Solidification of aluminium alloys in aerogel moulds

Abstract

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 plates. The excellent thermal insulation properties of aerogels lead to a nearly one-dimensional cooling and solidification process. This is reflected by the microstructure of the solidified samples. Owing to the transparency of the aerogels, it is also possible to study the cooling process with the help of optical measurements and video techniques. Using an infrared camera, the velocity of the solidification process and the temperature gradient ahead of the solid-liquid interface were obtained from video signals. These can be directly correlated with the microstructure. The successful results of these casting experiments have initiated a more detailed study of the potential offered by aerogels for researching solidification processes. One example is a new type of Bridgeman furnace using aerogels as a crucible material and a special feedback loop controlling the solidification processes without movable samples or heaters like in a classical Bridgeman configuration. The concept of such a furnace is presented and first experimental results are shown.