Evolution of EIS properties of composite polymer protective coatings in corrosive media

• V.A. Golovin and S.A. Dobriyan

A.N. Frumkin Institute of Physical Chemistry and Electrochemistry, Russian Academy of Sciences, Leninskii pr. 31, 119071 Moscow, Russian Federation

Abstract: Electrochemical impedance spectroscopy (EIS) was used for a comparative study of the evolution of the electrochemical characteristics of protective primers, inert insulating coatings, and multilayered polymer composite coatings in chloride media. It was shown that the layers of coating with inert fillers on an inert substrate could be described as the simplest equivalent circuit (EC) with a single characteristic relaxation process in the entire range of exposure times. The same EC describes coatings on a potentially corroding substrate at the initial exposure stage. Later, as underfilm corrosion develops, the EC evolves into a system with two relaxation processes. In thin-layer systems with an active filler (Zn), the two relaxation processes are manifested starting from the initial exposure period. In thick multilayered composite coatings that contain spatially separated layers with reactive and inert fillers on a corroding steel substrate, three characteristic relaxation times are observed. These findings agree with the model of multiphase laminated volume-filled polymer composite materials and provide a justification to the usage of Voigt’s additive ECs. Using this approximation, we performed a description of all EIS data for all the systems we considered at various temperatures, including inert layers based on steel and platinum, thin and multilayered Zn-rich primer layers, and multilayered coatings made of these materials. The results obtained allowed us to suggest a technique of nondestructive EIS monitoring of the physicochemical and corrosion processes in composite polymer protective coatings. The technique is based on performing comparative electrochemical impedance spectroscopy on various metal (corroding and inert) substrates at various temperatures and identification of the processes using characteristic frequencies, effective activation energies, and corrosion rate during exposure.

Keywords: corrosion protection, polymer coatings, underfilm corrosion, electrochemical impedance spectroscopy, equivalent circuit

Int. J. Corros. Scale Inhib., 2021, 10, no. 4, 1493-1515
doi: 10.17675/2305-6894-2021-10-4-8

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