Analysis by DSC of the drying and sintering processes of alkoxide-derived SiO 2–ZrO 2 gels

Abstract

The drying and sintering processes of SiO 2–ZrO 2 alkoxide-derived gels have been studied by means of DSC technique. In the drying process, most part of water and alcohols are removed from the gels. For the SiO 2 gel such elimination occurs at the end of the drying process, however for the ZrO 2 gel this elimination occurs during the whole drying time. An intermediate behavior is observed for the binary system SiO 2–ZrO 2 gels. In the sintering process, the DSC technique allows to determine the elimination of water and alcohols retained within the structure (open or close pores) and the well-known hydroxyl condensation of silica gel between 700° and 800°C is also observed. The ZrO 2 gel shows the final hydroxyl condensation at the heating temperature of 600°C. For the binary SiO 2–ZrO 2 gels, the hydroxyl condensation has been associated to the activation energy needed for the dissociation of silica hydroxyls. This energy decreases with the ZrO 2 concentration in the gel resulting in a sintering treatment of 500°C leading to the entire hydroxyl condensation for the gel with 75% ZrO 2–25% SiO 2. By studying the temperature of the DSC peaks, it is possible to know the temperature at which most part of water and alcohols are leaving the gel, and these results can be used in order to select the corresponding drying or sintering schedules for obtaining a well-fabricated material.