Results of transmission optical microscopy studies of coke were first reported by Marshall [1], who examined natural cokes formed as a result of igneous intrusion into a coal seam. The thin sections were reported to range in thickness from 0.2 to 0.4 pm so that even fusinite was translucent. In a later study, Taylor [2] examined thin sections of semicoke produced by carbonization of vitrinite and described the mosaic structure associated with the anisotropic coke. In both of the above studies, transmission microscopic techniques were reported to be preferable to reflected light methods for microstructural analyses of semicoke, because they more closely represent the bulk properties of the samples.
An important impediment to utiliiing transmission optical microscopy in the analyses of cokes on a more routine basis is the difficulty in preparing thin sections having thicknesses of less than 0.5 km. However, recent studies of normally opaque constituents in high volatile bituminous coals at this laboratory [3] (ORNL) by means of transmission IR microscopy (800-1200 nm) has shown that many normally opaque coal constituents are transparent to IR radiation in coal sections as thick as 10pm. The use of IR microscopy may therefore be a means of overcoming sample preparation difficulties. Thus, if semicoke has similar IR transmission characteristics to some of the normally opaque coal constituents, this technique should be useful in examining semicoke materials.
In this note we report use of the IR microscope in examining a polished thin section of a carbonaceous plug and a thin section of a coke produced from autoclaving a petroleum pitch. The plug consisted of semicoke matrix surrounding minerals and unreacted fusinite fragments, whereas the pitch product consisted entirely of semicoke. In both samples, no visible light was transmitted through the thinned coke segments,
The anisotropic coke from the plug observed by means of transmitted plane polarized IR light revealed a columnar-like tResearch sponsored by the Division of Basic Energy Science, U.S. Department of Energy under contract W-7405-eng-26 with the Union Carbide Corporation,