Emissivity Measurement of Liquid Metals and Alloys using Cold Crucible

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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.