Drying of large monolithic aerogels between atmospheric and supercritical pressures

The objectives of this investigation are to show the feasibility of produci ng large monoliths with minimal shrinkage at subcritical conditions, and to understand the drying behavior. Crack-free SiO2 monoliths (5.6 cm in diame ter and 25 cm in length) were repeatedly dried with little shrinkage (<2%). Some gels showed increasing shrinkage with decreasing pressure. However, t his shrinkage was reduced to negligible levels at conditions considerably l ess than supercritical pressure by increasing both the pore size and the ge l strength. This moderate pressure drying (MPD) process may make aerogel fa brication economically more feasible due to reduced pressure chamber costs.