Carbon aerogels can be manufactured from biopolymeric aerogels and thermoset resin aerogels by pyrolysis under an inert gas or CO2. Under such anaerobic conditions in a pyrolysis furnace between 500°C and 2000°C the polymeric molecules are transformed into varieties of carbon ranging form amorphous modifications at lower to graphitic ones at higher temperatures. The transformation, especially under CO2 atmosphere leads on the one hand to a drastic mass loss, but also increases the specific surface area considerably and yields an electrically conducting material. The same procedure allows to transform Silica-hybrid-aerogels into Si-O-C or even Si-CN-aerogels.
Carbon, Silica and Si-O-C aerogels are stable at higher temperatures (> 1000°C) and are applied in sand castings or permanent mold casting routines in foundries using sand cores. Here aerogels in granular form are added to sand-binder-mixtures to drastically reduce a lot of well-known casting defects, mainly originating from the decomposition of the resin binders used in foundries. Typical cast defects are like pin or gas holes, metal penetration between sand grains, burnt sand, inclusion of sand grains into the cast part surface can be avoided by just adding a small amount of aerogel granulates of the same size spectrum as the sand used (typically a few volume percent is sufficient) to get rid of these defects. This new technology was tested for Al-alloy, brass and bronze casting as well as cast iron with great success. Currently DLR is working to transfer the know-how obtained in the last years together with industrial partners from the lab scale to the pilot plant scale and especially to built up the know-how in industry, how to manufacture large scales of suitable aerogels at acceptable costs.