Normal Spectral Emissivity of Liquid Copper and Liquid Silver at 684.5 nm

摘要

Up to now temperature measurements on pulse-heated liquid metal samples reported by different authors have always been performed under the assumption of a constant emissivity in the whole liquid phase because of the lack of data for the liquid metals. The emissivity for most metals is known at the melting point and it is also known that large changes in specific volume occur between the melting point and maximum experimental temperatures. Since electronic structures, optical properties, and emissivities have a large dependence on the electron density of a material, it follows that the emissivity of the liquid cannot be assumed to be constant and equal to the value at the melting point a priori. The key innovation which removes the ambiguity present in all previous measurements is that uncertainty in temperatures is eliminated by the direct measurement of material optical properties and emissivities for the first time during the experiments. Normal spectral emissivity measurements at 684.5 nm have been successfully established by linking a laser polarimetry technique to our high speed measurements of thermophysical properties on liquid metal samples during microsecond pulse-heating experiments. This work presents results of these measurements on copper (Cu) and silver (Ag) from melting up into the liquid phase and compares them with literature data. Both materials have been chosen for investigation because their melting points are very accurately known, due to their use as temperature fixed points in the ITS-90.