Preparation and characterization of C/Al₂ O₃ composite aerogel with high compressive strength and low thermal conductivity

Carbon/alumina (C/Al₂O₃) composite aerogel with high compressive strength and low thermal conductivity has been successfully synthesized by sol–gel method, followed by CO₂ supercritical drying and carbonization. SEM images and compressive Young’s modulus measurements show that the C/Al₂O₃ aerogel with a molar ratio of Resorcinol/Alumina (R/Al) of 1.0 presents homogeneous pore structures and obtains excellent compressive Young’s modulus up to 90 MPa. Three weight losses regions are observed during heat treatment process, confirmed by TG/DSC measurements. XRD patterns and TEM images indicate that α-Al₂O₃ phase transition occurs only when heat treatment temperature reaches up to 1500 °C with the adding of carbon source, 200 °C higher than pure Al₂O₃ aerogel. The as-dried RF/Al₂O₃ aerogel possesses thermal conductivity as low as 0.025 W m⁻¹ K⁻¹. The thermal conductivities of C/Al₂O₃ aerogels increase gradually with the increase of heat treatment temperatures, caused by increasing solid thermal conductivity. The thermal conductivities range from 0.033 to 0.049 W m⁻¹ K⁻¹, suitable for efficient thermal insulations uses.