Effective medium theory and the thermal conductivity of plasma-sprayed ceramic coatings

The thermal diffusivity of plasma-sprayed zirconium oxide-7% yttrium oxide and aluminium oxide-3% titanium oxide ceramic coatings was measured by using a periodic heat-flow method. Samples with different porosities allowed the thermal diffusivity as a function of porosity to be determined. The effect on thermal diffusivity of replacing air with silicone oil in the pores was determined. The experimental results were compared with effective medium theories representing three different microstructures: (1) a continuous ceramic matrix with dispersed pores, (2) a continuous ceramic matrix with continuously interconnected pores, (3) dispersed ceramic particles loosely bonded together. The latter two microstructures gave the best agreement between experimental data and theory. 21 refs.