A method for measuring the high temperature emittance of refractory metal surfaces

Abstract For high temperature applications, such as lighting components or heating elements, the thermal emittance of refractory metals such as tungsten can be improved by altering the surface of the material. Laser structuring or porous sintered coatings have been shown to increase the emittance, which leads to improvements in process stability and component lifetime. Measuring the emittance is generally performed at room temperature by reflectometry as high temperature measurement is extremely difficult. This has to be taken into account when comparing surface modifications, as emittance at application temperature might differ. In this paper, a method is described with which samples are heated by a direct current flow and the emittance is measured with an optical pyrometer by comparing temperature values with the actual surface temperature. The method allows a comparative measurement of different surface treatments at the application temperature. Degradation of the surface emittance at the application temperature is also possible to observe. Measured values for tungsten with different surface modifications are shown and discussed.