Experimental setup for the determination of spectral normal emissivity of conductive materials in the 1–18 μm wavelength range at 300–1700 °C in air

This article describes the measurement procedure and data processing features of an apparatus for measuring the spectral emissivity of electrically conductive opaque materials in air. The developed laboratory setup has the following three main features: induction heating of the sample, correction in order to exclude the surrounding radiation reflected by the sample, and the use of multiwavelength pyrometry. Single-sided induction heating of the sample eliminates the contribution of stray radiation from the heating element to the recorded signal. The correction on surrounding radiation increases the accuracy of emissivity determination, especially at low temperatures. The multiwavelength pyrometry is used to obtain the true temperature of a sample. This technique makes it possible to obtain the surface temperature of the sample directly from its thermal radiation spectrum, allowing to examine the material during the oxidation process. The emissivity spectra of zirconium and hafnium diboride samples were measured with the created setup. The obtained spectra reveal several features, which correlate with chemical transformations on the surface of the materials during oxidation.