| Emissivity is an important thermophysical parameter that measures the ability of a given surface to emit thermal radiation.It is a non-negligible physical quantity in many technical applications and scientific research fields,such as radiation temperature measurement technology,high-temperature coating technology,photovoltaic applications and thermal radiation heat transfer technology.In addition,it also has the vital research significance and application value in the aerospace,military and civil fields,such as real-time monitoring for the temperature field of aero-engine turbine blades,infrared guidance and stealth technology,and infrared heating technology.However,the emissivity is greatly affected by many factors such as temperature,wavelength,surface roughness,and surface oxidation,the data of material emissivity at high temperatures is serious lacking.Therefore,researches need to carry out more work to determine the emissivity value and improve the measurement accuracy.In this paper,based on multi-temperature calibration method,a set of spectral emissivity measurement device with a temperature range of 673-1173 K and a wavelength range of 2-27 μm is built,which mainly includes a Fourier transform infrared spectrometer,sample heating furnace,reference blackbody and optical system.In order to improve the accuracy of emissivity measurement results,the multi-temperature calibration method is used to calibrate the response function,and the emissivity value is determined by the improved method with eliminating background radiation interference.Firstly,the comparing results of the response function obtained by the dual-temperature calibration and the multi-temperature calibration show that the accuracy of the response function is close to the result obtained by the multi-temperature calibration method when the blackbody radiation signal with a large enough temperature difference is used for dual-temperature calibration.Secondly,the linearity of the detector is tested,and the results indicate that the radiation intensity at each wavelength is uniformly distributed on the fitting curve.The residual distribution of fitting results is analyzed,the residual values of the fitting curve are within 0.12,which has low dispersion.Finally,the spectral emissivity data reported in the literatures is compared with the measurement results of Si C sample at different temperatures（673 K,873 K,and 1073 K）.The relative combined uncertainty of emissivity at temperatures of 673 K and 1073 K is further evaluated,the results of which demonstrate the reliability of the measuring device.Based on the emissivity measurement device built in the article,the spectral emissivity of red copper,brass and cupronickel in argon atmosphere and oxidation environment is measured.The results show that the spectral emissivity of three copper samples under argon atmosphere has a similar trend increasing as the temperature increases and decreasing as the wavelength increases.By comparing the spectral emissivity of three copper samples under argon atmosphere,it is found that the difference of the sample composition and content has a great influence on the spectral emissivity.In addition,the oxidation of the samples caused significant changes in the infrared radiation characteristics of the surface by analyzing the spectral emissivity of the three copper samples before and after oxidation.During the oxidation process,by comparing the oxidation temperature of three copper samples,it is found that the red copper is the lowest,while the cupronickel is the highest.Finally,the effects of temperature,wavelength,oxidation and heating time on the spectral emissivity are further studied,explaining that the spectral emissivity oscillates due to interference effects at short wavelengths,while it is caused by oxide lattice oscillations at long wavelengths.The mathematical model of emissivity versus heating time effectively reduces the uncertainty of emissivity caused by fluctuations in the surface temperature of the sample. |
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