Skip to content

A reactive force field molecular dynamics simulation of nickel oxidation in supercritical water

Summary

Ai et al. investigate nickel oxidation in supercritical water (SCW) using ReaxFF molecular dynamics, motivated by corrosion of Ni-based alloys in fossil and nuclear plants operating toward higher steam temperatures. The abstract reports simulations spanning 300–800 °C and water densities 26–164 kg m⁻³, tracking water adsorption, dissociation, deprotonation, and Ni hydroxylation/oxidation. The article positions SCW as a stronger oxidizing environment than ambient liquid water for the conditions sampled, and analyzes charge evolution during deprotonation to argue that homolytic water cleavage becomes more plausible at high temperature and relatively low density than heterolytic pathways familiar near ambient conditions.

Methods

Alternate pdf_path (papers/ReaxFF_others/Ai_NiO_supercritical_JSupFluids_2018.pdf) for DOI 10.1016/j.supflu.2017.10.025; scientific protocol matches [[2017ai-the-journal-reactive-force]] (§2). LAMMPS runs employ Assowe Ni–O–H ReaxFF on a 28.896 × 28.896 × 51.896 ų Ni + SCW cell (968–1078 atoms by facet, Table 1), PBC in x/y, reflecting-wall z closure, NVT Berendsen thermostat, Δt = 0.25 fs, and 4,000,000-step (~1 ns) production segments at supercritical water conditions spanning roughly 300–800 °C and 26.1–164 kg m⁻³ as in the abstract. Bulk SCW NPT segments (~0.25 ns each) support EOS comparisons (Fig. 4). CASTEP PBE (571 eV, ultrasoft PP) supplies QM spot checks. The interface leg is NVT (no barostat there); electric fields and replica / enhanced sampling are not used.

Findings

Trajectory analysis tracks adsorption → dissociation → hydroxylation → oxide with interfacial charge evolution; SCW is portrayed as a stronger oxidizer than ambient liquid water for the sampled temperature–density grids, with bond metrics (Ni–O, O–H cutoffs in §3) used to follow reaction progression. Compared to near-ambient interfaces, the authors argue rate increases with temperature and fluid density in the studied regime. CASTEP PBE spot checks in §2 support qualitative energetics but are not an exhaustive benchmark of all oxide stoichiometries. Limitations include staying within the Assowe training manifold and short production windows (~1 ns per state in §2). This duplicate pdf_path should defer pagination-locked claims to [[2017ai-the-journal-reactive-force]] when needed.

Limitations

ReaxFF accuracy depends on training scope; SCW chemistry pushes bond rearrangements that should be spot-checked against QM where feasible. This slug is corpus bookkeeping for an alternate pdf_path; use [[2017ai-the-journal-reactive-force]] when pagination must match a specific PDF hash, and prefer one primary narrative for citations unless provenance requires both digests.

Confidence rationale: med—duplicate ingest; core claims from abstract/extract.

Reader notes (navigation)