Process for drying sol-gel derived porous bodies at elevated subcritical

Abstract

A process is disclosed for drying sol-gel derived porous wet bodies without inducing cracks therein. The wet gel preferably is immersed in a liquid solvent before being placed inside a drying chamber capable of withstanding relatively high pressures and temperatures. After the wet gel is loaded, the chamber is sealed from the outside environment, and then is heated from outside the chamber in a controlled manner until a prescribed subcritical pressure is reached. The final temperature and pressure are always lower than the critical temperature and pressure of the drying solvent. The solvent vapor is then evacuated from the chamber in a controlled fashion to decrease the pressure until ambient pressure is reached, while preferably maintaining the temperature inside the chamber at the prescribed level. Thereafter, the inside of the chamber is purged with an inert gas for a prescribed time period, after which the chamber is cooled to ambient temperature and the dry crack-free porous gel is removed. The resulting dry gels are crack-free and monolithic.