SEM and reflected light petrography: A case study on natural cokes from seam XIV, Jharia coalfield, India

Abstract

This paper is an attempt to characterize the natural coke (local name ‘jhama’) and associated unaltered coal drawn from seam XIV, Burragarh colliery, Jharia coalfield with help of Scanning Electron Microscopy (SEM) and organic petrography techniques. The organic petrography was carried out using DM4500 advanced polarizing microscope, while scanning electron micrography was performed on a JEOL-840A JSM. The coal and natural coke samples were pulverized and beneficiated, and fractions of different sizes (50–0.50 mm) at varying specific gravities (1.4 to >1.8) were subjected to this study with a view to expose the concentrations of microstructures and microtextures of natural coke in different specific gravity fractions. In addition, an effort was made to compare the variety of textures as seen with the help of optical microscopy with those as revealed under scanning electron microscope. SEM photographs revealed some textural features of natural coke, which remained unexposed in optical microscopy. This may be due to the use of unpolished samples and greater depth of focus achieved by SEM. The features which were studied through these two microscopy methods are characterization of carbonized matrix, mosaics, flow textures, micro, meso and macropores and cracks formed due to escape of volatiles including properties of mineral matter or their altered products (glassy matrix). The different washability fractions of Burragarh natural coke have shown that there is gradual decrease of reactive macerals and increase of anisotropic mosaics, flow textures and deposited carbons up to specific gravity of 1.70. The approach thus enabled a combined maceral–mineral analysis, which bears good implications on academic and industrial use of natural cokes.