ABSTRACT
Aerogel technology is becoming increasingly im-
portant because of its numerous novel applications,
such as for:
Thermal insulators, both in domestic and indus-
trial use (e.g., in solar collectors, multilayer
windows)
Acoustic transducers (e.g., in ultrasonic meters,
sound-delay lines, sound absorbers)
Components of high-quality glass (e.g., in optic
elements, light pipes)
Catalyst carriers (e.g., with oxides or noble metals
deposited on silica-based aerogels)
Liquid thickeners (e.g., to convert liquid nitrate
acid into thixotropic fluid)
Insecticides (living cell dewatering due to high
adsorption capacity of aerogels)
Porous materials from gels can be obtained by [8]:
. Supercritical drying from the native solvent,
usually alcohol . Solvent replacement and subsequent supercrit-
ical drying using CO2 or other low-critical-point
solvent . Convective drying at very low drying rates or
using the drying control chemical additive
(DCCA) . Freeze drying
The first two methods yield a highly porous (porosity
above 0.9) and transparent aerogel; the other methods
produce less perfect andmoredense porous solids called
xerogels. The principles and practice of the above
methods are summarized in the following sections.
