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This paper presents the development of instrumentation for the measurement ofhigh-temperature thermal conductivity of bulk and coatings using a modulatedphotothermal radiometry (MPR) method, where a sample is heated by anintensity-modulated laser to probe into different layers of the sample. WhileMPR has been previously established, most of the previous studies only focus onthe measurement at room temperature. The MPR has not been well studied formeasurements of bulk and coating materials at high temperatures, which areincreasingly important for a multitude of applications, such as materials usedin the concentrating solar power (CSP) plants and the nuclear reactors. MPR isa non-contact technique that utilizes the intrinsic thermal emission from thespecimens for thermometry, which is favorable for measurements at hightemperatures in harsh environment. The authors designed and utilized a sampleholder suitable for high temperature measurement up to 973 K with goodtemperature uniformity within the sample. The high-temperature MPR setup wasvalidated by measuring bulk materials with known thermal conductivity. Thesetup and technique were then extended to the measurement of blacksolar-absorbing coatings of 10 to 50 {\mu}m thick on various substrates bymodulating the frequency of the laser heating beam and the thermal penetrationdepth. The studies showed that thermal conductivities of typicalsolar-absorbing coatings are 0.4 ~ 0.8 W m-1 K-1, indicating a possibly largetemperature drop within the coating under high solar irradiation flux, such asover 1000-sun for central solar towers in CSP plants.

Measurement of High-temperature Thermophysical Properties of Bulk and Coatings Using Modulated Photothermal Radiometry