Abstract
In a recent past, silicon carbide (SiC), silicon nitride (Si3N4) and silicon carbonitride (Si/C/N) systems attracted increasing interest for environmental (diesel filters, water treatment) and energy (fission nuclear reactors) applications according to their properties (high thermal robustness, oxidation and corrosion resistance, low bulk density, high thermal conductivity, high mechanical strength). The manufacturing process of SiC was initiated by Acheson in 1892 (1) and is still today applied to produce the commercially available SiC (α-SiC). However, most of the actual and future industrial challenges related to SiC require the development of materials in which compositions, shapes and textures are tuned on demand. Traditional techniques are energy-ineffective and severely limit the shape and texture complexities of the part which can be manufactured. Furthermore, the ability to control the purity and crystalline form of the product is restricted. These inherent difficulties can be overcome by the development of synthetic paths where molecular chemistry and chemistry of materials are combined rationally. The Polymer-Derived Ceramics(PDCs) route represents one of these synthetic path solutions. The chemistry (elemental composition, compositional homogeneity and atomic structure), the processing properties and the reactivity (thermal and chemical) of related polymers can efficiently be controlled and tailored to supply, after shaping and pyrolysis processes, ceramics with the desired compositional phase distribution and homogeneity as well as shape. This concept is applied here to the preparation of silicon carbide. Inparticular, we demonstrate that we can provide various shapes of SiC going from powders to monoliths, some of them can be prepared with controlled porosity by controlling the chemistry of SiC precursors at very small length scales in an early stage of thefabrication of SiC. This study gives us information about the chemical and physical properties of SiC precursors based on infrared and NMR spectroscopies coupled with thermogravimetric analysis. In particular, we demonstrate that the boron content has a strong effect on the chemistry and processability of SiC precursors. The high temperature of SiC is also investigated. (1) A. G. Acheson, British Patent No.17911, 1892