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。发射率是样品与黑体在与样品相同温度下的辐射强度之比。在熔点上方的近红外区(900 nm-1400 nm)测量了液态铜的发射率。测量值约为0.55，与波长无关。这些值比以前报道的要大得多，这是由于炉壁辐射和坩埚样品污染的双重影响。为了避免这些问题，炉子被换成了冷坩埚。在熔点的可见光区(550 nm-750 nm)测量了固态和液态铜的发射率。固体的发射率值在0.25-0.06之间，液体的发射率值在0.30-0.10之间，在这两种状态下，发射率值都随着波长的增加而急剧下降。大多数公布的值都在本研究中记录的固体和液体铜的值之间，由此证实了该装置的合理性。此外，还测量了固体和液体贵金属(金、银和铜)在熔点的近红外区(1000 nm-2500 nm)的发射率。固态铜的值在0.043到0.033之间，液态铜的值在0.076到0.060之间。在每种金属中，发射率在液体状态下都较大，并随着波长的增加而逐渐减小。结果表明，液体金属的光是通过电子-声子、电子-电子和电子-表面散射以及带间跃迁四种机制发射的。基于这些机理建立的模型可以描述测量的发射率值。此外，本研究建立的发射率测量装置也适用于其他金属和合金。

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.