ABSTRACT
Aerogels, hailed as one of the top ten scientific and technological developments, are highly porous materials consisting of an expanded small particle solid matrix interspersed by a non-condensable gas, i.e. air. It is this nanoporosity that renders aerogels a class of materials with extraordinary properties.
Aerogels enjoy a high thermal and acoustical insulative power, have a good light transmission and a low bulk density (<0.2 gm/cm3 compared to 2.2 gm/cm3 for glass), attributed to their high porosity (>98%). Also, the low refractive index of aerogels (ranging from 1.04 to 1.1 compared to an index of 1.3 for most solids) creates the visual illusion that the phase boundary is actually disappearing into thin air. Therefore, they have successfully been used in a wide range of applications, i.e. architectural, solar, acoustical, etc..
Owing to high energy requirements in producing aerogels, mainly during the drying process of the gel, a large scale commercial production has not yet been realised.
This paper reports on the most important methods to produce and dry aerogels using supercritical drying (SCD). It also describes the optical-acoustical and thermal properties of aerogels. The paper investigates their environmental applications, in particular those relevant to passive solar energy use, i.e. in trombe walls as a transparent insulation material and shutter, windows, etc..
