Neutron Radioscopic Measurement of Water Adsorption Coefficients in Aerogels

Abstract In this work, neutron radioscopy was utilized to investigate water vapor uptake by a hydrophilic silica aerogel. Aerogel is an unusual porous material, produced by a sol-gel process that results in a solid material with a unique microstructure composed of nanometer-size particles and pores. Aerogels have an extraordinarily large internal surface area which is accessible via open pores, making them candidates for filters and gas adsorption media. The water vapor deposition was modeled both analytically and computationally, and an estimate for adsorption coefficients for water vapor in aerogel yielded 1.08 × 10-3 ± 2.58 × 10-4 cm2/s. Initial tests to measure water vapor uptake from moist air were very successful. Dry air was bubbled through water and then flowed past an aerogel. The aerogel was shown to uptake the water vapor readily from moist air. After uptake, the aerogel dried out rapidly in dry air. This phenomenon was repeatable, indicating that the aerogel could be reused with little change in its sorption properties. Neutron radiography was shown to be an effective nondestructive method for evaluating the real-time movement of water vapor in aerogel, as deposition patterns can be analyzed quantitatively as a function of time and penetration distance into the aerogel.