Electromagnetic levitation containerless processing of metallic materials in microgravity: thermophysical properties

Transitions from the liquid to the solid state of matter are omnipresent. They form a crucial step in the industrial solidification of metallic alloy melts and are greatly influenced by the thermophysical properties of the melt. Knowledge of the thermophysical properties of liquid metallic alloys is necessary in order to gain a tight control over the solidification pathway, and over the obtained material structure of the solid. Measurements of thermophysical properties on ground are often difficult, or even impossible, since liquids are strongly influenced by earth’s gravity. Another problem is the reactivity of melts with container materials, especially at high temperature. Finally, deep undercooling, necessary to understand nucleus formation and equilibrium as well as nonequilibrium solidification, can only be achieved in a containerless environment. Containerless experiments in microgravity allow precise benchmark measurements of thermophysical properties. The electromagnetic levitator ISS-EML on the International Space Station (ISS) offers perfect conditions for such experiments. This way, data for process simulations is obtained, and a deeper understanding of nucleation, crystal growth, microstructural evolution, and other details of the transformation from liquid to solid can be gained. Here, we address the scientific questions in detail, show highlights of recent achievements, and give an outlook on future work

Excess-entropy scaling in supercooled binary mixtures

Supercooled liquids near the glass transition show remarkable non-Arrhenius transport phenomena, whose origin is yet to be clarified. Here, the authors use GPU molecular dynamics simulations for various binary mixtures in the supercooled regime to show the validity of a quasiuniversal excess-entropy scaling relation for viscosity and diffusion

Structure and bonding in WCn (n = 2–5) clusters

Stochastic explorations of the configurational spaces for WC n (n = 2–5) clusters lead to densely populated spin states at each molecularity. We found 8, 16, 42, and 68 well-defined minima for n = 2, 3, 4, 5, respectively, in spin states ranging from singlets to quintuplets. The lowest energy isomers are triplets in all cases, except for n = 2 where there is competition between a quintuplet and a triplet state for the global minimum. The transition from planar to 3D structural preferences occurs between n = 4 and n = 5. For the global minima, the structures may be considered as the result of the interaction between two fragments: a tungsten cation and a covalently bonded anionic carbon chain. We found that spin–orbit (SO) effects reduce energy differences among isomers. Likewise, SO effects diminish as a function of the carbon content in the clusters to the point that for n = 5 they become negligible

ADVANCED MEASUREMENT DEVICES FOR THE MICROGRAVITY ELECTROMAGNETIC LEVITATION FACILITY EML

This paper reports on two advanced measurement devices for the microgravity electromagnetic levitation facility (EML), which is currently under construction for the use onboard the “International Space Station (ISS)”: the “Sample Coupling Electronics (SCE)” and the “Oxygen Sensing and Control Unit (OSC)”. The SCE measures by a contactless, inductive method the electrical resistivity and the diameter of a spherical levitated metallic droplet by evaluating the voltage and electrical current applied to the levitation coil. The necessity of the OSC comes from the insight that properties like surface tension or, eventually, viscosity cannot seriously be determined by the oscillating drop method in the EML facility without knowing the conditions of the surrounding atmosphere. In the following both measurement devices are explained and laboratory test results are presented

Reference Correlation for the Density and Viscosity of Eutectic Liquid Alloys Al+Si, Pb+Bi, and Pb+Sn

In this paper, the available experimental data for the density and viscosity of eutectic liquid alloys Al+Si, Pb+Bi, and Pb+Sn have been critically examined with the intention of establishing a reference standard representation of both, density and viscosity. All experimental data have been categorized as primary or secondary according to the quality of measurement, the technique employed, and the presentation of the data, as specified by a series of carefully defined criteria. The proposal standard reference correlations for the density of liquid Al+Si, Pb+Si, and Pb+Sn are, repectively, characterized by deviations of 2.0%, 2.9%, and 0.5% at the 95% confidence level. The standard reference correlations for the viscosity of liquid Al+Si, Pb+Bi, and Pb+Sn are, repectively, characterized by deviations of 7.7%, 14.2%, and 12.4% at the 95% confidence level