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Determination of Scattering and Absorption Coefficients for Plasma-Sprayed Yttria-Stabilized Zirconia Thermal Barrier Coatings at Elevated TemperaturesThe temperature dependence of the scattering and absorption coefficients for a set of freestanding plasma-sprayed 8 wt% yttria-stabilized zirconia (8YSZ) thermal barrier coatings (TBCs) was determined at temperatures up to 1360 C in a wavelength range from 1.2 micrometers up to the 8YSZ absorption edge. The scattering and absorption coefficients were determined by fitting the directional-hemispherical reflectance and transmittance values calculated by a four-flux Kubelka Munk method to the experimentally measured hemispherical-directional reflectance and transmittance values obtained for five 8YSZ thicknesses. The scattering coefficient exhibited a continuous decrease with increasing wavelength and showed no significant temperature dependence. The scattering is primarily attributed to the relatively temperature-insensitive refractive index mismatch between the 8YSZ and its internal voids. The absorption coefficient was very low (less than 1 per centimeter) at wavelengths between 2 micrometers and the absorption edge and showed a definite temperature dependence that consisted of a shift of the absorption edge to shorter wavelengths and an increase in the weak absorption below the absorption edge with increasing temperature. The shift in the absorption edge with temperature is attributed to strongly temperature-dependent multiphonon absorption. While TBC hemispherical transmittance beyond the absorption edge can be predicted by a simple exponential decrease with thickness, below the absorption edge, typical TBC thicknesses are well below the thickness range where a simple exponential decrease in hemispherical transmittance with TBC thickness is expected. [Correction added after online publication August 11, 2009: "edge to a shorter wavelengths" has been updated as edge to shorter wavelengths."]
Document ID
20120012834
Document Type
Reprint (Version printed in journal)
Authors
Eldridge, Jeffrey I. (NASA Glenn Research Center Cleveland, OH, United States)
Spuckler, Charles M. (NASA Glenn Research Center Cleveland, OH, United States)
Markham, James R. (Advanced Fuel Research, Inc. East Hartford, CT, United States)
Date Acquired
August 26, 2013
Publication Date
October 1, 2009
Publication Information
Publication: Journal of the American Ceramics Society
Volume: 92
Issue: 10
Subject Category
Plasma Physics
Report/Patent Number
E-18246
Funding Number(s)
WBS: WBS 561581.02.08.03.15.03
Distribution Limits
Public
Copyright
Other