Evaluation of localized corrosion phenomena with electrochemical impedance spectroscopy (EIS) and electrochemical noise analysis (ANA)

The use of electrochemical impedance spectroscopy (EIS) and electrochemical noise analysis (ENA) for non-destructive evaluation of corrosion processes is illustrated for three model systems. EIS can be used to detect and monitor localized corrosion of Al alloys and determine pit growth laws which can be used for lifetime prediction purposes. Electrochemical potential and current noise data can be analyzed in the time and the frequency domain. A comparison of noise data obtained for Pt and an Al 2009/SiC metal matrix composite (MMC) exposed to 0.5 N NaCl has shown that the use of potential noise data alone can lead to erroneous conclusions concerning corrosion kinetics and mechanisms. The electrochemical noise data have been evaluated using power spectral density (PSD) plots in an attempt to obtain mechanistic information. The system Fe/NaCl has been used to determine the relationship between the polarization resistance R_p obtained from EIS data and the noise resistance R_n determined by statistical analysis of potential and current noise data. Potential and current noise can be recorded simultaneously allowing construction of noise spectra from which the spectral noise resistance R can be obtained as the limit for zero frequency. Good agreement between R_P, R_n and R has been observed for iron exposed to NaCl solutions of different corrosivity. For polymer coated steel exposed to 0.5 N NaCl for five months analysis of EIS data allows to draw conclusions concerning the degree of disbonding of the coating and the decrease of the coating resistivity with exposure time. R_n and R obtained from electrochemical noise data for an alkyd coating on cold rolled steel agree with each other and show the same time dependence as R_p and the pore resistance R_po determined from EIS data, but are significantly lower than R_p and R_po. The relationships of derived noise parameters such as R_n and R to coating properties and to the remaining lifetime of a polymer coating are not clear at present.     

Evaluation of the corrosion resistance of anodized aluminum 6061 using electrochemical impedance spectroscopy (EIS)

The corrosion resistance of anodized Al 6061 produced by two different anodizing and sealing processes was evaluated using electrochemical impedance spectroscopy (EIS). The scanning electron microscope (SEM) was employed to determine the surface structure and the thickness of the anodized layers. The EIS data revealed that there was very little change of the properties of the anodized layers for samples that were hard anodized in a mixed acid solution and sealed in hot water over a 365 day exposure period in a 3.5 wt% NaCl solution. The specific admittance A_s and the breakpoint frequency f_b remained constant with exposure time confirming that the hard anodizing process used in this study was very effective in providing excellent corrosion resistance of anodized Al 6061 over extended exposure periods. Some minor degradation of the protective properties of the anodized layers was observed for samples that were hard anodized in H₂SO₄ and exposed to the NaCl solution for 14 days.     

Corrosion protection of galvanized steel and electroplating steel by decanoïc acid in aqueous solution: Electrochemical impedance spectroscopy, XPS and ATR-FTIR

The inhibiting action of decanoïc acid towards the corrosion behaviour of galvanized steel and electroplating steel in aqueous solution has been studied using electrochemical impedance spectroscopy (EIS) techniques. Data obtained from EIS show a frequency distribution and therefore a modelling element with frequency dispersion behaviour, a constant phase element (CPE) has been used. Results obtained revealed that decanoïc acid is an effective inhibitor. The better performance was obtained in the case of electroplating steel. X-ray photoelectron spectroscopy surface analysis shows that, decanoïc acid is chemisorbed on surface of galvanized steel and electroplating steel. These studies have shown that the active site for binding the film on metal surface is the anionic carboxylate head. Attenuated Total Reflectance-Fourier Transform Infrared (ATR-FTIR) spectroscopy was used to identify the nature of the deposits on the metal surface.     

Corrosion behaviour of solar reflector coatings on AA 2024T3 - an electrochemical impedance spectroscopy study

Electrochemical impedance spectroscopy in the 100 kHz-5 mHz frequency range was applied to the study of corrosion behaviour of solar reflector coatings on AA 2024 exposed to 3.5% NaCl solution. Solar reflector coatings were obtained by sulphuric acid anodization of the alloy in presence of oxo-anions of molybdenum or vanadium. Corrosion behaviour of the oxide films was evaluated by determining the film resistance and capacitance values with exposure time. Comparison of the results reveals that, vanadium addition confers better barrier properties and corrosion resistance than molybdenum additions. Analysis using damage function based on the impedance at 100 mHz shows that solar reflector coatings have improved corrosion behaviour than normal sulfuric acid anodized oxide films on AA 2024.     

Evaluation of the properties of anodized aluminum 6061 subjected to thermal cycling treatment using electrochemical impedance spectroscopy (EIS)

The corrosion resistance of anodized Al 6061 produced by two different anodizing and sealing processes was evaluated for 30 days during exposure to 3.5 wt% NaCl using EIS. Thermal cycling treatments at 120, 160 and 200 °C have been applied for the two types of samples. The degradation of the properties of the anodized layers has been determined by thorough analysis of the EIS data for control samples and samples that had undergone thermal cycling. Scanning electron microscopy has been used to evaluate the damage to the anodized aluminum layers due to thermal cycling. It was found that the thermal treatment produced considerable damage of both the porous layer and the barrier layer. The EIS data suggest that some cracks extended into the bare metal. The damage of the oxide layers increased with increasing thermal cycling temperature for both types of samples. Self-sealing of the porous layer and the barrier layer occurred during immersion in NaCl.     

非晶合金Mg_(65)Y_(10)Cu_(25)在3.5%NaCl溶液中的腐蚀行为

利用电化学极化曲线方法、交流阻抗 (EIS)技术和扫描电子显微镜 (SEM )研究了Mg65Y10 Cu2 5非晶及相应的晶化合金在 3 5 %NaCl溶液中的腐蚀行为。极化曲线测试结果表明 ,非晶合金Mg65Y10 Cu2 5在NaCl溶液中为活性溶解 ,腐蚀反应由阴极反应和阳极反应共同控制。EIS测试表明 ,随着浸泡时间延长 ,非晶合金耐蚀性下降 ,EIS由 3个时间常数变为 2个时间常数。SEM测试表明 ,非晶合金经过 2 4h浸泡后 ,表面发生了极为不均匀的腐蚀 ;EDAX能谱表明 ,非晶合金经过浸泡后 ,表面成分发生了较大变化 ,含镁量减少 ,表面出现了浓度分布不均匀的氧元素。晶化后Mg65Y10 Cu2 5合金的耐蚀性略有提高。探讨了非晶合金在 3 5 %NaCl溶液中的腐蚀机理     

Application of EIS to cathodically protected steel: Tests in sodium chloride solution and in chloride contaminated concrete

The efficiency of cathodic protection is usually checked by switching off the current and either by measuring the polarized potential or by recording the evolution of the potential decay. These methods although based on a long experience are not indicating directly on the state of the metal, and the interpretation of the results is not always evident. It remains as an interesting goal for the research on alternative methods to verify the efficiency of the cathodic protection. In this paper, a study made by using linear polarization and EIS is presented based on the behaviour of the two cathodically protected systems. The results indicate that the impedance diagrams show important and consistent changes in shape and associated parameters when the steel is protected or unprotected. Although changes have been noticed before by other authors in the EIS diagrams, this study assumes that the system is a galvanic couple.     

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.     

Corrosion inhibition of carbon steel in hydrochloric acid solution by fruit peel aqueous extracts

The inhibitive action of the aqueous extracts of fruit peels against corrosion of carbon steel in a 1 M HCl solution was investigated using electrochemical impedance spectroscopy, potentiodynamic polarization curves, weight loss measurements and surface analysis. We analyzed aqueous extracts of mango, orange, passion fruit and cashew peels in different concentrations and found that the extracts act as good corrosion inhibitors for the tested system. The inhibition efficiency increases with increasing extract concentration and decreases with temperature. The adsorption of components of the fruit peel extracts on the surface of the carbon steel follows the Langmuir adsorption isotherm.     

Corrosion resistance of AISI 1018 carbon steel in NaCl solution by plasma-chemical formation of a barrier layer

The oxidizing OH and NO radicals generated by a gliding electric discharge in humid air induce passive film formation at the surface of AISI 1018 steel discs, as showed by changes in corrosion electric parameters (E_cor, J_cor) in aqueous (0.5 M) NaCl solution with the exposure time to the plasma. The protecting treatment and wettability are largely improved by rotating the sample during exposure. X-rays analysis evidences the apparition of -Fe phase at the surface and Mössbauer spectra enlights a slight contribution of lepidocrocite FeOOH phase.     

Corrosion mechanisms of steel concrete moulds in contact with a demoulding agent studied by EIS and XPS

The behaviour of E24 mild steel was studied by XPS analysis and electrochemical impedance spectroscopy (EIS) in a filtered solution of cement (pH 13), and an alkyl N-aminodiphosphonate aqueous solution called Aquadem^® (7?pH?13). XPS results showed that the corrosion products developed in both media consisted of Fe₂O₃, covered by a very thin layer of goethite. The thickness of this oxide layer was estimated to be 3 nm. XPS analysis also demonstrated the adsorption of Aquadem^® on the outer layer of FeOOH for pH lower than the zero charge pH of goethite (7.55). From XPS and EIS results, physical models of the E24 steel/electrolyte interface are proposed as a function of pH. For 11?pH?13, the steel is covered by a passive film, while for pH?10, pitting corrosion takes place. At pH 7, an additional mass transport phenomenon must be taken into account. The fitting procedure provided values for several physical parameters (electrolyte resistance, passive film resistance), from which the film capacitance and the dielectric constant of the oxide layer were calculated.     

Comparative study on the corrosion behavior of milled and unmilled magnesium by electrochemical impedance spectroscopy

The corrosion behavior of milled Mg prepared by high-energy ball milling for 10 h has been investigated in alkaline solutions by electrochemical impedance spectroscopy and compared with that of unmilled Mg. X-ray powder diffraction indicates a crystallite size of 34 nm for the milled Mg compared to >100 nm for the unmilled powder. Chemical analyses show no significant iron contamination in milled Mg powder, indicating the absence of tools erosion during the milling procedure. In contrast, significant MgO enrichment in the milled powder is observed (6.5 wt.% after 10 h milling compared to 1.0 wt.% before milling). The oxygen contamination is mainly attributed to the powder oxidation occurring during milling. From XPS analyses, no MgO enrichment is detected on milled Mg electrode surface, confirming that MgO is dispersed homogeneously in the bulk of the material rather than to segregate on its surface. Electrochemical impedance spectroscopy demonstrates clearly the better corrosion resistance of milled Mg compared to unmilled Mg in passive conditions (KOH solution, pH=14) and in more active corrosion conditions (borate solution, pH=8.4). This is illustrated by a nobler corrosion potential and by a significant increase of the interfacial resistance related to the film and charge-transfer reaction. Moreover, the variation of the different electrochemical parameters (corrosion potential, interfacial resistance and capacitance) with immersion time is less accentuated and tends more rapidly to a steady state with milled Mg, suggesting an enhancement of the Mg(OH)₂ formation kinetic. The origin of the distinctive passivation behavior of ball-milled Mg is discussed.     

Corrosion of the component phases presents in high copper dental amalgams. Application of electrochemical impedance spectroscopy and electrochemical noise analysis

The corrosion resistance of three of the constituent phases in high copper dental amalgams has been investigated by electrochemical methods in 0.9% NaCl solution. Polarization curves show corrosion potentials most positive for γ₁-Ag₂Hg₃, followed by Ag-Cu, and γ-Ag₃Sn in agreement with the order of corrosion resistance deduced from the corrosion currents. Complex plane impedance plots at the open circuit potential showed distorted semicircles with diffusional components at low frequency for Ag-Hg and Ag-Cu, while for γ-Ag₃Sn a layer of corrosion products is formed, partially or completely covering the surface of the electrode. Impedance and noise spectra have been compared in the frequency domain, and show good agreement.     

Electrochemical quartz crystal microbalance and electrochemical impedance spectroscopy study of copper corrosion inhibition by imidazoles

The aim of this work is to obtain deeper insight into the mechanism of the protective action of three imidazole-based corrosion inhibitors. Investigations were performed on copper in 3% NaCl, by electrochemical impedance spectroscopy and electrochemical quartz crystal microbalance measurements. The kinetic changes in the corrosion processes were monitored over time. In spite of similar molecular structure, differences in the inhibiting mechanism of three imidazole compounds were observed. The two inhibitors with a tolyl substituent decreased the copper corrosion rate due to the formation of a thin adsorbate layer; however, slow formation of a thick layer was observed for 4-methyl-1-phenyl imidazole. From electrochemical impedance spectroscopy studies, it was observed that all three inhibitors protected the copper efficiently, and in some cases, the degree of the protection increased with time.     

Corrosion electrochemical mechanism ofchemical mechanical polishing of copper in K3Fe（CN）6 solution

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Corrosion protection properties of lacquer coatings on steel modified by carbon black nanoparticles in NaCl solution

Nanometer carbon black (CB) grafted with polyvinyl alcohol was obtained by surface modification, and its size was about 60 nm. In the ultrasonic field, the composite lacquer coatings with different contents of CB nanoparticles were prepared by mechanical agitation. Electrochemical impedance spectroscopy (EIS), anodic polarization curves, immersion measurements and salt fog tests were used to evaluate the corrosion performances of the composite coatings applied on steel in NaCl solution. It was observed that composites coatings with 1 wt% CB nanoparticles reduced drastically the corrosion rate of steel.     

Electrochemical and analytical study of corrosion inhibition on carbon steel in HCl medium by 1,12-bis(1,2,4-triazolyl)dodecane

1,12-bis(1,2,4-triazolyl)dodecane (dTC12) is an excellent corrosion inhibitor for carbon steel in deaerated 1 M HCl solution. In this work electrochemical and analytical techniques were used to study the inhibition of corrosion on carbon steel in acidic medium. The carbon steel corrosion inhibition of dTC12 was attributed to the synergistic effect between chloride anion and quaternary ammonium ion. The protective efficiency of the film was higher than 90%, indicating that corrosion of carbon steel in 1 M HCl is reduced by dTC12.The effect of dissolved oxygen on the inhibition efficiency was also investigated. The results show that the inhibition efficiency increases in early stage and decreases for a long immersion time.     

Cu-P-Cr钢及其焊接接头的周期腐蚀性能

通过中试轧制、电渣压力焊制备了Cu-P-Cr钢及其焊接接头,利用光学显微镜研究了电渣压力焊接接头的组织晶粒度,利用干湿交替实验机、SEM、EPMA、XRD研究了Cu-P-Cr钢及其焊接接头在1.0×10-2mol/L的Na HSO3溶液中的耐腐蚀性能、锈层元素分布及组成,分析了母材与焊接接头的耐腐蚀机理及其影响因素。研究结果表明:焊接接头与母材的腐蚀速率相比碳钢分别为64.6%与61.5%。焊接接头锈层中Cu、Cr元素的大量富集、α-Fe OOH相的转变是腐蚀性能优异的主要原因,而焊缝及熔合区形态各异的铁素体+珠光体+魏氏组织和晶粒尺寸不均等导致了锈层中Cu、Cr富集程度低于母材、腐蚀性能稍弱于母材。     

Corrosion inhibition study of pure Al and some of its alloys in 1.0 M HCl solution by impedance technique

This paper describes the use of the potentiodynamic polarization and electrochemical impedance spectroscopy technique (EIS) in order to study the corrosion inhibition process of pure Al, (Al + 6%Cu) and (Al + 6%Si) alloys in 1.0 M HCl solution at the open circuit potential (OCP) in the temperature range 10-60 °C. Dodecyl phenol ethoxidate as a non-ionic surfactant (NS) inhibitor has been examined. The Nyquist diagrams consisted of a capacitive semicircle at high frequencies followed by a well defined inductive loop at low frequency values. The impedance measurements were interpreted according to a suitable equivalent circuit. The results obtained showed that the addition of the surfactant inhibits the hydrochloric acid corrosion of the three Al samples. The inhibition occurs through adsorption of the surfactant on the metal surface without modifying the mechanism of corrosion process. Potentiodynamic polarization measurements showed that the surfactant acts predominately as anodic inhibitor. The inhibition efficiency increases with an increase in the surfactant concentration, but decreases with an increase in temperature. Maximum inhibition is observed around its critical micelle concentration (CMC). The inhibition efficiency for the three Al samples decreases in the order: (Al + 6%Si) > (Al + 6%Cu) > Al. Kinetic-model and Frumkin adsorption isotherm fit well the experimental data. Thermodynamic functions for both dissolution and adsorption processes were determined.