Silica Glass Monoliths from Alkoxide Gels; An Old Game With New Results,

Cylindrical monolithic silica dry gel bodies, up to 250 grams in weight, are routinely produced from alkoxide sols free of colloidal particles, using tetraethylorthosilicate precursor. These dry gel bodies, after sintering in controlled chlorinated atmosphere, yielded clear, bubble free, dense glass rods 3.0-4.0 cm in diameter and 15-20 cm in length. Uv-vis-ir spectra, of properly dehydrated and sintered glass samples tested from 180 nm to 3200 nm, showed no detectable absorption peak at 2700 nm and a UV band edge at around 185 nm implying that resultant glasses are reasonably free of impurities and hydroxyl ions. Effect of sol composition on gel ultrastructure was carefully investigated. It was found that by careful choice of sol composition, type and amount of catalyst and aging conditions, it is possible to tailor the gel ultrastructure for ease of drying. For example, we have been able to produce gels with unimodal pore distributions, and average pore sizes in the range from 8 to 300 A and surface area in the range from 150 - 1 100 m2gram. As a result of this ability to tailor gel ultrastructure, including pore size, bulk density and skeletal density of the gel bodies, we have been able to optimize gel ultrastructure to maximize its strength, so that it can withstand capillary forces generated during the drying processes. The result of this preliminary investigation has led us to believe that high quality fused silica glass of much larger sizes can be produced by the alkoxide route and experiments to scale up the process is under way. Up to date results of this investigation will be presented at the conference.