A Spectral Emissivity Measurement Apparatus Based On The Grating Monochromator

In this article, a spectral emissivity measuring system, which can perform accurate measurements of material emissivity, is designed based on the energy method by using grating monochromator. The spectral emissivity of two common metals: aluminum and copper is system investigated. In Chapters one we give a brief introduction of this research background, meanings and important applications of material emissivity. A summary of emissivity measurement methods and the comparison of these measurement methods are also presented in the final section of this chapter. In Chapters two, the thermal radiation theories and the basic definitions of the emissivity are shown.Chapter three shows the detail introduction of the emissivity measuring system. It is composed of five parts as follows: sample heating and temperature control system, blackbody furnace, grating monochromator, lock-in amplifier and chopper, off-axis parabolic gold-coated mirror and motorized rotation stage. This system can measure spectral emissivity of opaque solid materials at temperatures between 300 K and 1073 K and spectral range from 0.8μm to 2.2μm, in addition, spectral range can be extended by replacing grating and detector. In addition, the principle of this emissivity measurement system is analyzed and the influences of possible factors on the spectral emissivity were discussed. At last, the measuring formulas of this system is presented.Chapter four presents the spectral emissivity results of pure aluminum and aluminum alloy. The spectral emissivity of pure aluminum 1060 is system measured by using this emissivity measuring system with the temperatures range from 300 up to 873 K and the spectral range between 0.8 and 2.2μm. The results show: for an unoxidized surface of pure aluminum under the argon environment, its emissivity decreases slowly with the increase of wavelength and increases with the rise of temperature. The emissivity of an oxidized metal surface is mainly dependent on the thickness of oxide film on its surface. The growth of oxide film accords with a parabolic relationship to oxidation time. The interference effect may occur when the oxide film reaches a certain extent. Additionally, emissivity of aluminum alloy Al5052 at the wavelength of 1.55μm is measured by the other emissivity measuring apparatus in our laboratory, which is based on the reflection emissivity measurement method.Chapter five presents the spectral emissivity results of red copper and brass. The spectral emissivity of brass and red copper are investigated systematically with the temperatures range from 300 up to 1123 K by using the reflection emissivity measuring apparatus and the influences of temperature, oxidation and heating time on the spectral emissivity of two kinds of specimens are also discussed. The experimental data show the spectral emissivity increases with increase of temperature and appears its peak value and valley value when the thickness of oxide film is at some degree. The formula for calculating the thickness of oxide film is derived from the reflection model composed of a metal and oxide film, then the peak and valley thickness of the red copper are estimated according to this model. The experimental data of constant temperature measurements show that the spectral emissivity has a slight increase with increase of heating time and the values of spectral emissivity at high temperatures are always larger than that of low temperatures.