High-performance Al2O3-SiO2 aerogel/mullite fibre composites with exceptional thermal stability and ultralow thermal conductivity using dual-silicon-source strategy combined with silica sol deposition modification

Driven by the urgent demand for lightweight and high-efficiency thermal insulation materials in aerospace and high-temperature industrial equipment, our study has further improved the temperature resistance and insulation properties of traditional aluminium-silicon matrix composites. We proposed an innovative dual-silicon-source system utilizing tetraethyl orthosilicate (TEOS) and large-particle silica sol (SS, d = 20 nm). Through a sol-gel method integrated with silica sol aging deposition, high-specific-surface-area Al₂O₃-SiO₂ aerogels (SS-ASA) and the mullite fibre-reinforced composites (SS-ASA/MF) were successfully fabricated. The dual-silicon-source strategy suppressed high-temperature creep flow by modulating gel network coarsening, while silica sol aging induced Al-O-Si bond reconfiguration, promoting in situ mullite phase nucleation. Remarkably, SS-ASA retained a high specific surface area of 143 m²/g even after thermal treatment at 1200 °C. When composited with mullite fibre mats, SS-ASA/MF exhibited outstanding integrated performance: under a 1000 °C closed heat source for 20 min, the cold-side temperature remained at 98.96 °C, with a thermal conductivity as low as 0.071 W·m^-¹·K^-¹ at 1000 °C. Notably, the composite showed no dimensional shrinkage after annealing at 1200 °C for 2 h, and only 1.5 % in the thickness direction after heat treatment at 1300 °C for 2 h. This work establishes a novel approach for optimizing Al₂O₃-SiO₂ aerogels and fibre-reinforced composites, demonstrating significant application potential in spacecraft thermal protection systems and high-temperature industrial kilns.