Normal and Directional Spectral Emittance Measurement of Semi-Transparent Materials Using Two-Substrate Method: Alumina

The normal and directional spectral emittance of alumina is measured using a Fourier transform infrared spectrometer. A new measurement method, called the two-substrate method, is developed to measure infrared optical properties of semi-transparent materials, which comes over the limitations of the substrate heating method. The uncertainty of the emittance is evaluated with the calibration method (black surroundings), phase correction, temperature measurement, background radiation reflection by the sample surface, and the size-of-source effect. The maximum relative combined relative uncertainty (k = 1) is less than 4.3 % at 4 mu m, and the minimum value is less than 0.57 % at 10 mu m in the case of an alumina sample at 300 A degrees C. The directional spectral emissivity of alumina is successfully measured in semi-transparent and opaque regions, showing a typical behavior of dielectric materials.