SOLIDIFICATION OF ALUMINUM-ALLOYS IN AEROGEL MOLDS

A new application of silica aerogels is presented, using them, for the first time, as a mould material for the casting of metals. Aluminium alloy melts were cast into forms machined from thick silica aerogel pl ates. The excellent thermal insulation properties of aerogels lead to a nearly one-dimensional cooling and solidification process. This is r eflected by the microstructure of the solidified samples. Owing to the transparency of the aerogels, it is also possible to study the coolin g process with the help of optical measurements and video techniques. Using an infrared camera, the velocity of the solidification process a nd the temperature gradient ahead of the solid-liquid interface were o btained from video signals. These can be directly correlated with the microstructure. The successful results of these casting experiments ha ve initiated a more detailed study of the potential offered by aerogel s for researching solidification processes. One example is a new type of Bridgeman furnace using aerogels as a crucible material and a speci al feedback loop controlling the solidification processes without mova ble samples or heaters like in a classical Bridgeman configuration. Th e concept of such a furnace is presented and first experimental result s are shown.