XRD study of coal microstructure evolution during air oxidation

Abstract

Coal oxidation in air at 270°C of three bituminous coalsduring 2-6 days, was studied. The microstructure of theoxidized samples was studied by XRD and also the evolution of porosity by CO2 adsorption at 298 K. It was found that under these conditions, coals lose weight due tochemical reactions. Analysis of XRD of these materials revealed that in first stages of oxidation, aliphatic groupsin coal disappear leaving a more aromatic microstructure. Also in the initial steps, stacks of low number of graphenelayers react, increasing the mean number of layers perstack in the structure and decreasing the fraction of ordered structure. The decrease in the interplanar distance between layers, d002, and the increase in the mean number of layers per stack suggests coal reorganization, leaving amore ordered structure in oxidized coals. Analysis of the surface area available for CO2 adsorption revealed that porosity was not accessible in the oxidized samples