3.2. Thermal analysis of precursor powder
First of all, TG-DTA analysis of precursor powder in argon was conducted to understand the processes of pyrolysis of the precursor. The complementary information obtained allows differentiation between endothermic and exothermic events, which have no associated weight loss (e.g. melting and crystallization) and those which involve a weight loss (e.g. degradation). TG analysis showed that a considerable weight loss occurred in a temperature range of 100–550 °C for the precursor, as shown in Fig. 2. An in-depth analysis showed that the weight loss was ca. 8.0% from 100 to 240 °C, and ca. 25% from 240 to 550 °C (see Fig. 2). To clarify why the weight loss occurred during heating, the reaction (6) has to be considered firstly, although it had finished during the process in which the wet gel was dried under vacuum at 120 °C.