The goal of this project is to measure a key physical property that governs how gasses flow through aerogels. An aerogel is a material that is approximately 90% air by volume and has unique properties such as a high surface area, low density, excellent insulating properties, and tolerance for high temperatures. In addition they can be made to be nearly optically transparent, and their chemistry can be easily adjusted to include, for example, catalysts. These unique properties make aerogels exceptionally well suited for many widely varied applications such as insulation in between glass window panes or as catalysts in automotive catalytic converters. For many applications an aerogel’s performance will depend critically on how gasses can move into, out of, and through it. This transport behavior is primarily governed by the aerogel’s “diffusivity” which is the key material property that relates the amount of flow to the magnitude of the gradient driving the flow. Data on the diffusivities of aerogels are not widely available, and this need motivates my project.
An apparatus and associated methodology, based on the work of Stumpf et al. , have been developed for testing Union fabricated aerogels. The technique depends on recording the pressure change that occurs in a chamber containing an aerogel sample after it is exposed to a step change in pressure. Details of the experimental apparatus, the theory and methods underlying its use, and the diffusivity values of several different silica aerogel types will be presented. The diffusivity of TMOS aerogel monoliths measured with the apparatus have values on the order of 10-5 m2/s, which are comparable to values found in the literature. Future work to measure the diffusivities of other non-silica aerogels, for which diffusivity values are not available in literature, is also discussed.
 C. Stumpf, K. von Gässler, G. Reichenauer, J. Fricke, 1992, “Dynamic Gas Flow Measurements on Aerogels,” Journal of Non-Crystalline solids, 145, pp. 180-184.