Aerogels for Foundry Applications

Abstract

The casting of metals and alloys is very often performed into molds made of sands bonded by polymers. Resins based on, for instance, phenol–formaldehyde build bonding bridges between the sand grains, establishing a macroporous tight and strong sand form having a shape mirroring the workpiece to be cast. Any cavity in a casting is mapped by so-called cores, which are also made of polymeric-bonded sands. Organic aerogels can replace conventional polymers and offer a variety of advantages due to their nanostructure and composition, especially for cores. The development of these organic aerogels for lightmetal and nonferrous heavy metal casting is described, their properties elaborated and compared with conventional ones. Transforming especially resorcinol–formaldehyde aerogels into carbon aerogels allows bonding sand grains by amorphous, nanostructured carbon with special advantages. New developments in the last few years are described, revealing that inorganic and organic aerogels in a granular form can replace a part of any sand used in foundries, leading to improved cast parts. In contrast to polymeric aerogels, silica-based ones have been used for more than a decade in solidification engineering to study fundamental aspects of metal solidification and casting. The final section describes various applications of inorganic aerogels with respect to solidification science.