Abstract
Emissivity is a fundamental thermos-physical property, defined as the ratio of emitted intensity from a real surface to an ideal surface (blackbody) at same temperature. Tailored emissivity, showing wavelength-selectivity or direction-dependence is important in energy-harvesting, optoelectronics, and thermal applications. In this study, a numerical model for obtaining optical constants using infrared emissivity spectra of different emission angles was successfully established. The numerical model was verified with thermal radiative properties of ZnS in the wavelength range between 8 um and 14 um. The other contribution of this study was to develop an automatic measurement system for high temperature directional emissivity. This system was composed of a blackbody oven, sample heater, optical elements, FTIR spectrometer and a LabVIEW user interface. The emissivity of sapphire, gold, iron, and SiC was used to verify the working range of measurement system from 400 K to 700 K in temperature, 0º to 60º in emission degree, and 4 μm to 25 μm in wavelength. Measurement results of directional emissivity agree well with those from numerical prediction. They are also consistent with results in the published references. The two contributions, the developed numerical model and automatic measurement system, show results supporting each other.Both can provide large beneifits to insightful investigation on radiative properties of materials at high temperatures as well as utilization of these properties.