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In this work a new spectroelectrochemical method based on an inductively coupled plasma atomic emission spectrometry has been developed and used to measure the elementary dissolution rates of Fe, Cr, Ni, Mn, Mo, and Cu simultaneously during linear scan voltammetry of a 304 stainless steel in the active region. Simultaneous dissolution was observed for all elements with the exception of copper, which appeared in solution at a potential approximately 100 mV more positive. The Tafel slopes for Fe, Cr, Ni, and Mn partial dissolution rates were measured around the corrosion potential and found to be identical within experimental error, between 59 and 68 mV/decade. The anodic dissolution of copper in acidic chloride and sulfate solutions was used to establish the quantitative relationship between the concentration transients and the dissolution rate. The residence time distribution of the electrochemical flow cell was determined using galvanostatic pulses of copper or stainless steel dissolution. The experimental residence time distribution could be approximated to a high degree of accuracy at both long and short times by a log-normal distribution. The effect of the residence time distribution on the shape of partial elemental current transients during linear scan voltammetry was investigated by numerical simulation.

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Current density and pH mapping techniques have been used to characterize the chemical and electrochemical phenomena which occur on the cut edge of galvanized steel. pH variations between 7 and 11 were observed, primarily due to the formation of hydroxyl ions by the cathodic reaction. Zinc‐based corrosion products precipitated in zones of intermediate pH were identified as ZnO and 3normalZnfalse(OH)2·2ZnCO3 for model samples. The efficiency of these corrosion products as cathodic inhibitors was demonstrated by the absence of cathodic activity at open circuit and a −300 mV negative shift of the onset potential for hydrogen formation in the affected zones. The cathodic current, localized over the steel, was independent of potential, consistent with a diffusion‐limited reduction of oxygen. The anodic current, localized over the zinc, varied with potential, with a Tafel slope of 44 mV/decade for an order of magnitude decrease of potential below open circuit. The addition of SrCrO4 to the electrolyte increased the Tafel slope to 63 mV/decade, consistent with a passivating inhibitor on the anode surface. © 2000 The Electrochemical Society. All rights reserved.

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The scanning vibrating electrode technique ͑SVET͒ 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 ͑NH 4 ͒ 2 SO 4 , 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.