Yes. Presence of precipitates could accelerate localized corrosion because precipitates varies the corrosion rates on the surface
Dear Dr. Wan Mohamad Ikhmal,
in addition to chloride deposits, other more complex chemical compounds, containing oxygen, magnesium, sulphur, potassium, calcium, aluminium, silicon, etc. in variable percentages, could also found to be present on specimens exposed to marine atmospere. These deposits weaken the passivation film, and are likely to trigger new localised corrosion sites. Their origin can be both directly correlated to the marine-urban atmosphere in the area where the structure is positioned, and ascribed to other processes the specimens had undergone before it was put up.
In particular, using SEM technique in order to see a surface at higher magnification (2000X), small NaCl crystals could be visible arranged all along the grain edge. This is by itself a particularly critical area from a chemical and morphological point of view, because of poor protection passivation layer development. In addition, NaCl crystals are likely to further promote localised corrosion.
The presence of NaCl cristals is particularly dangerous, if the samples have been coated, in areas where there are damages and / or high porosity of the protective system.
Best regards, Pierluigi Traverso
Thank you very much for such in-depth explanation. Really appreciate it !!
Yes, the presence of salt precipitate on the metal of coating has damaging corrosion effect as the salts facilitate the movement of ions on the surface, and increasing corrosion rate.
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