Ceramic coating formation during carbothermic reaction of polysiloxanes with carbon and graphite materials

Abstract

Polysiloxane resins-derived ceramic precursors were used as a binder to manufacture polygranular carbon and graphite-based composite materials. Two types of poly[methyl(phenyl)siloxane]-based resins differing in the structure and O/Si and C/Si ratios were used. During controlled annealing the composite samples up to 2000 °C, the ceramic polymer precursors were transformed into amorphous silicon oxycarbide (SiOC) or nanocrystalline β-SiC (nc-3C) phase. Resins-derived ceramic residues obtained at 2000 °C formed a nanocrystalline layer surrounding graphite grains, whereas in the anthracite material the ceramic phase precipitated between the grains forming separated, single crystallites. The differences in morphology of the carbide compounds formed in the presence of anthracite and graphite grains resulted from the difference in their structural stability and from the nature of interfacial bonding formed at the early stage of composites preparation. Strong interfacial adhesion between the anthracite grains and the polysiloxane resin caused the formation of large cracks in the composite samples during their heating to 1000 °C. The oxidation resistance was higher for graphite-based composites compared to anthracite-containing samples.