Abstract
Aerogels have been known for its low density, high porosity, high specific surface area, low dielectric constant, and low thermal conductivity for decades. Porosity, contact angle, BET surface area, TGA, and thermal conductivity of aerogel monolith, morphology, UV-vis reflection spectra, and contact angle of aerogel film with different synthesizing parameters or composition are studied in this thesis. Monolithic SiO2 aerogels, SiO2-PVP hybrid aerogels, and SiO2-PbO composite aerogels were prepared and dried under ambient pressure. PVP is added as a mechanical strength enhancing additive to improve monolithicity of aerogels, and PbO is selected to lower thermal conductivity at high temperature, when radiation is prominent. Aerogel films are prepared to investigate the feasibility to serve as inverse structure for preparation of porous film electrochemically. Experimental results showed that monolithic aerogels with lower molar ratio of ethanol used have higher BET surface area. Hybrid/composite aerogels have better monolithicity, but lower porosity and higher thermal conductivity. Thermal conductivities of SiO2 aerogel, 0.14 wt% SiO2-PVP hybrid aerogel, and 0.5 wt% SiO2-PbO composite aerogel at ambient temperature are 0.031, 0.046, and 0.037 W/K-m, respectively. 5.0 wt% SiO2-PbO composite aerogel have the lowest thermal conductivity at 500 ℃, which is 0.075 W/K-m. An unusual phenomenon is found for all SiO2-PbO and SiO2-TiO2 composite aerogels, thermal conductivity of composite aerogels at 400 ℃ are all lower compared to thermal conductivity at 300 ℃, and the phenomenon is expected to be caused by enhancement of extinction coefficient of composite aerogels is by addition of opacifier at 400 ℃. Thickness of aerogel films prepared is ~200 nm. Polymer, metal, metal with magnetic property, and oxide porous film were successfully prepared, polypyrrole, silver, nickel, and TiO2¬ are selected respectively. Porous films prepared are characterized with SEM, UV-vis reflectance and contact angle measurement.