Observation of self-healing functions on the cut edge of galvanized steel using SVET and pH microscopy

The scanning vibrating electrode technique (SVET) and pH microscopy were used to study the effect of electrolyte composition and steel thickness on the precipitation of zinc-based corrosion products on the cut edge of galvanized steel. Current distributions were measured with the SVET, and the distribution of pH was measured using liquid membrane glass capillary electrodes. In NaCl solution, a clear correlation was observed between the spatial pattern of precipitated corrosion products, and the anodic/cathodic current and pH distribution: zinc dissolution occurred at localized points on the cut edge, suggesting that the zinc surface was passivated in this solution and that a pitting mechanism was predominate. Precipitated corrosion products formed rings around the anodic sites. In the presence of (NH4)(2)SO4, the zinc surface was entirely active with only minimal corrosion product precipitation visible on the steel during the early stages of the reaction, and no significant increase in pH was observed in the vicinity of the cathodic reactions. At later stages, a film was formed and identified as a zinc hydroxysulfate compound by Raman spectroscopy. The experimental results are interpreted in terms of the equilibrium chemistry of the electrolytes. (c) 2005 The Electrochemical Society.