Abstract
Atmospheric corrosion of stainless steel can take place when airborne salt particles deposit on the metal surface, forming droplets when the relative humidity (RH) reaches a critical value: the deliquescence relative humidity of the salt. Most work to date has focused on single salts such as MgCl2 or NaCl. In the present work, the effect of mixed salts is investigated at 45% RH, above the deliquescence relative humidity of MgCl2 but below that of NaCl. Dish-shaped pits were found in pure MgCl2 solutions and mixed solutions. Crevice corrosion takes place under NaCl crystals. This is shown both with ex situ measurements and in situ time-dependent measurements using X-ray microtomography, where pit growth was also monitored.
Highlights
In marine environments, airborne sea salt particles can be deposited on stainless steel surface by coastal winds.[1]
Salt will absorb moisture from the environment when its deliquescence relative humidity (DRH) is below the relative humidity (RH) of the surrounding environment until the vapor pressure of the solution reaches that of the environment
For ex situ lab-based tests, characterization was carried out at the end of the test whereas for synchrotron X-ray microtomography tests, in situ characterization was performed at several points during the exposure period
Summary
Airborne sea salt particles (salt aerosols) can be deposited on stainless steel surface by coastal winds.[1]. Localized corrosion under MgCl2.—Figure 1 shows a typical droplet after deposition (Figure 1a) and exposure at 45 ± 2% RH and 21◦C for 48 h (Figure 1b) in a lab-based experiment.
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