Property of hexagonal boron nitride material

Hexagonal boron nitride (hBN) can be prepared by melting B2O3 with NH4Cl or burning boron in NH3. Generally, Boron nitride has graphite-like layered structure. It is a white powder with loose, lubricating, moisture absorption, light weight, insoluble, high temperature resistance and other properties, so it is also called "white graphite". hBN powder could be sintered by hot pressing to form a machinable ceramic material. Composite ceramic material is also possible. Usually the boron nitride composite ceramic has BN and zirconia or aluminum nitride (according to de description of QS Advanced Material's website)

Hexagonal boron nitride has no obvious melting point. It sublimates at 3000 ℃ in 0.1MPa nitrogen, melts at 3000 ℃ in inert gas, and is heat-resistant to 2000 ℃ in neutral reducing atmosphere. It can be used at 2800 ℃ in nitrogen and argon, and has poor stability under 1000 ℃ in oxygen atmosphere. Hexagonal boron nitride is insoluble in cold water and hydrolyzes very slowly when the water is boiling, resulting in a small amount of boric acid and nitrogen; It doesn't react with weak acid and strong base at room temperature, but slightly dissolves in hot acid. It can be decomposed only after being treated with dissolved sodium hydroxide and potassium hydroxide.

Hexagonal boron nitride (hBN) is one of the most thermal conductive ceramic materials. Its thermal conductivity is ten times that of quartz, and its high thermal conductivity is 33W / m.k, which is the same as that of pure iron; The coefficient of thermal expansion is equivalent to quartz, which is the smallest in ceramics. The coefficient of thermal expansion is 41x10 ^ 6 / C in the c-axis direction and - 2.3x10 ^ 6 / C in the d-axis direction, so the thermal shock resistance is very good. Boron nitride is also the best high temperature insulating material in ceramics, with breakdown voltage of 3KV / mm, low dielectric loss of 2.5x10 ^ - 4 at 108hz, and dielectric constant of 4. It can transmit microwave and infrared rays.

The friction coefficient of hexagonal boron nitride is as low as 0.16 and does not increase at high temperature. It has higher temperature resistance than molybdenum disulfide and graphite. The oxidation atmosphere can reach 900 ℃ and vacuum can reach 2000 ℃. Boron nitride powder dispersed in oil or water can be used as a lubricant for wire drawing or pressing forming, and can also be used as a lubricant for sliding parts of high temperature furnace. The sintered body of boron nitride can be used as a material for bearing and sliding parts with self-lubricating performance.

The compressive strength of hexagonal boron nitride is 170Mpa, its machinability and hardness are Mohs 2, so it can be processed into parts with high precision by general machining methods.