Synthesis of near net-shape carbon aerogel composites for high-temperature thermal insulators with complex structures

The evolving aircraft technology has spurred an urgent need for carbon aerogel thermal insulation composites with intricate structures, which require good near net-shape forming capability and excellent mechanical and thermal insulation properties. However, large shrinkage and thermal conductivity often undermine these properties. Herein, the near net-shape carbon aerogel composite with complex structure was prepared by using pre-carbonized phenolic fibers as reinforcement and chitosan-added carbon aerogels as matrix. Thanks to the polymerization and hydrogen bonding between chitosan and resorcinol-formaldehyde oligomers, the strength of the gel network is enhanced and the shrinkage is reduced, which in turn effectively alleviates the shrinkage stress of the composite, resulting in a composite with an intact structure. In addition, due to the zero shrinkage and low intrinsic thermal conductivity of the pre-carbonized phenolic fiber and the typical mesoporous structure of the chitosan-added carbon aerogel, the composite (0.337 g/cm³) has a low pyrolysis shrinkage (as low as 7.47 %), low thermal conductivity (0.241 W/m·K at 1200 °C), and high compressive strength (17.75 MPa). Notably, compared to the composite prepared by the co-shrinkage strategy with similar density and thermal conductivity, our composite demonstrates significantly reduced pyrolysis shrinkages of 97.95 % and 72.14 % in the X-Y and Z directions, respectively. This study presents a groundbreaking method for producing carbon aerogel composites that excel in near net-shape forming and thermomechanical properties, advancing the development of high-performance complex thermal insulation components for diverse applications.