Low density TEOS based silica aerogels using methanol solvent

Highly transparent monolithic silica aerogels based on the TEOS precursor were prepared by the two-step (acid-base) sol–gel process. The hydrolysis and condensation reactions of tetraethoxysilane (TEOS) proceeded in methanol solvent with oxalic acid and NH₄OH as the catalysts, respectively. The wet gels were supercritically dried using methanol. The aerogels were characterized by transmission electron microscopy (TEM) and measurements of optical transmission, bulk density, volume shrinkage, porosity and thermal conductivity. Monolithic silica aerogels with high optical transmission (∼93%), low density (∼0.055 g/cm³), low thermal conductivity (∼0.04 W/mK), and minimum volume shrinkage (∼10%), were obtained for the molar ratio of TEOS:MeOH:acidic H₂O:basic H₂O at 1:33:3.5:3.5 alongwith the oxalic acid and NH₄OH concentrations at 0.001 M and 1 M, respectively.