Fabrication of mullite-corundum foamed ceramics for thermal insulation and effect of micro-pore-foaming agent on their properties

Mullite-corundum foamed ceramics were prepared by direct-foaming method using white clay and industrial alumina as raw materials, and micro-pore-foaming agent (MPFA, the main composition was sodium dodecyl benzene sulfonate) as foaming agent. Effect of the MPFA addition on the phase compositions, microstructures and physical properties of the foamed ceramics were investigated by X-ray diffractometer (XRD), scanning electron microscopy (SEM) and energy dispersive spectrometer (EDS), etc. The results showed that the specimens fired at 1500 °C mainly consisted of needle-like mullite, corundum, and a small amount of glass phase. The MPFA decreased the viscosities and then increased the volume expansion of foamed slurries. Meanwhile, the adding of the MPFA caused the increases of apparent porosities and average pore sizes, and the decrease of strengths of the fired specimens. The optimized product was a specimen with 1.0 wt% MPFA fired at 1500 °C which had a high porosity of 73.7%, a proper compressive strength of 3.05 MPa, a low thermal conductivity of 0.287 W/(mK) (1000 °C) and a positive reheating linear change. Based on the experimental dates, an emendatory GE model was presented, which could predict accurately the effective thermal conductivity at 1000 °C of the mullite-corundum foamed ceramics with different pore characteristics.