Abstract

Surface oxidation can dramatically change the spectral emissivity of a metallic surface that is maintained at an elevated temperature over a period of time. Many kinds of metallic specimens, in particular for steel in use in industrial conditions, are usually heated in an oxidizing environment at high temperatures for a relatively long time. For this reason, in this paper, the SPHC steel was chosen as the specimen to investigate the effect on the spectral emissivity by surface oxidization over the temperature range from 800 K to 1000 K. The experimental setup for the spectral emissivity measurement operates at a wavelength of \(1.5\,\upmu \)m with a bandwidth of 20 nm. The temperature of the sample surface is determined by averaging two R-type platinum–rhodium thermocouples. The radiant energy from the surface of the SPHC specimen is received by an infrared detector. On the one hand, it is found in a detailed study that the spectral emissivity varies as the temperature for a given heating time; on the other hand, it was investigated that the spectral emissivity varies as the heating time at a given temperature. We find that the relationship between the spectral emissivity and the temperature can still be fitted to an exponential function by the least-squares method. The peculiar behavior of the spectral emissivity is discussed at an early stage when the oxidation film on the surface of the SPHC sample is grown. The conclusion is drawn that the contribution to the spectral emissivity by the surface oxidation mainly comes from the oxidation growth during the first 3 h.

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