Electrochemical Impedance Spectroscopy of Epoxy-Vinyl Coating in Aqueous Medium Analyzed by Dipolar Relaxation of Polymer

Abstract

The performance of electrochemical devices, namely, the potentiostat, has increased considerably lately, and some commercial devices determine impedance on the order of teraohms (10 12 ⍀). At the same time, the protective effectiveness of paint films has also improved markedly, and the paint films exhibit capacitance behavior only in the millihertz range. Up to now, electrochemical impedance spectroscopy ͑EIS͒ spectra of polymer-coated specimens were interpreted with a mechanism involving only the film resistance due to flaws through the polymer layer and the film capacitance. However, since almost no flaw should be present at huge impedance, a new insight in the modeling of EIS data for polymer coated metal electrode is needed. Therefore, the concept of dipolar relaxation developed in polymer science is introduced to interpret EIS data. To compare the dipolar relaxation and the electrode impedance, the Cole-Cole capacitance determined straightforwardly from impedance spectra was found to be a very powerful tool. It is shown that the water uptake of a paint film could be evaluated from the Cole-Cole capacitance at infinite frequency C(ϱ), because the plasticizing effect induced by absorbed water in lower frequencies may lead to an overestimation of water uptake.Organic polymer coatings are widely used to reduce the corrosion of metallic structures exposed to aggressive media. Generally, it is considered that the paint film acts as a barrier layer that isolates the substrate metal from aggressive agents. 1,2 Therefore, the water uptake and ion migration inside the coating are determining factors of protective performance. [3][4][5] Electrochemical impedance spectroscopy ͑EIS͒ constitutes a powerful tool to evaluate these parameters. The EIS technique was applied for the first time in the early 1970s to the corrosion study for evaluating the protective effectiveness of paint film. 3 In early work, the measured impedance was low, and the resistance of organic coating was associated with the ionic conductance of electrolyte due to coating film breakdown, such as pores or crevasses. Electrolyte is then directly in contact with substrate metal, and the corrosion process takes place at delaminated areas of coating. This model is largely applied even in these days, and describes many corrosion circumstances. 6-8 In the last decade, the performance of electronic devices is considerably improved, which allows the measurements of higher and higher impedances. Nowadays, the measured modulus is huge, on the order of teraohms. 9 EIS becomes then sensitive to the intrinsic film conductance, due to ionic impurities in the film. The mobility of macromolecular chains and that of ions inside polymer layer becomes the determining factor of the film properties. Consequently, it becomes necessary to associate the EIS spectra to the relaxation of organic macromolecules and intrinsic ionic conduction. 10 A coating of epoxy-vinyl paint often protects pumping stations and tubing with mild steel structures in agricultural irrigation system...

Effect of some tripodal bipyrazolic compounds on C38 steel corrosion in hydrochloric acid solution

“…The recorded EIS spectra in uninhibited and inhibited medium show one depressive capacitive loop. The depressed semicircular appearance is often attributed to Cole-Cole [15,16] and/or ColeDavidson [17] representations and referred to frequency dispersion as a result of the non-homogeneity or the roughness of the solid state [18]. The equivalent circuit involves only one time constant (R e -(R ct -C dl )), fits well the experimental results.…”

New Mechanism Synthesis of 1,4-Benzothiazine and its Inhibition Performance on Mild Steel in Hydrochloric Acid

“…A depressed semicircle, as often obtained in acidic media [4,5,11] can be seen. The difference from theoretical results is generally attributed to Cole-Cole [35,36] and/or Cole-Davidson [37] representations inherent to frequency dispersion, generally attributed to the generation of microscopic roughness at the surface during the corrosion process [38,39]. The existence of single semicircle relates the presence of single charge-transfer process, which is unaffected by the presence of 1,4-BT.…”

Interpretation of EIS data from accelerated exposure of coated metals based on modeling of coating physical properties

“…Electrochemical impedance spectroscopy (EIS) is commonly used to examine and rank the protective ability of corrosion protective organic coatings [1][2][3][4][5][6][7][8][9][10]. The method, in general, is used in a qualitative or semi-quantitative manner, due to large variances between replicates and the difficulty in producing identical coating samples.…”