The effects of initial sol parameters on the microstructure and optical transparency of TiO2-SiO2 binary aerogels

The effects of initial sol parameters on the pore structure and optical transparency of TiO2-SiO2 binary aerogels are investigated. Different silicon alkoxides, catalysts and water to alkoxide ratios were considered as initial sol parameters to control the hydrolysis and condensation reactions in each reaction stage. Strongly acidic conditions gave rise to the most transparent monolithic aerogels for both tetra-ethyl ortho silicate (TEOS) and tetra methyl ortho silicate (TMOS) based systems. In the TMOS-based system, due to a larger number of monosilicic acids acting as equivalent nucleation centres for further growth, smaller and uniformly distributed particles and interstitial pores were produced during the gellation and supercritical drying. Therefore, with the same catalyst and water content, better transparency was observed in the TMOS-based system than in the TEOS-based system.