In this paper the radiative properties of air plasma sprayed (APS) thermal barrier coatings are investigated by measuring the spectral diffuse reflectance and transmittance of samples with various thickness and porosities in a broad spectral band ranging from 0.25 to 15μm. The spectral absorption and scattering coefficients are obtained by a four flux model based on the experimental data. The results show that the porous zirconia ceramics exhibits high scattering coefficient (> 15000 m−1) and low absorption coefficient (< 500 m−1) in the spectral range from 0.5 to 6μm, and the corresponding spectral scattering albedo reaches up to 0.99. In addition, this study also found that the spectral scattering coefficient increases with increasing porosity, while the spectral absorption coefficient is not quite sensitive to the change of porosity. This result confirms the fact that scattering is mainly caused by the refractive index mismatch between bulk YSZ and internal void. Spectral scattering coefficient heavily depends on the microstructures of coatings, i.e., pore size, porosity and pore distribution, and this will in turn considerably affect the thermal radiation heat transfer inside the coating.

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