Analytical characterization of coal surfaces and interfaces

Diffuse reflectance infrared spectroscopy (DRIS) was used as a major instrumental technique for studying spectral regions in all of the coals of the Argonne Premium Coal Sample (APCS) set to obtain information regarding stretching and bending frequencies of the various bond types found in the coals represented by this highly standardized set of coal specimens. This technique clearly delineates the 0-H stretching frequencies from about 3500 to 2500 wave numbers. It was also a good tool for studying the complex frequency regime from about 2000 to 500 wave numbers, representing a dense regime of bending modes. Fourier seer deconvolution was used to distinguish details In the hydrocarbon'' spectral region around 3000 wave numbers. Pocahontas No. 3 coal was found to have a minimum of seven spectral peaks in this region. The coalification'' of the various materials in the APCS was clearly discernible from the details observed in the region near 3000 wave numbers. For example, Beulah Zap, a lignite, and Wyodak, a sub-bituminous, both presented relatively simple and weak spectral responses in the 0-H stretching frequency range, whereas Upper Freeport, a medium volatiles bituminous, and Pocahontas No. 3, low volatile bituminous, both exhibited rich spectral detail in this region. Studiesmore » of coal samples were carried out to determine the initial effects of oxidation upon the coal structures. These oxidations were often carried out at 300[degrees]C for periods up to 200 h. Large changes were observed In the spectra near 3000 wave numbers, indicating the oxidation of the coal surface from these exposures. Transmission electron microscopy techniques were developed for characterizing the interfaces between included minerals and the coal structure in a number of the coals, but most of the effort was focused on Pittsburgh No. 8, a high volatile bituminous which was considered representative of many bituminous coals.« less