Abstract
Zirconium oxide (ZrO2) is widely used as the thermal barrier coating in turbines and engines. Accurate emissivity measurement of ZrO2 coating at high temperatures, especially above 1000 °C, plays a vital role in thermal modelling and radiation thermometry. However, it is an extremely challenging enterprise, and very few high temperature emissivity results with rigorously estimated uncertainties have been published to date. The key issue for accurately measuring the high temperature emissivity is maintaining a hot surface without reflection from the hot environment, and avoiding passive or active oxidation of material, which will modify the emissivity. In this paper, a novel modified integrated blackbody method is reported to measure the high temperature normal spectral emissivity of ZrO2 coating in the temperature range 1000 °C to 1200 °C and spectral range 8 μm to 14 μm. The results and the associated uncertainty of the measurement were estimated and a relative standard uncertainty better than 7% (k = 2) is achieved.
Highlights
Thermal barrier coating materials capable of withstanding extreme temperatures are continually being developed for the generation of gas turbines
Previous emissivity measurement results reported by some major national measurement research institutions, such as the National Institute of Standards and Technology (NIST) [2], the National Physical Laboratory (NPL) [3], the NASA Langley Research Center [4], the Laboratoire Commun de Métrologie (LNE-Cnam) [5], the PhysikalischTechnische Bundesanstalt (PTB) [6], the National Institute of Metrology (NIM) [7], were mainly focused on the mid-temperature range, i.e., below 1000 ◦C
The relative combined standard uncertainties of the ZrO2 coating artefacts at both the temperatures of 1000 ◦C and 1200 ◦C are less than 3.5% (k = 1) and the corresponding relative expanded uncertainties are less than 7% (k = 2)
Summary
Thermal barrier coating materials capable of withstanding extreme temperatures are continually being developed for the generation of gas turbines. The former method can cause a temperature gradient inside the sample, leading to a poor uniformity of the sample surface temperature In the latter method, one needs to consider the influence of the cavity effect formed by coupling between the heat pipe and the sample coupling. One needs to consider the influence of the cavity effect formed by coupling between the heat pipe and the sample coupling Another difficulty of the above studies lies in the measurement of the true temperatures of the sample surface, which is usually estimated directly by radiation temperature measurement or contact temperature measurement. These contributions rise at higher temperature, becoming the primary cause for the measurement uncertainty
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