Normal spectral emissivitiy of Al-Ti liquid alloys

Abstract

The normal spectral emissivt of four compositions of the binary Al-Ti liquid alloy system is measured in dependence of the wavelength and the temperature T. Due to the increased chemical reactivity of liquid Ti, the investigated specimen are processed containerlessly in electromagnetic levitation. A DC magnetic field of 3T is superimposed to the AC levitation field in order to suppress turbulent magneto-hydrodynamic fluid flow. It is found that the emissivity depends on temperature only weakly. Nevertheless, the emissivity as function of temperature obeys a linear law. The dependence on the wavelength agrees with the Hagen-Rubens relation and the simple Drude model. The calculated penetration depth amounts to approximately 3 nm correspond to 10-30 monolayers in the surface near region. At a wavelength of 940 nm and for T=1943 K, the emissivity amounts to 0.37, 0.40, 0.32, and 0.31 for Ti, Al20Ti80, Al50Ti50 and Al70Ti30, respectively. This data is in good agreement with results from literature. The results are compared to the ideal solution model. A positive excess emissivity is hereby encountered which can (roughly) be modeled by Nordheim-rule.