Boron nitride is a crystal composed of nitrogen and boron atoms, with crystal structures categorized into hexagonal boron nitride, cubic boron nitride, and dense hexagonal boron nitride. The hexagonal boron nitride has a crystal structure similar to the layered structure of graphite, presenting as a loose, lubricious, hygroscopic, pale white powder, hence also known as "white graphite."

Hexagonal Boron Nitride boasts excellent electrical insulation, thermal conductivity, and chemical stability without a distinct melting point. It can withstand temperatures up to 3000°C under a 0.1MPA nitrogen atmosphere, and up to 2000°C in nitrogen or argon atmospheres, but has poor stability in oxygen atmospheres, below 1000°C. The thermal expansion coefficient of hexagonal boron nitride is comparable to that of steel, but its thermal conductivity is ten times higher. It is insoluble in cold water. When water boils, hydrolysis is very slow, producing a small amount of boric acid and ammonia. At room temperature, it does not react with weak acids or strong bases, is slightly soluble in hot acids, and can only be decomposed after being treated with molten sodium hydroxide and potassium hydroxide.

The performance parameters of hexagonal boron nitride are:

High thermal resistance: Sublimates at 3000°C, its strength at 1800°C is twice that of room temperature, withstands wind cooling to room temperature over ten times at 1500°C, and remains crack-free and softening at 2800°C in an inert gas atmosphere.

2. High thermal conductivity: The thermal pressure products have a thermal conductivity of 33 W/M.K, identical to pure iron, and are among the materials with the highest thermal conductivity in ceramics above 530°.

3. Low thermal expansion coefficient: With a coefficient of 2.1x10^-6, it ranks second only to borosilicate glass in ceramics and is one of the smallest. Additionally, it boasts high thermal conductivity, thus exhibiting excellent resistance to thermal shock.

4. Excellent Electrical Properties: Good high-temperature insulation, with a value of 1014 -cm at 25°C and 103 -cm at 2000°C. It is an excellent high-temperature insulating material for ceramics.

Applications of Hexagonal Boron Nitride

Hexagonal boron nitride is used in the production of TiB2/BN composite ceramics, refractory materials, ultra-hard materials, isolation rings for horizontal rolling, high-temperature lubricants, and high-temperature coatings, as well as raw materials for the synthesis of cubic boron nitride. Boron nitride is suitable for high-temperature solid lubricants, extrusion anti-wear additives, ceramic composite additives, refractory materials, and antioxidant additives, particularly in situations involving anti-melting metal slag, thermal strengthening additives, and high-temperature insulating materials.

Boron nitride is used as a thermal sealing desiccant for transistors and as an additive for plastic resins and other polymers. Molding boron nitride into various shapes allows it to serve as high-temperature, high-pressure, insulating, and heat dissipating components. Boron nitride is an insulating material in the aerospace field and, with the involvement of catalysts, can be transformed into cubic boron nitride as hard as diamond through high-temperature and high-pressure treatment. It is a structural material for atomic reactors, suitable for the nozzles of aircraft and rocket engines. Boron nitride acts as an insulator for high-voltage, high-frequency electricity and plasma arcs, and is used as encapsulation material to prevent neutron radiation.

Boron nitride superhard materials can be made into high-speed cutting tools, drill bits for geological exploration and oil drilling, separator rings for continuous steel casting in metallurgy, gating gaps for amorphous iron, and release agents for continuous aluminum casting. Boron nitride is used for various capacitor films, picture tube films, and evaporating boats for aluminum-coated displays, as well as for various aluminum-coated preservation packaging bags.