Synthesis of Dioctahedral Fluorine Mica Ceramics by Using Kaolinite as Raw Material

Abstract

Dioctahedral mica ceramics containing fluorine muscovite and amorphous phase were prepared by solid state reaction in air with using kaolinite and K2SiF6 as raw materials. The appropriate molar ratio for obtaining high contents of fluorine muscovite was 0.6K2SiF6: 1.5 kaolinite. Fluorine muscovite crystallites were precipitated at 600-700°C for shorter sintering times of 3-6h, developing house of cards microstructure with remaining relatively high porosity of 18-28%. The porosity depended on the heating rate. The lattice constant b of precipitated fluorine muscovite slightly increased with increasing temperature from 600°C to 700°C, coinciding with that of fluorine muscovite synthesized as a single phase in the closed system by using γ-Al2O3 as a raw material. This indicates that tetrahedral aluminium substitution slightly increases with increasing temperature and that fluorine muscovite having an ideal composition is formed at 700°C. However, topaz crystallized as a stable high temperature phase at higher temperatures over 750°C.