Enhanced Thermal Stability and Resistance Properties of Gel-Stabilized Foam for Inhibiting Coal Spontaneous Combustion

To overcome the limited thermal stability and fire retardancy of single-component organic foam and gel for coal spontaneous combustion prevention, this study developed a novel gel foam via a “gel-organic foam composite” approach. Comparative tests with conventional materials showed that the gel foam maintained 86.47% water retention at 60°C and over 50% at 180°C, outperforming organic foam and gel. Its layered-porous structure, formed by gel-foam synergy, controlled volatile release and reinforced the char layer. Fire retardancy tests revealed a 20°C higher cross-point temperature and a 16% relative enhancement in CO 2 suppression rate at 150°C versus organic foam. Programmed heating and field tests confirmed rapid cooling of a 900°C coal sample to below 100°C within 600 s without re-ignition, whereas single-component materials re-ignited. The gel foam achieves “physical encapsulation–chemical stabilization–oxidation inhibition” synergy: CMC-Na and NaCit cross-linking form a dense network that adsorbs free radicals on foam walls, inhibits active coal functional groups (  OH,  CH 2  ), and reduces oxygen contact area by 40%. This structurally optimized material offers broad potential for long-term fire suppression in complex coal fire zones.