Novel sodium silicate/polymer composite gels for the prevention of spontaneous combustion of coal

Highlights: • New composite gels are prepared for fire prevention and extinction in coal mines. • Sodium silicate gel is blended with ionic polyacrylamide or carboxymethyl cellulose gel. • Aluminum citrate (Al-Cit) is added as crosslinker to form interpenetrating network. • Gels with anionic polyacrylamide/Al-Cit show the best fire extinction performance. • They reduce fire-source temperature as well as CO generation. -- Abstract: Novel gel materials are proposed for fire prevention and extinction in coal mines, where spontaneous combustion of coal continues to pose a significant risk. Cationic polyacrylamide (CPAM), anionic polyacrylamide (HPAM), and carboxymethyl cellulose (CMC) were each introduced separately into a sodium silicate (WG) gel, to obtain three gels labeled as CPAM/WG, HPAM/WG, and CMC/WG. A crosslinking agent, aluminum citrate, was subsequently added to the HPAM/WG and CMC/WG gels to afford two novel interpenetrating network hydrogels, HPAM-Al³⁺/WG and CMC-Al³⁺/WG, respectively. Among the various gels, the HPAM-Al³⁺/WG hydrogel exhibits the best seepage capacity, water retention capacity, compressive strength, and inhibition characteristics, which effectively resolve the post-water-loss cracking and pulverization problems commonly associated with inorganic consolidated silica gels. The microstructures of all the gels were investigated by scanning electron microscopy and their inhibitory effects on the oxidation of hydroxyl and methylene groups in coal at high temperatures were analyzed by Fourier transform infrared spectroscopy. Elemental mapping by energy dispersive X-ray spectroscopy indicated that the inorganic silica gel blends uniformly with the polymeric gel. Fire extinction experiments indicated that the HPAM-Al³⁺/WG gel reduces the fire-source temperature, heat radiation, and CO generation. Thus, the HPAM-Al³⁺/WG gel is an ideal fire prevention and extinction material.