Surface tension measurements of industrial iron-based alloys from ground-based and parabolic flight experiments: Results from the Thermolab Project

Industrial alloys are generally multi-component systems with volatile and highly reactive components. Consequently, their processing in the liquid state requires special precautions. Electromagnetic levitation allows containerless positioning and melting of liquid metals and provides an ultrapure environment. For measurements of the surface tensions the oscillating drop technique is employed: the temperatures and the video sequences of the levitated, molten alloy are recorded without contact by a pyrometer and by a high-speed camera, respectively. With the help of Fast-Fourier-Transformation (FFT) this method yields the frequencies of the surface oscillations of the sample around the equilibrium shape from the spectra and, eventually, the values of the surface tension. In the framework of ESA’s Thermolab project, the surface tensions of two representative steels; one low-carbon steel, and one stainless steel, have been determined. The measurements were carried out in an earthbound levitation device, as well as during parabolic flights in the TEMPUS facility, taking advantage of the microgravity environment. The results obtained are compared and discussed in the framework of thermodynamic models