Green synthesis route of Al2O3-SiO2 aerogels,possible alternative for the synthesis with propylene oxide

Abstract

Silica-alumina aerogels exhibit tremendous potential in high-temperature applications because of their excellent temperature stability at temperatures up to 1200°C. The synthesis of these aerogels is wellstudied using propylene oxide as a gelation initiator which is unfortunately toxic and carcinogenic. [1] Within this presentation we report on a new synthesis route which is developed to replace propylene oxide by non-toxic urea receiving silica-alumina gels. The gel bodies are dried under supercritical CO2 conditions to receive the aerogel. The route provides a significant advantage given their easy scalability. A systematic and conscious approach is followed to develop a green synthesis route for developing Al2O3-SiO2 aerogels. With the aim of improving the temperature stability of the Al2O3-SiO2 matrix, the molar ratios of urea, the type of solvent and the admixture of added metal oxides, such as ZrO2, are optimized. All aerogel variants are analyzed with respect to gelation, their density, porosity, internal surface area and thermal conductivity. Furthermore, the influence of heat treatment (25–1100°C) on the granular aerogels is investigated and additionally supported by X-ray powder diffraction, scanning electron microscopy and thermal analysis coupled with Fourier-Transform-Infrared (FT-IR) spectroscopy. In the contribution, all aspects concerning the importance of the careful examination on material parameters to ensure long term thermal stability will be presented. The results will be discussed and an outlook on potential applications will be demonstrated.