Micro-Mechanism of Nitrogen Inhibition of Spontaneous Coal Combustion: A Multi-Scale Study Based on Radical Modulation and Functional Group Reorganization

The present study centered on the multiscale regulatory function of the nitrogen (N₂) environment in relation to the microscopic inhibition mechanism of coal spontaneous combustion. A systematic approach was adopted to elucidate the mechanism by which N₂ exerts directional regulation over free radical evolution and oxygen-containing functional group reorganization by ESR, FTIR, and theoretical analyses. The findings indicated that the presence of N₂ environment significantly curtailed the generation and chain propagation of free radicals in coal. Within the temperature range of 20 to 80 °C, the ESR signal intensity exhibited a systematic decrease in conjunction with an increase in temperature. Concurrently, the free radical concentration (Ng) diminished by 61.5%, and the g factor underwent a decline from 2.002854 (in raw coal) to 2.002375 (at 80 °C).These observations suggest that N₂ contributed to the radical type by impeding the oxidation reaction from oxygen-containing radicals to aromatic π radicals. FTIR analysis further confirmed that the N₂ atmosphere accelerated the physical desorption of hydroxyl radicals (−OH) and chemical condensation. Additionally, the N₂ atmosphere inhibited the oxidative breakage of the aliphatic chain, thereby promoting directional recombination of aromatics. Furthermore, the results of temperature gradient experiments indicate an augmented effect of N₂ on the radical annihilation pathway. At temperatures above 40 °C, there is an enhancement in coal matrix mobility is enhanced, and radical complexation reactions (R±R-→R-R) become the predominant contributors to the net consumption of stabilized radicals.