Chemical reactions in hexagonal boron nitride system

Chemical reactions of synthesis of hexagonal boron nitride and their mechanisms are discussed and classified. Based on their analyses, a ternary B-N-O diagram is suggested, in which virtual compositions of hexagonal boron nitride ceramic and preceding materials, starting with a mixture of raw materials, through oligomolecular semi-organic precursors and turbo-stratic boron nitride powder are specified. Beside the composition, processes of conversion between particular substances, such as synthesis, decomposition and crystallization of boron nitride powder, and sintering and hydrolysis of ceramic, are characterized by vectors-elements of the ternary diagram. The dynamic model is suggested to be generally applied to systems with prevailingly covalent character, where the polymerization is regarded as a controlling chemical process. (C) 1996 Academic Press, Inc.