Date of Award
Bachelor of Science
aerogel, hydraulic, reactions
Silica aerogels were prepared using the precursor tetraethylorthosilicate (TEOS) and an organically modified TEOS derivative (methyltriethoxysilane, MTES) via a rapid supercritical extraction (RSCE) method. Multiple consistent batches of monolithic TEOS-based aerogels were fabricated via an eight-hour RSCE process. Fabricating TEOS-based aerogels with an RSCE method offers some distinct advantages. The main advantage is the relative simplicity of the RSCE approach: liquid precursors are mixed and poured into a mold in a hydraulic hot-press, where gelation, aging and extraction of liquid from the pores occur. The precursor recipe employs TEOS, ethanol, water, oxalic acid to catalyze hydrolysis, and ammonia to catalyze the subsequent polycondensation reactions. Earlier work on silica aerogels by our group focused on the use of tetramethylorthosilicate (TMOS)-based precursor mixtures. Reaction of TEOS to form sol gels yields ethanol as a byproduct. A process that releases ethanol, rather than methanol (as in the TMOS-based aerogels) may be more appealing for commercial applications, involving scale-up of the process. The TEOS-based aerogels have good optical transparency, bulk densities of 0.099(±0.003) g/cm3, surface areas of 460(±10) m2/g, and contain internal and external Si-O framework bonds as observed in FTIR spectra. Using SEM, the surface morphology of the aerogel samples was studied. MTES-based aerogels were also successfully fabricated using Union’s RSCE process, but with less consistent results than for the TEOS-based aerogels. About half the MTES aerogels remained monolithic. FTIR spectra indicate that the aerogels are organically modified; Si-CH3 groups are present in the aerogel framework. The MTES aerogels are hydrophobic.
Estok, Suzanne K., "Fabrication and Analysis of TEOS- and MTES-based Aerogels Prepared via Rapid Supercritical Extraction" (2011). Honors Theses. 973.