SiOC Ceramic Aerogels with High Optical Transparency and Ultralow Thermal Conductivity for Solar Power Application

Transparent SiOC aerogels were synthesized from methylene-bridged and Si-H-containing preceramic aerogels after pyrolysis in an Ar-H2 atmosphere at 800 °C and 1000 °C. The presence of Si-H groups in the starting hybrid aerogel facilitates the incorporation of carbon into the amorphous silicon oxycarbide network, thereby reducing the tendency for free carbon formation and enabling the synthesis of transparent silicon oxycarbide aerogels. Various characterization techniques, including FTIR, Raman spectroscopy and SEM, are applied to analyze the structural and microstructural features of the porous materials. Nitrogen physisorption was employed to characterize the surface area, pore volume, and pore size distributions of the SiOC. All samples exhibit high surface areas, ranging from 915 to 1300 m2 g−1 at 800 °C and from 565 to 855 m2 g−1 at 1000 °C. The thermal conductivity ranges from 15 to 60 mW m−1-K for samples pyrolyzed at 800 °C and from 35 to 156 mW m−1-K for those treated at 1000 °C. Furthermore, the normalized transmittance of the SiOC aerogels is approximately 91 ± 2% at 780 nm and 95 ± 1% at 900 nm, respectively, for an equivalent thickness of 1 mm. The combination of low thermal conductivity, high transmittance in the visible-NIR range, strong infrared absorption, and excellent microstructural stability at high temperatures makes SiOC aerogels exceptional candidates for solar power tower applications.