Electrochemical behavior of organic and inorganic complexes of Zn(II) as corrosion inhibitors for mild steel: Solution phase study

This work intends to study inhibitive performance of organic and inorganic complexes of Zn(II) using electrochemical techniques along with surface analysis. In this regard, inorganic zinc aluminum polyphosphate pigment as modified zinc phosphate and zinc acetylacetonate and benzimidazole mixture representing organic replacement of zinc phosphate were employed. Through taking advantage of electrochemical impedance spectroscopy and DC polarization, two mentioned approaches were indicated to be efficient. Charge transfer resistance and corrosion current density values exhibited superiority of zinc aluminum polyphosphate and mixture of zinc acetylacetonate and benzimidazole compared to zinc phosphate and also zinc acetylacetonate and benzimidazole as individual inhibitors. Corrosion inhibition efficiencies calculated based on charge transfer resistance in consistent with those calculated from corrosion current density showed the following sequence; zinc aluminum polyphosphate > mixture of zinc acetylacetonate and benzimidazole > zinc acetylacetonate > zinc phosphate > benzimidazole. Showing film formation, surface analysis SEM/EDX confirmed the results obtained by electrochemical methods.     

A comparative study of epoxy and polyurethane based coatings containing polyaniline-DBSA pigments for corrosion protection on mild steel

Organic coatings based on epoxy and polyurethane matrices containing polyaniline doped with dodecyl benzene sulfonic acid (Pani-DBSA) were prepared and applied over steel plates (SAE 1020). The plates were submitted to salt spray chamber for up to 30 days in order to evaluate the corrosion protection of these coatings. The properties of the coated plates were analyzed as a function of time by electrochemical impedance spectroscopy, open circuit potential, optical microscopy, and Raman spectroscopy. In general, results indicate a decrease in the electrical resistance, increase in capacitance and decrease in open circuit potential. Epoxy based coatings have improved performance when Pani-DBSA is used as pigment, whereas for the polyurethane coatings, Pani-DBSA seems to play an adverse effect. Raman spectroscopy indicates a possible chlorination of the epoxy matrix after 30 days exposure to salt spray chamber.     

Protection of copper corrosion by modification of dodecanethiol self-assembled monolayers prepared in aqueous micellar solution

A novel method of preparing 1-dodecanethiol (DT) self-assembled monolayers (SAMs) on copper in aqueous micellar solution is explored. The resulting SAMs are characterized by XPS, contact angle tests and electrochemical measurements. It is found that DT dissolved in aqueous micellar solution can adsorb rapidly to the copper surface through strong thiolate bonds to form well-organized SAMs, which have properties comparable to those formed in ethanol solution. The electrochemical measurements show that the inhibition efficiency (IE) increases with an increase in the immersion time of copper in the aqueous micellar solution. After self-assembly for 1 h, the SAMs are able to effectively protect the underlying copper against corrosion in chloride-containing solution by hindering the cathodic process. Overall, the inhibition efficiency can reach 98.94%.     

An in situ electrochemical impedance spectroscopy/synchrotron radiation grazing incidence X-ray diffraction study of the influence of acetate on the carbon dioxide corrosion of mild steel

A combination of electrochemical impedance spectroscopy (EIS) and in situ synchrotron radiation grazing incidence X-ray diffraction (SR-GIXRD) has been used to study the influence of acetate on the carbon dioxide corrosion of mild steel. The SR-GIXRD data demonstrated that normal corrosion - in a carbon dioxide saturated brine - induced the formation of a thick corrosion scale of Fe₂(OH)₂CO₃ and Fe₂O₂CO₃, and this totally obscured the α-Fe diffraction peaks of the underlying steel substrate after 24 h. On the other hand, the carbon dioxide corrosion of mild steel in the presence of acetate also detected the Bragg diffraction peaks for Fe₂(OH)₂CO₃ and Fe₂O₂CO₃; however, the α-Fe diffraction peaks of the underlying steel substrate were not extinguished with time, and there was a reversal in the pattern of evolution of the intensities of the Fe₂(OH)₂CO₃ and Fe₂O₂CO₃ phases in acetate. Accordingly, the EIS data showed a poorly defined medium frequency time constant for the corroded steel specimen in brine spiked with acetate, and this medium frequency time constant was extinguished as a function of time. Alternatively, EIS of the corroded specimen also revealed a medium frequency time constant after 24 h. In addition, EIS complex-plane impedance plots showed that the corroded electrode had become passivated in an acetate-spiked brine, as evidenced by a three-fold enhancement in the charge transfer resistance at low frequency. These EIS/SR-GIXRD outcomes suggest that acetate affects the crystallization chemistry of the Fe₂(OH)₂CO₃/Fe₂O₂CO₃ corrosion scale, and this causes a mild passivation of the corroded steel surface.     

Galvanic corrosion of titanium-based dental implant materials

This paper describes an investigation of the corrosion behavior of Ti-based dental materials with Au, CrNi and CoCr in Ringer solution by the use of Tafel plots, Evans diagrams and EIS Nyguist diagrams. The galvanic potentials and currents obtained for various implant couples are as follows: For, Ti6Al4V/CrNi couple −0.030 V (Ag/AgCl (3 M NaCl)) and 7.94 μA cm⁻²; for Ti6Al4V/CoCr couple −0.020 V (Ag/AgCl (3 M NaCl)) and 7.08 μA cm⁻²; for Ti6Al4V/Au couple −0.020 V (Ag/AgCl (3 M NaCl)) and 5.62 μA cm⁻². The Ti6Al4V/Au couple was found to be the most suitable one against galvanic corrosion according to both the Tafel method and mixed potential theory. The corrosion behaviors of Ti6Al4V/CoCr and Ti6Al4V/CrNi couples were found to be similar.     

Investigation of the first stages of the localized corrosion of pure copper combining EIS, FE-SEM and FE-AES

During the first 48 h that pure copper is submerged in a chloride containing solution, an oxide layer is formed that acts as a barrier layer between the aggressive solution and the substrate, offering some protection to the material. This barrier layer itself is subsequently attacked and localized corrosion is observed. The study of the corrosion behavior was based on open circuit potential (OCP) measurements. The evolution of this value was concurrent with the evolution of the state of the oxide layer. Furthermore the surface state was evaluated by taking impedance spectra every 2 h. This method proved to be insufficient to elucidate the surface evolution and additional techniques were employed. The thickness and the composition of the oxide layers as well as the different composition of the corrosion products in and around the zones of localized attack were determined by means of an FE-AES equipped with an ion gun. The scanning electron microscope (SEM) allowed us to visually discriminate between the three stages the surface passes through during the first 48 h. Mathematically the equivalent circuit used in literature fits the impedance data very well. The observations in this work are however in contradiction with the different physical meanings attributed to the circuit elements found in literature. Further research is necessary to reveal the real mechanism of copper corrosion in this sort of systems.     

Enhancement of corrosion protection of mild steel by chitosan/ZnO nanoparticle composite membranes

The development of active corrosion protection systems for metallic substrates is an issue of prime importance for many industrial applications. Nanostructured chitosan/ZnO nanoparticle films were coated on mild steel by sol–gel process, dip coating technique. Sol–gel protective coatings have shown excellent chemical stability, oxidation control and enhanced corrosion resistance for metal substrates. Further, the sol–gel method is an environmentally friendly technique of surface protection which has traditionally been used for increasing corrosion resistance of metals. Films so formed were characterized by UV–vis absorption spectroscopy (UV–vis), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive X-ray fluorescence spectrometry (EDX). Corrosion protection behavior of these coated mild steel substrates in 0.1 N HCl solutions was evaluated by potentiodynamic polarisation studies (Tafel), linear polarisation studies (LPR), electrochemical impedance spectroscopy studies (EIS).     

Long-term corrosion of copper in a dilute anaerobic sulfide solution

The mechanism of corrosion of oxygen-free copper has been studied in stagnant aqueous sulfide solutions using corrosion potential and electrochemical impedance spectroscopy (EIS) measurements. Film structure and composition were examined on surfaces and on cross-sections prepared by focused ion beam (FIB) milling using scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). Experiments were conducted in anaerobic 5 × 10⁻⁵ mol dm⁻³ Na₂S + 0.1 mol dm⁻³ NaCl solutions for exposure periods up to 4000 h (∼167 days) to mimic (at least partially) the conditions that could develop on a copper nuclear fuel waste container in a deep geologic repository. The corrosion film formed was a single cellular Cu₂S layer with a non-uniform thickness. The film thickness increased approximately linearly with immersion time, which implied that the sulfide film formed on the Cu surface is non-protective under these conditions up to this exposure time. The film growth process was controlled by HS⁻ diffusion partially in the aqueous solution in the pores in the cellular sulfide film and partially in the bulk of the aqueous solution.     

The influence of thin benzoate-doped polyaniline coatings on corrosion protection of mild steel in different environments

The corrosion process of mild steel in the presence of benzoate-doped polyaniline coatings exposed to different environments (3% NaCl, atmosphere, and the Sahara sand) has been investigated. This system was also tested for cathodic protection and it has proven more efficient comparing to mild steel alone. Possible mechanisms of the corrosion protection of mild steel in the presence of a polyaniline-based coating in different corrosion media were also proposed.     

Inhibition of nickel coated mild steel corrosion by electrosynthesized polyaniline coatings

Polyaniline (PANI) coatings were electrochemically synthesized on nickel (Ni) coated mild steel (MS) and their corrosion protection properties were investigated. In this work, the Ni layer (∼1 μm thick) was electrodeposited on MS under galvanostatic condition. Thereafter, the PANI coating was deposited over the Ni layer from aqueous salicylate medium by using cyclic voltammetry. These bi-layered composite coatings were characterized by cyclic voltammetry, UV–vis absorption spectroscopy and Fourier transform infrared (FTIR) spectroscopy. The corrosion protection properties of Ni coated MS (Ni/MS) and PANI coated Ni/MS (PANI/Ni/MS) were investigated in aqueous 3% NaCl by using open circuit potential (OCP) measurements, potentiodynamic polarization technique and electrochemical impedance spectroscopy (EIS). It was shown that the top layer of PANI exhibits a lower porosity behavior with respect to Ni coating and reduces the corrosion rate of Ni/MS almost by a factor of 3500 and increases the lifetime of Ni coating.     

Application of multisine impedance spectroscopy, FE-AES and FE-SEM to study the early stages of copper corrosion

During the first 24 h of immersion of a pure copper surface in a NaCl containing solution, this surface is in constant evolution. The reactions going on the surface are still not known; discrepancies are found between different published studies. This study resolves these discrepancies using broadband impedance spectroscopy, field emission Auger spectroscopy and field emission electron microscopy. The surface evolution was studied using time series of impedance spectra. Also the experimental variables convection and electrolyte concentration were varied. Parameter evolutions were obtained by fitting the obtained impedance spectra to an equivalent circuit. Combining the calculated parameter values and their evolution with the spectroscopic data led to the identification or replacement of the elements present in the very general equivalent circuit found in the literature: a double layer, two circuit films in parallel and mass transfer.     

Inhibition of corrosion of mild steel by homopolymer and bilayer coatings of polyaniline and polypyrrole

Homopolymers and bilayers of polyaniline (PAni) and polypyrrole (PPy) coatings have been electropolymerized on mild steel by potentiodynamic synthesis technique in aqueous oxalic acid solutions. Characterization of coatings was carried out by cyclic voltammetry. Corrosion behavior of the polymer coated mild steel electrodes was investigated using linear anodic potentiodynamic polarization, Tafel test and electrochemical impedance spectroscopy (EIS) techniques in various aqueous corrosive solutions. Corrosion test results clearly showed that PPy and PAni/PPy bilayer coatings served as a stable host matrix on mild steel against corrosion. However, bilayers of PAni and PPy did not exhibit good combined properties of each polymer, unlike expected. PPy exhibited the best corrosion resistance among all coatings.     

Self-assembled 1-octadecyl-1H-1,2,4-triazole films on copper for corrosion protection

A film of 1-octadecyl-1H-1,2,4-triazole (OTA) was formed on a fresh copper surface by self-assembly technique. The optimum concentration of OTA and immersion time for the formation of a protective OTA film have been established using electrochemical impedance spectroscopy (EIS). These are (i) 15 mM concentration of OTA in methanol and (ii) immersion period of 48 h. X-ray photoelectron spectroscopy (XPS), reflection absorption FTIR spectroscopy, atomic force microscopy (AFM), and contact angle measurements have been used to characterize the OTA film on copper surface. The efficiency of OTA film to protect copper from corrosion in aqueous NaCl environment has been investigated using EIS, potentiodynamic polarization studies, cyclic voltammetry and weight-loss studies. All these studies showed that the OTA film affords excellent protection against corrosion of copper.     

Coatings based on electronic conducting polymers for corrosion protection of metals

In this work, corrosion protection of mild steel by a novel epoxy resin (EP)-based coating system containing polyaniline (PAni) as an anticorrosive agent was studied. The corrosion behavior of mild steel samples coated with an EP/PAni-EB (emeraldine base), EP/PAni-ES (emeraldine salt), EP/SPAN (PAni sulfonated), EP/PAni-fibers, EP/PhoZn (zinc phosphate), EP/ChroZn (zinc chromate) or EP/Charge was investigated in 3.5% NaCl solution. For this purpose, electrochemical impedance spectroscopy measurements were utilized. It was found that the addition of three forms of PAni—undoped, sulfonated and fibers—to the EP resin increased its corrosion protection efficiency.     

The electrochemical synthesis of poly(aniline-co-o-anisidine) on copper and their corrosion performances

The copolymer films PANI-co-POA and poly(aniline-co-o-anisidine) were carried out on copper (Cu) electrode, by applying two different scan rates (20 and 50 mV s⁻¹) and using two different thicknesses at high scan rate. Synthesizes were achieved under cyclic voltammetric conditions from 0.075 M aniline and 0.075 M o-anisidine containing sodium oxalate solutions. The synthesized copolymer films were strongly adherent and homogeneous in both cases. AC impedance spectroscopy (EIS), anodic polarization plots and open circuit potential–time curves were used to evaluate the corrosion performance of copolymer coated and uncoated electrodes in 3.5% NaCl. It was shown that the copolymer film coated at low scan rate exhibited a better property initially when compared with the copolymer film produced at high scan rate. However, it could not resist the attack of corrosion products, in longer time and meanwhile its barrier property significantly diminished. It was found that the thin copolymer film produced at high scan rate by its catalysing effect led to the formation of highly protective copper oxides on the surface whereby providing a better protection for long exposure times. It also emerged that the corrosion resistances of thin copolymer film produced at high scan rate and copolymer film synthesized at low scan rate were almost same and relatively higher for much longer periods when compared with the one observed for bare copper electrode.     

The effect of Thyme leaves extract on corrosion of mild steel in HCl

The aqueous extract of Thyme leaves was investigated for its efficacy as corrosion inhibitor for mild steel in 2 M HCl using weight loss measurements and various electrochemical techniques. Experimental results show that corrosion inhibition efficiency increases with concentration of the Thyme leaves extract. A corrosion inhibition efficiency of 84% was achieved in 2 M HCl. Polarization studies show that Thyme leaves extract acts as a mixed inhibitor. The adsorption of Thyme leaves extract on the steel surface is found to follow Langmuir adsorption isotherm.     

Phase angle analysis for stress corrosion cracking of carbon steel in fuel-grade ethanol: Experiments and simulation

The stress corrosion cracking (SCC) of carbon steel in simulated fuel-grade ethanol (SFGE) was investigated using electrochemical impedance spectroscopy (EIS) and slow strain rate test (SSRT). Phase angle at low frequency range (<1 Hz) is sensitive to SCC process of carbon steel in SFGE. Phase angle decreases during an active crack growth. Frequency at maximum phase angle also increases towards an active cracking region at around 1 Hz. A transmission line model (TLM) is used to simulate the EIS response for SCC based on real geometrical parameters. By systematically changing the values of the circuit elements, the activities of the sample surface, crack tip and crack wall were studied in detail. By comparing the Bode plots from both experiment and simulation during SCC, a detailed mechanistic picture is derived to describe the behavior of the stress corrosion crack on carbon steel in the fuel-grade ethanolic environment.     

Luffa aegyptiaca leaves extract as corrosion inhibitor for mild steel in hydrochloric acid medium

The performance of methanol extract of Luffa aegyptiaca leaves (MLA) as corrosion inhibitor for mild steel (MS) in 1 M HCl was investigated by potentiodynamic polarization and electrochemical impedance spectroscopy. Polarization measurements showed that the MLA acts as a mixed inhibitor. It was found that the percentage inhibition efficiency increased with MLA concentration and decreased with temperature. Thermodynamic parameters indicate the spontaneous adsorption of MLA on MS surface. In addition, it has been established that the adsorption process obeyed Langmuir isotherm. Additions of halide ions considerably increase the inhibition efficiency. Synergistic parameters confirm the synergistic effect of halide ions. The adsorption of the chemical constituents of MLA on MS surface was confirmed by Fourier transform infrared spectroscopy and atomic force microscopy.     

Schiff bases: An overview of their corrosion inhibition activity in acid media against mild steel

Abstract

This paper deals with a review of the inhibition activity of various reported Schiff bases on the deterioration of mild steel in hydrochloric acid and sulfuric acid media. Mild steels find wide applications in structural, automobile and petrochemical industry, where acid solutions such as hydrochloric acid, sulfuric acid are commonly being used as pickling or descaling agents. The undue deterioration of metal during pickling can be controlled by adding a suitable inhibitor to the pickling solution. Schiff bases are widely being employed in such applications. This paper highlights the influence of structure–inhibition activity relationship of Schiff base compounds on their performance as corrosion inhibitors of mild steel in acid media. The information provided finds a useful practical application for different industrial fields in the selection of best-performing inhibitors and also for the researchers involved in the development of new novel corrosion inhibitors for mild steel in acid media.     

Electrochemical corrosion characteristics of type 316 stainless steel in simulated anode environment for PEMFC

The corrosion behavior of type 316 stainless steel in simulated anode environment for proton exchange membrane fuel cell (PEMFC), i.e., dilute hydrochloric acid solutions bubbled with pure hydrogen gas at 80 °C, was investigated by using electrochemical measurement techniques. The main purpose is to offer some fundamental information for the use of stainless steels as bipolar plate material for PEMFC. Both polarization curve and electrochemical impedance spectroscopy (EIS) measurements illustrate that 316 stainless steel cannot passivate spontaneously in the simulated environments. The absorbed (and/or adsorbed) hydrogen atoms from cathodic corrosion reactions on the steel surface may deteriorate the passivity and corrosion resistance. The oxidation of these hydrogen atoms gives rise to a second current peak in the anodic polarization curve, and the current increases with immersion time. EIS spectra also reveal that a porous corrosion product layer formed on the steel surface during the active dissolution in the test solutions. 316 stainless steel exhibits the similar corrosion behavior in sulfate ions containing dilute hydrochloric acid solution.