Spectral emissivities in the visible and infrared of liquid Zr, Ni, and nickel-based binary alloys

This article reports: (i) values of the spectral emissivities at lambda=0.633 mu m for liquid Zr, Ni, Ni-25% Sn, Ni-32.5% Sn, Ni-40% Nb, and Ni-75% Zr over a wide temperature range including undercooled and superheated conditions, (ii) experimentally determined infrared radiance temperatures (effective center wavelength about 2.0 mu m) as functions of true temperature, and (iii) derived values of the spectral emissivity of these liquid materials in the infrared. Based on the thermal arrest, which occurs upon heating the solid at the melting point, we also report melting points for some of the alloys. For zirconium, temperature dependence of emissivity is reported at other wavelengths in the visible. For Ni-75% Zr, the emissivity dependence on wavelength was determined and compared with previously reported results for liquid zirconium and nickel. The spectral emissivity measurements were obtained using pulsed-dye laser ellipsometry on electromagnetically levitated liquid metals and the radiance temperatures of the specimens were recorded using three pyrometers. Two of these pyrometers had an operating wavelength near 650 nm. The third pyrometer had an operating wavelength range of 1-2.5 mu m. Most of the materials studied exhibited moderate temperature dependence of the optical properties and emissivities. Only nickel and zirconium could be undercooled significantly in our apparatus. The infrared and 0.633 mu m emissivities of the materials were consistent with the behavior of a typical metal showing emissivity variations with wavelength on the order of -0.07 mu m(-1). (C) 1996 American Institute of Physics.