Thermal Transformation of Various Potassium Aluminosilicate Precursors

The isothermal amorphization of potassium exchanged zeolite A and recrystallization of the formed amorphous phase as well the crystallization of the X-ray amorphous K-aluminosilicates (prepared in two ways: (A) by ion-exchange of sodium ions from zeolitic Na-aluminosilicate gel with the alkaline cation K resulting in K-gel(A) and (B) by direct precipitation from the corresponding K-aluminate and K-silicate solutions resulting in K-gels(B)) at three different temperatures were investigated by powder X-ray diffraction method. Phase analyses of the transformation/crystallization processes have shown that: pure crystalline tetragonal leucite crystallizes from K-gel (A) in the temperature range from 1423 to 1483 K whereas pure hexagonal kalsilite crystallizes from K-gel (B) and K-exchanged zeolite A in the temperature range between 1423 and 1483 K and 1258 and 1298 K, respectively.