Water and Halide Adsorption to Corrosion Surfaces: Molecular Simulations of Atmospheric Interactions with Aluminum Oxyhydroxide and Gold

Atmospheric corrosion due to adsorption of water and solutes onto metal and metal oxide surfaces is a critical factor in the long term reliability of electronic devices. To investigate the atomistic mechanisms of corrosion, we used molecular dynamics (MD) simulations to study the structure of water adsorbed onto both boehmite (γ-AlO(OH)) and gold (Au) surfaces and electrolyte adsorption and surface speciation on the boehmite (010) surface. Boehmite forms a thin film on aluminum metal under oxidizing conditions, is hydrophilic, and readily adsorbs water from the atmosphere. In contrast, gold surfaces are hydrophobic, and condensed water does not readily bond with the surface. Our MD simulations were performed using the CLAYFF force field that maintains full flexibility of water and substrate and allows for full energy and momentum transfer among all atoms. The boehmite (010) and gold (111) surfaces were initially simulated with no water present and then with incremental additions of water molecules. The calculations indicate the boehmite (010) surface structure strongly controls the organization of the first monolayer of interfacial water. In contrast, the structure of water on the gold (111) surface is controlled by hydrogen bonding among the water molecules. To investigate Cl − adsorption to the boehmite surface, Na + and Cl − ions were added to two boehmite−water simulation cells, one with 3.5 monolayers of water on the boehmite surface and the other representing water-saturated conditions. In both scenarios, the addition of NaCl solute disturbed the first monolayer of water adsorbed to the surface. Chloride ions displaced water molecules that were originally bound to the boehmite surface. In contrast, the Na + ions do not disturb the arrangement of these water molecules. Na + −Cl − pairs were observed to occur on the surface. Both the near-surface water structure and the effects of ion adsorption were similar regardless of the number of monolayers of water present in the simulation cells.