High-temperature behaviour of hexagonal boron nitride

Abstract

Three boron nitride processes have been studied—synthesis of turbostratic powder, sintering of hexagonal ceramics and transformation into diamond-like phases. It is shown that the crystallization of boron nitride proceeds in three distinctive steps. The first step is the recombination of boron and nitrogen forming semi-organic oligomers; this is followed by a double coalescence on the basis of this mechanism, three fundamental sub-polytypes of layered boron nitride (turbostratic, mesographitic and graphitic) have been defined. Compared with most other inorganic materials, the chemical properties and the character of the interaction with the environment are strongly dependent on the crystallographic direction. The crystal structure of boron nitride is thus a result of a competition between the combination of boron nitride monolayers and their chemical interaction with the environment.