What are difference between hot pressed boron nitride and pyrolytic boron nitride?
Boron nitride is an advanced ceramic material that comes in four different variants, the most common are cubic boron nitride (c-BN) and hexagonal boron nitride (h-BN). c-BN is similar to diamond , mainly used to make cutting tools; h-BN is a layered structure similar to graphite, which is loose, lubricated, easy to absorb moisture, and light in weight, also known as white graphite, with excellent thermal conductivity and insulating properties .
According to the different manufacturing process, h-BN can be divided into hot pressing boron nitride (HPBN) and pyrolytic boron nitride (PBN). Hot-pressed boron nitride adopts hot-pressed sintering technology, and the product has the advantages of high density, high strength and low production cost; pyrolytic boron nitride adopts chemical vapor deposition technology, which has the advantages of less impurities and high purity.
1. Hot Pressed Boron Nitride (HPBN)
Hot pressed boron nitride is made by pressing and sintering with powder pouring into a mold. It is an excellent electrical insulator with excellent lubricity and high temperature stability. Even at extremely high temperatures, It can also maintains its lubricity and inertness. Hot pressed boron nitride has low mechanical strength and wear resistance, but has high heat capacity, excellent thermal conductivity, outstanding dielectric strength and ease of processing. In an inert atmosphere, boron nitride can withstand high temperatures exceeding 2000 °C, so it is an ideal high-temperature thermally conductive insulating material.
Utilizing the excellent chemical stability of boron nitride ceramics, it can be used as crucibles, boats, liquid metal conveying pipes for melting and evaporating metals, crucibles for synthesizing GaAs crystals, rocket nozzles, bases for high-power devices, pipes for melting metals, and pump parts , steel casting molds, insulating materials, etc.
2. Pyrolytic Boron Nitride (PBN)
Pyrolytic boron nitride belongs to the hexagonal crystal system and is a typical layered material. It is formed by chemical vapor deposition (CVD) of ammonia and boron halides under high temperature and high vacuum conditions. It can be deposited into thin sheet materials, or directly into PBN final products such as tubes, rings or containers with thin walls . The purity of pyrolytic boron nitride is very high, which can reach more than 99.99%.
Pyrolytic boron nitride has excellent properties such as high purity, high thermal conductivity, high mechanical strength, good electrical insulation, good chemical inertness, and non-toxicity, making it an ideal container mateial for element purification and semiconductor crystal growth. The main applications are OLED evaporation units, semiconductor single crystal growth (VGF, LEC) crucibles, molecular beam epitaxy (MBE) evaporation crucibles, MOCVD heaters, polycrystalline boats, high temperature, high vacuum equipment insulation boards, etc.
Difference between HPBN and PBN
1. Different production processes: HPBN use traditional mold forming and hot pressing sintering process; PBN use chemical vapor deposition process.
2. Different products can be produced: HPBN is easy to machining, and can be machined to obtain the required shape and size; PBN is only suitable for the production with thin thickness or walls.
3. Different material purity: HPBN needs to add sintering aids in the production process, so the purity cannot reach as high as PBN; production process of PBN does not need to add sintering aids, and the purity can reach more than 99.99%.
4. Different application fields: PBN is suitable for the production of crystal growth containers in the semiconductor industry due to its extremely high purity, high production cost and difficult processing; Due to its relatively low production cost and easy processing, HPBN is suitable for high temperature furnace insulation parts, thermocouple protection tubes, crucibles or molds for molten metal, amorphous belt nozzles and powder metal atomizing nozzles, etc.
