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

Area of Science:

• Materials Science
• Surface Chemistry
• Physical Chemistry

Background:

• Bare aluminum surfaces readily form a protective aluminum oxide layer.
• Water plays a crucial role in mediating subsequent corrosion processes.
• Understanding water's behavior at the oxide interface is key to predicting corrosion kinetics.

Purpose of the Study:

• To model the behavior of aqueous aluminum ions on aluminum oxide surfaces under varying humidity conditions.
• To investigate the influence of interfacial water structure and dynamics on aluminum corrosion.
• To assess the relationship between metal ion diffusivity and corrosion reaction rates.

Main Methods:

• Utilized molecular dynamics simulations with a reactive force field.
• Modeled aqueous aluminum ions in water adsorbed onto aluminum oxide surfaces.
• Varied ion concentrations and water film thicknesses to simulate different relative humidity levels.

Main Results:

• Both water and aluminum ion structure and diffusivity are strongly dependent on environmental humidity and position within the water film.
• At 30% relative humidity, aqueous aluminum ion diffusion is over two orders of magnitude slower than bulk water self-diffusion.
• Metal ion diffusivity was parametrically linked to corrosion kinetics using a 1D reaction-diffusion model.

Conclusions:

• Interfacial water properties significantly influence aluminum corrosion.
• Predictive models for aluminum corrosion must account for the specific characteristics of interfacial water.
• Humidity is a critical factor governing aluminum ion mobility and corrosion rates.