DFT, MC, and MD investigation of H₂MoO₄ adsorption on model AISI 304 stainless steel surfaces: effects of inhibitor loading, temperature, and confined shear.

CONTEXT: Molybdate-based inhibitors are promising candidates for corrosion protection of stainless steels; however, the molecular mechanisms controlling their adsorption behavior under different interfacial conditions remain insufficiently understood. This study investigates the adsorption behavior of H₂MoO₄ on model surfaces relevant to AISI 304 stainless steel, focusing on the effects of inhibitor loading, temperature, and confined shear. Electronic-structure analysis revealed that oxygen-containing regions act as electron-donating sites, whereas the Mo-centered region exhibits electron-accepting characteristics. Molecular simulations showed favorable adsorption interactions on Fe(110) and a representative Cr₂O₃-Fe₂O₃-NiO passive oxide model. Increasing inhibitor loading enhanced the overall adsorption interaction, while temperature affected adsorption energetics without a monotonic trend. Under confined shear conditions, H₂MoO₄ maintained a predominantly parallel orientation relative to the surface, indicating stable adsorption behavior under the investigated conditions.

METHODS

Density functional theory (DFT), Monte Carlo (MC), and molecular dynamics (MD) simulations were performed using Materials Studio. DFT calculations were carried out using the DMol3 module with the GGA/PBE functional and DNP basis set. HOMO, LUMO, and condensed Fukui function analyses were used to evaluate molecular reactivity. Adsorption configurations were obtained using Monte Carlo simulations with the Metropolis method and Universal force field. MD simulations were performed using the Forcite module with the Universal force field under the NVT ensemble to analyze adsorption behavior under different inhibitor loading, temperature, and confined-shear conditions.