An atomic force microscopy study of coal nanopore structure

Coal nanopore structure is an important factor in understanding the storage and migration of absorbed gas in coal. A new method for studying coal nanopore structures is proposed. This idea is based on the nano-level resolution of atomic force microscopy, which can be employed to observe the structural features of coal nanopores clearly, conduct quantitative three-dimensional measurements and obtain structural parameters. Analysis results show that coal nanopores are mainly metamorphic pores and intermolecular pores. The metamorphic pores are commonly rounded and elliptical, increasing quantitatively with the coalification degree. The forms of intermolecular pores change markedly. The average pore size of low-rank coal is bigger than high-rank coal, and the number of intermolecular pores decreases as the coal rank increases. Section analysis effectively characterizes the coal pore microstructure, bearing analysis is a vital approach to measure microporosity, and grain analysis can be employed to study the pore size distribution. Atomic force microscopy is a tool for the in-depth research of coal pore microstructure and the coal-bed methane adsorption mechanism.