29. What is the principle of zinc coating anti-corrosion?

The use of zinc coatings to protect underlying steel substrates from corrosion has proven effective in general atmospheric conditions. The corrosion resistance mechanism primarily involves: (1) A thin, dense zinc oxide layer forms on the zinc coating surface. As this layer is highly insoluble in water, it provides protection for the underlying zinc metal. However, when the oxide layer reaches approximately 300 nanometers in thickness, it becomes prone to detachment. When zinc oxide reacts with atmospheric components to form insoluble zinc salts, the corrosion resistance becomes even more effective.
(2) Zinc coating as a dense thin film layer covers the steel surface, it can avoid the steel substrate contact with any corrosion solution, protect the steel substrate from corrosion.
(3) Once the small leakage or the exposed iron surface is found on the steel matrix, the zinc layer can produce the iron-zinc couple microcell under the condition of the electrolyte formed by the water film on the surface, and the adjacent zinc layer can repair the leakage and exposed iron surface, and continue to play the role of protection.