Preparation of high temperature stable SiOC aerogels for foundry applications

Abstract

Silica Aerogels are highly porous nanostructured materials with an open three-dimensional silica network. Their low density, high surface area and low thermal conductivity are interesting for several industrial applications. Casting of metals and alloys simply means the pouring of a liquid metal into a form which most often is made from resin bonded quartz sand. Replacing a fraction of sand by aerogels can improve the casting quality, since the contact of the hot melt leads to a huge gas evolution and induces many casting defects. The huge internal surface of aerogels helps to absorb this decomposition gases and thus improves casting quality. Unfortunately the thermal load on the aerogels can lead to a rapid sintering and shrinkage and then induce other casting defects. We therefore developed a new thermally stable Si-O-C aerogel. These are synthesized using a mixture of MTMS and TEOS as precursor materials in a conventional two-step acid-base sol-gel routine. After ambient drying of the aerogels these are transformed into to Si-O-C aerogels by pyrolysis at 1000 °C. A systematic variation of the TEOS: MTMS ratio allows to vary the Oxygen and Carbon content. The aerogels are characterized by envelope and skeletal density, nitrogen adsorption (BET, BJH) and SEM. Tests in foundries are on the way.