Springer Handbook of Aerogels 62. 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 light metal and nonferrous heavy metal casting is described; their properties are elaborated and compared with conventional ones. Transforming especially resorcinol–formaldehyde (RF) aerogels into carbon aerogels allows bonding sand grains by amorphous, nanostructured carbon with special advantages. New developments in the last years are described, revealing that inorganic, organic, or hybrid aerogels in a granular form can replace a part of any sand used in foundries, leading to improved cast parts. These nano-additives made from RF aerogels, carbon aerogels, or silica-based ones have the great advantage that only small amounts are needed and the conventional processes of mold and core making need not to be changed. In contrast to polymeric and carbon aerogels, the silicabased ones are used for more than a decade in solidification engineering to study fundamental aspects of metal solidification and casting also in space laboratories. A new application of silica aerogels in metal casting was developed: Beds of silica granules were infiltrated with liquid aluminum leading to a new class of porous metal.