Demonstration of the effect of stirring on nucleation from experiments on the International Space Station using the ISS-EML facility

A K Gangopadhyay,G P Bracker,M E Sellers,P K Galenko,R W Hyers,D Holland-Moritz,A K Pauls,K F Kelton,D C Van Hoesen,S Koch

doi:10.1038/s41526-021-00161-9

Abstract

The effect of fluid flow on crystal nucleation in supercooled liquids is not well understood. The variable density and temperature gradients in the liquid make it difficult to study this under terrestrial gravity conditions. Nucleation experiments were therefore made in a microgravity environment using the Electromagnetic Levitation Facility on the International Space Station on a bulk glass-forming Zr57Cu15.4Ni12.6Al10Nb5 (Vit106), as well as Cu50Zr50 and the quasicrystal-forming Ti39.5Zr39.5Ni21 liquids. The maximum supercooling temperatures for each alloy were measured as a function of controlled stirring by applying various combinations of radio-frequency positioner and heater voltages to the water-cooled copper coils. The flow patterns were simulated from the known parameters for the coil and the levitated samples. The maximum nucleation temperatures increased systematically with increased fluid flow in the liquids for Vit106, but stayed nearly unchanged for the other two. These results are consistent with the predictions from the Coupled-Flux model for nucleation.

Highlights

Crystal nucleation[1] and subsequent growth[2] in supercooled liquids are the two fundamental processes that determine the solidification microstructure[3]
The fluid flow calculations were made using the experimental data for the liquid viscosity, which was measured using the ground-based ESL facility, are presented in the Supplementary section (Supplementary Fig. 1)
A typical fluid flow velocity distribution in a Ti39.5Zr39.5Ni21 liquid is shown in Supplementary Fig. 2 for illustration

Summary

Introduction

Crystal nucleation[1] and subsequent growth[2] in supercooled liquids (i.e., liquids at a temperature below the equilibrium melting temperature, Tl) are the two fundamental processes that determine the solidification microstructure[3] Studies of these processes, occupy a central role in condensed matter physics, materials science, and biology. Spontaneous random processes in the liquid lead to the formation of dense, ordered, regions that are characteristic of the nucleating crystal. Heterogeneous nucleation is catalyzed by foreign objects such as undissolved impurities or the container walls The minimization of these catalytic sites is crucial for the studies of homogeneous nucleation; containerless processing, using electrostatic (ESL)[4], electromagnetic (EML)[5], aerodynamic[6], and acoustic[7] levitation, allows such studies. While useful for oxide materials, aerodynamic and acoustic levitations are not recommended for metallic liquids since even the highest purity inert gases often contain impurities that catalyze nucleation

Methods

Results

Conclusion