Emissivity Measurement of Liquid Metals and Alloys using Cold Crucible

将传统的电阻炉与光学系统相结合，构建了发射率测量装置。发射率被导出为在与样品相同的温度下来自样品的辐射强度与来自黑体的辐射强度的比率。在熔点以上的近红外区域（900 nm-1400 nm）测量液态铜的发射率。测量值约为0.55，与波长无关。这些值比以前报道的值大得多，这是由于炉壁辐射和坩埚样品污染的两个影响。为了避免这些问题，将炉更换为冷坩埚。在熔点下，在可见光区（550 nm-750 nm）测量固体和液体铜的发射率。固体的Escore值在0.25和0.06之间，液体的Escore值在0.30和0.10之间，并且在这两种状态下，随着波长的增加，Escore值急剧下降。大多数文献的测定值都在本研究所记录的固态铜和液态铜的测定值之间，从而证实了本装置的合理性。此外，固体和液体贵金属（金，银和铜）的发射率在近红外区域（1000 nm-2500 nm）在熔点测量。固态铜的值在0.043和0.033之间，液态铜的值在0.076和0.060之间。在每种金属中，液态时的发射率较大，并随着波长的增加而逐渐减小。可以得出结论，液态金属通过四种机制发射光，即，电子-声子、电子-电子和电子-表面散射以及带间跃迁。基于这些机理建立的模型可以描述测量的发射率值。此外，本研究所建构之发射率量测装置亦可应用于其他金属及合金。

The apparatus for the emissivity measurement was constructed, where a conventional resistance furnace was combined with the optical system. The emissivity was derived as the ratio of the radiation intensity from the sample to that from the blackbody at the same temperature as the sample. The emissivity of liquid copper was measured in the near-infrared region (900 nm-1400 nm) just above the melting point. Measured values were about 0.55, irrespective of wavelength. These values are much larger than those reported previously, which is due to two effects of the radiation from the furnace wall and of the contamination of the samples from the crucibles.To avoid these problems, the furnace was replaced with the cold crucible. The emissivity of solid and liquid copper was measured in the visible region (550 nm-750 nm) at the melting point. Emissivity values for the solid range between 0.25 and 0.06, those for the liquid between 0.30 and 0.10 and, in both states, the values decrease drastically as wavelength increases. Most of published values fall between the values for solid and liquid copper recorded in this study, from which the reasonability of the apparatus has been confirmed. Furthermore, the emissivity of solid and liquid noble metals (gold, silver and copper) was measured in the near-infrared region (1000 nm-2500 nm) at the melting point. Values for solid copper lie between 0.043 and 0.033, those for liquid copper between 0.076 and 0.060. In each metal, the emissivity is greater in the liquid state and decreases progressively as wavelength increases.It has been concluded that light is emitted from liquid metals via four mechanisms, viz., the electron-phonon, electron-electron and electron-surface scatterings and the interband transition. The model developed based upon these mechanisms can describe the measured emissivity values. In addition, the apparatus for the emissivity measurement constructed in this study can also be applied to other metals and alloys.