Date of Award
Union College Only
Bachelor of Science
aerogels, modified, thermal, silica, conductivity
Aerogel is a material that is comprised of 90-99% air. Since air is a very good insulator the resulting thermal conductivity of aerogels is very low, typically between 0.008 – 0.017 W/mK. However, silica aerogels are very brittle and break easily. Their fragile structure prevents using them in a wide variety of applications of which their thermal properties could be advantageous. The purpose of this study is to increase the mechanical strength of silica aerogels without hindering their thermal insulating properties. Aerogels were fabricated using a rapid supercritical extraction method, where the methanol is taken up to the supercritical state for removal from the gel. Experiments have been conducted to characterize the properties of non-modified and modified silica aerogels. Compression, thermal conductivity, surface area, and pore distribution tests were done in order to define the standard mechanical and physical properties inherent in the silica aerogels. Compression, thermal conductivity, surface area, and pore distribution tests were done in order to define the standard mechanical and physical properties of non-modified and modified silica aerogels. Compression, thermal conductivity, surface area, and pore distribution tests were done in order to define the standard mechanical and physical properties inherent in the silica aerogels. Typical results show strain hardening behavior as the aerogels are compressed with loads of up to 5000N. The modulus of elasticity for these standard silica aerogels ranges from 0.50MPa-0.70MPa at low strain values and 150MPa-170MPa at high strain values. Using the current literature, we chose the strengthening technique of fiber addition (or other materials) during the fabrication stage. Aerogels with 5, 10, and 15% (by weight) activated carbon have been successfully synthesized. Results show that the thermal conductivity increases with the addition of activated carbon (going from 0.038 W/mK to 0.085 W/mK), and that the aerogels have lower maximum strain before failing (decreasing from approximately 90% to 25% strain). However, the modulus of elasticity at low strains increased to approximately 0.9MPa. The carbon aerogels also exhibited higher bulk densities and nitrogen desorption tests showed differences in the pore size distribution for the carbon modified samples as compared to the non-modified samples. Modified aerogels with glass wool fiber additions were also made. The orientations of the fibers were varied from horizontally and vertically set in the cylindrical samples, for these samples, the fibers lengths were as long as the orientation they were set parallel with the sample (about 2.0cm for horizontal orientation, and 1.7cm for vertical orientation) and had diameters of about 40µm. Samples were also made with chopped glass wool fibers, where the average length of fibers was less than 1mm. The results showed a small increase in thermal conductivity for the samples (increasing to about 0.067 W/mK). These glass wool modified aerogels were able to reach much higher strain rates and elastic moduli up to 233.75MPa.
Sherman, Matthew Adam, "Modifying the mechanical strength of aerogels" (2009). Honors Theses. 1402.