Thermal conductivity of highly porous mullite materials

The thermal conductivity of highly porous mullite materials (from 72 to 86 vol% porosity) has been measured by the transient plane source (TPS) technique at room temperature. These materials were fabricated by foaming and starch consolidation and showed similar microstructures with different porosities. From the point of view of heat conduction, these materials can be considered as a two-phase system, viz. a dense mullite skeleton and air, and their thermal conductivities describe heat transfer through these composite materials. Through comparing experimental data and predicted values derived from theoretical models, these materials can be classified as “internal porosity” materials and their thermal conductivities are bounded between the Maxwell–Eucken 1 model and the effective medium theory (EMT) equation. Then the porosity dependence of thermal conductivity was modeled by a simple model which assumes that components were contained in a uniform medium with thermal conductivity km.