Assessment on thermal safety of aluminum hydroxide doping hydrophobic silica aerogels

The thermal safety of hydrophobic silica aerogels (SA) attracts much concern in the field of heat insulation. It is urgent to develop SA composites with excellent thermal insulation properties to meet the current demands for efficient thermal insulation materials. In this work, alumina hydroxide (AH) doping SA (SA/AH) composites were prepared to enhance the thermal safety of hydrophobic SA. The microstructures and FTIR spectra of SA/AH indicate that it is the physical combination between SA and AH. The lower density of 0.11 g/cm³ and the low thermal conductivity of 25.4 mW/(m·K) are still maintained despite of a slight increase with the AH content. The TG-DSC results demonstrate that the introduced AH improves the onset temperature of the thermal oxidation of Si-CH₃ groups by 55.2 °C. Furthermore, the oxidation kinetics verifies that the apparent activation energy of SA/AH4 (20% AH content) is much greater than that of the pure SA, indicating the thermal oxidation of Si-CH₃ groups in the SA/AH requires more energy to be triggered. The GCV of SA/AH4 is 8.44 MJ/kg, which is 29.6% lower than that of pure SA. The heat release rate (HRR), peak heat release rate (pHRR), and total heat release rate (THR) of SA/AH are significantly reduced. From the perspective of CO and CO₂ production during the combustion process, the smoke toxicity of SA/AH is significantly lower than that of the pure SA. Thus, this work concludes that doping AH is feasible and effective to improve the flame resistance of hydrophobic SA, which provides a technical basis for developing hydrophobic SA composites with enhanced thermal safety.