Mullite-Corundum-Al2TiO5 Foamed Ceramics with Extremely Low Thermal Conductivity Induced by Multiple Thermal Resistance

In the context of the global implementation of the dual carbon strategy, enhancing the thermal insulation performance of kiln insulation layers to reduce energy consumption is a highly effective route to achieving energy conservation and emission reduction. In this work, mullite foamed ceramics were fabricated via a direct-foaming method using industrial alumina and white clay as raw materials, and the thermal conductivity was decreased by introducing a secondary phase and increasing the interfacial thermal resistance. The influence of the TiO2 addition on the phase composition, pore characteristics, and properties was systematically investigated by means of XRD, SEM, and EDS. The results indicate that the foamed ceramics are mainly composed of mullite, with minor phases including corundum and aluminum titanate. It has been demonstrated that increasing the TiO2 addition decreased the ceramic’s thermal conductivity, due to the formation of low-thermal-conductivity Al2TiO5 phases and the elevation of the interfacial thermal resistance. The specimen exhibiting the optimal properties is characterized by a porosity of 77.8%, a strength of 1.86 MPa, and a thermal conductivity of 0.216 W/(m·K) (1000 °C), achieved with a TiO2 addition of 6 wt%.