Optical Parameters as a Tool To Study the Microstructural Evolution of Carbonized Anthracites during High-Temperature Treatment

The graphitization process of two different carbonized anthracites in the temperature interval of 2000−2800 °C was studied by using the optical properties of the materials prepared. These optical properties are defined by the main axes (,, and ) and parameters ( R ev, R st, and R am ) of the reflectance-indicating surface (RIS) and the anisotropy indexes ( B W and oil bireflectance ratio). Two temperature segments, with the second one being a plateau, were found to occur in the evolution of the structural organization (textural anisotropy) of the materials. The variation with the temperature of the structural order of the materials as determined from X-ray diffraction and Raman crystalline parameters followed a similar tendency, thus confirming the validity of the optical properties as another indicator of the textural and structural changes occurring during anthracite high-temperature treatment. Moreover, as shown by the optical microscopic observation of the materials, crystalline aggregates, microspheres, and flake microstructures, which were previously detected in natural graphites, were developed from the dense and massive particles, with their proportion being higher in those materials with a larger degree of textural anisotropy and/or structural order.