Surface Orientation-Dependent Corrosion Behavior of NiCr Alloys in Molten FLiNaK Salt
Summary¶
Molten fluoride salts such as FLiNaK are discussed widely for thermal energy storage and nuclear heat-transfer applications, but structural alloys can suffer corrosion that depends on temperature, salt chemistry, and interfacial transport. This ACS Appl. Mater. Interfaces article uses ReaxFF-based reactive molecular dynamics (RMD) to study molten FLiNaK attack on Ni\(_{0.75}\)Cr\(_{0.25}\) as a function of surface orientation, temperature, and uniform electric fields normal to the interface—motivated by the idea that corrosion is not always isotropic even when bulk alloy composition is fixed. The abstract frames the problem around Cr dissolution and near-surface diffusion leading to pitting-like roughening, and it highlights orientation-dependent susceptibility and field-dependent suppression or acceleration of attack. Adri C. T. van Duin coauthors the study as part of the group’s molten-salt / alloy interface simulation portfolio.
Methods¶
The simulations employ ReaxFF reactive MD with parameters consistent with prior Ni–Cr–F/K/Li training discussed in the article (see Methods/SI for the precise parameter line and validation hooks). The authors compare (100), (110), and (111) surface terminations of Ni\(_{0.75}\)Cr\(_{0.25}\) in contact with molten FLiNaK over a temperature range 600–800 °C (reported in °C; convert to K when comparing to other MD literature), including runs with and without uniform electric fields perpendicular to the interface reported as +0.10 V Å\(^{-1}\) and −0.10 V Å\(^{-1}\) in the abstract-level summary. Structural evolution is interpreted in terms of dissolution, diffusion, and morphological roughening metrics described in the full text; local extract normalized/extracts/2025hamdy-arkoub-acs-surface-orientation-dependent_p1-2.txt aligns with the title-page framing. N/A in this short summary: time step, trajectory duration, thermostat type and damping, barostat (if any), full PBC slab supercell atom counts, and full NPT vs NVT ensemble labelling—see version-of-record PDF/SI (the melt on faceted Ni–Cr slabs is treated with 3D PBC in the standard LAMMPS slab pattern described there). Replica / metadynamics-class sampling: N/A — not part of the abstract-level description.
Findings¶
The abstract reports that Cr dissolution and near-surface diffusion drive pitting-like roughening, with a clear orientation ranking: (110) is the most corrosion-prone, while (100) and (111) are comparatively more resistant, and (111) is described as the most stable among the facets compared. Arrhenius analysis yields activation energies in the 0.27–0.41 eV range, described as consistent with limited experiments but much smaller than bulk diffusion barriers—interpreted as evidence for near-surface kinetic control rather than bulk-diffusion limitation of the simulated process. Regarding electric fields, a positive normal field is reported to promote Cr dissolution, whereas a negative field strongly suppresses corrosion, suggesting a possible mitigation lever for interfacial engineering under polarized conditions. Full numerical protocol details (timestep, sizes, equilibration) should be confirmed in the article and SI beyond the p1–2 extract. The orientation-dependent ranking is especially relevant for interpreting polycrystalline alloy exposures where multiple facets present simultaneously: simulations provide a facet-resolved hypothesis that can be tested against post-mortem microscopy and depth profiles where available. Finally, the reported field response should be read as a qualitative lever for interfacial driving forces in molten salts, not a literal reproduction of full electrochemical cell polarization without explicit electrode chemistry. Corpus note: numbers above follow the abstract and p1–2 extract; the PDF is authoritative for cutoffs, sample statistics, and SI detail.
Limitations¶
Field magnitudes and boundary conditions are idealizations of complex electrochemical environments; long-time extrapolation from nanoscale MD requires experimental corroboration.
Relevance to group¶
van Duin-group ReaxFF for molten-salt corrosion on alloys relevant to high-temperature energy systems.
Citations and evidence anchors¶
https://doi.org/10.1021/acsami.5c06557 — ACS Appl. Mater. Interfaces 17, 38708–38719 (2025).