Spherical Kaolinite: Synthesis and Mineralogical Properties

Shinji Tomura, Yasuo Shibasaki, Hiroyuki Mizuta and Masao Kitamura
Government Industrial Research Institute Nagoya, Seto Branch 110, Nishiibara, Seto, Aichi, 489, Japan
Department of Geology and Mineralogy, Faculty of Science Kyoto University, Sakyo-ku, Kyoto, 606, Japan

Abstract: Spherical kaolinite has been synthesized for the first time from noncrystalline aluminosilicate material in hydrothermal experiments conducted between 150° and 250°C and under autogenous vapor pressure. Spherules, whose mean diameters depended on growth conditions (0.1–0.6 µm), were formed surrounding the noncrystalline aluminosilicate in all products of 150° and 200°C runs and coexisted with platy or lath-shaped kaolinite in the products of 250°C runs. The estimated percentages of spherules in the products increased from about 1% in the 150°C-15 days product to about 74% in 200°C-8 days product, and decreased from about 21% in 250°C-2 days product to 0% in 250°C-8 days product. Lattice images by high-resolution electron microscope indicated that the spherules consisted of nearly concentric stackings of layers with a unit spacing of 7Å, which were sectored by radiating boundaries. The mean chemical composition of the spherules (Al2O3/SiO2 = 0.58) analyzed by the analytical electron microscope is similar to that of kaolinite (Al2O3/SiO2 = 0.5). Even in the case of the product abundant in spherule (200°C-8 days), X-ray powder diffraction patterns of the wetted products, e.g., of the 200°C-8 day run, showed the 7.14-Å (001) reflection of kaolinite. The 020 reflection was broad, indicating the existence of abundant (001) layer displacements. The b axis (8.94 Å) were within the kaolinite range (8.93–8.94 Å). No infrared absorption peaks were observed at 3550 cm−1 which would correspond to halloysite. The differential thermal analysis slope ratios of the endothermic peak at about 550°C (1.4–2.3) were in the kaolinite range (0.78–2.39).

Key Words: Halloysite • High resolution electron microscopy • Infrared spectroscopy • Kaolinite • Spherules • Synthesis • X-ray powder diffraction

Clays and Clay Minerals; December 1983 v. 31; no. 6; p. 413-421; DOI: 10.1346/CCMN.1983.0310602
© 1983, The Clay Minerals Society
Clay Minerals Society (www.clays.org)