Investigation of the corrosion behavior of carbon steel with a protective superhydrophobic coating by impedance spectroscopy method

• L.E. Tsygankova¹, M.N. Uryadnikova¹, V.I. Kichigin² and L.D. Rodionova¹

¹ Derzhavin State University, Internatsyonalnaya str., 33, 392000 Tambov, Russian Federation
² Perm State University, str. Bukireva, 15, 614990 Perm, Russian Federation

Abstract: The impedance spectra of a steel electrode with a superhydrophobic coating obtained at the corrosion potential Е_cor in solutions of NaCl (50 g/L) and NACE (0.25 g/L CH₃COOH, 5 g/L NaCl, pH=3.6) in the absence and presence of 400 mg/L H₂S are analyzed. Frequency impedance spectra were recorded after 15 minutes of exposure in the working solution and every day for 168 hours without removing electrode from the solution. Three equivalent circuits are considered that model the processes occurring on the electrode at the corrosion potential. The most acceptable circuit is one that is characterized by smaller deviations of the calculated impedance values from the experimental ones. It is a parallel connection of four circuits: electrical double layer capacitance C_dl; a series combination of resistance R_c and diffusion impedance Z_d simulating the cathodic process; anodic reaction resistance R_a; a series combination of R₁ and C₁ (the elements R_a, R₁, C₁ model the anodic process). This equivalent circuit can describe impedance spectra with three time constants, which are observed in some cases experimentally. Calculation of corrosion rates in the studied media using impedance data showed that in the NACE environment in the presence of H₂S after 24 hours of exposure, the corrosion rate is 40% lower, and after 168 hours, 2.3 times higher than in the absence of H₂S. These results are in qualitative agreement with those obtained by the method of polarization curves. The observed changes in the parameters of the equivalent circuit with time are mainly associated with the influence of two processes – gradual degradation of the hydrophobic coating and the growth of a protective film of corrosion products.

Keywords: steel, superhydrophobic coating, corrosion rate, solution, hydrogen sulfide, impedance spectroscopy, equivalent circuit

Int. J. Corros. Scale Inhib., 2021, 10, no. 1, 186-205 PDF (815 K)
doi: 10.17675/2305-6894-2021-10-1-11

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