Full Paper Localised Measurements of pH and Dissolved Oxygen as Complements to SVET in the Investigation of Corrosion at Defects in Coated Aluminum Alloy A. C. Bastos ,* O. V. Karavai, M. L. Zheludkevich, K. A. Yasakau, M. G. S. Ferreira DECV/CICECO, Universidade de Aveiro, 3810-193 Aveiro, Portugal *acbastos@ua.pt Received: January 29, 2010 Accepted: March 8, 2010 Abstract This paper presents measurements of local pH and local oxygen reduction current performed to complement SVET (Scanning Vibrating Electrode Technique) in the characterization of the chemical environment near artificial defects on coated 2024-T3 aluminum alloy during corrosion and inhibition. The main purpose is to give examples on how micropotentiometry and microamperometry can add supplementary information to SVET, providing important insights for the understanding of corrosion mechanisms and inhibition processes necessary to develop effective self- healing coatings. Keywords: Corrosion, Microelectrodes, Oxygen reduction, pH, SVET DOI: 10.1002/elan.201000076 Presented at the International Conference on Modern Electroanalytical Methods Prague, December 9 – 14, 2009 1. Introduction Application of protective organic coatings is the most widespread anticorrosive method due to low cost, versatility and simple application [1, 2]. Frequently, the degradation of coated metals begins in small areas where the metallic substrate becomes exposed, either due to improper paint application (e.g. pinholes) or by later damage (e.g. scratch- es) [1, 3]. It is important to understand the mechanisms of corrosion in these confined areas and how inhibitors that may be added to the coatings can retard the corrosion progression. The majority of the techniques give the average response of the whole sample area, overlooking the differ- ence in reactivity at the defects and at the remaining area. The spatial distribution of the corrosion processes can be obtained by localized techniques. The application of SECM (Scanning Electrochemical Microscopy) with micro- and nanoelectrodes for localized electrochemical studies has been recently reviewed [4]. In the case of coated metallic substrates, SECM operating in AC mode allows the identification of the areas with higher conductivity, resulting from the increased concentration of ionic species near the active defects. This method is rather qualitative and can be used only in low-conductivity solutions [5], which hardly is the case of corrosive aqueous environments. Another technique, the Scanning Vibrating Electrode Technique (SVET), detects the potential gradients that develop around anodic and cathodic areas as a consequence of current flow [6, 7]. It makes possible to know the spatial evolution of cathodic and anodic processes in a corroding sample. This information is unique and extremely useful for the descrip- tion of many corrosion systems. The technique is only sensitive to charged species and doesnt give the identity of the species detected. Such identification can be done using potentiometric [8 – 12] and amperometric [13 – 16] micro- electrodes. In this paper, micropotentiometric measurements of pH and microamperometric measurements of dissolved oxygen were used as complements to SVET in the investigation of corrosion and inhibition of coated 2024-T3 aluminum alloy with artificial defects. The samples were immersed in 0.05 M NaCl and measurements were performed before and after the addition of a corrosion inhibitor (cerium nitrate) to the solution. The objective was to simulate the release of the inhibitor (it was added directly to solution instead of the slow leaching from the coating) and check the potential of these techniques to study the kinetics of corrosion and inhibition processes. Ultimately, the idea is to verify their ability to probe self-healing properties of new coatings, which is, these days, a hot topic in the protective coatings field [17, 18]. Here, only two species were probed. A better, more complete, picture would be obtained if more species were measured. Full Paper Electroanalysis 2010, 22, No. 17-18, 2009 – 2016  2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim 2009