Fabrication of silica-based inorganic thermal insulation foam enhanced by aerogel and fly ash synergistically

Traditional inorganic thermal insulation materials often require high-temperature sintering and face a trade-off between thermal insulation and mechanical strength. Silica aerogels provide low thermal conductivity but are brittle, while fly ash is an abundant aluminosilicate that can reinforce silicate networks. In this work, a silica-based inorganic porous foam was fabricated at 400 °C using water glass as the matrix, silica aerogel as both a thermal filler and foaming regulator, and fly ash as a reinforcing filler, followed by FDTS hydrophobic treatment. The optimized formulation containing 10 wt% aerogel and 12 wt% fly ash exhibits a density of 0.11 g/cm³, a thermal conductivity of 0.038 W·m⁻¹·K⁻¹, a compressive strength of 0.53 MPa, a water contact angle of 139.8°, and a primary pore size of 190–250 μm. Although samples D0 and D1 show lower thermal conductivity (0.0299 and 0.0251 W·m⁻¹·K⁻¹, respectively), their compressive strength remains below 0.3 MPa, which is insufficient for practical applications. The optimized sample therefore represents a compromise between thermal insulation and mechanical reinforcement, with a compressive strength about 100% higher than that of aerogel-only foam while maintaining acceptable thermal insulation. Microstructure and spectroscopic analyses indicate that aerogel regulates foaming and participates in a Q³ silicate network, whereas fly ash chemically incorporates into a Si–O–Al network. The resulting silica-based porous foam is a promising low-energy inorganic thermal insulation material.