Holistic model for atmospheric corrosion Part 6 – From wet aerosol to salt deposit

Abstract

This paper is the sixth paper outlining a holistic model of atmospheric corrosion. Previous papers outline how airborne salinity could be estimated at any given location and how the deposition onto a surface could be modelled. This paper investigates the initial reactions of raindrops or deposited marine aerosols on metal surfaces (zinc, galvanised steel, aluminium and gold). It combines short term field exposures with a series of controlled laboratory experiments. Surface changes to the metal upon field exposure are characterised by the nature and distribution of corrosion nodules, oxide films and retained salts. Eleven distinct forms of surface change are observed. The conditions promoting each pattern of surface changes were estimated by comparison with laboratory tests with a variety of deposition modes. Laboratory tests included deposition of saline droplets in three size ranges. A strategy to use the results in a holistic model of corrosion is proposed.CEST/2132

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

“…The sizes of the salt particles are important to correctly simulate the initiation and propagation of atmospheric corrosion in the laboratory, as the initiation and propagation mechanisms can be dependent on the salt-particle size. As compared to the atmospherically-deposited salt particles (dry) determined by Cole et al, 4 many studies [24][25][26][27][28] have actually used very coarse NaCl particles that may be more relevant to splash-spray zones as compared to the smaller airborne salt particles that are found in natural marine atmospheres. 34 The types of the salt particles are also important since different types of salt have different critical relative humidity (RH), which affects the wetting of the sample surfaces.…”

“…4,34 The importance of studying the deposition of natural salt particles lies in the determination of the sizes and types of the salt particles. The sizes of the salt particles are important to correctly simulate the initiation and propagation of atmospheric corrosion in the laboratory, as the initiation and propagation mechanisms can be dependent on the salt-particle size.…”

“…33 Despite the enormous amount of studies on NaCl particle-induced corrosion, few investigations have focused on the naturally deposited airborne marine salt particles on metal surfaces (especially carbon steel), including their characterization and effects on the initial stages of metallic corrosion. 4,34 The importance of studying the deposition of natural salt particles lies in the determination of the sizes and types of the salt particles. The sizes of the salt particles are important to correctly simulate the initiation and propagation of atmospheric corrosion in the laboratory, as the initiation and propagation mechanisms can be dependent on the salt-particle size.…”

“…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.…”

“…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][2][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.…”