Amorphous structure of superfine pulverized coal based on pair distribution function

Abstract

The amorphous carbon structure of coal exhibits many intriguing properties during particle size reduction, which can be accurately characterized by atom pair distribution function. Here, the synchrotron radiation-induced X-ray diffraction is employed to investigate the local structure of superfine pulverized coal, while the combined illustration of long-range average structural parameters is introduced to support the findings based on local structural analysis. The influences of particle size, coal rank, and demineralization are emphasized. In addition, the evolution of amorphous carbon structure during coal superfine comminution is focused on. Results indicate that the amorphous carbon structure contains mainly 2H graphite and graphene crystal structures. During the grinding, bituminous coal exhibits numerous defects and dislocations due to mechanical forces, resulting in the leftward shifts in peak positions. In contrast, anthracite’s mixed structure transitions from 2H graphite to multilayer graphene. It is worth noting that around the particle size of 20 µm, there is a noticeable turning point in the peak parameters, causing the variations of peak positions and intensities. In addition, after the acid treatment, the removal of minerals causes the peak positions to shift leftward both coals. Simultaneously, the amorphous carbon undergoes rearrangement, leading to changes in peak values. Combined the short- and long-range structural analysis, the work reveals the molecular-level changes in amorphous carbon structure in coal, which innovatively explains the evolution in defect types under mechanochemical effects. The findings contribute to better understanding of coal macromolecular models, which provide new perspectives for inspecting inherent nature of coal amorphous carbon.