Surface Tension and Viscosity of Zr₈₀Pt₂₀ Measured on the International Space Station and Its Implication on Nucleation Mechanism

The surface tension and viscosity are important thermophysical properties of any liquid. Using the electromagnetic levitation facility aboard the International Space Station (ISS-EML), these properties were measured in the equilibrium and supercooled states of a quasicrystal forming Zr₈₀Pt₂₀ alloy liquid. A negative temperature coefficient of the surface tension and no indication of surface oxides in the X-ray photoelectron spectroscopy measurements indicate that the surface tension data are likely not influenced by oxygen contamination. Interestingly, the surface tension is smaller than expected for a liquid with large negative heat of mixing. Estimates from ideal and regular solution models raise the possibility that the surface is enriched in Zr, lowering the surface tension. These results may have important ramifications to the recently reported heterogeneous nucleation mechanism in this liquid (J. Chem. Phys. 162, 134502 (2025)).