Surface tension and density measurement of liquid industrial steels and alloys by means of the oscillating drop method using an electromagnetic levitation apparatus
Thomas Leitner
Institute of Experimental Physics, TU Graz
14:00 - 14:30 Tuesday 04 February 2020 P2

The temperature dependent surface tension and density of liquid steels and alloys are two thermophysical properties that are of great interest for a large variety of industrial applications but also in fundamental research and space science. Since in today’s metalworking industry, not only product development but also the optimization of novel production routes heavily involves preceding modeling and simulation, accurate experimental data used as input parameter for those simulations are highly demanded.

Surface tension and density are deduced from the observed volume and surface oscillations of a levitated liquid droplet by applying the Oscillating Drop (OD) method. An electromagnetic levitation (EML) apparatus is used to levitate the sample freely in space, only environed by an inert gas atmosphere, thus achieving non-contact and container-less conditions throughout the experiment. This is favorable due to the high melting temperatures and chemical reactivity of liquid metals, dooming traditional contact-based measurement techniques to fail or potentially deliver falsified results.

In a first step, the dependence of surface tension on the composition in the binary iron-nickel system was investigated. Although results of pure iron showed a good agreement with literature data, the measurements on the iron-nickel alloy samples delivered unexpected results. Therefore, comparison measurements were conducted at the electrostatic levitator (ESL) of NASA Marshall Space Flight Center that did not completely uncover the reason for the discrepancy observed in our EML measurements. Later, an additional study was executed to verify data of pure nickel originating from a previous study, that also did not fit the overall picture. While the ESL measurements were unsuccessful for the iron-nickel samples, surface tension data of an industrial steel were acquired that showed good agreement with data obtained with our EML setup, thus validating our EML measurement procedure for a complex alloy the first time.

While further investigating selected industrial steels by our project partner voestalpine BÖHLER Edelstahl GmbH & Co KG, a sample carousel was developed, and sample temperature control was improved to facilitate a reduction of experiment duration for a single sample. Therefore, evaporation of volatile alloy components and thus mass loss and changes in composition during the experiment, which would otherwise lead to falsified results, can be minimized too.