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

Excerpt

Abstract: Porous calcium hexaluminate (CaAl₁₂O₁₉ or CA₆) is a promising refractory material for thermal insulation applications because it combines low thermal conductivity (0.1-0.5 W∙(m∙K)^-1 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 CA₆-based materials, using alternative sources of Al₂O₃ 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 CA₆ 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. …