New apparatus for measurement of the spectral, angular, and total emissivity of solids

An apparatus is being developed at NPL to measure the emissivity of solids over the temperature range 150 to 1800 °C, wavelengths 0.6 to 9.6 μm, and angles to the normal of up to 70°, by a transient technique to ensure accurate measurement of the sample surface temperature. The main features of the apparatus are described. A Fourier-transform spectrometer is used, allowing emissivity measurements with high spectral resolution, from which total angular emissivity values can be calculated. Results of emissivity measurement are presented for polished tantalum, Fecralloy steel, boron nitride, and graphite specimens at temperatures up to 1300 °C.