Effect of filler addition on porosity and strength of polysiloxane-derived porous silicon carbide ceramics

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Polycarbosilane (PCS) or silicon carbide (SiC) fillers were used as fillers in fabricating partially interconnected, open-cell porous SiC ceramics by carbothermal reduction of polysiloxane-derived SiOC and subsequent sintering process. The effects of filler type (PCS or SiC), filler content (0–50 mass %) and sintering temperature (1800–1950°C) on microstructure, porosity, and strength of the polysiloxane-derived porous SiC ceramics were investigated. The spherical pore morphology was retained with SiC filler addition, while irregular cells were dominant with PCS filler addition after sintering at low temperatures. The pore morphology became mostly irregular while the grain morphology changed from a mixture of small, equi-axed grains and large faceted grains to the large faceted grains with increase in sintering temperature from 1800 to 1950°C. Porosity decreased and strength increased with increase in sintering temperature irrespective of the filler source and content. PCS filler addition continuously increased the porosity and decreased the strength, whereas the porosity decreased and strength increased beyond 30 mass % SiC filler addition in the starting composition. Less strength was recorded for the ceramics prepared with PCS fillers. It was possible to adjust the porosity from 34 to 59% and flexural strength from 16 to 96 MPa by controlling the filler type, filler content, and sintering temperature.