Microstructure Development in Porous Calcium Hexaluminate and Application as a High-Temperature Thermal Insulator: A Critical Review

Abstract

Porous calcium hexaluminate (CaAl 12 O 19 or CA 6 ) is a promising refractory material for thermal insulation applications because it combines low thermal conductivity (0.1–0.5 W∙(m∙K) at 1200–1400 °C), suitable mechanical strength (1–10 mPa, uniaxial compression), chemical inertia, good refractoriness (melting temperature of 1830 °C), high resistance to thermal shock, and straightforward processing conditions. There are several routes to obtaining porous CA 6 -based materials, using alternative sources of Al 2 O 3 and CaO, as well as different processing methods, generating structures of distinct levels of total porosity, mechanical properties, and pore-size distribution. This paper represents a critical review of the technical and scientific literature on CA 6 with emphasis on the production of porous materials and on the conditions required to attain optimized microstructure and properties for thermal insulation at high temperatures.