RESULTS OF THERMAL AND HYDROTHERMAL TREATMENT OF THE ALUMINOSILICATE GELS PREPARED AT DIFFERENT BATCH CONCENTRATIONS

The results obtained during the thermal (thermogravimetry, TG, and dif ferential thermal gravimetry, DTG) and the hydrothermal (heating at 80 degrees C for appropriate time) treatment of the gels prepared at dif ferent batch concentrations [Al2O3](bN) and different batch molar rati os [SiO2/Al2O3](bN), are presented. The presence of structurally order ed subunits (quasicrystalline zeolite phase) formed in the gel matrix during its precipitation, causes the appearance of higher-temperature minimum (peak-2) in the DTG curves of the precipitated solids. The int ensity of the higher-temperature minimum increases with increasing con centration of structurally ordered subunits (quasicrystalline zeolite phase) in the gel matrix. The increase in concentration of structurall y ordered subunits in the solids precipitated at increased batch conce ntration [Al2O3](bN) is caused rather by the increase in batch alkalin ity than by the increase in concentration of the aluminosilicate part of the system. The influence of alkalinity on the formation of structu rally ordered subunits in the gel matrix is explained by the 'olation' condensation mechanism. (C) 1998 Elsevier Science B.V.