CORROSION MECHANISMS FOR ALUMINUM EXPOSED TO THE ATMOSPHERE.

Upon exposure to the indoor or outdoor atmosphere and during some manufacturing processes, aluminum degrades with the formation of a variety of corrosion products. This paper relates those products to the atmospheric constituents that are their precursors, explores the chemical processes involved in corrosion product formation, and evaluates the magnitudes of the sources for the major corrosive anions. A three-layer structure is identified: the aluminum itself and its native oxide, the corrosion layer atop the oxidized aluminum, and a surface contamination layer. At low to moderate humidities, this last layer can be pictured as a moist agglomeration of deposited particles and common ionic compounds. At high humidities or in circumstances where active precipitation is falling on the surface, this top layer incorporates a dozen monolayers of water and becomes a slurry of deposited particles in an electrolyte solution.