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

• Low heat conductivity

• High stability

• Non-flammability

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 compared to 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 can be produced using the sol-gel-process, where the solution of a network building material (commonly 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

One 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 for re-use

• Non-toxicity of CO₂

• Non-flammability of CO₂