Insights into the thermal safety of ambient pressure dried hydrophobic montmorillonite/silica aerogel composites

To improve the thermal safety of hydrophobic silica aerogels (SAs), montmorillonite (MMT) was used as a dopant to prepare MMT/silica aerogel composites (MMT/SAs) and their basic physicochemical properties and thermal safety were investigated in detail. It finds that a physical combination is formed between MMT and SAs, and the introduction of MMT does not change the three-dimensional mesoporous structures of the MMT/SAs. With the MMT content increasing, the MMT/SAs maintain a low density (0.12-0.19 g/cm(3)), high porosity (91.1-93.5 %), low thermal conductivity (0.023-0.025 mW/(m center dot K)) and high hydrophobicity (>140 degrees). Compared with pure SAs, the thermal stability of the MMT/SAs was significantly improved, with the onset and peak temperatures of thermal decomposition increasing by 147 degrees and 117 degrees, respectively. The gross calorific value, peak heat release rate (PHRR) and total heat release (THR) decrease by 50.8 %, 29.6 % and 34.7 % respectively, while the time to ignition (TTI) increases, all of these verify the greatly reduced flammability and fire risk. This work confirms that introducing MMT into hydrophobic SAs is feasible to improve their thermal safety without impairing their excellent properties too much, thus contributing to the expansion of their thermal insulation applications.