As shown in Fig. 3

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The corrosion behavior of carbon steel coated with a zinc-rich paint containing two metallic compounds, Al 2 (SO 4 ) 3 and CaO, as anticorrosive additives was examined under wet and dry cyclic corrosion test conditions. The zinc-rich paint coating without the two metallic compounds formed a white corrosion product and red iron rust on the surface after the corrosion test, whereas the coating with the metallic compounds showed reduced surface corrosion products. The corrosion current density of the painted steel substrate decreased drastically due to the incorporation of metallic compounds in the paint. The zinc-rich paint coating modified with the metallic compounds contained dispersed simonkolleite (Zn 5 (OH) 8 Cl 2 •H 2 O) phase and possibly very fine CaSO 4 particles, which remarkably improved the protectiveness of the zinc-rich paint coating.

We have examined the corrosion behavior of a rusted carbon steel coated with a paint containing metallic salt under wet and dry cyclic condition. The rust layer of the carbon steel was already grown in a coastal region of Japan before the coating. It was found that the addition of metallic salt to the coating film decreased the corrosion rate of the coated steel. The X-ray diffraction analysis of the rust layer revealed that the addition of metallic salt resulted in drastic increase of α-FeOOH during the cyclic corrosion test. The rust layer under the coating film containing metallic salt suppressed penetration of Clto the steel surface. Electrochemical analyses indicated that the coating with metallic salt decreased cathodic reduction rate of the rust layer due to the formation of α-FeOOH in the rust layer.

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