The point of zero charge (pzc) of kaolinite and SiO2+AI2O3 mixtures

Abstract
The pzc of H+-kaolins determined by titration method is nearly pH = 3. The pzc of SiO2 + Al2O3 mixtures is not additive, and depends principally on Al2O3 content in mixture. The curve pzc—t°C (t°C = temperature of treatment of kaolins) has two maxima: 4·7 after treatment at 800-900°C, and 5 after treatment at 1300°C.