TRANSPARENT ULTRALOW-DENSITY SILICA AEROGELS PREPARED BY A 2-STEP SOL-GEL PROCESS

Interest in lowering aerogel densities for applications involving high energy charged particle detection via the Cherenkov effect has led to the development of a two-step sol-gel method for preparing ultralow-density aerogels. This method has been used in the authors' laboratories to produce uncracked, transparent aerogel tiles with densities from 3 to 80 kg/m3. Comparative characterization of conventional single-step base-catalyzed aerogels to aerogels prepared by this two-step approach is presented. Results indicate that the aerogel microstructure for the two-step approach differs from the bead-like structure proposed for single-step base-catalyzed TMOS aerogels. TEM micrographs of aerogels prepared by the two-step method show an interlinked polymer-chain-like structure with an average chain diameter of 2-3 nm and an average chain length of approximately 15 nm. UV-VIS spectrophotometry shows the transmittance over the visible spectrum (400-800 nm) to be improved for the two-step aerogels by as much as 30%. Other measurements of the ultralow-density aerogels include BET surface area, and compressive modulus.