Characteristics of polymorphic foam for inhibiting spontaneous coal combustion

For inhibiting the spontaneous combustion of coal, a technique using polymorphic foam (PF) synthesized from a sol foam/polycaprolactone (SFP) solution and organic acid is described. This study includes zeta potential measurements of the SFP solution and formation of the PF, and a differential scanning calorimeter/thermogravimetric, X-ray diffraction, X-ray photoelectron spectroscopy and infrared analysis of the PF. It was found that the PF solution that included a polycaprolactone concentration of 0.7 wt% had the strongest electrostatic repulsion. Within 30 s of the organic acid being injected into the SFP solution, an aqueous foam was generated via injecting gas, subsequently, within 2-3 min, the PF could form due to the chemical reaction between sodium silicate and the organic acid. The PF had the properties of adsorbing the significant heat produced by coal low-temperature oxidation, wrapping in coal from oxygen ingress by the colloid-fused polycaprolactone, providing the moisture for coal to inhibit coal self-heating. The PF could maintain a weight of 12% non-flammable residue, composed of mainly SiO2 and a small amount of Na2CO3, forming a thermally stable coating layer on the surface of the combustible to extinguish fire. The PF mainly contained C-O and CO functional groups, resulting in its surface being much more hydrophilic. It also inhibited the formation of new -CH2/CH3 and -OH functional groups in the process of coal low-temperature oxidation. It was concluded that PF has the potential to prevent and control the spontaneous combustion of coal.