Boron Nitride Ceramics in Vacuum Furnaces

Boron nitride (BN) ceramics, especially hexagonal boron nitride (h-BN), excel in vacuum furnaces mainly due to their unique physical and chemical properties. The following is a detailed analysis of their excellent performance:

1. Excellent high temperature resistance

High melting point: The melting point of boron nitride is about 3000℃, and it can be used stably in vacuum environment for a long time at a high temperature of 1800~2000℃, which is far more than most of the ceramic materials (e.g., the melting point of alumina is 2072℃).

Thermal shock resistance: low coefficient of thermal expansion (≈1×10-⁶/°C, similar to quartz) combined with high thermal conductivity (30~60 W/m-K, vertical laminar direction), so that it is not easy to crack in the rapid temperature change.

2. Excellent chemical stability

Inert environment adaptability**: under vacuum or inert atmosphere, it has strong corrosion resistance to molten metals (e.g. aluminum, copper), salts and acidic environment, avoiding reaction with furnace materials.

Low outgassing rate: almost no release of gases (e.g. H₂O, CO₂) at high temperatures, maintaining a high vacuum (≤1×10-⁵ Pa), reducing the risk of contamination.

3. Unique electrical insulation and lubrication properties

High-temperature insulation: Resistivity as high as 10¹⁴~10¹⁶ Ω-cm (still maintains 10⁶ Ω-cm at 1000℃), suitable for insulating parts of neighboring electric heating elements.

Self-lubricating: the laminar structure gives a low coefficient of friction (0.2~0.3), reducing wear and tear of contact parts and extending service life.

4. Balance between machinability and mechanical strength

Easy machinability: Mohs hardness is only 2, it can be machined into complex shapes (such as thin-walled crucibles, precision fixtures), reducing manufacturing costs.

Moderate strength: Flexural strength is about 30~100 MPa, which is lower than that of silicon carbide (400~600 MPa), but the load capacity can be enhanced by composite reinforcement (e.g. adding SiC fiber).

5. Typical Application Scenarios

Semiconductor manufacturing: Used as heating plate of MOCVD equipment, uniform heat conduction to ensure the quality of epitaxial wafer.

Metal treatment: used as crucible material for vacuum sintering furnace, melting high purity titanium alloy (such as Ti-6Al-4V) without pollution.

Crystal growth: heat insulation screen for sapphire single crystal furnace, working continuously at 2000℃ for 1000 hours without deformation.

6.Comparative advantages with other materials

vs Graphite: graphite is conductive and has low strength at high temperature (softens easily in inert atmosphere), while h-BN is insulating and stable at high temperature.

vs Al₂O₃: Aluminum oxide has poor thermal conductivity (~30 W/m-K) and weak thermal shock resistance (thermal expansion coefficient of 8×10-⁶/°C), not suitable for rapid temperature rise and fall scenarios.

vs Si*: Silicon carbide is electrically conductive and difficult to process, and cannot be used for insulating parts.

7. Potential Limitations and Improvements

Risk of oxidation: oxidizes to B₂O₃ in air above 800°C, requires strict maintenance of vacuum or inert atmosphere.

Strength Improvement: By composite of h-BN and TiB₂, the flexural strength can be increased up to 200 MPa, extending its application under heavy load conditions.

Shengyang New Material Co., Ltd. is committed to the production of boron nitride and boron nitride processed products, and can customize various boron nitride insulating ceramic parts according to customer needs. Contact us if necessary.
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