Spectral-directional emittance of oxidized copper

Abstract

The surface emittance of fully oxidized copper is experimentally determined as functions of wavelength between 2-10 /tin, the direction between the normal and grazing angles, and the temperature between 400-700°C. Clean copper surfaces, heated and exposed to air, begin to oxidize immediately. After a sufficient heating time, the oxide layer becomes thick enough that the radiative surface properties are those of copper oxide, independent of the properties of the underlying copper. The experimental apparatus measures emitted flux over discrete bands of wavelength and solid angles centered about a direction, and is calibrated with a radiating cavity (hohlraum). Emittance results are presented in both spectral and polar form, and also integrated to obtain the spectral-hemispherical emittance of fully oxidized copper. By assuming copper oxide to be a dielectric, the real part of the index of refraction is reduced from emittance data. This index is found to decrease with wavelength and temperature. This technique of spectral-directional emittance determination by direct emission measurement, together with index of diffraction identification (if found to fit Fresnel or other relations), should prove useful for other engineering materials as well as copper oxide.