Infrared Directional Spectral Emissivity of Tungsten-Copper Alloy in the 400–700 ℃ Temperature Range

The tungsten-copper alloy is commonly used for the electrical contact in high current vacuum switch, where precise temperature monitoring of the contact is crucial for ensuring stable operation of the switch by radiation thermometry. However, accurate emissivity data of this alloy is necessary when using radiation thermometry for temperature measurement. Thus, the directional spectral emissivity of tungsten-copper alloy is investigated within the temperature range of 400–700 ℃ under vacuum in this work. The hemispherical total emissivity is calculated by numerically integrating the directional spectral emissivity. Experimental results found this tungsten-copper alloy agrees with the theoretical prediction of the electromagnetic theory, that is, the emissivity increases with increasing temperature, and decreases with increasing wavelength. A convergence phenomenon of spectral emissivity occurs when the polar angle exceeds approximately 50°. This means that the normal wavelength dependence undergoes a shift at high polar angles, which is typical behavior of metallic emissivity. Additionally, the effects of thermal cycle, surface roughness, and chemical composition on emissivity are analyzed in detail. Surface stress relaxation process results in a significant decrease in emissivity. Emissivity increases as the surface roughness and tungsten composition of alloy increases. However, the effects of surface roughness and chemical composition on emissivity gradually disappear at long wavelengths and high polar angles.