A brief introduction to Pyrolytic Boron Nitride
Pyrolytic Boron Nitride is abbreviated as Pyrolytic BN or PBN, which is also called Chemical vapour-deposited Boron Nitride、Chemical Vapour-deposition of Boron Nitride or CVD-BN.
Pyrolytic boron nitride is a kind of boron nitride prepared by chemical vapor deposition and pyrolysis at high temperature. Pyrolytic boron nitride has two main structures: hexagonal and cubic, which is very similar to the two crystal forms of carbon: graphite and diamond. With many similarities with graphite, the hexagonal boron nitride is also named white graphite. Pyrolytic boron nitride is hexagonal; but strictly speaking, it has a certain amount of disordered layer structure. When PBN is prepared by chemical vapor deposition, its purity can reach as high as over 99.99%.
Structure and morphology of PBN
Pyrolytic boron nitride (PBN) is a typical layered material that belongs to hexagonal crystal system. There is a great difference between the inter-layer and intra-layer atomic spacing. The inter-layer atomic spacing is 3.33 while the intra-layer atomic spacing is 1.45. The structure of PBN consists of B and N atoms alternately located in the layer and along the C-axis respectively. In the microscope we can see that the PBN presents stacking structure, which explains why its average layer spacing is larger than the theoretical layer spacing.
PBN is an advanced material with excellent performance. Under high temperature and high vacuum conditions, it is formed by the reaction and deposition of halides of ammonia and boron. It can be deposited into PBN sheet and PBN final products such as tubes, rings or thin-walled containers. Unlike ordinary hot-pressed boron nitride (BN), it does not need to go through the traditional hot-pressed sintering process, so it has no sintering agent involved. Therefore, the products have the following characteristics:
(1) Non-toxic and smelliness;
(2) High purity, up to 99.999%;
(3) It does not react with acid, alkali, salt or organic reagent at room temperature, and slightly corrodes in molten salt and alkali solution, but can resist the corrosion of various acids at high temperature;
(4) It does not react with most of molten metals, semiconductors and their compounds;
(5) Under 1000 ℃, the oxidation resistance is good.