What is pyrolytic boron nitride (PBN)? 

PBN

Pyrolytic boron nitride ceramics are also written as PBN or pyrolytic BN. It is a high-purity ceramic with high chemical resistance and commendable strength at high temperatures. Boron nitride is a compound composed of boron and nitrogen. This material has good thermal conductivity and is often used to make electrical insulators and cutting tools.

Production of pyrolytic boron nitride ceramics

As previously mentioned, pyrolytic boron nitride ceramic is a high-purity ceramic. In some cases, the purity is as high as 99.9%. Therefore, it must be produced under precise conditions.

Pyrolytic boron nitride ceramic is a kind of boron nitride prepared by pyrolysis reaction at extremely high temperature. It is produced by chemical vapor deposition of boron halide and ammonia. The production process of pyrolytic boron nitride ceramics is different from that of hot pressed boron nitride ceramics. One advantage of the chemical vapor deposition process used in the manufacture of pyrolytic boron nitride ceramics is that the finished product has a uniform layer. Therefore, the thermal conductivity of pyrolytic boron nitride is anisotropic.

Hexagonal structure of pyrolytic boron nitride ceramics

Pyrolytic boron nitride ceramics have hexagonal structure. This leads to the question, what is hexagonal boron nitride structure? Hexagonal structure is the most stable and soft crystalline form of boron nitride ceramics. Boron nitride with this structure is very similar to graphite. For this reason, it is sometimes called graphite boron nitride or white graphite.

Each layer of the structure has boron and nitrogen atoms. These boron and nitrogen atoms are bound together by covalent bonds. The layers within the structure are not bonded together by covalent bonds.

Physical Properties of Pyrolytic Boron Nitride (PBN) Ceramics

Pyrolytic boron nitride ceramics have some characteristics different from other similar materials. These properties can be physical or chemical.

Pyrolytic boron nitride ceramics have ivory or orange appearance. In addition, it has a smooth surface without pores. Its density is about 2.15 g/cm3.

Pyrolytic boron nitride ceramics usually have no obvious odor. It is a tasteless compound. In addition, the structure of pyrolytic boron nitride makes it smooth. It is layered and has a honeycomb appearance.

The dielectric strength of pyrolytic boron nitride ceramics is 56 kV/mm at room temperature. In addition, the tensile strength of the material is 153.84 N/mm2, while its elastic modulus is 235690 N/mm2. The strength of PBN increased with temperature until it reached 2473 K.

At 3273 K, the pyrolytic boron nitride ceramics are decomposed into boron and nitride. In addition, it has satisfactory thermal shock resistance. This means that when the temperature changes suddenly, it will not break easily.

Chemical Properties of Pyrolytic Boron Nitride (PBN) Ceramics

Pyrolytic boron nitride ceramic is a kind of high purity compound. It is a non-toxic material. At room temperature, the compound does not react with acids, bases or salts. However, it will be slightly corroded in alkali liquor and oxidized at temperatures above 1273 K.

summary

Pyrolytic boron nitride is a high quality ceramic material with hexagonal crystal structure. Its high oxidation resistance and anisotropic thermal conductivity make it an ideal material for heaters and crucibles.