Diffusivity of Various Aerogels

The focus of this project is studying how gas flows through aerogels for potential applications as diverse as window insulators and motor vehicle catalytic converters. The interaction between gas and aerogels is characterized by the diffusivity value. To measure diffusivity, a known amount of gas was introduced to a pressure chamber around the aerogel and the pressure change outside of the aerogel was recorded as the gas diffuses through the aerogel. The correct value of the aerogel's diffusion can be inferred by adjusting the diffusivity parameter in the analytical solution to the 2-D transient diffusion equation until the results match the experimentally obtained pressure results. Building on previous work, improvements were made on the experimental data collection process by solving for the pressure chamber volumes to adjust for pressure transducer drifts. The analytical solution was also improved by deriving the analytical pressure change outside of the aerogel to match a greater portion of the experimental results, thus increasing the accuracy of the diffusivity measurement. Furthermore, various types of aerogels, including silica aerogels and silica aerogels with copper nanoparticles, were tested on three gases: Helium, Argon, and Nitrogen to compare how the diffusivities differ. The diffusivity result of the plain silica aerogel agreed to results in the published paper by Stumpf et al. closely. Helium was found to have a higher diffusivity in both studies as it is lighter and moves faster. The diffusivity result of silica aerogels with copper nanoparticles, however, did not agree with anticipated trends. Nitrogen had a significantly higher diffusivity value compared to Helium and Argon, which were similar in diffusivity. These diffusivity values were recollected and retested to confirm their validity, but further studies are needed in understanding the reason behind this behavior.