Boron Nitride

Boron nitride (BN) is a synthetic ceramic material that exhibits a combination of properties, including high thermal conductivity, high dielectric strength and low friction. Available in several structural forms, ceramic boron nitride is used in sectors such as electronics, aerospace and thermal management.

Important Structural Forms of Boron Nitride

Hexagonal Boron Nitride (hBN)

Known as "white graphite" due to its hexagonal structure, hBN displays properties of softness and lubricity that are observed in graphite. It also functions as an electrical insulator with high thermal conductivity, thereby making it suitable for:

• High-temperature lubricants and release agents.
• Materials for thermal management in electronics.
• Components for vacuum furnaces.

Pyrolytic Boron Nitride (P-BN)

Manufactured by chemical vapour deposition (CVD), P-BN is an ultra-pure material that demonstrates thermal and chemical stability. It is employed for:

• Containers for high-purity materials and compound semiconductors.
• High-temperature and chemically inert components.
• Thin-walled structures such as tubes, rings and crucibles.

Cubic Boron Nitride (cBN)

Being isoelectronic with diamond, cBN exhibits hardness comparable to that of diamond, while having increased chemical and thermal stability. It is used for:

• Abrasives and cutting tools.
• Oxidation-resistant coatings.
• Materials for use in extreme conditions.

Amorphous Boron Nitride (aBN)

The non-crystalline equivalent of amorphous carbon, aBN is utilised in specialised applications where disordered forms are required.

Material Advantages

• Thermal management: High thermal conductivity and efficient heat dissipation.
• Electrical isolation: Low dielectric constant and high dielectric strength.
• Heat resistance: Stable at temperatures above 2 000 °C in inert atmospheres.
• Machinability: Easily formed into custom shapes with precise tolerances.
• Chemical inertness: Resists most chemicals and oxidation, thereby maintaining performance in demanding conditions.
• Non-wetting: Suitable for applications involving liquid metal and glass.

Applications of Boron Nitride

• Thermal management: Heat dissipation components in electronics and aerospace.
• Handling of liquid metal: Crucibles, nozzles and protective tubes for thermocouples.
• High-temperature insulation: Electrical insulators and supports for vacuum furnaces.
• Abrasives and coatings: Cutting tools, oxidation-resistant metal coatings and release agents.
• Optical components: Radar components, laser nozzles and antenna windows.
• Plasma processing: Chamber linings and connections for semiconductor manufacturing.
• High-purity processing: Pyrolytic boron nitride is the preferred material for high-purity containers and semiconductor growth.

Manufacturing Process

The modern production of BN begins with boric acid (H₃BO₃) or boron trioxide (B₂O₃) combined with ammonia or urea as the nitrogen source. The intermediate product, amorphous BN (aBN), is purified and converted into:

• Hexagonal BN (hBN) through high-temperature heating.
• Cubic BN (cBN) through high-pressure and high-temperature synthesis, under conditions similar to those used for synthetic diamond production.
• Pyrolytic BN (P-BN) via chemical vapour deposition (CVD) at high temperatures under vacuum, thereby ensuring ultra-high purity and structural precision.

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