CHARACTERIZATION OF CSSJ REFERENCE CLAY SAMPLES USING VARIOUS ELECTRON MICROSCOPIC TECHNIQUES (PART II)

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Kaolinite, dickite, and pyrophyllite in the CSSJ reference clay samples were investigated using S/TEM, X-ray microanalysis via SEM-EDS and STEM-EDS, and XRD in order to characterize mineral impurities, grain sizes, crystal structures, and other physicochemical properties. The new lot of Kampaku kaolinite (JCSS-1101c) is nearly free of quartz and alunite, both of which were abundant in the previous lot (JCSS-1101b). Svanbergite (SrAl₃(PO₄)(SO₄)(OH)₆) was identified as a minor mineral impurity in both lots through STEM-EDS analysis. The characteristic 02,11 band reflections of well-ordered kaolinite (kaolinite-1A) are more distinct in the new lot, as evidenced by a higher Hinckley Index (1.17), indicating a greater proportion of large, well-crystallized kaolinite grains. Shokozan dickite (JCSS-1301) also contains svanbergite, along with quartz, diaspore, and pyrophyllite as mineral impurities. XRD analysis revealed the presence of kaolin group polymorphs, including significant amounts of nacrite and kaolinite in addition to dickite. S/TEM imaging indicated a bimodal grain-size distribution: smaller grains, with lateral dimensions less than 0.1 µm, likely represent a disordered kaolin phase, while the larger grains correspond to well-ordered dickite or nacrite, exhibiting a two-layer periodicity. Shokozan pyrophyllite (JCSS-2101) was found to contain quartz and diaspore as mineral impurities. HRTEM revealed pronounced stacking disorder, characterized by two alternative interlayer displacements. This structural disorder accounts well for the profile of the 02, 11 band in the XRD pattern.