SYNTHESIS OF DENSE SILICON-BASED CERAMICS AT LOW-TEMPERATURES

THE conventional preparation of advanced ceramic parts based on silicon carbide or nitride involves pressureless sintering, hot pressing or hot isostatic pressing of appropriate ceramic starting powders 1. Owing to the covalent nature of the Si-C and Si-N bonds and hence the low diffusion coefficients in SiC and Si3N4, high sintering temperatures and the addition of sintering aids are normally used to enhance densification. During densification, the sintering additives form second phases located at grain boundaries, which commonly impair the mechanical and physical properties of the material, especially at higher temperatures. New processing routes that overcome these problems are therefore desirable. Here we report the direct transformation of a metalloorganic precursor into non-oxide silicon-based ceramics with relative densities of up to 93%. This process can be used to make ceramic components and matrix composites at unusually low temperatures (1,000-degrees-C) and without the addition of sintering aids.