Faraday forcing of high-temperature levitated liquid metal drops for the measurement of surface tension

Abstract

In this work, a method for the measurement of surface tension using continuous periodic forcing is presented. To reduce gravitational effects, samples are electrostatically levitated prior to forcing. The method, called Faraday forcing, is particularly well suited for fluids that require high temperature measurements such as liquid metals where conventional surface tension measurement methods are not possible. It offers distinct advantages over the conventional pulse-decay analysis method when the sample viscosity is high or the levitation feedback control system is noisy. In the current method, levitated drops are continuously translated about a mean position at a small, constant forcing amplitude over a range of frequencies. At a particular frequency in this range, the drop suddenly enters a state of resonance, which is confirmed by large executions of prolate/oblate deformations about the mean spherical shape. The arrival at this resonant condition is a signature that the parametric forcing frequency is equal to the drop’s natural frequency, the latter being a known function of surface tension. A description of the experimental procedure is presented. A proof of concept is given using pure Zr and a Ti39.5Zr39.5Ni21 alloy as examples. The results compare favorably with accepted literature values obtained using the pulse-decay method.

Surface Tension of the Oxide Skin of Gallium-Based Liquid Metals

“…Generally, surface tension measurements of liquids are performed via force-based measurements, i.e., Wilhelmy plate 19 and du Nouÿ ring, 19 pressure-based approaches, i.e., pendant drop, 20 (maximum) bubble pressure, 21 and spinning drop method, 22 and so on. 23 For the measurement of metals, the surface tension is measured via sessile drop, 24 pendant drop, 25 and levitated drop methods 26 in a high-temperature furnace, while oxygen is excluded. A prerequisite for these methods is that an equilibrium is established in the time scale of the experiment.…”

Resonance conditions of electrostatically levitated drops in microgravity

“…Recent developments in levitation technologies, such as electrostatic levitation [1][2][3][4][5][6][7][8] (ESL), electromagnetic levitation [9][10][11] (EML), and aerodynamic levitation [12][13][14] (ADL), have allowed contamination-free measurements of high melting materials 2 . The oscillating drop method is used to obtain surface tension and viscosity of levitated liquid droplets 1 .…”