Preparation and inhibition performance of dry water materials for preventing spontaneous combustion of coal

This work aimed to effectively prevent the spontaneous combustion of coal in goafs by preparing a type of dry water material with a solid-in-liquid structure through the mechanical stirring method, with nano-aluminum hydroxide aqueous solution as the core material and hydrophobic nano-silicon dioxide as the wall material. The effects of solid-to-liquid ratio, stirring time, and mass concentration of nano-aluminum hydroxide on the particle size and microstructure of dry water were studied. Results showed that the prepared dry water powder was the most uniform and fine when nano-silica, nano-aluminum hydroxide, and water were mixed at a mass ratio of 5:0.75:49.25 and stirred at a speed of 23,000 r/min for 25 s. The samples were characterized by using a temperature-programmed oxidation device, a thermogravimetric analyzer, and a Fourier-transform infrared spectrometer, and the inhibition performance of dry water was evaluated. Results revealed that dry water effectively slowed the oxidation rate of coal and inhibited the release of CO in the low-temperature environment, and the cross-point temperature increased from 125.1 °C to 155.4 °C for raw coal. In a high-temperature environment, dry water delayed the process of spontaneous combustion of coal, the temperature leading to the maximum mass increased from 308.6 °C to 369.4 °C, and the ignition temperature rose from 458.2 °C to 484.7 °C. In addition, the dry water material can inhibit the oxidative decomposition of aliphatic hydrocarbons and the transformation of oxygen-containing functional groups in coal samples, thus indicating, from a microscopic level, that it has good inhibition performance.