Electrochimica Acta 53 (2008) 6484–6488 Contents lists available at ScienceDirect Electrochimica Acta journal homepage: www.elsevier.com/locate/electacta Impedance characterization of the electrochemical environment under a polymer ﬁlm artiﬁcially delaminated A. Rubin a , R. Oltra a,∗ , B. Vuillemin a , K. Ogle b a Institut CARNOT de Bourgogne, UMR 5209 CNRS-Universit´ e de Bourgogne, Dijon, France b Laboratoire de Physico-Chimie des Surfaces, UMR 7045 CNRS-ENSCP, Paris, France article info Article history: Received 25 January 2008 Received in revised form 7 April 2008 Accepted 8 April 2008 Available online 16 April 2008 Keywords: Steel Organic coatings Delamination Microelectrodes Impedance abstract Knowledge of the electrical conductivity of the zone under a delaminated paint ﬁlm is one necessary input parameter for the simulation of electrochemically driven underpaint corrosion. In this work, a micro- electrode array system has been developed, tested, and applied to measure the spatial distribution of resistivity in the delaminated zone along the metal/polymer interface. The experimental device consists of a linear array of six 100 m diameter stainless steel microelectrodes (100 m in diameter) embedded in a steel substrate. A polymer coating was applied and an artiﬁcial “delaminated zone” was created using the laser-induced decohesion technique. The electrochemical impedance was measured between the ﬁrst uncovered electrode and the electrodes at progressively increasing distances in the artiﬁcial delaminated zone. A steady decrease in the impedance with time can be observed, probably due to the continued ingress of electrolyte and a variation of the gap width. © 2008 Elsevier Ltd. All rights reserved. 1. Introduction The delamination of paint ﬁlms on metal surfaces may be pro- voked by electrochemical reactions occurring under the paint [1,2]. Although many basic questions remain unanswered, there has been signiﬁcant progress in the mechanistic understanding of delami- nation phenomena in the last two decades, due to the advent of new experimental methodologies such as the Kelvin probe [3–9], impedance spectroscopy [10–13], and the use of underpaint micro- electrodes to detect impedance characteristics and pH changes [14]. Recently a ﬁnite element model for underpaint corrosion was based on empirical parameters determined from Kelvin probe experiments [15,16]. The model, although oversimpliﬁed and requiring a large number of adjustable parameters, was able to predict the order of the delamination reaction and several other experimental features of the curves. There are two major issues for this model: (1) the nature of the rate limiting step for cathodic delamination is not well understood; (2) the geometry of the delaminated metal/polymer interface is not well deﬁned. Recent work has strongly suggested that the rate limiting step for cathodic delamination involves the attack of the oxide conver- sion coating by hydroxide species [7] and a characterizing in the ∗ Corresponding author. Tel.: +33 380 39 61 62. E-mail address: roland.oltra@u-bourgogne.fr (R. Oltra). chemical stability of the conversion layers has been proposed using ICP atomic emission spectroelectrochemistry and microelectrodes embedded under the paint layer. This paper addresses the problem of the geometry of the delam- inated layer and electrical conduction along the metal/polymer interface. The idea is to place a series of microelectrodes under the organic ﬁlm at an increasing distance from the artiﬁcial defect. In this way, the impedance characteristics of the interface may be accurately measured and used to determine a hypothetical geom- etry for ﬁnite element modelling of delamination phenomena. It is thought that a transmission line model could be used to account for the electrical impedance of the interface. This paper describes the development of a microelectrode array allowing an in situ electrochemical impedance spectroscopy analy- sis under polymer coating artiﬁcially delaminated from the metallic substrate. To develop such an inserted microelectrode array, a critical issue lies in the experimental steps regarding the microelec- trodes insertion and the generation of the delaminated area. In the literature previous works report several designs which reproduce an artiﬁcial delaminated gap. This gap can be simulated by con- ﬁning the electrolyte under an artiﬁcial holiday [17–19] or under an actual polymer [4,7]. Among these artiﬁcial conﬁned volumes, two types of technique emerged: electrodes stand outside or above the conﬁned volume [17,18] or are inserted inside the sample, as proposed by Leng and Li [4,19]. Like these later studies, the present work focuses on in situ measurements but using smaller microelec- trodes inserted in a steel matrix. 0013-4686/$ – see front matter © 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.electacta.2008.04.022