From the synthesis of boron-modified silicon carbide and silicon carbonitride precursors to the design of porous structures

Reference Presenter Authors
17-077 Samuel Bernard Bernard, S.(Institut de Recherche sur les Céramiques); Inherent difficulties to the traditional techniques for the formulation of high performance ceramics can be overcome by the development of synthetic paths where chemistry, processing and material science are combined rationally. The Polymer-Derived Ceramics (PDCs) concept, which is based on the shaping then pyrolysis of inorganic (= preceramic) polymers into advanced ceramics, mostly of non oxide-type, is a chemical route which can offer original and new preparation opportunities in ceramic science. Here, a series of boron-modified polyorganosilanes was synthesized by reaction between polycarbosilane/polysilazane and controlled amounts of borane dimethyl sulfide, then characterized in details. Then, the relationship between the chemical behavior and the processability of the polymers was examined. Polymers with low boron contents display appropriate requirements for facile processing in solution such as impregnation of host carbon foams resulting in the design of monoliths with hierarchical porosity, significant pore volume and high specific surface area after pyrolysis. Polymers with high boron contents are more appropriate for solid-state processing. Macroporous ceramics can thus be obtained by direct warm-pressing or extrusion of polymer-PMMA mixture and pyrolysis. The chemical and mechanical stability of these porous structures has been investigated.
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