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, CaCl 2 , and MgCl 2 . 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. Atmospheric corrosion has been extensively studied ever since W.H.J. Vernon's work in the 1920s. Its complexity is based on numerous influential parameters, including both meteorological and pollution parameters. Among these variables are the airborne sea salts in coastal regions (marine aerosols), which are generated either in the open sea or the surf zone.1-3 Marine aerosols consisting of wet aerosols, partially wet aerosols, and non-equilibrium aerosols depending on the atmosphere humidity, 4 are carried by the wind and can reach offshore structures and greatly accelerate the corrosion of metals. The sizes of the three types of aerosols and the resultant dry aerosols were estimated by Cole et al. 4 The amount of marine aerosols present in a specific marine atmosphere, known as airborne salinity, is usually measured in both atmospheric and corrosion studies. For corrosion studies, correlating marine salinity and metallic corrosion is a major focus. By compiling worldwide research on atmospheric corrosion that was conducted in the last 40 years, Morcillo et al. 5 reported that the metallic corrosion rate increases fastest with respect to chloride deposition when its values are between 100 and 400 mg Cl − /m 2 /day, and slower when the chloride deposition is less than 100 mg Cl − /m 2 /day or more than 400 mg Cl − /m 2 /day. Studies have also focused on the behavior of marine aerosols, including their production, transport and deposition. 1,6,7 Cole et al.1 proposed a comprehensive model that requires the input of significant amounts of data; whereas, Meira et al. 7 generated a simplified model that depends only on aerosol characteristics and has wind velocity and distance from the sea as independent va...

Atmospheric corrosion prediction: a review

“…In marine site with high amount of chloride deposition, β-FeOOH is produced as for chloride accelerative effect, while the main corrosion products are γ-FeOOH and α-FeOOH in exposure station with low or no chloride. Chloride mainly comes from the ocean and deicing (ISO, 2012a).The deposition rate of chloride from the ocean is affected by wind speed and wind direction (Cole et al 2003b;Li and Hihara 2014;Roberge et al 2002), distance from the coast (Cole et al 2003b;Cole et al 2003a;Guerra et al 2019), rainfall (Cole et al 2004a), temperature and humidity (Castaneda et al 2018;Cole et al 2003b), terrain (Cole et al 2003c;Cole et al 2004a) and other factors (Cole et al 2011). The influence of chloride has a significant relationship with the distance from the sea (Abbott 2008;Feliu et al 1999).…”

“…The types, size and distribution of aerosols can influence the initiation and propagation of the corrosion process in more complex ways (Li and Hihara 2014;Risteen et al 2014). Take zinc as an example, the presence of acidified aerosols may lead to enhanced corrosion by disrupting any protective oxide films and subsequently establishing electrochemical cells, relatively uniform oxide layers are formed, which may be dissolved by typical aerosol with pH values of 1-4 and slightly acidified rain (<5) (Azmat et al 2011) and thus may not constitute as an effective barrier against corrosion.…”

A Micro-Raman Spectroscopic Study of Marine Atmospheric Corrosion of Carbon Steel: The Effect of Akaganeite

“…[1][2][3][4][5] The high corrosion rates in marine environments greatly reduce the lifetime of steel structures. Therefore, a better understanding of the corrosion mechanisms of steel is necessary for evaluating the performance and developing corrosion-control strategies.…”

Recent Progress and Required Developments in Atmospheric Corrosion of Galvanised Steel and Zinc

“…Li et al [ 21 ] looked at salt deposition and corrosion for very short exposure times (30 min) in a marine Hawaiian locations on low carbon steel and zinc. In this, they duplicated the earlier test of Cole et al [ 22 ] in Australia with very similar results.…”

“…In this, they duplicated the earlier test of Cole et al [ 22 ] in Australia with very similar results. Li et al [ 21 ] found that the corroded region or the original droplet was from 10–30 µm. Corrosion occurred at all sizes and secondary spreading was observed for the larger droplets.…”