Localized Electrochemical Methods Applied to Cut Edge Corrosion

Abstract

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.

Galvanic Corrosion of a Zn/steel Couple in Aqueous NaCl

“…Several researchers have reported, based on SVETs, that cathodic reactions such as the ORR and HER are inhibited by the precipitation of zinc-based corrosion products. [10][11][12][13] The results obtained herein agree well with those reports. In addition, Yadav et al measured cathodic polarization curves for zinc with and without zinc corrosion products using a rotating ring disk electrode and reported the inhibition of ORR by the precipitation of zinc corrosion products.…”

Galvanic corrosion between zinc and carbon steel investigated by local electrochemical impedance spectroscopy

“…It is noteworthy that the corrosion potential of the galvanic couple was controlled by the cathodic reaction of dissolved oxygen (plateau current). Note that the SVET has been already used to determine localized polarization curves demonstrating the diffusion limited reaction on the steel and electron transfer limited reaction on zinc as demonstrated here in galvanic coupling [20]. Fig.…”

“…5. Some authors mentioned the presence of precipitated zinc corrosion products on the steel in more concentrated NaCl solution using a similar bi-electrode [20]. The change of the local current distribution occurring by the presence of such products should explain the unexpected increase of admittance in Fig.…”

“…More recently, with the development of local electrochemical techniques, which allow local processes at a microscale to be investigated, the study of galvanic coupling, has known a renewed interest. For example, scanning vibrating electrode technique (SVET) and scanning electrochemical microscopy (SECM) have been used to study the galvanic coupling between zinc and steel (or iron) [13][14][15][16][17][18][19][20][21]. Simoes et al reported that the SVET and the SECM techniques provide complementary and consistent information on the local ionic fluxes and local reagents and products concentrations due to the cathodic and anodic reactions occurring above the zinc/iron surface during the galvanic coupling.…”

Corrosion Mechanism Suggested Based on Electrochemical Analysis and SVET for Uncoated Tinplate and Post Coated With a Hybrid Film

“…The scanning vibrating electrode technique (SVET) has been applied to characterize a great variety of corrosion systems [21][22][23][24] . The visualization of the corrosion progression is given in terms of the identification of anodic and cathodic regions with an estimation of the respective currents and their evolution 25 .…”