Surface tension measurements of industrial alloys

Abstract

Industrial alloys are generally multi-component systems with volatile and highly reactive components. Consequently, their processing in the liquid state requires special precautions. Therefore, an existing electromagnetic-levitation device with a high-vacuum chamber, designed for surface tension measurements was modified and improved. Due to the necessity of an extremely pure experiment-environment the equipment was constructed with special consideration of very low oxygen concentration in the processing atmosphere: Only high-purity helium-hydrogen was used and special care was taken to avoid back-diffusion of air through venting valves. For the measurements of the surface tensions with the help of the oscillating drop technique the temperatures and the video sequences of the levitated, molten alloy were recorded without contact by pyrometer and by high-speed camera, respectively. This method yields the frequencies of the surface oscillations of the sample around the equilibrium shape and - using the modified Rayleigh law - eventually the values of the surface tension. With the help of this method some commercial industrial alloys were processed in the new EML-apparatus for ESA`s Thermolab project. The results of these measurements shall be presented and discussed.