Novel ultralight carbon foam reinforced carbon aerogel composites with low volume shrinkage and excellent thermal insulation performance

Abstract

Lightweight carbon aerogels are attractive for thermal insulation due to their low thermal conductivity and excellent high-temperature resistance under extreme environments. However, the preparation of monolithic carbon aerogels from phenolic resin precursor always faces the problem of large volumetric shrinkage during the drying and carbonization processes, thus resulting in the increasing density and thermal conductivity of aerogels. Here, to solve such issues, ultralight and rigid carbon foam was designed and synthesized as the reinforcement to fabricate carbon aerogel composites (CACs), which could significantly enhance the shrinkage resistance of monolithic carbon aerogels. The high rigidity of the carbon foam reinforcements (CFRs) was achieved through a pre-carbonization process, which also endowed the CFRs with a matched shrinkage with the monolithic carbon aerogels. As a result, the obtained CACs reinforced by the rigid CFRs showed not only crack-free structures, but also quite low shrinkage, which was about 5.9 % after carbonization. The low shrinkage of CACs then endowed them with quite low density (21.5 mg cm⁻³) and excellent thermal insulation performance (25.9 mW m⁻¹ K⁻¹). Furthermore, due to a highly rough nanostructure, the CACs also possessed outstanding hydrophobicity. These merits make the CACs a promising thermal insulation material even in humid environments.