抄録
The formation process of kaolinitc in the hydrothermal reaction of an amorphous calcium silicate with aluminum chloride was studied by XRD, IR, DTA-TG, TEM, and high-resolution solid state 29Si-MAS/NMR. The amorphous calcium silicate prepared from diatomite and calcium hydroxide was hydrothermally treated with an aluminum chloride solution in a Teflon pressure vessel at 220°C for a reaction period varying from 1 to 144 h. As the first step of the reaction, the Q2 state component of the starting material changed into an intcrmcdiate amorphous with the Q3 state. The degree of silica-polycondensation of this state is identical to that of the intermedicate phase observed in the kaolinitization from the amorphous mixture of silica and alumina. The intermediate amorphous phase was then converted directly into the crystalline kaolinite with a platy shape (the Q3 state), without forming a spherical kaolinite. The latter was observed in the reaction system started from an amorphous mixture of silica and alumina.
