Fabrication, Properties and Nonlinear Thermal Conductivity Model of Highly Porous Mullite Ceramics

Highly porous mullite ceramics were prepared by bauxite and silica fume as raw materials and corn starch as the pore-forming agent. The phase and morphology were characterized by XRD and SEM, respectively. The influence of corn starch content on apparent porosity, bulk density and flexural strength were studied. Thermal conductivity of porous mullite was measured at 473-1273 K. A new nonlinear thermal conductivity model and several models between bulk density, flexural strength and apparent porosity were established. The results indicate that, bulk density and flexural strength of porous mullite decrease with porosity increase and conform to the exponential function relationship. Thermal conductivity of porous mullite increases with the rise of temperature and the measured values are in good agreement with values calculated by nonlinear thermal conductivity model. The new model can accurately reflect the thermal conductivity correlations for temperature, porosity, radiation and mean pore size.