Drying of Aerogels
Aerogels - high performance insulation materials
Aerogels are products either in shaped form or as small particles which show several outstanding product characteristics. The most important ones being
- High stability
- Low heat conductivity
In former years, these materials have drawn attention as special insulation materials due to these properties. Since the heat conductivity is generally much lower than standard insulation materials, aerogels are of special interest in applications with small space requirements such as refrigerators, old-building renovation, planes and even space shuttles.
Aerogel production process
Aerogels are traditionally produced using the sol-gel-process, where a solution of a network building material (generally on silicate basis, but polymers are also possible) is used to form a fine porous structure. After the removal of the solvent from this material the aerogel is obtained. This process step is also the most critical, since a normal evaporation of the solvent would destroy the fine porous structure of the gel and thus lead to a considerable deformation of the product.
Aerogel drying process
An approach for the drying process is using supercritical CO2 as drying agent to replace the solvent in the aerogel. Afterwards, the supercritical CO2 can be expanded to the gaseous state preventing an unwanted phase change from liquid to gas.
Advantages of supercritical CO2
- No thermal stress which could damage sensitive material
- Solvent can be recovered purely for re-use
- Non-toxicity of CO2
- Non-flammability of CO2