Hydrothermal Formation of a Kaolinite-Like Product from Noncrystalline Aluminosilicate Gels

Noncrystalline aluminosilicate gels with Al 2 O 3 /(Al 2 O 3 + SiO 2 ) weight ratios from 0.3 to 0.5 were reacted in 0.1 N KOH at temperatures varying from 125° to 175°C. The pH of the solutions dropped sharply with increasing gel:solution ratios, indicating that the coordination number of Al in the products changed from IV to VI. The degree of hydrolysis appeared to be higher with KOH than with NaOH. X-ray powder diffraction and infrared spectroscopy showed that disordered kaolinite was the only crystalline product formed. Thermal data and surface area measurements indicated that the kaolinite was formed by a condensation process.