Model for Humidity-Mediated Diffusion on Aluminum Surfaces and Its Role in Accelerating Atmospheric Aluminum Corrosion

JA Scher and SE Weitzner and Y Hao and TW Heo and ST Castonguay and S Aubry and SA Carroll and MP Kroonblawd, ACS APPLIED MATERIALS & INTERFACES, 15, 28716-28730 (2023).

DOI: 10.1021/acsami.3c02327

Barealuminum metal surfaces are highly reactive, which leads tothe spontaneous formation of a protective oxide surface layer. Becausemany subsequent corrosive processes are mediated by water, the structureand dynamics of water at the oxide interface are anticipated to influencecorrosion kinetics. Using molecular dynamics simulations with a reactiveforce field, we model the behavior of aqueous aluminum metal ionsin water adsorbed onto aluminum oxide surfaces across a range of ionconcentrations and water film thicknesses corresponding to increasingrelative humidity. We find that the structure and diffusivity of boththe water and the metal ions depend strongly on the humidity of theenvironment and the relative height within the adsorbed water film.Aqueous aluminum ion diffusion rates in water films correspondingto a typical indoor relative humidity of 30% are found to be morethan 2 orders of magnitude slower than self-diffusion of water inthe bulk limit. Connections between metal ion diffusivity and corrosionreaction kinetics are assessed parametrically with a reductionistmodel based on a 1D continuum reaction-diffusion equation.Our results highlight the importance of incorporating the propertiesspecific to interfacial water in predictive models of aluminum corrosion.

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