A review of thermal hazard formation mechanisms and regulation strategies of hydrophobic silica aerogels

• Recent advances in HSA: synthesis, thermal hazards, and flame retardant strategies. • Organic groups introduced by hydrophobic modification are the origin of HSA flammability. • Current strategies to enhance thermal stability and flame retardancy are compared. • Future directions are outlined for safer thermal insulation applications of HSA. Hydrophobic silica aerogels (HSA) are a class of nanoporous materials characterized by low density, high porosity, and ultralow thermal conductivity. Owing to these outstanding properties, HSA have demonstrated great potential as high-performance thermal insulation materials in applications such as building insulation, petrochemical engineering, thermal management for new energy systems, and aerospace. However, with the continuous expansion of their thermal insulation applications, increasing attention has been drawn to the potential thermal hazards introduced by organic moieties grafted during hydrophobic modification. The inherent flammability of HSA severely limits their further application in thermal insulation scenarios with high fire safety requirements. To address this challenge, extensive efforts have been made to investigate the pyrolysis and combustion mechanisms of HSA, which have confirmed that their flammability primarily originates from the introduction of organic groups. Based on this understanding, various strategies, including reducing the content of organic groups, incorporating flame retardants, and applying heat treatment strategy, have been developed to enhance the thermal stability and flame retardancy of HSA. This review systematically summarizes the synthesis methods of HSA, elucidates the origins of their thermal hazards, and critically reviews the current strategies for improving their thermal safety. Furthermore, future research directions are discussed, aiming to provide theoretical guidance and new insights for the safe and efficient application of HSA in thermal insulation fields.