Status and development of fire protection materials based on super thermal insulator and their application prospect in urban underground space

Fire-protective super thermal insulator is an inorganic material with a nanopore structure and super-low thermal conductivity. It can be classified as either a sol-gel aerogel-based composite or a fumed oxide-based composite. The matrix oxides are investigated from SiO₂ to oxides with higher melting temperatures, including Al₂O₃ or ZrO₂. It was found that the complex component oxides with the appropriate ratios exhibit better thermal stability than single oxide when exposed to fire. The infrared opacifier is a key component to this material that can significantly reduce its high-temperature thermal conductivity. The appropriate selection of opacifiers becomes possible by determining the specific infrared extinction coefficient and performing a numerical calculation based on Mie scattering theory. This fire protection material has high fireproof efficiency while also being very thin and is rated as having high fire resistance. With the development of ambient pressure drying for aerogel-based composite from supercritical drying, this fire protection material can be manufactured at low overall cost and will play an important role in passive fire protection systems in urban underground spaces.