation layer of boron oxide. Boron nitride can be well bonded to metals because of the formation of alternating layers of boron or nitrogen alloys.

Cubic boron nitride crystal materials are often used in the cutting head of cutting tools. When used for abrasives, synthetic resins, porous ceramics, and the like are generally used as the binder. Sintered cubic boron nitride is a non-conductive heat sink material, so it has potential application value in the field of microelectronics.

3. Boronite in the form of wurtzite (w-BN; point group = C 6v; space group = P 6 3 mc) has the same structure as ite, a rare hexagonal carbon polymorph. As in the cubic form, boron and nitrogen atoms are grouped into tetrahedrons. As in the cube form, boron and nitrogen atoms are divided into 6-membered rings; in the cube form, all rings are in a chair configuration, and in w-BN, the rings between "layers" are in a boat configuration. Earlier optimistic reports predicted that the water-like zinc-stone is very strong and can be estimated to be 18% stronger than diamonds by simulation, but it has not been experimentally verified due to the small amount of minerals in nature. Recent studies have measured w-BN hardness at 46 GPa that is slightly harder than commercial borides, but softer than cubic forms of borohydride.

TRUNNANO (Luoyang Trunnano Tech Co., Ltd ) is a professional Boron nitride  manufacturer with over 12 years experience in chemical products research and development. If you are looking for high quality Boron nitride, please feel free to contact us and send an inquiry.
 
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