Optimizing SiO₂-based thermal insulation materials via CSH/SiO₂ composite design: Effects of synthesis conditions on phase composition, microstructure and properties

Traditional SiO 2 -based thermal insulation materials face critical limitations, such as low strength and high synthesis cost. To address these challenges, composite design strategies have been explored to optimize the properties. In this study, Calcium Silicate Hydrate (CSH)/SiO 2 composites were prepared by a hydrothermal method, and the effects of Ca/Si molar ratio, holding time and hydrothermal temperature on phase composition and properties were systematically studied. The relationship between material properties and the content/type of CSH phases was revealed. Results demonstrate that compared with conventional SiO 2 -based materials, the CSH/SiO 2 composites exhibit excellent properties. The samples prepared at a Ca/Si ratio of 0.6 and a holding time of 12 h show the best overall performance, with a low thermal conductivity of 0.117 W/(m·K), high compressive strength of 3 MPa, as well as excellent thermal stability, evidenced by only 2.89 % linear shrinkage and 212 % strength retention after exposure to 800 °C. Additionally, the synthesis process is relatively simple, energy-efficient, and scalable. These findings highlight the potential of CSH/SiO 2 composites for thermal insulation applications in aerospace, energy, and construction industries.