Delaying the crystallisation and enhancing the thermal stability of HfO₂ aerogel through Y and Si doping

Oxide aerogels are promising as high-efficiency thermal insulation materials under extreme conditions owing to their low density, high porosity, large specific surface area, and ultralow thermal conductivity. However, their limited temperature resistance, volumetric changes during crystallisation and phase transitions, hinder their widespread application. To overcome this bottleneck, a novel strategy to retard the crystallisation and enhance the thermal stability of HfO₂ aerogel through the controlled incorporation of Si and Y was proposed. HfO₂ and ternary HfO₂–Y₂O₃–SiO₂ (HYS) aerogels were synthesised via sol–gel method. The HfO₂ aerogel crystallised below 600 °C and underwent sintering at 1200 °C. Conversely, the HYS aerogel comprised low-crystallinity Y₂Hf₇O₁₇ nanocrystals after heat treatment at 900 °C, demonstrating a large specific surface area of 310.23 m2/g. The dopant elements were found to effectively inhibit sintering, enabling the HYS aerogel to retain a significantly large specific surface area of 48.72 m2/g even after heat treatment at 1200 °C. Y₂Hf₇O₁₇ exhibited a minimum thermal conductivity of 0.89 W m−1 K−1, providing the HYS aerogel with superior high-temperature thermal insulation performance. Furthermore, the comparatively lower linear shrinkage during the high-temperature heating process revealed HYS as a promising novel thermal insulation material for extreme environmental applications. This study expands on the oxide aerogel system and provides valuable guidance for component selection and design strategies for high-thermal-stability oxide aerogels.