Modeling and Predicting the Effect of Surface Oxidation on the Normal Spectral Emissivity of Aluminum 5052 at 800 K to 910 K

Abstract

In this study, we tried to develop a model to predict the effect of surface oxidization on the normal spectral emissivity of aluminum 5052 at a temperature range of 800 to 910 K and wavelength of $1.5\,\upmu \hbox {m}$. In experiments, specimens were heated in air for 6 h at certain temperatures. Two platinum–rhodium thermocouples were symmetrically welded onto the front surface of the specimens near the measuring area for accurate monitoring of the temperature at the specimen surface. The temperatures measured by the two thermocouples had an uncertainty of 1 K. The normal spectral emissivity values were measured over the 6-h heating period at temperatures from 800 K to 910 K in increments of 10 K. Strong oscillations in the normal spectral emissivity were observed at each temperature. These oscillations were determined to form by the interference between the radiation stemming from the oxide layer and radiation from the substrate. The present measurements were compared with previous experimental results, and the variation in the normal spectral emissivity at given temperatures was evaluated. The uncertainty of the normal spectral emissivity caused only by the surface oxidization was found to be approximately 12.1 % to 21.8 %, and the corresponding uncertainty in the temperature caused only by the surface oxidization was approximately 9.1 K to 15.2 K. The model can reproduce the normal spectral emissivity well, including the strong oscillations that occur during the initial heating period.