Foam-Based Materials for the Prevention of Coal Spontaneous Combustion: Mechanisms, Performance Evaluation, and Engineering Applications

Coal spontaneous combustion remains a major threat to underground coal-mine safety, resource recovery, and environmental protection. Foam-based materials have attracted increasing attention because they integrate wide-area coverage, oxygen isolation, evaporative cooling, active inhibition, and adaptability to fractured or leakage-prone goaf environments. However, existing studies are dispersed among different foam systems, and the relationships among formulation design, suppression mechanisms, performance indicators, and engineering applicability remain insufficiently clarified. This review summarizes recent advances in two-/three-phase foams, gel foams, inhibitor foams, and solidified foams for coal spontaneous-combustion prevention. Unlike reviews focused on a single material type, this work develops a comparative framework linking material composition, dominant mechanisms, key performance indicators, field applicability, and environmental compatibility. Representative components, preparation routes, suppression mechanisms, quantitative performance data, engineering cases, and limitations are compared. The main challenges include high-temperature structural degradation, limited adaptability to heterogeneous leakage pathways, incomplete multi-parameter evaluation systems, and potential ecological risks. Future research should focus on multifunctional and environmentally benign formulations, improved high-temperature durability, standardized laboratory–field evaluation methods, and scenario-oriented material selection for large-scale mine applications.