Aerosol Salt Particle Deposition on Metals Exposed to Marine Environments: A Study Related to Marine Atmospheric Corrosion

Abstract

The characterization and corrosive effect of marine salt particles and seawater droplets that naturally deposited onto carbon steel and pure zinc that were exposed to marine test sites were studied. Most of the salt particles had diameters ranging from approximately 2–10 μm, and varied in their composition ranging from almost pure NaCl or KCl to mixtures of NaCl, KCl, CaCl2, and MgCl2. The differences in composition may depend on whether the seawater droplets dehydrate, crystallize, and fragment while airborne, or if they deposit as liquid droplets prior to crystallizing. The deposition of salt particles also decreased as the wind velocity decreased. The initial stage of marine atmospheric corrosion of the carbon steel and pure zinc induced by the salt deposition was also investigated. On the carbon steel substrate, NaCl-containing seawater droplets smaller than approximately 30 μm could not initiate corrosion even after 30 minutes of exposure; whereas, droplets larger than approximately 30 μm induced corrosion within approximately 30 minutes with lepidocrocite as the corrosion product. Corrosion initiated on the pure zinc samples under droplets of all sizes within 30 minutes. On the zinc samples, simonkollite formed in the central anodic region; whereas, hydrozincite formed in the peripheral cathodic region.