Investigation of the monochromatic emissivity of liquid copper

The monochromatic normal emissivity of copper at a wavelength of $0.656$ mem is experimentally investigated in the temperature range from $1300$ to $1700$ K. The experimental data are obtained for samples of different purity, which are indicative of the influence of the chemical composition of metal on its emissivity in the molten state. A change in the emissivity is found during the transition of metal from the solid phase into the liquid one. It is shown that the model including the effect of the relaxation time of free electrons of metal produces the best agreement with the experiment in the liquid phase.