Effect of relative humidity on corrosion of steel under acidified artificial seawater particles

The aim of this work was to elucidate the relationship between the hygroscopic behavior of acidified artificial seawater (ASW) microparticles, as a proxy for sea salt aerosol (SSA), and the atmospheric corrosion of mild steel contaminated with them. The wetting and drying behavior of acidified ASW microparticles deposited on an inert interdigitated electrode sensor was characterized by impedance measurements. Carbon steel coupons loaded with the same contaminant were subjected to isohumidity exposures for up to 30 days. The resulting damage was quantified by optical profilometry. Sustained corrosion was detectable down to 11% RH, with significant admittance of the salt deposits on the sensor at <2% RH after 24 h, likely due to the presence of trapped electrolyte. Trends in corrosion loss versus RH were not directly reflective of the major liquid-solid phase transitions observed for particles on the sensor. The results bring into question whether SSA-contaminated surfaces ever dry with regard to corrosion being possible in ambient outdoor environments.