Fabrication, characterization and thermal-insulation modeling of foamed mullite-SiC ceramics

Abstract Foamed mullite-SiC ceramics were prepared by using white clay, industrial alumina and silicon powder as raw materials. The effects of the clay content on the phase composition, microstructure and thermal properties of foamed ceramics were investigated by X-ray diffractometer (XRD), scanning electron microscopy (SEM) and energy dispersive spectrometer (EDS). The fired foamed mullite-SiC ceramics contained mullite, corundum and β-SiC. With an increase of clay content, the apparent porosity decreased, while the compressive strength and thermal conductivity increased. The optimized composition had a clay content of 44 wt% clay, which yield a high porosity of 72.9%, an excellent compressive strength of 5.6 MPa and a low thermal conductivity of only 0.267 W/(m·K). An adjusted GE thermal conductivity model assuming an appropriate emissivity of 0.35 was highly capable to predict the effective thermal conductivities of the foamed mullite-SiC ceramics with different pore characteristics at 800 °C.