Directional emissivity characteristics of yttria-stabilised zirconia thermal barrier coatings

Abstract The use of infrared (IR) thermography techniques is increasingly common in gas turbine research. A current area of interest, for example, is the assessment of component overall cooling effectiveness using IR full-surface temperature measurements. To achieve high accuracy in such experiments, it is necessary to know the emissivity characteristics of the surfaces under test. For many surfaces, there is high view-angle dependence of emissivity for observation angles above 55°. Two common surface types used in gas turbine experiments are thermal barrier coatings (TBCs) and high-emissivity paint. In this paper, we present experimental measurements of the directional emissivity characteristics for a range of yttria-stabilised zirconia (YSZ) TBC samples, and a range of high-emissivity paints sprayed onto a smoother metal (copper) surface (as used for in-situ calibration assemblies). TBC samples were taken from engine parts. Semi-physical curve fits to the data are explicitly provided. The purpose of this study is to provide accurate directional emissivity characteristics that can be used by the experimental community.