THERMAL-CONDUCTIVITY, DEGREE OF TOTAL EMI SSIVITY AND SPECTRAL EMISSIVITY OF THE NEXTEL-VELVET COATING-811-21 (RAL-900-15 DARK BLACK FLAT)

Thermal conductivity and emissivity were determined in the temperature range between 30 degrees C and 120 degrees C (conductivity), between - 60 degrees C and 150 degrees C (total emissivity), and between 90 de grees C and 150 degrees C (spectral emissivity) for the Nextel Velvet 811-21 coating. The very high total emissivity of epsilon(n)=0,97, whi ch, in the temperature range investigated does not depend on temperatu re and wavelength makes such a coating a suitable reference material. As the deviation of the angular distribution of the emissivity from th e ideal Lambertian distribution is small, a sample with such a coating can in many cases replace a blackbody cavity. Within the measurement uncertainty there was good agreement between the values of the total e missivity determined directly and those determined from the spectral v alues.