Facile preparation of high-strength SiC/C aerogels from pre-reacted resorcinol–formaldehyde and siloxane

Carbon aerogels are ideal thermal insulation materials in the field of aerospace. However, their poor oxidative resistance at high temperatures is a significant drawback. Therefore, there is considerable interest in developing SiC/C aerogels. In this study, using pre-reacted resorcinol–formaldehyde gel (RF) as the carbon source, homogeneous silica/phenolic resin (SiO2/RF) hybrid aerogels were prepared via atmospheric pressure drying using a simple process. The SiC/C aerogels were subsequently obtained via carbon thermal reduction. As the C/Si ratio decreased (from 6 to 4.5 and 3), the density, thermal conductivity, and compressive strength of the aerogels decreased from 0.19 to 0.26 g·cm−3, 0.0330 to 0.0983 W/(m·K), and 0.57 to 4.83 MPa, respectively. The linear shrinkage rate was 16.4–18.3 %, which is lower than those of most reported SiC/C aerogels. Here, the carbon improved the strength of the SiC-based aerogels while maintaining their thermal insulation characteristics. A composite material prepared using the relatively low-strength aerogels and mullite fibre felt could achieve long-term insulation at 1400 °C in an air environment. This study lays the foundation and outlines various options for achieving an optimal balance between the strength and thermal conductivity of SiC/C aerogels for industrial applications.