Crystallite size evolution in hydrothermal formation of kaolinite

摘要

In the present work, kaolinite was hydrothermally precipitated from solutions of amorphous aluminosilicates, with different weight fractions of Al_2O_3, at two temperatures (200 and 250°C) and at different aging times. X-ray Diffraction (XRD) microstructural anal ysis was applied to the obtained materials. Crystallite size was studied applying the Warren Averbach method to 001 and 002 kaolinite reflections using "Xpowder" software, and the Voigt function method was also applied to the 001 reflection. Results from both methods were strongly correlated. For a given chemical composition, kaolinite crystallite size increases with temperature or aging time. The volume-weighted average crystallite sizes are in the range: 17.2-39.1 nm. Symmetry of crystallite size distributions (CSDs) also increases with time and temperature, due to the growth of part of the crystallites obtained in the first stage of formation. The study of the shape of CSDs allows the deduction of the crystallite growth mechanism.