Synchrotron x-ray μ-tomography to model the thermal radiative properties of an opaque ceramic coating at T = 1000 K

Synchrotron x-ray μ-tomography has been used to reconstruct the three-dimensional view of a rough surface extracted from a heterogeneous ceramic coating composed of Pr₂NiO_4+δ. Radiographs with a resolution of 0.7 μm have been recorded at T = 300, 600, and 900 K. The analysis of surface geometry makes use of the geometrical optic approximation up to T = 900 K possible. Subsequently, a large number of rays (10⁵) are impinged onto the numerical surface, as revealed by x-ray tomography, to reproduce the normal emissivity of the coating. This normal emissivity was obtained beforehand by infrared emittance spectroscopy at T = 1000 K. Comparison of the two approaches suggests that the optical contribution of the coating micropores can be integrated into the ray tracing code. The effective medium approximation is used for this purpose. Finally, the applicability of this hybrid approach is discussed.