Results of thermal and hydrothermal treatment of the aluminosilicate gels prepared at different batch concentrations

The results obtained during the thermal (thermogravimetry, TG, and differential thermal gravimetry, DTG) and the hydrothermal (heating at 80 degrees C for appropriate time) treatment of the gels prepared at different batch concentrations [Al2O3](bN) and different batch molar ratios [SiO2/Al2O3](bN), are presented. The presence of structurally ordered 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 intensity of the higher-temperature minimum increases with increasing concentration of structurally ordered subunits (quasicrystalline zeolite phase) in the gel matrix. The increase in concentration of structurally ordered subunits in the solids precipitated at increased batch concentration [Al2O3](bN) is caused rather by the increase in batch alkalinity than by the increase in concentration of the aluminosilicate part of the system. The influence of alkalinity on the formation of structurally ordered subunits in the gel matrix is explained by the 'olation' condensation mechanism. (C) 1998 Elsevier Science B.V.