Effect of NO3- ion on the corrosion behavior of galvanized coating in alkaline solution

The influence of NO3− ion contamination of saturated Ca(OH)2 solution (pH ∼13.2) on the corrosion behavior of the hot-dip galvanized (HDG) coating was studied by means of open-circuit potential, potentiodynamic polarization test, electrochemical impedance spectroscopy, and scanning electron microscopy in this paper. Results showed that the presence of NO3− ion modified the general scheme of the dissolution and passivation of the HDG coating in the saturated Ca(OH)2 solution. NO3− ion not only increased the anodic reactivity of the HDG coating in the early corrosion process but also inhibited hydrogen evolution. The presence of NO3− ion shortened the passivation time of galvanized steel in the alkaline solution. In addition, the morphology of the passivating products on the HDG coating in the alkaline solution containing NO3− ion was modified after long-time immersion. A possible mechanism of the NO3− ion’s effect on the corrosion behavior of galvanized steel in the alkaline solution was also discussed.