Determination of corrosion characteristics of steel protected by a latex coating in Nyquist coordinates

Abstract

This paper investigates the corrosion process of steel St3 protected by latex coating 69Б-2к produced by Kapitel Ltd (Irkutsk). Electrochemical impedance spectroscopy of steel samples with a threefold latex coating was carried out by a PGSTAT302 + FRA2 potentiostat-galvanostat equipped with NOVA 1.8. Corrosion studies were carried out under thermostating (25 ± 0.2°C) of the working environment. The corrosion rate was determined by gravimetric tests with the recording of mass changes over a controlled period of time (up to 10 h). A 3% sodium chloride solution was used as the electrolyte. In most cases, the mechanism of the corrosion process can be reliably described by an equivalent electrochemical circuit with Warburg and Cotangent Hyperbolic elements, which simulates the reaction at the electrodeelectrolyte interface. According to the conducted visual, gravimetric and electrochemical studies of the St3 steel surface protected with the 69B-2k latex coating, the impedance remains almost unchanged for a prolonged period of time. It is obvious that the surface process is associated with the limiting stage of solvent diffusion through the protective layer. Thus, the electrochemically determined corrosion rate was low and amounted to ~ 0.164 mm/year (for reference samples – 0.75 mm / year). Our studies confirmed high protective qualities of latex 69B-2k. The corrosion properties of the coating under study are related to its composition, the components of which not only exhibit good adhesion, but are also active with respect to other interactions, including chemical interactions of the components with each other and with metal surface crystallites. The model calculation of the process, carried out using the developed equivalent electrochemical circuit, describes experimental curves in Nyquist coordinates almost comprehensively.