Boron nitride is a crystal composed of nitrogen atoms and boron atoms. The crystal structure is divided into hexagonal boron nitride (HBN), closely packed hexagonal boron nitride (WBN), and cubic boron nitride. Among them, hexagonal boron nitride has a similar graphite layered structure in its crystal structure, presenting a loose, lubricating, hygroscopic, and lightweight white powder, so it is also known as "white graphite". Theoretical density is 2.27g/cm3, specific gravity is 2.43, Mohs hardness is 2. Hexagonal boron nitride has good electrical insulation, thermal conductivity, chemical stability, and no obvious melting point. It can withstand heat up to 2000 ℃ in a neutral reducing atmosphere at 0.1MPA nitrogen gas and up to 2800 ℃ in nitrogen and argon. Its stability is poor in an oxygen atmosphere and it can be used at temperatures below 1000 ℃. The expansion coefficient of hexagonal boron nitride is equivalent to that of quartz, but its thermal conductivity is ten times that of quartz.