Role of Corrosion Products on Corrosion Prevention of Galvanized Steels

摘要

Using a synthesized zinc corrosion product containing a rare earth metal ion, such as La~(3+) or Ce~(3+), corrosion rate of the substrate steel was measured by polarization resistance method during wet and dry corrosion cycles. Addition of La~(3+) was effective to some extents for corrosion prevention, however, Ce~(3+) showed no effect because it existed in the corrosion products as insoluble oxide. Role of Zn~(2+) and other additional alloying elements for corrosion prevention is explained by adsorption onto the steel surface as a corrosion inhibitor and by pH buffering action to maintain the surface in neutral condition. The effect of these ions on the corrosion prevention decreased with the progress of wet and dry cycles, due to formation of insoluble oxide or carbonates.