CHEMICAL-REACTIONS IN HEXAGONAL BORON-NITRIDE SYSTEM

Chemical reactions of synthesis of hexagonal boron nitride and their m echanisms are discussed and classified. Based on their analyses, a ter nary B-N-O diagram is suggested, in which virtual compositions of hexa gonal boron nitride ceramic and preceding materials, starting with a m ixture of raw materials, through oligomolecular semi-organic precursor s and turbo-stratic boron nitride powder are specified. Beside the com position, processes of conversion between particular substances, such as synthesis, decomposition and crystallization of boron nitride powde r, and sintering and hydrolysis of ceramic, are characterized by vecto rs-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.