Structure of kaoline–alumina based foam ceramics for high temperature applications

Light weight refractory materials were developed applying the aerated concrete technology. Kaolinite based suspensions were agitated with Al powders or Al pastes. Under release of hydrogen gas, foams were formed at pH values from 7 to 9, stabilised, dried and fired at temperatures up to 1600 °C. Loading fractions of alumina up to 80 vol.% were demonstrated. The porosity varies with the amount of the metal precursor Al. A macro porosity of 0.2–1 mm was formed which was characterised by image analysis and X-ray tomography. The working temperature of the produced refractory materials depends on the prefiring temperature, the filler character and content and the macroscopic structure. Silica free pure porous mullite or mullite-corundum ceramics were obtained. Thermal analysis shows that the porous refractories meet the ASTM requirements for application temperatures up to 1550 °C.