What are boron nitride ceramics made of?
Basic Overview of Boron Nitride Ceramics
Hexagonal boron nitride (HBN) in its solid form is often referred to as “white graphite” because its microstructure is similar to graphite. However, unlike graphite, HBN is an excellent electrical insulator with a high oxidation temperature. It has high thermal conductivity and good thermal shock resistance and can be easily machined to tolerances of almost any shape. After machining, it is ready for use without additional heat treatment or sintering operations.
The chemical equation of boron nitride ceramics
Boron nitride, with the chemical formula BN, is chemically composed of 43.6% boron and 56.4% nitrogen and comes in four different variants: hexagonal boron nitride (HBN), rhombic boron nitride (RBN), cubic boron nitride (CBN), and fibrous zincite boron nitride (WBN).
What are pyrolytic boron nitride ceramics?
Pyrolytic boron nitride (PBN) ceramics are boron nitride ceramics prepared by chemical vapor deposition through high-temperature pyrolysis reaction.
What are hexagonal boron nitride ceramics?
Hexagonal boron nitride (HBN) is white in color, chemically stable, and resistant to leaching by most molten metals. It has good self-lubricating properties. It has low hardness and can be machined with an accuracy of 1/100mm.
Characteristics of hexagonal boron nitride ceramics
Hexagonal boron nitride has good electrical insulation, thermal conductivity, chemical stability, and no significant melting point. The highest use temperature in 0.1MPA nitrogen can reach 3000℃, in a neutral reducing atmosphere, it can be heat resistant to 2000℃, in nitrogen and argon the use temperature can reach 2800℃, in an oxygen atmosphere the stability is poor, and the use temperature is below 1000℃. The expansion coefficient of hexagonal boron nitride is equivalent to quartz, but the thermal conductivity is ten times that of quartz.
In addition, hexagonal boron nitride is insoluble in cold water and hydrolyzes very slowly when boiled in water, and produces a small amount of boric acid and ammonia. It does not react with weak acids and strong bases at room temperature, but is slightly soluble in hot acids and needs to be treated with molten sodium hydroxide and potassium hydroxide to decompose.
Application of boron nitride ceramics
Hexagonal boron nitride ceramics (HBN) can be used to manufacture crucibles for melting semiconductors and high-temperature containers for metallurgy, heat dissipation, and insulation parts for semiconductors, high-temperature bearings, thermocouple sleeves, and glass-forming molds, etc.
Properties of boron nitride.
Excellent thermal shock resistance
High resistivity-excluding aerosols, coatings, and ZSBN
High thermal conductivity
Good chemical inertness
High dielectric breakdown strength
Low dielectric constant
Uses of boron nitride.
Fracture rings for continuous casting of metals
Heat treatment jigs
High temperature lubricants
Mold release agents
Molten metal and glass castings
Nozzles for transfer or atomization
Induction heating coil holders Gaskets
High temperature and high voltage electrical insulators
Furnace supports where the resistivity is required
Crucibles and containers for high purity molten metals
Radar assemblies and antenna windows
Ion thruster discharge channels