纯钨红外光谱发射率特性研究

光谱发射率是一个重要的热物性参数,在辐射测温、热传输计算等领域有着广泛的应用。钨作为一种重要的金属,关于其光谱发射率的研究报道较少。利用黑体炉、傅里叶红外光谱仪、加热装置和光学系统搭建了一套能量对比法光谱发射率测量装置,该装置能够测量3~20μm的光谱发射率,测量装置的整体不确定度优于5%。利用该装置测量了纯钨在4个温度点(573, 673, 773和873 K)的法向光谱发射率,重点探讨了氧化、温度、波长和加热时间对纯钨光谱发射率的影响。研究结果表明:纯钨在表面未氧化的情况下,光谱发射率在几个温度点的变化规律基本一致,且数值相差较小,而当其表面发生氧化后光谱发射率迅速增加,在某些波长处出现了强烈的振荡。表面未氧化时纯钨的光谱发射率受温度的影响较小,随着温度的增加仅出现微小的增加,但是当表面发生氧化后,随温度的升高而迅速增大。纯钨的光谱发射率整体上随着波长的增加而减小,但是当表面发生氧化后,由于表面氧化膜与钨金属基底发生干涉效应,在4, 9, 12.5和16.5μm处均出现了峰值。在573和673 K,纯钨的光谱发射率随着加热时间的增加无明显变化。然而,随着温度的升高,在773和873 K时,光谱发射率随着加热时间增加而增大,在773 K时光谱发射率随加热时间的增加增幅较大,因为在该温度点,纯钨表面刚开始发生氧化,氧化速率较大,在873 K时光谱发射率随加热时间的增加增幅较为平缓,并且随着加热时间的增长呈现稳定的趋势。综上,纯钨的光谱发射率在温度较低和表面未氧化时较为稳定。随着温度的升高,当表面发生氧化后,光谱发射率迅速增大,并且在多个波长位置出现了强烈的振荡。由此可见,纯钨光谱发射率受温度、波长、加热时间的影响较大,在实际应用过程中,特别是在辐射测温过程中,如果把纯钨的光谱发射率看做常数将会带来较大的测量误差。该研究将进一步丰富钨的光谱发射率数据,并为其在科学研究和应用中提供数据支持。

Experimental Investigation of Infrared Spectral Emissivity of Pure Tungsten

Spectral emissivity can be considered as a surface thermal physical property of materials, which is widely applied in radiation thermometry, heat transfer calculation and so on. Tungsten is a significant metal, but its spectral emissivity is rarely reported. Based on energy contrast method, a device measuring spectral emissivity is built, which is composed of four parts: standard reference blackbody, a Fourier transform infrared(FTIR) spectrometer, sample heating chamber, and optical system. This device can measure the spectral emissivity of samples in the wavelength range of 3~20 μm, and the overall uncertainty of this apparatus is better than 5%. The normal spectral emissivity of pure tungsten is measured by this device at four temperatures(573, 673, 773, 873 K), and the effects of oxidation, temperature, wavelength and heating time on the normal spectral emissivity of pure tungsten are analyzed in detail. The results showed that the variations of the spectral emissivity of unoxidized pure tungsten at four different temperatures were basically similar, and the difference of these values was relatively small, however, the spectral emissivity rapidly increased when the sample was oxidized and the strong oscillations were found at some wavelengths. The effect of temperature on the spectral emissivity of pure tungsten was slight when the sample wasn’t oxidized, while the spectral emissivity rapidly increased with increasing temperature when the samples was oxidized. The spectral emissivity of pure tungsten decreased with increasing wavelength. When the surface of the sample was oxidized, four peaks appeared at 4, 9, 12.5 and 16.5 μm due to the interference effect between the oxide layer and the metal substrate. At 573 and 673 K, the spectral emissivity of pure tungsten does not change significantly with increasing heating time. However, as the temperature increased, the spectral emissivity increased with increasing heating time at 773 and 873 K. At 773 K, the rate of the spectral emissivity increasing with increasing heating is relatively fast, and the surface of pure tungsten begins to be oxidized with large oxidation rate. At 873 K, the increase of spectral emissivity with increasing heating time is relatively flat, and remains stable. In summary, the variation of spectral emissivity of pure tungsten is relatively stable at lower temperature and unoxidizedstate. As the temperature increases, the spectral emissivity increases rapidly and strong oscillation occurs at multiple wavelengths when the surface is oxidized. It can be seen that the spectral emissivity of pure tungsten is greatly affected by the heating time, temperature and wavelength. In practice, especially in radiation thermometry, if the spectral emissivity of pure tungsten is regarded as a constant, the measurement error will be large. This study will further enrich the data of spectral emissivity of pure tungsten, and provide reference for scientific research and applications.