When corrosive ions (e.g., H+) penetrate into the film, the ion-exchanged silica particles, due to their large specific surface area, effectively adsorb and exchange hydrogen ions, and the released calcium ions migrate to the metal surface of the substrate. Due to the inevitable elector-chemical reaction on the surface of the metal substrate, OH- is formed, which in turn partially generates silicate ions with silicon dioxide particles. During an elector-chemical reaction, iron atoms are oxidized into iron ions. The resulting iron ions and the released calcium ions combine with silicate ions to form inert silicates, which are deposited on the surface of the metal substrate. These two silicates are chemically stable and deposited on the surface of the metal to form a composite passivation layer, which can play a long-term protective role and delay the corrosion of the metal.
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