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April 15, 2024

Properties and synthesis of hexagonal boron nitride

Hexagonal boron nitride is a kind of synthetic inorganic material with many excellent properties, which is more and more widely used in a variety of new technologies and products, improving the technical level of modern industry and promoting the development of new material industry to deeper and wider fields.

BN RODS 202404
BN RODS 202404

Properties of hexagonal boron nitride

(1) High heat resistance. Hexagonal boron nitride (h-BN) in 0.1Mpa nitrogen heated to more than 3000 ℃ will sublimate, at 1800 ℃ when the strength of the room temperature for twice, so has excellent thermal shock resistance, in 1500 ℃ air-cooled to room temperature dozens of times will not rupture.

(2) High thermal conductivity. The thermal conductivity of hexagonal boron nitride products is about 34W/m-k, which is similar to that of stainless steel, and the thermal conductivity is larger.

(3) Low expansion coefficient. The expansion coefficient of hexagonal boron nitride is (2.0~6.5)*10-6/℃, second only to quartz glass, coupled with its high coefficient of thermal conductivity, so have excellent thermal shock resistance.

(4) Excellent electrical insulation. Hexagonal boron nitride has good high-temperature insulation, high purity hexagonal boron nitride maximum volume resistivity up to 1016 ~ 1018Ω-m, even at 1000 ℃ high temperature, there is still 104 ~ 106Ω-m.

(5) Good corrosion resistance. Hexagonal boron nitride has good chemical stability and is not wetted by most molten metals, glass, and salt, so it has strong resistance to acid, alkali, molten metal, and glass erosion, and good chemical inertia.

(6) Low coefficient of friction. Hexagonal boron nitride has excellent lubricating properties, the coefficient of friction is 0.16, which does not increase at high temperatures and is more resistant to high temperatures and oxidation than molybdenum disulfide and graphite.

(7) Machinability. Hexagonal boron nitride is very easy to use conventional metal cutting technology for product finishing, with a turning accuracy of up to 0.05mm, so the hexagonal boron nitride blanks can be processed to get the complex shape of the product.

Synthesis of hexagonal boron nitride

There are various methods to prepare hexagonal boron nitride, such as the elemental boron method, boric acid method, borate method, boron halide method, and so on. The basic principle is that boron compounds (such as boric acid, elemental boron, boron halide, and other borates) and nitrogen-containing compounds (such as ammonia, urea, ammonia chloride, melamine, etc.) together with the heating reaction can be obtained after chemical treatment of hexagonal boron nitride of different purities.

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