Discontinuity in normal spectral emissivity of solid and liquid copper at the melting point

Abstract

Normal spectral emissivities for solid (ε ,solid ) and liquid (ε ,liquid ) copper at the melting point have been determined, and the discontinuity in ε ,liquid and ε ,solid at the melting point has been discussed. The spectral emissivity was determined by comparing the spectral radiation intensity of the sample to that of the fixed-point blackbody over the wavelength range 550 to 750 nm. The samples and fixed-point blackbody were heated in the continuous casting type cold crucible. Values of ε ,liquid and ε ,solid at 650 nm were 0.167 and 0.108, respectively. The emissivity ratio of ε ,liquid /ε ,solid increased from approximately 1.2 to 1.8 as the wavelength increased in the range 550 to 750 nm. The discontinuity in ε ,liquid and ε ,solid at the melting point has been qualitatively explained by the optical absorption mechanism due to the intraband transition.

Numerical Simulation of Laser Fusion Zone Profile of Lotus-Type Porous Metals

“…The reason is considered as follows; the laser beam mostly reflects on the copper surface due to the high reflectivity of copper, about 95% at room temperature. 41,42) In the perpen- dicular direction, a part of laser beam deeply penetrates into open pores because the growth direction of original pore nearly equals to the incident direction of the laser. In this case, the multiple reflections of the laser beam along the pore wall side extraordinarily increase the absorbable laser power.…”

Temperature and compositional dependencies of normal spectral emissivities at 632.8 nm for solid Cu-Ni alloys—Ellipsometric measurements and formulation of empirical prediction equation

“…In copper, for example, the decrease in wavelength to about 600 nm produces a slight increase in the emissivity but a further decrease causes a very steep increase. [9] By contrast with the DOS for copper, this wavelength dependence of the emissivity suggests that the excitation-relaxation process of free electrons dominates the emissivity at wavelengths higher than about 600 nm, whereas the contribution from the process of inner shell electrons, i.e., electrons at the d-like levels (d-electrons) joins at lower wavelengths.…”

“…Most previous attempts have focused mainly on pure metals and semiconductors such as copper, [4][5][6][7][8][9][10][11] Ag, [4,5,[10][11][12] Au, [5,6,10,11,13] nickel, [5,7,14] Co, [5,7,14] Fe, [5,7,14,15] Ge, [17,18,19] Si, [16,17,[19][20][21][22][23] etc. Furthermore, radiation mechanisms of these pure materials have been discussed from the wavelength dependence of the emissivities, which is a reflection of the electronic structure (density of states (DOS) of electrons) for the metals at high temperature.…”

“…However, emissivity data obtained in such a way have the possibility of being contaminated by the stray radiation from the surroundings of the sample. Watanabe et al [9][10][11]14,16] have overcome this problem using a continuous casting type cold crucible for heating the sample and the blackbody and have successfully measured the emissivities of solid and liquid copper, Ag, Au, Fe, Co, nickel, Ge, and Si at the melting point. In this method, a sample is heated inductively but its surroundings (copper segments) are water cooled; therefore, only the sample is heated and makes thermal radiation.…”

“…However, this method is not suitable for measurements on solid materials since it is very difficult to control the temperature of the cold crucible at the lower temperature range. Because of this difficulty, the conventional measurements by this method [9][10][11]14,16,29] have been limited only to temperatures above the melting points or liquidus temperatures of the samples.…”