Spectroscopie d'impédance électrochimique appliquée à l'étude de la corrosion

Abstract

Résumé -Nous allons présenter différentes applications de la spectroscopie d'impédance électrochimique réalisées depuis 40 ans. Au début de cette longue histoire, l'emploi de signaux alternatifs était destiné à remplacer la méthode stationnaire dite de Stern et Geary, c'est-à-dire la mesure de la résistance de polarisation. Cependant, rapidement nous avons constaté que le spectre d'impédance contenait plusieurs informations sur les phénomènes se déroulant à l'interface métal | électrolyte. Ils se manifestent par une constante de temps propre à chaque processus, donc généralement distinguables par une analyse en fréquence. Après avoir présenté la différence majeure entre la méthode stationnaire et la méthode d'impédance dans l'étude de la corrosion à la fois en termes de compréhension des méca-nismes et de prévision de sa vitesse, nous aborderons plusieurs applications de cette dernière méthode : la résistance d'électrolyte, l'effet protecteur d'inhibiteurs organiques et la protection de bronzes archéologiques recouverts de patine. Key words:Faradic impedance; inhibitor; relaxation; bronze; cultural heritage Abstract -Electrochemical Impedance spectroscopy applied to the corrosion study. Various applications of the Electrochemical Impedance Spectroscopy over the last 40 years are described. At the beginning of this long history, ac signal has been used simply to determine steady state entity, the polarisation resistance to apply Stern-Geary method. However, it was remarked immediately that the impedance spectrum contains many useful information on the processes taking place at the corroding interface. These processes are revealed by a specific time-constant for each phenomenon, therefore they can be distinguished by analysing the impedance spectrum in the frequency domain. After describing the main difference between the steady-state and impedance methods for the corrosion investigation for the understanding of corrosion mechanism as well as the estimation of corrosion rate, we will show several aspects of the latter method: Electrolyte resistance, protective effect of corrosion inhibitor and the protection of bronze archaeological artefacts covered with patina.

Impedance Analysis of Electrochemical Systems

“…A generalized electrochemical system can be expressed as a function of the interfacial potential V and a quantity X which is a characteristic of the system (e.g., the surface concentration of bulk species c i (0) or the surface coverage of adsorbed species ). In the time domain, the Faradaic current can thus be expressed as a function of V ( t ) and X ( t ), i.e., The response to a perturbation can be derived from the first-order Taylor expansion around the steady-state value as where and are steady values. Similarly, for a small perturbation amplitude, a state function may be expressed as where and Equation developed in section provides an example of the type of expression given as eq .…”

“…A generalized electrochemical system can be expressed as a function of the interfacial potential V and a quantity X which is a characteristic of the system (e.g., the surface concentration of bulk species c i (0) or the surface coverage of adsorbed species k γ ). In the time domain, the Faradaic current can thus be expressed as a function of V(t) and X(t), i.e., 85 i…”

Corrosion inhibition of API5L X60 steel in sulfuric acid using gum arabic

“…The decrease in Cdl shows that the adsorption of the inhibitor takes place on the metal surface in acidic solution; which can result from a decrease in local dielectric constant and/or an increase in the thickness of the electric double layer. 27,29 It also supports the same fact that tested inhibitor has highest adsorption capability due to its higher surface coverage area and a higher number of hetero atoms in its structure. 25 Furthermore, we note from Table 5 that inhibition efficiency increases with increase in concentration of GA with the highest value of 82% obtained at inhibitor concentration of 4 g /L.…”

“…Surface properties, electrode kinetics and mechanistic information can be obtained from the impedance diagrams. 27,28 In order to get more information about the corrosion behavior of the carbon steel, in acidic solution with and without GA, EIS measurements have been carried out at room temperature after 90 min of immersion. The Nyquist plots recorded for the corrosion inhibition of API 5L X60 steel with different concentrations of GA at OCP in 0.5 M H2SO4 are shown in Fig.…”