Formation process of kaolinite from the amorphous mixture of silica and alumina

Abstract

The formation process of kaolinite from the amorphous mixture of silica and alumina by hydrothermal reaction was studied by XRD, IR, DTA-TG, TEM, and high-resolution solid state 29 Si- and 27 Al-MAS/NMR. The amorphous mixture of the starting material prepared with commercially available silica-sol and alumina-sol was hydrothermally treated with distilled water in a Teflon pressure vessel at 220°C for a reaction time varying from 1 to 144 hours. The Q 4 state component of the amorphous starting material changed into an intermediate amorphous Q 3 state. The intermediate amorphous phase converted into crystalline kaolinite with spherical shape (Q 3 state). The yield and crystallinity of kaolinite increased with an increase in the reaction time