Thermal behaviour of the TiO.sub.2-based gels obtained by microwave-assisted sol-gel method

In order to establish the influence of the preparation method on thermal behaviour of gels obtained by the sol-gel and microwave-assisted sol-gel methods, a comparative thermal analysis study was conducted by the thermogravimetric and differential thermal analysis (TG/DTG/DTA) and evolved gas analysis (EGA) on TiO.sub.2 and V.sub.2O.sub.5-doped TiO.sub.2 gels, where TiO.sub.2:V.sub.2O.sub.5 molar ratio was set to 99.95:0.05 and 98.0:2.0. In contrast to TiO.sub.2 gels, for which the thermal behaviour was not significantly influenced by the preparation method, the microwave-irradiated binary samples showed a more complex and prolonged decomposition compared to their non-irradiated counterparts. This observation was correlated with influence of microwaves in enhancing the reaction rate between the Ti and V reagents leading to formation of more complex compositions of gels. Based on TG/DTG/DTA results, the temperatures of 300 and 450 °C were chosen for the processing of powders in air. All samples thermally treated at 300 and 450 °C crystallized in a single anatase phase except the TiO.sub.2:V.sub.2O.sub.5 with a molar ratio 99.95:0.05, obtained by microwave-assisted sol-gel method that contains also small amount of rutile phase. At 550 °C all samples contain mixture of anatase and rutile phases.