About Boron NitrideHexagonal Boron Nitride is a technical ceramic material that offers an unusual combination of high thermal conductivity, high temperature capability, and high electrical resistance. Depending upon subsequent processes and additives, these properties can be enhanced or minimized. It is a chalky material with a microstructure very similar to that of graphite, causing it to sometimes be referred to as “white graphite”.
Boron Nitride generally has reduced mechanical properties, however, it can reliably withstand very high temperature environments. In reducing and inert atmospheres, some grades of Boron Nitride are able to withstand temperatures in excess of 2,000°C, However, in oxidizing atmospheres it should not be used much above 1000°C. It also can offer excellent thermal conductivity and outstanding dielectric strength. In solid form, Boron Nitride can be easily machined to very tight tolerances in almost any shape. After machining, it can be used without extra heat treatment or firing operations. BN comes in a variety of different grades in solid and powder form, all with unique properties.
Boron Nitride Rods & Bars
Boron Nitride Sheets & Blocks
Boron Nitride Aerosol Sprays
Boron Nitride Paintable Coating
Boron Nitride Industrial Powders
Available Grades of Solid Hexagonal Boron NitrideSolid hot-pressed hBN grades are differentiated by their binders. The following are the hBN grades that Precision Ceramics offers from Saint-Gobain:
Grade AX05 is considered the pinnacle of BN materials and is the highest purity hBN available at 99.7% +. It is available in slabs up to 490mm x 490mm x 35-40mm thick, hollow shapes such as crucibles that are 300mm dia x 300+mm tall, or other machined shapes in between. Its high purity permits it to be used in inert or vacuum environments in excess of 2000C, where it still remains an outstanding electrical insulator with a dielectric strength of >40kV/mm. This makes it an excellent choice for applications where high temperature capabilities and corrosion resistance are important.
AX05 is unique because it does not depend on B2O3 or other binders for mechanical integrity. Instead, it is a diffusion bonded ceramic and consequently is non-wet by almost all molten metals. This ultra-high purity allows for applications where other hot pressed boron nitride solids fail, such as crucibles for high-purity molten metals. AXO5 is comparable to Momentive HBC and HBT hot-pressed boron nitride, although it does have a much higher thermal conductivity. Due to its high thermal conductivity and its close-to-zero thermal expansion, AX05 literally cannot be thermal shocked.
Finally, the manufacturing process for AX05 can be 6-8 weeks. However, Precision Ceramics has a considerable inventory of AX05, allowing quick turnaround of components in many cases.
B2O3-bonded, A Grade is the oldest form of hot-pressed BN. Specified into applications 50+ years ago, A Grade still finds a substantial replacement business as high-temperature insulators in legacy semiconductor equipment and defense markets. Components up to 410mm x 495mm x 245mm can be produced. However, its B2O3 binder is hygroscopic, and care must be taken to ensure components are isolated from moisture during storage and use. Precision Ceramics uses many methods of packaging to maintain the high quality of its machined components.
HP Boron Nitride is useful when low thermal expansion, high thermal shock resistance, and increased spall resistance is required. To minimize the moisture issues of A Grade, HP was developed to incorporate a calcium borate binder (like Momentive HBR boron nitride). HP is the workhorse commodity BN being used in many applications worldwide today. It is available in shapes up to 410mm x495mm x 245mm. With its excellent machinability and good to over 1000C in inert or vacuum, it finds many diverse applications.
Here again, Precision Ceramics has a considerable inventory of large shapes of HP available for rapid prototyping.
Designed by Saint-Gobain for a specific semiconductor equipment OEM, HPL has many of the properties of HP Grade, except a somewhat increased temperature range. It is primarily marketed in Asia, but with growing application in the US. It is softer than Grade HP due to its lower binder content, and still very machinable to complex shapes and tight tolerances.
Unique in the hBN world, M26 is a composite of very specific hBN powders in a silica matrix. With 60% hBN and 40% semiconductor grade SiO2, M26 combines hardness and machinability with a somewhat lower thermal conductivity. The silica (SiO2) binder system contributes to its excellent moisture/thermal shock resistance. These grades can operate up to 1400°C, however, M26 contains more boron nitride than M which gives it higher thermal conductivity. Grade M is more resistant to moisture and has a MIL-I-10A grade of L542, a test requiring immersion in water for 48 hours prior to testing at elevated frequencies. While these materials are excellent thermally, it is their electrical properties that are most in demand. Their high dielectric strength (>40KV/mm) along with a low dielectric constant k (<4) in a machinable, hard ceramic are invaluable for microwave environments in the GHz ranges.
Here again, Precision Ceramics has a considerable inventory of large shapes of M26 available for rapid prototyping.
ZSBN is unique because it is a composite material that combines the best properties of hot-pressed boron nitride with the non-reactivity and strength of zirconia and silicon carbide. Originally developed for break rings for horizontal continuous casters, its unique thermal, chemical, electrical, wear and machinability properties permit a wide variety of molten-metal-contact applications. hBN is an inherently soft material. However, with ZSBN’s hard ZrO2 particles evenly dispersed with BN platelets in the hard borosilicate glass matrix, it has great wear properties added to the inherent non-wetting aspects of the hBN. Grade ZSBN is a uniquely high-performing solid that is especially suited for molten metal applications such as continuous casting breakrings where wear resistance and thermal conductivity are essential. There are many applications in molten-metal atomizing nozzles, glass contact wear components, and countless guides and rollers in diverse light-metal baths of Zn, Mg and Al.
General Hexagonal Boron Nitride PropertiesTo make solid shapes, hBN powders are put into a hot-press up to 490mm x 490mm x 410mm in size at pressures up to 2000 psi and at temperatures up to 2000°C. This process forms a material that is dense and easily machined. It is available in standard and custom hot-pressed shapes and has several unique characteristics and physical properties which make it valuable for solving tough problems in a wide range of industrial applications.
- Excellent thermal shock resistance
- High electrical resistivity – excluding aerosols, paints, and ZSBN
- Low density
- High thermal conductivity
- Anisotropic (thermal conductance is different in different planes relative to pressing direction)
- Corrosion resistant
- Good chemical inertness
- High temperature material
- Excellent lubricating properties – low coefficient of friction
- Non-wetting (without oxidization)
- High dielectric breakdown strength
- Excellent Machinability
Technical Boron Nitride Properties
|Properties||Units||Hexagonal BN Grades|
|Crystaline Phase||Hexagonal BN||Hexagonal BN >99%||BN - 40%, SiO2 - 60%||BN - 45%, ZrO2 - 45%, Borosilicate Glass <10%|
|Binder Type||Calcium Borate||Self Bonded||SiO2||Borosilicate|
|* Pressing Direction||Parallel / Perp.||II||┴||II||┴||II||┴||II||┴|
|Thermal Conductivity at 25°C||W/mK||27||29||78||130||11||29||24||34|
|Max. Temp - Oxidizing/Inert||°C||850||1150||850||2000||1000+||850||1600|
|Specific Heat at 25°C||j/gK||0.81||0.81||0.77||0.64|
|Coeff. Of Thermal Expansion (10-6)|
|25 - 400°C||0.6||0.4||-2.3||-0.7||3.0||0.4||4.1||3.4|
|400 - 800°C||1.1||0.8||-2.5||1.1||2.5||0.1||5.6||4.3|
|800 - 1200°C||1.5||0.9||1.6||0.4||3.0||0.1||7.2||5.2|
|1200 - 1600°C||2.8||2.7||0.9||0.3||4.6||3.4|
|1600 - 1900°C||0.5||0.9|
|Dielectric Constant at 1MHz||4.3||4.0||4.0||4.0||4.5||3.8|
|Dissipation Factor at 1MHz||E-03||1.5||2.1||1.2||3.0||1.7||6.7|
|RT Resistivity||Ω cm||>10^13||>10^13||>10^13||>10^14||>10^13||>10^14||>10^14||>10^15|
Boron Nitride Applications
- Break rings for continuous casting of metals
- Refractory applications
- Continuous casting
- Deck plates
- Heat treatment fixtures
- High temperature lubricant
- High temperature valves
- Molds/mold release agent
- Motel metals and glass casting
- Nozzles for transfer or atomization
- Laser Nozzles
- Nuclear Shielding
- Induction heating coil supports
- High-temperature & high-voltage electrical insulators
- Vacuum furnace supports which require electrical resistivity
- Crucibles and containers for high purity molten metals
- Radar components and antenna windows