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∼20 nm, while pores of 50∼60 nm, 60∼70 nm, and 70∼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∼200 °C): the removal of water molecules and weakly adsorbed gases causes the carbon skeleton structure to become relatively loose; thermal decomposition (200∼300 °C): the intensification of pyrolysis reactions leads to a much higher polycondensation of aromatic layers. • The pore structure of long-flame coal tends to be simpler during heating. • Anthracite is more active in early heating, while lean coal is more stable. • The PSD uniformity of coal is also positively correlated with temperature. • The pores of 10∼20 nm dominate the changes of mesopores during coal heating. • The microcrystalline structure of coal undergoes two stages during heating.