Microscopic examination of polished coke surfaces etched by ion bombardment

Abstract

The purpose of this study was to assess the use of ion etching as a means of enhancing the more ordered features of the surface of polished coke sections so as to examine more closely details of the mosaic units identified in polarized-light microscopy. A series of 1000 °C vitrain cokes were examined by polarized-light and scanning-electron microscopy before and after etching of the surface by argon-ion bombardment. Using light microscopy, determinations were made of the anisotropic composition of the cokes and size of the mosaic units. From the scanning-electron microscopy a morphological description of the anisotropic type and a diametral sizing of the mosaic units were obtained. Ion etching of a polished coke surface is shown to be useful in producing a surface suitable for examination by the scanning-electron microscope. The results confirm that the units which constitute the mosaic anisotropy are in the form of distorted spheres, that the size of the units is directly related to coal rank, and that the flow-type anisotropy apparently results from the alignment and overlapping of the same basic units. The results also indicate that the maximum size of the individual units which make up the anisotropy is less than 2 μm.