Pyrolytic Boron Nitride, abbreviated as Pyrolytic BN or PBN, also known as Chemical vapour-deposited Boron Nitride, Chemical Vapour-deposition of Boron Nitride or CVD-BN, etc. As the name suggests, this is a kind of boron nitride prepared by high temperature pyrolysis reaction by chemical vapor deposition method. Speaking of boron nitride, we must first talk about the two main structures of boron nitride: hexagonal and cubic. This is very similar to the two crystal forms of carbon: graphite and diamond. Hexagonal boron nitride and graphite are very similar in many respects, hence the name white graphite. Pyrolytic boron nitride is hexagonal boron nitride, but strictly speaking, it has a certain amount of disordered layer structure. The main feature of PBN prepared by chemical vapor deposition is that the purity is very high, which can reach more than 99.99%.
The structure and morphology of PBN
Pyrolytic Boron Nitride (PBN) belongs to the hexagonal system and is a typical layered material. The inter-layer and intra-layer atomic distances are quite different, the inter-layer atomic distance is 3.33 Å, and the intra-layer atomic distance is 1.45 Å. The structure of PBN consists of B and N atoms arranged alternately in the layer and along the C axis, and the stacking method is ababab•••. It can be observed under a high-power microscope that PBN exhibits stacking faults, which causes its average interlayer spacing to be greater than the theoretical interlayer spacing. Since PBN grows along the C axis during the deposition process, it exhibits a high level of layer orientation, and the preferred orientation direction is the C axis.
PBN performance characteristics
PBN is an advanced material with excellent properties. It is deposited by the reaction of ammonia and boron halides under high temperature and high vacuum conditions. It can be deposited into PBN sheet materials or directly deposited into PBN final products such as tubes, rings or thin-walled containers. It is different from ordinary hot-pressed boron nitride (BN). It does not need to go through the traditional hot-pressed sintering process and does not add any sintering agent. Therefore, the obtained product has the following remarkable characteristics:
(1) Non-toxic and tasteless;
(2) High purity, reaching over 99.999%;
(3) It does not react with acids, alkalis, salts and organic reagents at room temperature. It is slightly corroded in molten salt and lye, but it can resist the corrosion of various acids at high temperatures;
(4) It does not react with most molten metals, semiconductors and their compounds;
(5) The oxidation resistance is good under 1000℃;
(6) Good thermal shock resistance, no cracks were found when dropped into water at 2000℃;
(7) The use temperature is high, there is no sublimation point, and it can be directly decomposed into B and N above 3000℃;
(8) High resistance and good electrical insulation performance;
(9) The surface is smooth, without pores, and not wet with most semiconductor melts.
