Characteristics of polymorphic foam for inhibiting spontaneous coal combustion

Abstract

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 0.7wt% had the strongest electrostatic repulsion. Within 30s of the organic acid being injected into the SFP solution, an aqueous foam was generated via injecting gas, subsequently, within 2–3min, 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.