Characterization of Biofilm Formation and Coating Degradation by Electrochemical Impedance Spectroscopy

Samanbar Permeh,Kingsley Lau,Matthew Duncan

doi:10.3390/coatings9080518

Samanbar Permeh, Kingsley Lau + Show 1 more

Open Access

https://doi.org/10.3390/coatings9080518

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Abstract

Recent findings showed severe localized corrosion of submerged steel bridge piles in a Florida bridge and was associated with microbial activity in the presence of marine foulers. Microbiologically influenced corrosion (MIC) can cause severe degradation of submerged steel infrastructure with the presence of biofilm associated with microorganisms such as sulfate reducing bacteria (SRB). Coatings have been developed to mitigate MIC and marine fouling. Coating degradation and disbondment can occur as a result of microbial attack due to the production of metabolites that degrade coating chemical and physical properties. In the work described here, electrochemical impedance spectroscopy (EIS) was conducted to identify microbial activity and degradation of an antifouling coating exposed to SRB-inoculated modified Postgate B solution. The measurements resulted in complicated impedance with multiple loops in the Nyquist diagram associated with the coating material, development of surface layers (biofilm), and the steel interface. Deconvolution of the impedance results and fitting to equivalent circuit analogs were made to identify coating characteristics and surface layer formation. EIS test results revealed coating degradation and subsequent formation of surface layers associated with SRB due to coating self-polishing and depletion of biocide components.

Highlights

For steel civil infrastructure, protective coatings can be applied to mitigate corrosion of the metal substrate by providing a barrier to the service environment [1].coating components such as active metallic layers or pigments can provide beneficial cathodic polarization of the steel substrate
The measurements resulted in complicated impedance with multiple loops in the Nyquist diagram associated with the coating material, development of surface layers, and the steel interface
electrochemical impedance spectroscopy (EIS) test results revealed coating degradation and subsequent formation of surface layers associated with sulfate reducing bacteria (SRB) due to coating self-polishing and depletion of biocide components

Summary

Introduction

Protective coatings (including organic and metallic coatings) can be applied to mitigate corrosion of the metal substrate by providing a barrier to the service environment [1] Coating components such as active metallic layers or pigments can provide beneficial cathodic polarization of the steel substrate. Potentiostatic EIS measurements over a wide range of perturbation frequencies can identify the electrical characteristics associated with the coating material, steel substrate, surface films, and surface polarizability Identification of these characteristics provides information on the coating condition, its degradation, film development, and steel corrosion activity. The impedance response of a commercially-available water-based copper-free ablative antifouling coating with organic metal-free biocide (Econea: 4-bromo-2-(4-chlorophenyl)-5-(trifluoromethyl)-1H-pyrrole-3-carbonitrile [22]), ZnO, TiO2 and zinc pyrithione, applied on steel immersed in solutions inoculated with sulfate-reducing bacteria, was assessed to identify its efficacy to reduce bacterial growth as well as coating corrosion durability. Comparative testing with polyurea coated steel specimens were made as well

Methodology

Overview of Impedance Response

High-Frequency Impedance Behavior

10. Resolved

Intermediate Frequency and Biofilm Development

Low-Frequency Behavior