Corrosion performance of epoxy coatings containing silane treated ZrO2 nanoparticles on mild steel in 3.5% NaCl solution

Clear epoxy coatings were modified by adding various levels of ZrO₂ nanoparticles. In order to achieve proper dispersion of nanoparticles in the epoxy-based coating and making possible chemical interactions between nanoparticles and polymeric coating, the surface of the nanoparticles was treated with amino propyl trimethoxy silane (APS). Corrosion performance of mild steel coated specimens was investigated employing EIS, electrochemical noise (ECN) techniques and salt spray test. Coatings with 2–3 wt% ZrO₂ nanoparticles possessed the best corrosion performance among the coating specimens. Possible chemical interactions between polymeric matrix and treated nanoparticles in nanocomposites cause high barrier properties and ionic resistances.     

Corrosion performance of steel coated with co-polyamides and polyaniline

The corrosion performance of steel coated with co-polyamide polymers and polyaniline in neutral salt spray (NSS) and accelerated corrosion testing is presented. A coating of the nylon polymer on steel is not sufficient to prevent corrosion in a chloride medium, the underlying steel showing signs of corrosion after only three days in the NSS environment. Open-circuit potential measurements indicate the steel is corroding forming soluble ferrous and ferric oxy-complexes. Polyaniline by itself is also insufficient in inhibiting corrosion on steel. A synergy exists between an under-layer of polyaniline and a top layer of the nylon coating in minimizing corrosion.     

Corrosion protection by multilayered conducting polymer coatings

Multilayered coatings, consisting of combinations of the conducting polymers polyaniline (Pani) and polypyrrole (Ppy), were galvanostatically deposited on to both carbon steel and stainless steel. Potentiodynamic polarisation was used to assess the ability of these copolymers to provide an effective barrier to corrosion in chloride environments. For carbon steel the performance of these multilayered coatings on carbon steel were not sufficiently better than for single Pani coatings to justify their more complicated deposition procedures. However, in the case of stainless steels the new multilayered coatings proved to be significantly better than previously reported single Pani coatings, especially at protecting against pitting corrosion. It was found that the degree of protection was a function of the deposition order of the copolymer, with films consisting of a Pani layer over the top of a Ppy layer yielding the best results. Scanning electronic microscopy observations and adhesion measurements, along with the electrochemical data suggested that the ability of a conducting polymer film to act as electronic and chemical barriers were more important in providing corrosion protection than its ability to act as a physical barrier.     

Polybenzoxazine/SiO2 nanocomposite coatings for corrosion protection of mild steel

A series of nanocomposite coatings (PBS) consisting of silane functional polybenzoxazine (PB-TMOS) and SiO₂ nanoparticles were developed for corrosion protection of mild steel. The influence of silica content on corrosion resistance of PBS coatings was investigated by electrochemical measurements. The surface chemistry of nanoparticles and its effect on morphology of the PBS coating was also studied utilizing Fourier Transforms Infrared Spectroscopy, ²⁹Si Nuclear Magnetic Resonance and Scanning Electron Microscopy analyses. The results indicate that the presence of the covalent bond between nanoparticles and PB-TMOS, greatly improves the interfacial interactions at the polymer/filler interfaces resulting in a better corrosion performance.     

Corrosion loss of mild steel in high temperature hard freshwater

This paper presents an interpretation of corrosion loss data for mild steel coupons exposed for up to 2.6 years to freshwater under a range of dissolved oxygen levels and temperatures 50-60 °C. The water total alkalinity was 0.5-0.6 mmol/l and pH 8.7-9.2. It is shown herein that the data is consistent with the early stages of the corrosion loss model proposed earlier for steel exposed to seawater, brackish water or freshwaters in the usual environmental range of 0-30 °C. The new data was found to be consistent with the effect of dissolved oxygen and the effect of water hardness on the model.     

Long-term anticorrosion behaviour of polyaniline on mild Steel

Anticorrosion performances of polyaniline emeraldine base/epoxy resin (EB/ER) coating on mild steel in 3.5% NaCl solutions of various pH values were investigated by electrochemical impedance spectroscopy (EIS) for 150 days. In neutral solution (pH 6.1), EB/ER coating offered very efficient corrosion protection with respect to pure ER coating, especially when EB content was 5-10%. The impedance at 0.1 Hz of the coating increased in the first 1-40 immersion days and then remained constant above 10⁹ Ω·cm² until 150 days, which in combination with the observation of a Fe₂O₃/Fe₃O₄ passive film formed on steel confirmed that the protection of EB was mainly anodic. In acidic or basic solution (pH 1 or 13), EB/ER coating also performed much better than pure ER coating. However, these media weakened the corrosion resistance due to breakdown of the passive film or deterioration of the ER binder.     

Corrosion inhibition of mild steel in hydrochloric acid solution by Schiff base furoin thiosemicarbazone

A heterocyclic Schiff base furoin thiosemicarbazone was tested for its corrosion inhibition towards mild steel in 1 M HCl solution using weight loss, Tafel polarization and electrochemical impedance spectroscopy techniques. Furoin thiosemicarbazone revealed good corrosion inhibition efficiency even at low concentrations towards mild steel in HCl medium. Comparison of corrosion inhibition efficiency of Schiff base and its parent amine and effect of temperature on inhibition efficiency were also investigated. The adsorption of furoin thiosemicarbazone on mild steel surface obeys Langmuir isotherm.     

Effect of sintering temperatures on corrosion and wear properties of sol-gel alumina coatings on surface pre-treated mild steel

Sol-gel alumina coatings were developed on the surface pre-treated (zinc-phosphated) mild steel substrate and subsequently sintered at 300 °C, 400 °C and 500 °C. The alumina sol was synthesised using aluminium iso-propoxide as a precursor material. FTIR of the boehmite (AlOOH) gel sintered at above-mentioned temperatures was employed to identify the presence of various functional groups. The microstructural features and the phase analysis of the sol-gel coated specimens were carried out using SEM and XRD respectively. The corrosion resistance of the sol-gel alumina coatings was evaluated by electrochemical measurement in 3.5% NaCl solution at room temperature. The abrasive wear behaviour of the sol-gel coated specimens was measured in two body (high stress) conditions. The experimental results revealed that the sol-gel coated specimen sintered at 400 °C has superior wear and corrosion resistance properties as compared to the sol-gel coated specimen sintered at 300 °C. However, the sol-gel coated specimen sintered at 500 °C has exhibited a very poor corrosion and wear resistance properties. Poor performance of the sol-gel coatings sintered at 500 °C could be explained to be due to (i) the presence of numerous cracks (ii) absence of organic groups in the coating.     

Corrosion inhibition of mild steel by ethylamino imidazoline derivative in CO2-saturated solution

The corrosion inhibition and adsorption behaviour of 2-undecyl-1-ethylamino imidazoline (2UEI) on N80 mild steel in CO₂-saturated 3% NaCl solutions was investigated using potentiodynamic polarization, electrochemical impedance spectroscopy techniques and SEM observation. Inhibitor efficiency increased with increase in 2UEI concentration. Temperature studies revealed an increase in inhibition efficiency with rise in temperature and corrosion activation energies decreased in the presence of 2UEI. A mechanism of chemical adsorption of 2UEI on the metal’s surface is proposed. The adsorption characteristics of the inhibitor were approximated by Temkin isotherm. The inhibition efficiency of 2UEI was enhanced in the presence of iodide ions.     

The changing topography of corroding mild steel surfaces in seawater

The corrosion of mild steel exposed to marine immersion conditions typically is not uniform although it is often idealized as such. Anodic regions and micro-pits develop very quickly after first exposure and eventually there is the development of shallow broad pits. This transition of the surface topography and the processes involved are still not completely understood. The present paper presents a number of images typical of the sequential evolution of the surface topology of mild steel corroding in sub-tropical coastal seawater. The sequence consists of the development of anodic areas, development of small pits and shallow broad pits, the apparent coalescence of small pits into larger localized corrosion and eventually the appearance of stepped or benched, perhaps irregular-shaped broad or macro-pits. This sequence is typical of that which has been observed many times and this suggests it is reasonable to infer a generic sequence that describes the changing surface of corroding mild steel in seawater. It will assist in developing a better understanding of the evolution of corrosion processes for mild steel in seawater and assist in identifying the various controlling processes.     

Long-term atmospheric corrosion of mild steel

A great deal of information is available on the atmospheric corrosion of mild steel in the short, mid and even long term, but studies of the structure and morphology of corrosion layers are less abundant and generally deal with those formed in just a few years. The present study assesses the structure and morphology of corrosion product layers formed on mild steel after 13 years of exposure in five Spanish atmospheres of different types: rural, urban, industrial and marine (mild and severe). The corrosion layers have been characterised by X-ray diffraction (XRD) and scanning electron microscopy/energy dispersive X-ray spectroscopy (SEM/EDS). Long-term corrosion is seen to be more severe in the industrial and marine atmospheres, and less so in the rural and urban atmospheres. In all cases the corrosion rate is seen to decrease with exposure time, stabilising after the first 4–6 years of exposure. The most relevant aspects to be noted are (a) the great compaction of the rust layers formed in the rural and urban atmospheres, (b) the formation of hematite and ferrihydrite phases (not commonly found) in the industrial and marine atmospheres, respectively and (c) identification of the typical morphological structures of lepidocrocite (sandy crystals and flowery plates), goethite (cotton balls structures) and akaganeite (cotton balls structures and cigar-shaped crystals).     

Corrosion stability of epoxy coatings on aluminum pretreated by vinyltriethoxysilane

The electrochemical and transport properties and adhesion of epoxy coatings electrodeposited on aluminum pretreated by vinyltriethoxysilane (VTES) were investigated during exposure to 3% NaCl. The VTES films were deposited on aluminum surface from 2% and 5% vinyltriethoxysilane solution. The electrochemical results showed that the pretreatment based on VTES film deposited from 5% solution provides enhanced barrier properties and excellent corrosion protection. The values of diffusion coefficient of water through epoxy coating on this substrate and water content inside the epoxy coating were the smallest, indicating the low porosity of the coating. In addition, the good adhesion was maintained throughout the whole investigated time period.     

An electrochemical study of the delamination of polymer coatings on galvanized steel

The relationship between the rate of polymer delamination and the intensity of either anodic or cathodic current under the paint has been investigated for the zinc/surface treatment/polymer system by using a special electrochemical cell. Three types of surface treatment were investigated: simple alkaline degreasing, trication phosphating, and a chromate free conversion coating. Significant differences were observed for the three substrates. The alkaline resistance of the conversion coatings was determined using an ICP atomic emission spectroelectrochemical method. The results are interpreted in terms of the differing chemical stability of the conversion layers towards hydroxide generated by oxygen reduction.     

Chlorinated rubber paints for corrosion prevention of mild steel: A comparison between zinc phosphate and polyaniline pigments

The anticorrosion performance of plasticized chlorinated rubber coated mild steel sheets incorporating polyaniline emeraldine salt or zinc phosphate as active pigments were compared using salt spray and immersion in 3.5% NaCl solution. The results obtained by different electrochemical methods indicate the superiority of polyaniline in comparison with zinc phosphate in terms of corrosion protection. The time of the emergence of the first rust spot in 3.5% NaCl solution for the film containing 1.5 wt% polyaniline reach 960 h, which is six times higher than that of the film without polyaniline. The protective mechanism by zinc phosphate and polyaniline pigments were discussed.     

Corrosion properties of steel protected by nanometre-thick oxide coatings

A comprehensive study of the corrosion properties of low alloy steel protected by 40–50 nm aluminium and tantalum mixed oxide coatings grown by atomic layer deposition is reported. Electrochemical and surface analysis was performed to address the effect of substrate surface finish and whether an oxide mixture or nanolaminate was used. There was no dissolution or breakdown for nanolaminate alumina/tantala stacks in acidic NaCl solution. Localised corrosion (pitting) took place when defects exposing the substrate pre-existed in the coating. Substrate pre-treatment by brushing and H₂–Ar plasma was instrumental to block or slow down pit initiation by reducing the defect dimensions.     

Corrosion behaviour of nanocomposite TiSiN coatings on steel substrates

Nanocomposite TiSiN coatings were deposited on tool steels. Detailed mechanisms that govern the corrosion of these coated steels were revealed, following immersion tests in a 70% nitric acid solution. Pitting originated preferentially from coating defect sites and expanded with increasing immersion time. Both Young’s modulus and hardness measured by nanoindentation decreased as the corrosion damage intensified. A thin oxide layer formed from the thermal annealing of the as-deposited samples at 900 °C was found to be effective against corrosive attack. In addition, compressive residual stress was noted to suppress the propagation of corrosion-induced cracks. The role of residual stress in controlling the corrosion resistance of these ceramic-coated steels is clarified by finite element analysis.     

Corrosion behaviour in alkaline medium of zinc phosphate coated steel obtained by cathodic electrochemical treatment

The present work evaluated the ability of zinc phosphate coating, obtained by cathodic electrochemical treatment, to protect mild steel rebar against the localized attack generated by chloride ions in alkaline medium. The corrosion behaviour of coated steel was assessed by open circuit potential, potentiodynamic polarization and electrochemical impedance spectroscopy. The chemical composition and the morphology of the coated surfaces were evaluated by X-ray diffraction and scanning electron microscopy. Cathodically phosphated mild steel rebar have been studied in alkaline solution with and without chloride simulating the concrete pore solution. For these conditions, the results showed that the slow dissolution of the coating generates the formation of calcium hydroxyzincate (Ca(Zn(OH)₃)₂·2H₂O). After a long immersion time in alkaline solution with and without Cl⁻, the coating is dense and provides an effective corrosion resistance compared to mild steel rebar.     

Heterogeneous corrosion of mild steel under SRB-biofilm characterised by electrochemical mapping technique

Heterogeneous corrosion of mild steel under sulphate reducing bacteria (SRB)-biofilm was characterised by wire beam electrode (WBE) technique and electrochemical impedance spectrum. The potential/current distributions of the WBE under SRB-biofilm showed that the potential maps could not indicate the localised corrosion of steels beneath biofilm due to the fact that all wire electrodes were short-circuited by the highly conductive sulphide precipitates embedded in SRB-biofilm. Instead, the galvanic current maps may give a good indication. The characteristic of super-capacitance (0.21 F/cm²) of SRB-biofilm was attributed to the huge specific surface area of conductive pore walls inside biofilm.     

Cathodic disbonding of an unpigmented epoxy coating on mild steel under semi- and full-immersion conditions

Cathodic disbonding of an unpigmented epoxy coating around a defect was studied with samples fully- and semi-immersed in 3.5 wt.% NaCl solution. Disbonding and the growth of blisters were monitored by scanning acoustic microscopy, which showed growth of blisters within the disbond for both type of samples. Scanning Kelvin probe potential maps suggest that blisters first form at local anodes. For semi-immersed samples, disbonding of the immersed part and the non-immersed part propagate with parabolic kinetics at identical rates, similar to fully-immersed samples. This implies that ion transport is along the coating–metal interface in both cases.     

Corrosion inhibition of mild steel by plant extract in dilute HCl medium

The inhibition effect of Zenthoxylum alatum plant extract on the corrosion of mild steel in 5% and 15% aqueous hydrochloric acid solution has been investigated by weight loss and electrochemical impedance spectroscopy (EIS). The corrosion inhibition efficiency increases on increasing plant extract concentration till 2400 ppm. The effect of temperature on the corrosion behaviour of mild steel in 5% and 15% HCl with addition of plant extract was studied in the temperature range 50-80 °C. Surface analysis (SEM, XPS and FT-IR) was also carried out to establish the corrosion inhibitive property of this plant extract in HCl solution. Plant extract is able to reduce the corrosion of steel more effectively in 5% HCl than in 15% HCl. The adsorption of this plant extract on the mild steel surface obeys the Langmuir adsorption isotherm.