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Boron nitride can be synthesized in hexagonal and cubic forms

wallpapers News 2021-06-09
Boron nitride (BN) is a synthetic material that, although discovered in the early 19th century, was not developed commercially until the second half of the 20th century. In the periodic table, boron and nitrogen are neighbors of carbon -- boron and nitrogen combine to have the same number of shell electrons -- and boron and nitrogen have similar atomic radii to carbon. It is therefore not surprising that boron nitride and carbon show similarities in their crystal structures.
Just as carbon exists in the form of graphite and diamond, boron nitride can be synthesized in hexagonal and cubic forms.
Hexagonal boron nitride powders were prepared by nitriding or ammoniation of boron oxide at high temperatures. Cubic boron nitride is formed by treating hexagonal boron nitride at high pressure and temperature.
Hexagonal boron nitride (H-BN) is equivalent to graphite in structure. Like graphite, its lamellar microstructure and lamellar lattice structure give it good lubrication properties. BHN is resistant to sintering and is usually formed by hot embossing.
Cubic boron nitride (C-BN) has the same structure and properties as diamond. Indeed, C-BN is the second hardest material after diamond. C-BN was first synthesized in 1957, but only in the last 15 years has it been commercially produced.
Key properties of cubic boron nitride
Under hot pressing, H-BN can be easily machined using traditional metal cutting techniques, so complex-shaped parts can be made from hot pressing billets.
Because of its ability to prevent surface oxidation, H-BN is not wetting by most molten metals, glass, and salts, and thus has a high resistance to chemical attack.
H-BN also has high dielectric breakdown strength; High volume resistivity; Good chemical inertia; Hot isostatic pressing
Its fire resistance and the fact that it is not wetting by molten glass led H-BN to be used in the production of hot isostatic pressing (HIP 'ED) materials, most notably ceramics. In this application, the prefabricated parts are coated with H-BN prior to glass encapsulation and hipping. This protects the HIP 'ed part from actually touching the glass, which in turn makes it easier to remove after the HIP 'ing.
Machine tool cutting tools and abrasives
Cutting tools and abrasive parts for low carbon ferrous metals were developed by using boron carbonitride technology. In this application, the tool behaves like a polycrystalline diamond tool but can be used on iron and low carbon alloys without the risk of reaction.
Substrates for electronic devices
C-BN is used as a substrate for the installation of high density and high power electronic components, and its high thermal conductivity allows for efficient heat dissipation.

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