Adsorption of Ambient Moisture by Silica Aerogel

Silica aerogel, an extremely low-density and high-surface-area material, is a vital component of many target designs for inertial confinement fusion and high-energy-density physics experiments. Silica aerogel utilized in targets is found in a variety of densities and configurations. Material properties must be well characterized to minimize uncertainties in experimental data. In particular, density must be accurately known to predict shock velocity and timing of diagnostics. One potentially problematic attribute of silica is its hygroscopic nature. Here we describe adsorption of ambient moisture by silica aerogel, based on its density and processing parameters. Quick and simple methods of characterizing water uptake are needed to provide confidence in aerogel components. We find that aerogel manufactured using supercritical methanol is much more stable toward moisture (and therefore more suitable for use in targets) than that produced using supercritical carbon dioxide. Aerogel materials were characterized by thermogravimetric analysis and Fourier transform infrared spectroscopy.