What is the “H” in HBN
The meaning of letter “H” in HBN boron nitride products could be high purity, hexagonal, or hot pressed. Except for very few cases when it is used as the item code for a certain product, “H” only means the “hexagonal” or “hot press”.
Hexagonal
Most of solid boron nitride ceramic materials and all of the large piece of machinable boron nitride, are hexagonal boron nitride, which means it has a hexagonal crystalline type. Another common boron nitride is cubic BN, which have a cubic form of crystal structure. Just like carbon, while HBN are graphite like flakes (micro scale), CBN are diamond like hard crystals.
Hot Press
Just like most of the graphite used in machined parts, the process to transform boron nitride powder/flake is hot pressing. The material is sintered under a quite high pressure, to form a low porosity, high density solid material, that could maintains relatively high mechanical strength making it possible to make fine BN parts by machining.
Another way to obtain hexagonal boron nitride material is the CVD process (Chemical Vapor Deposition). As the raw material BCl3 decomposed during the high temperature process, it is called Pyralytic Boron Nitride (PBN). However, this is still a hexagonal boron nitride material. As the material is deposited layer by layer, the crystal structure is close to perfect, providing significant improvement in strength, flexibility andanisotropic properties. However, due to the nature of CVD process, PBN products are much more expensive, and it is hard to obtain thick parts.