Development and characterisation of a novel DNGF for prevention of coal spontaneous combustion

In response to the urgent requirement to suppress coal spontaneous combustion, this study developed a novel Dual-Network Geopolymer Foam (DNGF) utilising fly ash. Optimised through single-factor and orthogonal experimental methodologies, the DNGF integrates fly ash with surfactants, foam stabiliser, alkaline gelling agent and NaHCO₃ to form a resilient composite possessing optimal foamability and appropriate gelation time. FTIR and SEM analysis reveals that the DNGF features a unique interpenetrating network comprising an inorganic gel and geopolymer framework. The reinforced dual-network skeleton significantly bolsters thermal stability and water retention. Viscosity test confirms that DNGF exhibits distinct shear-thinning behaviour and conforms to the Herschel-Bulkley model. Low-temperature oxidation tests reveal that DNGF effectively mitigates early-stage oxidation risks. Thermogravimetric and kinetic analyses demonstrate that DNGF significantly increases the reaction energy barrier, enhances thermal stability, and promotes higher residual char formation, indicating improved resistance to thermal degradation. Cone calorimetry results show that DNGF markedly delays heat release and reduces combustion intensity under sustained high-temperature exposure, while providing an extended warning window for gas monitoring and intervention. These findings position DNGF as a high-performance, environmentally sustainable, and engineering-feasible material for mitigating coal spontaneous combustion risk and improving mine fire safety.