23. How does the zinc coating corrode in seawater?

Seawater typically contains 1-25% salt content, with 3.5% being the standard reference. The water contains significant amounts of oxygen, nitrogen, and carbon dioxide, which accelerate zinc coating corrosion. Chloride ions (accounting for about 55% of total ions) hinder the formation of protective films, thereby accelerating corrosion. Conversely, magnesium and calcium ions readily form insoluble salts with zinc coatings, promoting the development of protective films and gradually slowing down the corrosion rate.
The products of the corrosion of the zinc coating are carbonate, hydroxide and chloride. The corrosion rate of the zinc coating in seawater is generally 50～650 mg/dm2·y.