Oxyhydroxide of metallic nanowires in a molecular H2O and H2O2 environment and their effects on mechanical properties

Evidence and attribution

Authority of statements

Prose sections below (Summary, Methods, Findings, etc.) are curated summaries of the publication identified by doi, title, and pdf_path in the front matter above. They are not new primary claims by this wiki.

For definitive numerical values, reaction schemes, and interpretations, use the peer-reviewed article (and optional records under normalized/papers/ when present)—not this page alone.

Summary

ReaxFF reactive MD simulates oxidation of iron nanowires in molecular H\(_2\)O and H\(_2\)O\(_2\), forming iron oxide and oxyhydroxide shells whose microstructure depends on the oxidizing environment (mild hydrolytic oxidation versus stronger peroxide-driven pathways). The work then connects these oxide shells to tensile mechanical response: pre-oxidation introduces defect-prone regions near the metal–oxide interface, lowering yield stress and Young’s modulus compared to cleaner wires, with H\(_2\)O\(_2\) oxidation producing especially detrimental mechanical weakening in the models studied. Deformation twinning remains the dominant plasticity mechanism in Fe, but it onsets earlier in oxidized wires because shell heterogeneity concentrates stress. Adri C. T. van Duin is a coauthor.

Methods

Force-field lineage (ReaxFF, Fe/O/H)

Simulations use the ReaxFF reactive potential for Fe/O/H chemistry as parameterized in the Aryanpour et al. line cited in §2.1 of the article, enabling variable atomic charges (electrostatic energy minimized each MD step in the implementation described there).

MD application — aqueous oxidation of Fe nanowires

Engine / code. Reactive MD is run in LAMMPS with the ReaxFF implementation referenced in §2.

System size and composition. The authors build BCC iron nanowires (NWs) with lattice constant \(a = 2.86\) Å inside an orthogonal simulation box of \((50\times 50\times 50)\,a\), i.e. \(\approx 14.315\) nm per side. The initial cylindrical Fe NW is \(\sim 5.0\) nm in diameter and \(\sim 14.3\) nm long (24 050 Fe atoms), oriented along [001] and centered in the cell. Oxidation benchmarks place 1334 H\(_2\)O molecules or 1000 H\(_2\)O\(_2\) molecules in the vacuum region \(\sim 6\) Å from the NW surface (Fig. 1 in the paper).

Boundaries / periodicity. Oxidation trajectories use periodic boundary conditions in all three directions. Tensile runs apply PBC along the loading ([001]) direction to mimic an infinitely long NW while suppressing artificial free-end effects, as stated in §2.

Ensemble. Oxidation simulations are performed in the NVT ensemble at 300 K with a Nose–Hoover thermostat. Mechanical deformation after energy minimization (conjugate gradient) begins with a Nose–Hoover NPT equilibration at 300 K with zero pressure in the \(z\) direction to relax residual stresses, then continues in NVT at 300 K for the tensile stage.

Timestep. Equations of motion are integrated with a velocity-Verlet scheme using \(\Delta t = 0.25\) fs.

Duration / stages. H\(_2\)O oxidation runs 0.4 ns; H\(_2\)O\(_2\) oxidation runs 1.1 ns (the paper reports differing consumption of O/H atoms to build the oxide shells). Tensile deformation extends 1.5 ns total while straining up to 15% of the initial box length.

Thermostat. Nose–Hoover thermostats control 300 K during NVT oxidation and NVT tensile loading; NPT equilibration before tension likewise uses Nose–Hoover coupling as described in §2.

Barostat. Nose–Hoover NPT is used only for the pre-tensile stress-relaxation step (\(T = 300\) K, \(P_z = 0\)). Oxidation and tension segments are NVT at fixed cell volume aside from the controlled uniaxial strain increments.

Temperature. 300 K for oxidation, equilibration, and mechanical tests.

Pressure / stress. Hydrostatic pressure control is not applied during NVT oxidation. NPT equilibration targets \(P_z = 0\) in the normal direction. Tensile loading applies a constant engineering strain rate of \(0.01\%\,\mathrm{ps}^{-1}\) (\(10^8\,\mathrm{s}^{-1}\)) along [001].

Electric field. N/A — no applied electric field or bias in the published protocol.

Replica / enhanced sampling. N/A — direct ReaxFF MD without umbrella sampling, metadynamics, or bond boost.

Analysis

The authors track oxide/oxyhydroxide phases (Fe\(_x\)O\(_y\)H\(_z\)), shell microstructure, coordination/density metrics, and virial stress–strain responses (Table 1).

Findings

Outcomes and mechanisms

Oxidation in molecular H\(_2\)O versus H\(_2\)O\(_2\) produces different iron oxide and oxyhydroxide microstructures on the NW surface. Pre-oxidation increases defect-prone regions near the metal–oxide interface, so plasticity initiates at lower stress/strain than in pristine wires. Deformation twinning remains the dominant plastic mechanism for all NWs, but twins appear earlier under load for oxidized systems.

Comparisons

Table 1 quotes linear yield strains and yield stresses of 6.0%, 4.9%, 4.8% and 6.8, 5.6, 4.3 GPa for pristine, H\(_2\)O-oxidized, and H\(_2\)O\(_2\)-oxidized NWs, respectively—H\(_2\)O\(_2\) gives the largest softening relative to pristine Fe.

Sensitivity and design levers

Oxidizer chemistry (H\(_2\)O vs H\(_2\)O\(_2\)) and the resulting local defect population strongly couple to yield and stiffness at fixed \(T = 300\) K loading conditions.

Limitations and outlook (as authored)

The study emphasizes nanosecond oxidation windows and model NW geometries; quantitative transfer to long-time corrosion or alloys should follow the article’s discussion of ReaxFF scope.

Corpus honesty

Protocol numbers above are taken from papers/Aral_PCCP_FeO_OH_2018.pdf §2; if pagination differs in another print, use the DOI version for locators.

Limitations

Nanowire diameter, strain rate, and temperature in MD influence quantitative moduli; compare to experiment where available. ReaxFF Fe/O/H parameter scope should be verified when extending to alloys, aqueous electrolytes, or long-time corrosion kinetics beyond the nanosecond oxidation windows modeled here.

Relevance to group

Demonstrates group ReaxFF practice on reactive metal oxidation coupled to nanomechanics.

Citations and evidence anchors

• DOI: https://doi.org/10.1039/C8CP02422G (see papers/Aral_PCCP_FeO_OH_2018.pdf).

Related topics

• reaxff-family

Reader notes (navigation)

Compare H\(_2\)O versus H\(_2\)O\(_2\) oxidation outcomes here with other Fe nanowire ReaxFF entries in the corpus when building retrieval clusters around aqueous corrosion plus mechanical loading.