Real-time evolution of the microstructure of coals with different metamorphic degrees during rising-temperature oxidation by synchrotron radiation SAXS-WAXS

Considering the difficulty of balancing real-time and simultaneous in previous studies on pore structure and microcrystalline structure during coal rising-temperature oxidation, this paper simulated the rising-temperature oxidation of three coals by setting the rising-temperature rate and range based on the sample heating furnace. The synchrotron radiation in-situ small-angle X-ray scattering and wide-angle X-ray scattering (SAXS-WAXS) simultaneous tests were carried out. The results show that as the temperature increases, the pore structure of long-flame coal tends to be simpler and more regular with more abundant macropores, and lean coal is relatively more stable, while anthracite is more active in the early period of rising-temperature oxidation with significant development of mesopores. The changes in mesopores of three coals during the entire rising-temperature oxidation are dominated by pores of 10 similar to 20 nm, while pores of 50 similar to 60 nm, 60 similar to 70 nm, and 70 similar to 80 nm dominate the changes in macropores of long-flame coal, lean coal, and anthracite, respectively. Furthermore, the changes in the microcrystalline structure of three coals show two stages: Physical desorption (20 similar to 200 degrees C): the removal of water molecules and weakly adsorbed gases causes the carbon skeleton structure to become relatively loose; thermal decomposition (200 similar to 300 degrees C): the intensification of pyrolysis reactions leads to a much higher polycondensation of aromatic layers.