Abstract
Steady-state solid-liquid interfaces allow both analytic description as sharp-interface profiles, and numerical simulation via phase-field modeling as stationary diffuse-interface microstructures. Profiles for sharp interfaces reveal their exact shapes and allow identification of the thermodynamic origin of all interfacial capillary fields, including distributions of curvature, thermochemical potential, gradients, fluxes, and surface Laplacians. By contrast, simulated diffuse interface images allow thermodynamic evolution and measurement of interfacial temperatures and fluxes. Quantitative results using both approaches verify these capillary fields and their divergent heat flow, to provide insights into interface energy balances, dynamic pattern formation, and novel methods for microstructure control. The microgravity environment of low-Earth orbit was proven useful in past studies of solidification phenomena. We suggest that NASA’s ISS National Lab can uniquely accommodate aspects of experimental research needed to explore these novel topics.
Highlights
Over the past decade, one of the present authors published studies applying field-theoretic methods to identify and quantitate interfacial thermodynamic fields[1,2]
Overlook higherorder energy and solute contributions that subtly derive from the higher-order actions of capillary forces, and represent small, but significant, deterministic interface perturbations that affect solidification kinetics
The purpose of this paper is to provide a wider awareness of higher-order interfacial capillary effects to researchers interested in exploring further uses of the microgravity environment for basic solidification research aboard NASA’s ISS-National Laboratory
Summary
One of the present authors published studies applying field-theoretic methods to identify and quantitate interfacial thermodynamic fields[1,2]. Steady-state simulations allow measurement of interfacial temperature fields along curved diffuse interfaces, described numerically by "isolines” of their paired phase-field indices[6,7,8] Results from those studies, when compared with predictions derived from variational analyses of shaped, but perfectly sharp, solid-liquid (s/l) profiles, led to understanding and appreciation of how capillary-mediated interfacial energy sources and sinks arise deterministically, modify interface energy balances in pure systems, and influence interface motion and pattern-formation dynamics. Kelvin’s thermodynamic rules, as applied to s/l interfacial equilibria, are captured by the Gibbs-Thomson equation that predicts the following linear change in the equilibrium interface temperature, Tint, caused by local curvature. The resulting profile at steady-state separates pure solid from its melt, each phase accorded identical thermal conductivity and molar volume This stationary microstructure supports continuous heat-flow throughout the bulk phases, precluding full thermodynamic equilibrium. GBGs are frequently employed experimentally to measure average solid-liquid energies for many different s/l systems[32,33,34,35,36,37], and studied dynamically for their effect on interfacial stability during solidification[38,39]
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