Abstract
Localized corrosion and biofouling cause very serious problems in the marine industries, often related to financial losses and environmental accidents. Aiming to minimize the abovementioned, two types of hybrid Zn-based protective coatings have been composed. They consist of a very thin underlayer of polymer-modified ZnO or CuO nanoparticles and toplayer of galvanic zinc with a thickness of ~14 µm. In order to stabilize the suspensions of CuO or ZnO, respectively, a cationic polyelectrolyte polyethylenimine (PEI) is used. The polymer-modified nanoparticles are electrodeposited on the steel (cathode) surface at very low cathodic current density and following pH values: 1/CuO at pH 9.0, aiming to minimize the effect of aggregation in the suspension and dissolution of the CuO nanoparticles; 2/ZnO at pH 7.5 due to the dissolution of ZnO. Thereafter, ordinary zinc coating is electrodeposited on the CuO or ZnO coated low-carbon steel substrate from a zinc electrolyte at pH 4.5–5.0. The two-step approach described herein can be used for the preparation of hybrid coatings where preservation of particles functionality is required. The distribution of the nanoparticles on the steel surface and morphology of the hybrid coatings are studied by scanning electron microscopy. The thickness of the coatings is evaluated by a straight optical microscope and cross-sections. The protective properties of both systems are investigated in a model corrosive medium of 5% NaCl solution by application of potentiodynamic polarization (PDP) curves, open circuit potential (OCP), cyclic voltammetry (CVA), and polarization resistance (Rp) measurements. The results obtained allow us to conclude that both hybrid coatings with embedded polymer-modified CuO or ZnO nanoparticles ensure enhanced corrosion resistance and protective ability compared to the ordinary zinc.
Highlights
Corrosion of metals, and, in particular, low-carbon steel, is a global problem that causes major economic, social, and environmental damage [1]
The protective properties of both systems are investigated in a model corrosive medium of 5% NaCl solution by application of potentiodynamic polarization (PDP) curves, open circuit potential (OCP), cyclic voltammetry (CVA), and polarization resistance (Rp) measurements
The results obtained allow us to conclude that both hybrid coatings with embedded polymer-modified CuO or ZnO nanoparticles ensure enhanced corrosion resistance and protective ability compared to the ordinary zinc
Summary
In particular, low-carbon steel, is a global problem that causes major economic, social, and environmental damage [1]. The higher protective ability of steel substrates from localized corrosion can be obtained, for example, by application of polyaniline-based composite coatings [7] or by deposition/electrodeposition of a modified ZnO nanoparticles layer on their surface [8,9,10,11,12,13,14]. Polarization curves of ZnO-alginate coated steel show a lower corrosion current compared to the bare steel It seems that electrophoretic deposition of colloidal particles is a fast and efficient method for obtaining uniform coatings on metallic surfaces [12,15,16]. Lowering the pH below 6.5 was found to increase the particles’ charge, but the ZnO dissolved rapidly under acidic conditions Another method for stabilization of particles suspension is surface modification using polyelectrolytes, which can control electrostatic (and steric) forces between particles. A comparative conclusion about the protective characteristics concerning both hybrid coating systems and ordinary zinc in that model medium is completed
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