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The construction of anticorrosion coatings containing antifouling agents is an effective way to ensure the long-term durability of marine steel infrastructures. In this work, an innovative hybrid coating was prepared by introducing biocide CuO nanoparticles in ordinary zinc coating to improve its protective ability for steel in aggressive salt water environments. The CuO nanoparticles were embedded inside the matrix of chitosan/alginate complexes to prevent spontaneous copper leaching during corrosive attacks. Two procedures were applied for the electrodeposition of hybrid/composite zinc-based coatings on low-carbon steel substrates (DC current): first—the co-electrodeposition of encapsulated CuO nanoparticles with zinc on a cathode (steel) electrode from a sulfate electrolyte with a relatively low pH value of about 4.5–5.0 and second—the encapsulated CuO nanoparticles were electrodeposited from aqueous solution as an intermediate layer between two zinc deposits. The particles size and stability of suspensions were evaluated using dynamic light scattering. Both hybrid coatings were compared in terms of surface morphology and hydrophilicity (SEM and AFM analysis, contact angle measurement) and corrosion resistance (potentiodynamic polarization curves, polarization resistance). The protective characteristics of the coatings were compared in a 3.5% NaCl solution and artificial sea water. The hybrid coating showed 2–4 times higher polarization resistance than the bare zinc coating during a 30 day immersion in artificial sea water, indicating that this coating has the necessary characteristics to be used in a marine environment.

The presented investigations demonstrate the corrosion behavior and protective ability of hybrid zinc coatings specially designed for combined protection of low-carbon steel from localized corrosion and biofouling. Polymer-modified copper oxide (CuO) nanoparticles as widely used classic biocide are applied for this purpose, being simultaneously electrodeposited with zinc from electrolytic bath. The corrosion behavior of the hybrid coatings is evaluated in a model corrosive medium of 5% NaCl solution and in artificial sea water (ASW). Scanning electron microscopy (SEM) and atomic force microscopy (AFM) are used to characterize the surface morphology of pure and hybrid zinc coatings. Contact angle measurements are realized with an aim to determine the hydrophobicity of the surface. X-ray photoelectron spectroscopy (XPS) is applied for evaluation of the chemical composition of the surface products appearing as a result of the corrosion treatment. Potentiodynamic polarization (PDP) curves and polarization resistance (Rp) measurements are used to estimate the protective characteristics in both model corrosive media. The results obtained for the hybrid coatings are compared with the corrosion characteristics of ordinary zinc coating with the same thickness. It was found that the hybrid coating improves the anticorrosion behavior of low-carbon steel during the time interval of 35 days and at conditions of external polarization. The tests demonstrate much larger corrosion resistance of the hybrid coating in ASW compared to 5% NaCl solution. The obtained results indicated that the proposed hybrid zinc coating has a potential for antifouling application in marine environment.

The authors have demonstrated that incorporation of poly(ethyleneimine) (PEI) coated polyaniline-silica (PANI-SiO2) particles into the zinc coating matrix improves the corrosion resistance of low c...

Nitrogen-containing heterocyclic dicationic compounds with antioxidant properties have been synthesized and characterized by NMR spectroscopy. Their corrosion inhibiting behavior for zinc and steel protection have been studied by electrochemical polarization methods to assess the potential suitability of those compounds in hybrid galvanic zinc protective coatings. The individual assessment for corrosion inhibiting activity will facilitate the shortlisting of eligible candidates, help to avoid potential incompatibilities of ingredients, and reduce times in the process of designing hybrid coatings for corrosion protection. This study has found that the compounds have significant corrosion protecting effect on steel and zinc and those molecules were shortlisted for our future studies on galvanic hybrid coating of steel.

Zinc oxide arouses considerable interest since it has many applications—in microelectronics, environmental decontaminations, biomedicine, photocatalysis, corrosion, etc. The present investigation describes the green synthesis of nanosized ZnO particles using a low-cost, ecologically friendly approach compared to the classical methods, which are aimed at limiting their harmful effects on the environment. In this study, ZnO nanoparticles were prepared using an extract of Mentha arvensis (MA) leaves as a stabilizing/reducing agent, followed by hydrothermal treatment at 180 °C. The resulting powder samples were characterized by X-ray diffraction (XRD) phase analysis, infrared spectroscopy (IRS), scanning electron microscopy (SEM), and electron paramagnetic resonance (EPR). The specific surface area and pore size distribution were measured by the Brunauer–Emmett–Taylor (BET) method. Electronic paramagnetic resonance spectra were recorded at room temperature and at 123 K by a JEOL JES-FA 100 EPR spectrometer. The intensity of the bands within the range of 400–1700 cm−1 for biosynthesized ZnO (BS-Zn) powders decreased with the increase in the Mentha arvensis extract concentration. Upon increasing the plant extract concentration, the relative proportion of mesopores in the BS-Zn samples also increased. It was established that the photocatalytic performance of the biosynthesized powders was dependent on the MA concentration in the precursor solution. According to EPR and PL analyses, it was proved that there was a presence of singly ionized oxygen vacancies (V0+) and zinc interstitials (Zni). The use of the plant extract led to changes in the morphology, phase composition, and structure of the ZnO particles, which were responsible for the increased photocatalytic rate of discoloration of Malachite Green dye.

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.

One-component CeO2 coatings and bi-component CeO2/ZrO2 multilayer coatings were obtained by a sol gel process. The phase composition, surface morphology and roughness of the samples were studied by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), Atomic force microscopy (AFM) and X-ray scanning electron microscopy (XPS). The corrosion resistance and protective ability were characterized by using salty solution of 3.5% NaCl at 25 °C. The multilayer configuration of CeO2 and ZrO2 ensure enhanced protection of the steel in comparison to the single CeO2 coatings and uncoated steel. The surface morphology and anticorrosion properties depend significantly on the treatment temperature of both CeO2 underlayer and ZrO2 top layer. At lower treatment temperatures, they are relatively dense and smooth. The corrosion resistance of the multilayers slows down, when ZrO2 coatings were heated above 500 °C. This probably is due to the more pronounced crystallization of cubic zirconium dioxide, resulting in deeper boundaries between the individual grains. The protective properties of a CeO2/ZrO2 multilayers could be attributed to the low crystallized structure with very fine crystallites. Potentiodynamic measurements showed that all multilayer systems have more negative corrosion potential values compared to the corrosion potential of the steel substrate and will protect it in the case of corrosion attack due to electrochemical reasons.

Core-shell nanocontainers (NCs) with corrosion inhibitor benzotriazole (BTA) are fabricated by electrostatic self-assembly of poly(diallyldimethylammonium chloride) (PDADMAC) and poly(acrylic acid) (PAA) on kaolinite and hematite particles. BTA is entrapped within the polyelectrolyte shell in one assembly step. The growth of the polymer shells and stability of the NCs suspensions against aggregation are followed by electric light scattering and electrophoresis The NCs loaded with BTA are incorporated into the matrix of ordinary zinc coatings by electrodeposition on steel substrates from acidic zinc sulfate solutions. The influence of the NCs on cathodic and anodic processes is analyzed in the starting zinc sulfate solution with cyclic voltammetry. The scanning electron microscopy shows random (near to uniform) distribution of the NCs in both hybrid coatings. The protective characteristics of the hybrid coatings in model medium of 5% NaCl are followed by means of potentiodynamic polarization curves, polarization resistance measurements and electrochemical impedance spectroscopy. XPS method is applied for determination of the nature of additional products appearing on the coatings as a result of the corrosion treatment. Both hybrid zinc coatings reveal improved corrosion protection of steel as compared to the pure zinc coating, the coating with kaolinite-based NCs showing better protective characteristics in comparison with the one incorporating hematite NCs.

Dense, highly textured, hydrophobic ZrO2-TiO2 (1:1) coatings with amorphous structure were prepared using the sol-gel method. Both organic and inorganic zirconium precursor salts were used. The present study dealt with the investigation of their protective ability in a selected model corrosive medium with chloride ions as corrosion activators. The coatings showed good anticorrosion performance during the test, which was demonstrated both by the weight loss method and potentiodynamic polarization curves. The samples were characterized by means of X-ray diffraction (XRD), Atomic Force Microscopy (AFM), contact angle measurements, Infrared spectroscopy (IRS), Scanning Electron Microscopy (SEM), Differential Thermal analysis (DTA-TG) and X-ray photoelectron spectroscopy (XPS). It was established that the extent of influence of some factors, like treatment temperature (Ttr) and type of zirconium precursor, was different. The PD curves of samples treated at 400 °C (A4 and B4, respectively) demonstrated an increased effect of the precursor in comparison to Ttr, since the application of organic Zr salt led to deterioration of the anodic passivation zones. Contrary to this, the coatings obtained from both the organic and inorganic Zr precursor salts with Ttr = 500 °C had similar corrosion efficiency, i.e., the influence of the precursor was minimized. All investigated coatings had no visible corrosion damage. It seems that some complex structural and surface parameters, such as amorphous dense structure, surface smoothness, hydrophobicity and the surface chemical composition (low hydroxyl groups content), were responsible for the increased anticorrosion properties of the composite films.

The present work describes one possible way to prepare a stable aqueous suspension of carbon sphere particles with a positive charge that is suitable for simultaneous electrodeposition with zinc on steel substrate. In order to stabilize the suspension against aggregation, tri-block amphiphilic copolymer Pluronic F127, which is commercially available, was adsorbed on the surface of carbon sphere particles. This polymer contained poly (ethylene oxide) blocks as hydrophilic segments and poly (propylene oxide) blocks as the hydrophobic part. Scanning electron microscopy and visual observations confirmed the stability of the obtained suspension. The carbon sphere particles were embedded into the zinc coating by the co-electrodeposition process. The surface morphology of the composite coating was investigated using scanning electron microscopy. The influence of the carbon spheres on the cathodic and anodic processes was evaluated with cyclic voltammetry studies. The electrochemical investigations were realized in a model corrosion medium (5% NaCl solution with pH 6.7) by application of selected methods such as polarization resistance, potentiodynamic polarization, and electrochemical impedance spectroscopy, which revealed higher protective ability of the composite coating against corrosion in an aggressive environment.

The aim of the present investigation was to demonstrate a preparation method for obtaining an electrodeposited composite zinc coating with incorporated carbon nanotubes (CNT). The composite coatings were additionally treated in a newly developed conversion solution based on a Cr(III)-containing compound. The surface morphology of the Cr(III) and non-Cr(III) samples was investigated with scanning electron microscopy (SEM), the metallographic structure with X-ray diffraction analysis (XRD) and the composition with X-ray photoelectron spectroscopy (XPS). Composite zinc coatings without and with the surface conversion film (CF) have been investigated in a standard test medium of 5% NaCl solution by use of potentiodynamic polarisation (PDP) curves, electrochemical impedance spectroscopy (EIS) and polarisation resistance (Rp) measurements. The results obtained show the synergistic effect of the incorporated CNT and conversion film for achieving better corrosion resistance of the system composite Zn/CF i...

Ultrahigh molecular weight polyethylene (UHMWPE) coating and UHMWPE‑copper (UHMWPE-Cu) coatings with different copper content were fabricated using a sintering method. The thermal conductivity of the coatings increased with the increasing copper content, but the resistance to cavitation erosion did not. The most optimised resistance was achieved by the coating with 8.3 wt% copper, whose thermal conductivity was 22.7% greater and total volume loss after 10 h cavitation erosion was 14% lower than those of pure UHMWPE coating. Underdosed and overdosed copper can significantly compromise the cavitation erosion resistance, as there is a trade-off between the benefit of enhancing thermal conductivity and the cost of weakening interface bonding. In addition, all the coatings exhibited the same damaged features. The in-situ observation was performed by a 3D profilometer to reveal the failure mechanism, finding that the process of the tilt-initiated pealing-off was the main source of the failure, which composed of preferential attack at the interface, tilting of the splats, and the detachment of the splat.

The influence of stabilised polymeric micelles (SPM) on the structure, corrosion properties and durability of electrodeposited composite zinc coatings is presented and discussed. The core-shell-typ...

Hybrid zinc-based coatings with embedded polyaniline (PANI) particles in the metal matrix are obtained in a one-step process via electrodeposition on low-carbon steel plates. The aim is directly to use the inhibitor properties of polyaniline for improved protection against corrosion in chloride containing medium (5% NaCl solution). PANI-particles (concentration of 0.025 g/L) are added to the starting zinc electrolyte in dispersed form&mdash, the latter being obtained via oxidation polymerization in the presence of stabilizers (polyvinyl pyrrolidone (PVP) or colloidal SiO2). Electrodeposition conditions are equal to those for obtaining an ordinary zinc coating. The surface morphology of the hybrid coatings before and after corrosion treatment in the model medium is characterized with SEM. The influence of the incorporated PANI/PVP- or PANI/SiO2-particles on the protective properties of the coatings is evaluated by the application of electrochemical (potentiodynamic polarization, open-circuit potential, polarization resistance, cyclic voltammetry) as well as X-ray based (X-ray diffraction and X-ray photoelectron spectroscopy) methods. A discussion and some conclusions about the reasons for the improved corrosion resistance and protective ability of the hybrid coatings in that model medium are proposed.

Incorporation of zinc oxide (ZnO) nanoparticles and ZnO based nanocontainers with corrosion inhibitor Safranin into the matrix of standard zinc coatings is applied for preparation of coatings with improved corrosion protection for mild steel. A cationic polyelectrolyte polyethylenimine (PEI) is used to stabilize the ZnO suspension before electrodeposition of the ZnO nanoparticles on the steel surface. Encapsulation of Safranin is realized in polymer coatings on ZnO nanoparticles prepared using layer-by-layer assembly of polyacrylic acid (PAA) and PEI. The average size and surface charge of the PEI coated ZnO nanoparticles and ZnO based nanocontainers with inhibitor are identified using dynamic and electric light scattering methods and microelectrophoresis. The ZnO nanoparticles or ZnO nanocontainers are electrodeposited on steel (cathode) substrates at pH 7.5 to minimize the effect of ZnO dissolution. In a second step, ordinary zinc coatings are electrodeposited on the ZnO nanoparticles or ZnO nanocontainers covered steel samples from zinc sulfate electrolyte at pH 4.5-5.0. The surface morphology of the coatings and their corrosion behavior are studied by scanning electron microscopy and electrochemical methods potentiodynamic polarization and polarization resistance. The results show better corrosion protection of steel by composite coatings as compare to the bare zinc coating. The composite coating with inhibitor shows better protective characteristics in comparison with the other one. The two-step approach described herein can be used for preparation of composite coatings where preservation of particles functionality is required.

Polymeric nanocontainers (NCs) impregnated with corrosion inhibitor benzotriazole are formed using layer-by-layer deposition of poly(acrylic acid) and poly(diallyldimethylammonium chloride) onto hematite particles in the presence of 0.1 M NaCl. Electric light scattering and electrophoresis are employed to control the formation and the size of NCs, as well as the stability of their suspensions. The inhibitor loaded NCs are incorporated into the volume of the galvanized coating during the electrodeposition of zinc on the steel substrate to ensure additional self-healing effect in the case of corrosion attack. The surface morphology and the uniformity of this composite coating as well as the lack of aggregation of the nanocontainers is demonstrated by scanning electron microscopy. The influence of NCs present in the zinc electrolyte on the cathodic and anodic processes is investigated by cyclic voltammetry. The corrosion behavior of the composite coatings at conditions of external cathodic and anodic polarization is tested with potentiodynamic measurements and the results are compared to pure zinc coatings. The composite coatings with embedded NCs revealed enhanced corrosion protection of low carbon steel in comparison with the pure zinc coatings in neutral corrosion medium.

The corrosion resistance and protective ability of black-colored chromite (Cr3+ based) and chromium-free conversion films (CFs) on electrodeposited zinc and Zn-Co alloy coatings having low cobalt content in a neutral model medium of 3% NaCl solution have been investigated and characterized. Test methods such as polarization resistance measurements, scanning electron microscopy, EDS, x-ray diffraction analysis, and x-ray photoelectron spectroscopy analyses have been applied in order to scrutinize the actual protective characteristics of these films as well as to determine the composition of the corrosion products appearing as a result of the treatment in the corrosion medium. The experimental results revealed better protective characteristics, consequently superior performance of the electrodeposits with chromite films compared to these with chromium free or without any additional CF. The processes occurring on the sample’s surface during the immersion in the chemical conversion solutions as well as the influence of the H3PO4 in the course of the treatment are also commented on and discussed.

The presented work reports on the peculiarities of the anodic behavior, corrosion resistance and protective ability of electrodeposited Zn-Ni-P alloys with a different composition in a model corrosion medium of 5% NaCl. Three characteristic coating types have been investigated using experimental methods such as potentiodynamic polarization (PD) technique and polarization resistance (Rp) measurements. In addition, X-ray diffraction (XRD) analysis as well as scanning electron microscopy (SEM) coupled with an Energy-dispersive X-ray (EDAX) device were applied to determine the differences in the chemical composition and surface morphology which appeared as a result of the corrosion treatment. The data obtained are compared to those of electrodeposited pure Zn coatings with identical experimental conditions demonstrating the enhanced protective characteristics of the ternary alloys during the test period in the model medium. The influence of the chemical and phase composition of the alloys on its corrosion resistance and protective ability is also commented and discussed.

The influence of Pluronic P123 (PEO20-PPO70-PEO20) non-stabilized micelles (of 10 nm size) on the corrosion behavior of low-carbon steel in cement extract was studied, using electrochemical impedance spectroscopy (EIS) and potentio-dynamic polarization (PDP). Mercury intrusion porosimetry (MIP) was employed to derive the impact of admixed P123 micelles on porosity and pore-size distribution of cement paste. As far as steel corrosion resistance is concerned, a positive effect was observed, initially denoted to the presence of the polymer itself, rather than the presence of micelles. Further, the P123 micelles were found to result in increased corrosion resistance in the presence of 1 % and 3.5 % NaCl in the alkaline environment of cement extract. There was no significant influence on porosity and pore size distribution of the admixed in cement paste P123 micelles. The observed phenomena are related to self-assembly of the micelles only within higher ionic strength and the presence of chloride, in which case the critical micelle concentration is reduced. At micelles concentration of 0.024 g/l for the chloride-free cement extract (and the solid cement paste specimens, respectively), the medium actually contain unimers that have minimal impact on electrochemical performance and/or microstructural properties. In contrast, with increased ionic strength of the medium (1−3.5 % NaCl and altered ion concentrations resulting from the anodic/cathodic reactions within steel corrosion), the positive effect of 0.024 g/l micelles (and higher of 0.072 g/l) is more pronounced, i.e., increased corrosion resistance and anodic control with external polarization was observed.

This work reports on the corrosion resistance of low-carbon steel in alkaline model solutions, i.e. “red mud” (RM) containing extracts of Ordinary Portland Cement (OPC) and Blast Furnace Slag (BFS) cement. The objective was to define the steel electrochemical behavior and the properties (morphology and composition) of the product layer that forms on the steel surface within treatment in chloride-free and chloride-containing model solutions. The motivation for this research is related to several aspects, mainly to exploring the possibility for achieving superior corrosion performance of steel in cement-based systems by using (combination of) waste materials. The study reveals that RM has a distinctive positive effect on the corrosion performance of steel, especially in chloride containing environment. The presence of RM in both OPC and BFS solutions (with and without NaCl) favors steel passivation and results in an increased corrosion resistance. The positive effect of RM is especially pronounced for steel, exposed to BFS solutions. The observed behavior is attributed to the presence of Fe2O3 and Al2O3 (from RM and BFS). The presence of Fe3+ stabilizes the passive layer. Additionally, the adhered red mud particles act as adsorption sites for Ca2+, resulting in a product layer with higher corrosion resistance. Further, the RM particles with regard to their Al2O3 content enhance steel passivity and increase the chloride threshold for corrosion initiation and/or propagation.

This paper reports on the corrosion performance of composite zinc layers (~ 8µm) on a steel substrate, considering the influence of nano-aggregates and Cr(III) conversion layers, compared to control (only Zn layers) conditions. The main factors, influencing the corrosion performance of Zn in this study are: a) the effect of two concentrations of polymeric nano-aggregates (0.1g/l and 0.3g/l PEO113-b-PS218 core-shell micelles in the starting electrolyte); b) the effect of Cr(III) conversion layers on both pure Zn and composite Zn layers. For most of the hereby investigated time intervals i.e. treatment in aerated 5% NaCl from 2h until 120h, the composite coatings present higher corrosion resistance, especially within longer treatment. Corrosion current densities are similar to Zn, however, anodic currents are significantly lower. After treatment in NaCl, the composite Zn coatings present a more homogenous product layer, formed as a result of the presence of the nano-aggregates. The additional Cr(III) treatment does not significantly improve the corrosion resistance of the composite coatings for the hereby investigated time intervals.

This work reports on the electrochemical performance of low-carbon steel electrodes in model alkaline solutions in the presence of 4.9.10-4 g/l hybrid aggregates i.e. cement extract, containing PDADMAC (poly (diallyl, dimethyl ammonium chloride) / PAA (Poly (acrylic acid)/ PDADMAC over a CaO core. The main objective was to determine if the addition of hybrid aggregates will lead to increased corrosion resistance of the steel surface layers, generally formed in the hereby investigated environmental medium. Further, it was expected that when chlorides are involved, as corrosion accelerating factor, the presence of hybrid aggregates will delay corrosion initiation and therefore lead to increased corrosion resistance. This investigation forms part of a novel approach to control steel corrosion in reinforced concrete, using self-healing mechanisms. The results from this study denote for indeed superior corrosion performance of steel in chloride-free and chloride containing alkaline solution, when hybrid aggregates are involved. The mechanisms are related to increased barrier effects of the formed layer and CaO release from the core of the aggregates.

The anodic behavior, corrosion resistance and protective ability of Zn and alloyed Zn–Co (∼3 wt.%) nanocomposite coatings were investigated in a model corrosion medium of 5% NaCl solution. The metallic matrix of the layers incorporates core–shell nano-sized stabilized polymeric micelles (SPMs) obtained from poly(ethylene oxide)-b-poly(propylene oxide)-b-poly(ethylene oxide) block co-polymers. The protective properties of the composite coatings were evaluated using potentiodynamic polarization technique, polarization resistance measurements and powder X-ray diffraction. The sizes and distribution of the stabilized polymeric micelles in the starting electrolytes used as well as in the metal matrices of the layers were investigated using scanning and transmission electron microscopy. The results obtained are compared to those of electrodeposited Zn and Zn–Co (∼3 wt.%) alloy coatings at identical conditions and demonstrate the enhanced protective characteristics of the Zn nanocomposites during the investigating period. The influence of the SPMs on the corrosion resistance of the nanocomposite layers is commented and discussed.

Chloride ions constitute one of the deleterious agents that may cause or promote corrosion of steel reinforcement in concrete. The influence of chloride ingress on mortar microstructure (including microstructural alterations of hydration products and of pore structure) has been studied by the authors on the basis of cross-section image analysis of reinforced mortar specimens [D.A. Koleva, J. Hu, A.L.A. Fraaij, N. Boshkov, Influences of chloride ions on plain and reinforced mortars, investigated by combined microstructure and electrochemical approaches, Paper 315, Eurocorr 2005, September 4–8 ’05, Lisbon, Portugal]. This paper specifically pursues exploring the morphological aspects and chemical compositions of the corrosion products deposited on steel surface. For this purpose, scanning electron images (SEM) were taken on the cylindrical surface of steel reinforcement and also on the corresponding positions on cement paste surface for visualisation and microstructural investigations of corrosion products. In addition, energy dispersive X-ray analysis (EDXA) and X-ray diffraction (XRD) are employed for quantitative characterisation of the corrosion products at the steel–paste interface. Electrochemical impedance spectroscopy (EIS) is used to estimate the corrosion current and corrosion rate for the reinforced mortars. The EIS measurements are in good agreement with the microstructural observations and quantitative analysis of various corrosion products. The combination of electrochemical measurements with quantitative microstructure analysis of the steel–paste interface constitutes a reliable and useful tool for quantitative characterisation of the interface microstructure and thereby provides better insight into the electrochemical processes during corrosion of the steel reinforcement in concrete.

Cathodic protection (CP) has been found as one of the most viable techniques for inhibiting chloride induced corrosion of steel in concrete structures. This contribution specifically pursues exploring the morphological alterations of corrosion products in reinforced mortars under cathodic protection. For this purpose, scanning electron microscopy (SEM) techniques are combined with energy dispersive X-ray analysis (EDXA) and X-ray diffraction (XRD) for microstructural analysis and quantification of the corrosion products. The combined characterisation provides important insight into the structural alterations induced by cathodic protection, and therefore, help to explain the efficiency of CP techniques. Furthermore, electrochemical measurements are employed to monitor the electrochemical process at the steel–paste interfaces. The beneficial microstructural alterations result in better corrosion resistance of the protected specimens, and turn out to be the mechanisms underlying the efficiency of CP techniques.

The corrosion resistance and protective ability of electrodeposited coatings of Zn, Zn–Mn(6%) and Zn–Mn(11%) alloys as well as of chromated and non-chromated multilayer galvanic systems were investigated in a free aerated medium of 1N Na 2 SO 4 (pH 6.0) at open circuit conditions (OCP– E corr ) using polarization resistance ( R p ) measurements. The anodic behavior of these objects was determined using potentiodynamic (PD) polarization curves. It was established that the corrosion products appeared after the treatment and known as zinc hydroxide sulfates–ZHS–increase the protective ability of the coating (or multilayer system) due to their low product of solubility P s (for example, P s of Zn 4 (OH) 6 SO 4 ·4H 2 O has a value of the order 10 − 57 ) and seems to be a reason for better protection toward the iron substrate. Surface morphology and its changes were registered with scanning electron microscopy (SEM).

The composition of the corrosion products of pure Zn galvanic coatings as well as of some zinc alloys (Zn–Mn and Zn–Co) after treatment in selected free aerated model media (5% NaCl and 1N Na2SO4) is studied and discussed. X-ray diffraction and X-ray photoelectron spectroscopy investigations are used for this purpose. It is concluded that the corrosion products (zinc hydroxide chloride hydrate in 5% NaCl and zinc hydroxide sulfates hydrates in 1N Na2SO4) play a very important role for the improved protective ability of the zinc alloys toward the iron substrate, compared to the pure Zn coatings. Another result is that, for a given medium, the corrosion products are one and the same for both alloys independently of the fact that the alloying component is electrically more positive or negative than the zinc. Some suggestions about the models of the appearance of these products and their protective influence are also discussed.

The electrochemical behaviour as well as the surface morphology characteristics of electrodeposited Zn and Zn-Co (≈3 wt-%) alloy coatings on low carbon steel samples, with and without included nanoparticles of organic co-polymers in their structure, are discussed. Their corrosion resistance and protective properties were studied in a model corrosion medium, 5 wt-% NaCl, using electrochemical methods such as polarisation resistance (R p) measurements and potentiodynamic (PD) polarisation curves. Scanning electron microscopy (SEM) was performed to examine the surface morphology changes of the samples before and after the corrosion treatment. Some conclusions are drawn about the influence and importance of the organic nanoparticles on the corrosion behaviour of the coatings presented.

The composition of the corrosion products of non-chromated and chromated galvanic coatings of Zn, Zn–Mn (6 wt.%) and Zn–Mn (11 wt.%) in a model free aerated solution of 1 N Na2SO4 (pH 6) is determined using X-ray powder diffraction analysis (XRD). Surface morphology and its changes are registered with scanning electron microscopy (SEM). Microprobe analysis is applied to specify the amounts of Zn, Mn and S after the corrosion treatment. The registered compounds on Zn and Zn–Mn alloys during the experiments—Zn4(OH)6SO4·5H2O, Zn4(OH)6SO4·4H2O, Zn4(OH)6SO4·3H2O, Zn4(OH)6SO4·H2O, Zn4(OH)6SO4·0,5H2O, Zn7(OH)12SO4·4H2O, Zn4(OH)6SO4—are known as zinc hydroxide sulfates (ZHS) hydrates and distinguish with low product of solubility (Ps). The relative amount of these compounds varies and depends on the nature of the galvanic coating as well as on the experimental conditions. Using potentiodynamic (PD) polarization curves as well as polarization resistance (Rp) measurements it is established that the appearance of ZHS lead to increased protective ability of the investigated galvanic coatings towards the steel substrate.

The electrodeposition conditions and the peculiarities of the phase composition of Zn–Mn alloys with different contents (∼6 and ∼11 wt.%) of the alloying component are described and discussed. Their corrosion behaviour and protective ability are investigated in a model medium of free aerated solution of 5% NaCl in open circuit conditions as well as under external anodic polarization—potentiodynamic polarization curves, polarization resistance ( R p ) measurements, etc. The results obtained are compared to these of pure zinc galvanic coatings. For determination of the corrosion products of the layers X-ray diffraction as well as X-ray photoelectron spectroscopy are used. As a result the compound zinc hydroxide chloride monohydrate (ZHC)—Zn 5 (OH) 8 Cl 2 ·H 2 O—is registered on Zn–Mn alloys. ZHC supplement increases the corrosion resistance due to its low product of solubility and ensures better protective ability. Some suggestions about the protective action of the manganese are also given.

The composition of the corrosion products of non-chromated and chromated galvanic coatings of Zn and Zn–Co(1–5wt.%) alloys in free aerated solution of 5% NaCl is described and discussed. Corrosion treatment is realized at open circuit conditions for different periods of time. The corrosion products of monolayer galvanic coatings were investigated using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). As a result of the treatment the compound zinc hydroxide chloride monohydrat (ZHC)—Zn 5 (OH) 8 Cl 2 .H 2 O—was registered on Zn–Co alloys after the experimental period. ZHC supplementary increases the corrosion resistance due to its low solubility product and ensures better protection. In addition, the protective ability of mono- and bilayer galvanic systems (chromated and non-chromated) was determined using polarization resistance measurements.

Corrosion resistance and erosion wear of the metal equipment (body, pipe bundles, steam generators etc.) are of great importance for the operating time limit of the nuclear power plants (NPP) bearing in mind their extremely heavy technological and water-chemical regime (WCR). The horizontally placed steam generators (SGs) used in the Energy Blocks of NPP “Kozloduy” work at exploitation conditions leading to corrosion and erosion provoked processes (Andreeva M. et. al., 2008). Similar is the situation in the greater part of the modern power plants (R.W. Staehle & J.A. Gorman, 2003; R.W. Staehle & J.A. Gorman, 2004; R.W. Staehle & J.A. Gorman, 2004). This fact predetermines the necessity of very careful daily and also periodical monitoring concerning the real operating state of the equipment during its exploitation time (Sviridenko, I., 2008; Hadavi, S.M.H., 2008; Viehrig, H.-W., et. al., 2006; Slugen, V., et. al., 2005). The evaluation and explanation of the obtained results for the electrochemical-corrosion parameters will ensure a realistic base for a precise prognosis and trouble-free operation of the installations (J. Congleton et all, 1985; Raichevski G. et al.,. 2007; Hojna A. et. al, 2007; Kaczorowski D. et. al., 2006). Markedly dangerous negative influences leading to technical failures and damages have the conglomerated corrosion products (CPs) the latter appearing as a result of the WCR mainly in the second contour of NPP. Considerable part of them enters the condense-feeding part of SGs and deposit as loose layers on the pipe surface or falls as middling slime on the bottom changing in such a way the overall electrochemical and hydrodynamic situation in the internal volume during the operation procedures. In general, CPs presenting in the steam generators consist of iron and copper oxides and hydroxides. If their adhesion to the surface is enough strong (for example, like in the case of magnetite – Fe3O4) it can be expected that a passive layer will appear on the surface of the equipment and in such a way this part of the installation will be additionally protected. If CPs are crumbly the operative situation in the SGs will be worsen since these deposits often lead to accelerated formation and development of local corrosion phenomena – holes, pits, cracks, including appearance of stress corrosion cracking process etc., the latter being one of the most dangerous events due to its practical invisibility up to the moment of the sudden physical-mechanical destroying (Zubchenko, A.S., et al., 2004; Slugen, V., et al., 2002; Lunin, G.L., et al., 1997; N.D. Budiansky, et al., 2005).

This study reports on a comparative investigation of the corrosion behavior of zinc (Zn) and nano-composite zinc (ZnC) galvanic layers in 5% NaCl solution. The metallic matrix of the ZnC layers incorporates nano-sized, stabilized polymeric aggregates, formed from the amphiphilic tri-block co-polymer: poly(2-hydroxyethyl methacrylate) - poly (propylene oxide - poly (2-hydroxyethyl methacrylate) (PHEMA15PPO34PHEMA15). The main objective was to evaluate the electrochemical properties and surface characteristics of both coatings, thus further to investigate if the nano-composite layers will have better corrosion resistance, compared to pure galvanic zinc. The electrochemical behavior, investigated by Impedance spectroscopy (EIS) and Scanning vibrating electrode technique (SVET), supported by surface analysis, using Atomic-force microscopy (AFM) and Scanning electron microscopy (SEM), reveals higher corrosion resistance and consequently better performance of the nano-composite layers, compared to pure galvanic zinc. The mechanism of incorporation of the polymeric nano-aggregates in the coating and their influence on the barrier properties of the composite layers are also briefly discussed.

The present study explores the formation of corrosion products on the steel surface in reinforced concrete in conditions of corrosion and subsequent transformation of these layers in conditions of cathodic protection (CP). Of particular interest was to investigate if the introduced pulse CP (as cost- effective alternative of CP) will lead to similar (or even better) transformation of the product layers on the steel surface, compared to conventional techniques. Qualification and quantification of the studied layers was performed using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and energy-dispersive X-ray analysis (EDAX), visualization of morphology and products distribution was achieved using environmental SEM (ESEM).

The electrochemical behavior of steel reinforcement in conditions of corrosion and cathodic protection (CP) was studied, using electrochemical impedance spectroscopy (EIS) and compared to reference (non-corroding) conditions. Polarization resistance (PR) method and potentio-dynamic polarization (PDP) were employed as well, in addition to AC 2 pin electrical resistance monitoring, thus deriving a comparison of the involved parameters. It was found out that EIS is readily applicable for evaluating electrochemical behavior of the steel surface not only for corroding or passive state, but also in conditions of CP, although the interpretation of derived parameters is not straightforward and is related to the properties of the product layers, formed on the steel surface in the different conditions. The evaluation of the electrochemical behavior of the steel surface, should take into account the crystallinity, morphology and composition of the surface layers, which were investigated by scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDAX).

The behavior of steel reinforcement was studied using electrochemical impedance spectroscopy (EIS) and polarization resistance (PR) techniques in conditions of chloride-induced corrosion in ordinary Portland cement-mortar specimens immersed in 7% NaCl for a test period of 120 days and compared to specimens immersed in demineralized water for the same period as reference specimens. This study was an initial phase of ongoing research on electrochemical methods for corrosion protection in reinforced concrete structures and aimed at investigating the applicability of widely accepted techniques as EIS and PR and their possible correlation with structural observations of the bulk matrix, relevant to cement-based materials science and product-layers distribution, to corrosion and further protection. The results indicate that the concept of EIS modeling and the components used in the latter correspond well to alterations in structural properties of the bulk matrix, while the electrochemical behavior can be additionally supported by morphological observations of the steel/cement paste interface.

Zinc and zinc-based electrogalvanized coatings have attracted remarkable interest because of the increasing demand for layers with better corrosion resistance. A new approach for improvement of the protective ability is the incorporation in the metal matrix of polymeric nanoparticles. The latter affect positively the protective properties of the nanocomposite coatings and result in increasing of their corrosion resistance in 5 % NaCl solution compared to the pure zinc and Zn-Co. The zinc coating process using the developed saturating mixtures excludes the phases of evaporation and condensation and the process is defined as hard-phase zinc coating. The hard phase zinc coating decreases the coating time 1, 5-2 times and powder dissipation with 20-25% compared to vapor-phase zinc coating. It does not require cooling the product together with the powder at the end of the process. The hard phase zinc coating has a high degree of automation and provides uniform coating of long-sized products and allows creating high-performing equipment. The prevention of the superficial roughness, during the hard phase zinc coating, leads to higher adhesion of varnishing coverings on the zinc-coated surface in comparison with vapor-phase zinc-coating.

An improved cathodic protection (CP), based on pulse regime was investigated in reinforced concrete, compared to conventional CP. Both regimes used CP current in the range of 2 to15 mA/m2. A voltage-to-current converter maintained the pulse current, the latter adjusted with duty cycle of 12% to 50 % and frequency of 500 Hz to 1 kHz. The efficiency of the improved CP was evaluated by means of electrochemical methods and microstructural investigation of the bulk concrete matrix, the steel/paste interface and the steel surface. The combination of techniques provides a detailed understanding of the electrochemical phenomena associated with corrosion and protection processes. The pulse CP achieves sufficient protection of the steel reinforcement and is less detrimental to the bulk concrete matrix. In this sense, pulse CP is able to minimize the negative side effects and to ensure better performance and protection in reinforced concrete.

We studied the optical reflectance profile of zinc layers with thickness of 2-10 μm electrodeposited on low carbon steel in the spectral range of solar radiation (0.3 - 2.5μm) and in the thermal infrared (2.5 - 15μm). Spectral selectivity is an important parameter of the solar absorbers used in solar thermal collectors. It is defined by low reflectance in the range 0.3 - 2.5 μ, and high reflectance in the thermal infrared, 2.5 - 15 μm. The Zn coatings are thick and their surface is rough. If the surface features size is in the order of the visible wavelengths, then absorption of light at the surface is possible. The investigations revealed the formation of ZnO on the Zn coating surface. The Raman study showed a weak peak around 512 cm−1, which can be attributed to the ZnO oxide phase. The longer wavelengths penetrate the oxide surface and reach the bulk part of the Zn coating where they are reflected. As a result, a step-wise profile is expected in the reflectance spectrum within the 0.3 -15 μm range, with a change from a comparatively low reflectance in the visible to a high reflectance in the infrared.

This work reports on monitoring chloride-induced corrosion in reinforced mortar specimens, with and without addition of polymeric nano-aggregates in the mortar mixture. The investigation is a novel approach to control steel corrosion in reinforced concrete, hereby reporting the preliminary results, related to one of the main objectives: studying the influence of admixed polymer nano-aggregates (in the form of PEO113-b-PS218 core-shell micelles with a very low concentration of 0.006 wt.% per mortar weight) on the corrosion behavior of the steel reinforcement, compared to reference, micelles-free mixtures