Constant-phase-element behavior caused by inhomogeneous water uptake in anti-corrosion coatings

The impedance of a substrate/coating/electrolyte system was calculated with the assumptions: (i) the coating uptakes electrolyte to an extent that progressively decreases from the coating/electrolyte interface to the substrate/coating interface where it becomes negligible; (ii) the volume fraction of the electrolyte varies along the coating thickness according to a power-law; (iii) the resistivity and permittivity profiles of the electrolyte-penetrated coating can be calculated through an effective medium theory (EMT) formula corresponding to a parallel combination of the two media (electrolyte and coating material); and (iv) some pores extend from the coating/electrolyte interface to the substrate/coating interface, providing a low resistance path. The impedance plots thus calculated exhibited a constant phase element (CPE) behavior in a large frequency range. Some experimental results obtained with 2024 aluminum alloy/hybrid sol–gel coating samples immersed in a NaCl solution were analyzed with reference to the above described model. The extension of the recently developed power-law CPE model to anti-corrosion coatings is shown to yield insight into the distribution of resistivity and associated water uptake. Evaluation of mixing rules for conductivities and permittivities of the two media (coating and electrolyte) showed that the linear combination provided results that were consistent with the observed impedance response; whereas, distributions resulting from a series combination of the two media, an EMT formula proposed in the literature, and the Maxwell approximation were incompatible with the observed CPE impedance response.

[1]  J. Jorcin,et al.  CPE analysis by local electrochemical impedance spectroscopy , 2006 .

[2]  Vincent Vivier,et al.  Constant-Phase-Element Behavior Caused by Resistivity Distributions in Films I. Theory , 2010 .

[3]  H. Takenouti,et al.  Influence of the coating-substrate interactions on the corrosion protection: characterisation by impedance spectroscopy of the inner and outer parts of a coating , 2003 .

[4]  F. Mansfeld,et al.  Evaluation of Corrosion Behavior of Coated Metals with AC Impedance Measurements , 1982 .

[5]  Su-Moon Park,et al.  Electrochemical impedance spectroscopy. , 2010, Annual review of analytical chemistry.

[6]  N. Pébère,et al.  Corrosion inhibition of 2024 aluminium alloy by sodium decanoate , 2010 .

[7]  I. Epelboin,et al.  Etude electrochimique, et par microscopie electronique a balayage, du fer recouvert de peinture , 1976 .

[8]  Charles W. Tobias,et al.  On the Conductivity of Dispersions , 1959 .

[9]  Vincent Vivier,et al.  Constant-Phase-Element Behavior Caused by Resistivity Distributions in Films II. Applications , 2010 .

[10]  D. M. Brasher,et al.  Electrical measurements in the study of immersed paint coatings on metal. I. Comparison between capacitance and gravimetric methods of estimating water-uptake , 2007 .

[11]  Mark E. Orazem,et al.  Enhanced Graphical Representation of Electrochemical Impedance Data , 2006 .

[12]  A. Roche,et al.  The Role of the Residual Stresses of the Epoxy-Aluminum Interphase on the Interfacial Fracture Toughness , 2006 .

[13]  G. G. Stokes "J." , 1890, The New Yale Book of Quotations.

[14]  Lorenzo Fedrizzi,et al.  Electrochemical impedance spectroscopy as a tool for investigating underpaint corrosion , 1996 .

[15]  Quan Su,et al.  Interpretation of EIS data from accelerated exposure of coated metals based on modeling of coating physical properties , 2006 .

[16]  Florian Mansfeld,et al.  Electrochemical impedance spectroscopy (EIS) as a new tool for investigating methods of corrosion protection , 1990 .

[17]  B. Hinderliter,et al.  Electrochemical impedance spectroscopy response of water uptake in organic coatings by finite element methods , 2006 .

[18]  Vincent Vivier,et al.  Local electrochemical impedance spectroscopy: Considerations about the cell geometry , 2008 .

[19]  M. Orazem,et al.  Constant-Phase-Element Behavior Caused by Coupled Resistivity and Permittivity Distributions in Films , 2011 .

[20]  A. Roche,et al.  Residual stresses and practical adhesion: effect of organo-metallic complex formation and crystallization , 2006 .

[21]  Michel Keddam,et al.  New methods for the study of organic coatings by EIS , 2001 .

[22]  Vincent Vivier,et al.  Determination of effective capacitance and film thickness from constant-phase-element parameters , 2010 .