Processing and properties of polysiloxane-derived porous silicon carbide ceramics using hollow microspheres as templates

Porous SiC ceramics were synthesized from carbon-filled polysiloxane using hollow microspheres as sacrificial templates. The fabrication process involved three steps: (i) the pyrolysis of polysiloxane at 1100 °C, which leads to the conversion of polysiloxane to silicon oxycarbide (SiOC); (ii) the carbothermal reduction of SiOC and the C mixture at 1450 °C, which converts the mixture to a SiC ceramic; and (iii) liquid-phase sintering of the SiC using Al2O3–Y2O3 as a sintering additive at 1800–2000 °C.The effects of the sintering temperature and template contents on the microstructure, porosity, mechanical strength and thermal conductivity of the resulting porous SiC ceramics were examined. The typical flexural and compressive strengths of the porous SiC ceramics with ∼40% porosity were ∼60 MPa and ∼240 MPa, respectively. The typical thermal conductivity of the porous SiC ceramics with ∼70% porosity was ∼2 W/m K.