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Emissivity measurements for Nextel Velvet Coating 811-21 between -36 °C and 82 °C
Eric Tang Kwor, Simone Matteï

Emissivity measurements on Nextel Velvet Coating 811-21 between -36 °C and 82 °C are presented. The method used is a periodic one. This method involves sample temperature modulation and signal processing of the sample temperature and the output signal of an infrared detector facing the sample. The Fourier transform at the modulation frequency of the infrared signal is proportional to the emissivity and to the Fourier transform of the temperature raised to the fourth power. As with ordinary methods, two measurements are necessary to obtain the emissivity: one on the sample and the other on a reference. Instead of a cold reference, the hemisphere method has been employed. The sample is glued onto a modulated sample-holder, the mean temperature of which can be chosen between -36 °C and 82 °C. This sample and the optical detection system are placed in a vacuum chamber. The pressure inside the chamber is less than 10-6 mbar. At each temperature, ten measurements have been carried out. The accuracy obtained is better than 1%. The emissivity of the coating studied remains constant over the temperature range explored. This coating can be employed as a reference in this temperature range. The values obtained are consistent with values from the literature.

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