Analysis of pitting corrosion rate

A method for estimating pitting corrosion rate is proposed. The method is based on the analysis of anodic and cathodic voltammograms that were measured on the specimens of two types: on the test specimen coated with an oxide film, which formed under the open-circuit conditions, and on the specimen, whose surface was totally activated with aggressive ions. The use of Tafel portions of these voltammograms in various combinations enables us to estimate the corrosion potential and corrosion current for general corrosion proceeding in the induction period, for pitting corrosion at the initial stage of its development, for a highly developed pitting corrosion, when the major area of specimen surface is occupied with pits, and also in the intermediate case.     

Corrosion resistances of passive films on low‐Cr steel and carbon steel in simulated concrete pore solution

The passive ranges of carbon steel rebar and 3Cr steel rebar in saturated Ca(OH)₂‐simulated concrete pore solution with pH 12.6 were determined by means of cyclic voltammetry and potentiodynamic polarization curves. Chronopotentiometry was used to obtain steady‐state conditions for the formation of passive films on rebar samples at different anodic potentials. Electrochemical impedance spectroscopy, Mott–Schottky and X‐ray photoelectron spectrometer curves were employed to compare the formed passive films at different potentials. Additionally, cyclic polarization curves were used to compare the corrosion resistances of formed passive films on the two rebars in saturated Ca(OH)₂‐simulated concrete pore solution with different concentration of Cl^?. The results show that the passive ranges of the two rebars are all between ?0.15 and +0.6 V, and more stable passive films can be formed on both rebars at the anodic potential of +0.3 V. In the absence of Cl^?, the stability and corrosion resistance of the passive film formed on the 3Cr rebar are better than those of CS rebar. The passive film of 3Cr steel has the relatively better pitting corrosion resistance than carbon steel in saturated Ca(OH)₂‐simulated concrete pore solution that contains different concentration of Cl^?. Copyright © 2016 John Wiley & Sons, Ltd.     

基于电化学噪声研究模拟海洋大气环境下304不锈钢的点蚀行为

基于电化学噪声技术建立了不锈钢海洋大气点蚀监测系统,利用该系统对处于干湿循环环境下不锈钢的点蚀行为进行监测. 使用时域谱图、时域统计、频域谱图和散粒噪声理论等分析方法对采集到的电化学噪声数据进行处理分析,并结合动电位极化法,形貌分析法共同研究不锈钢的点蚀行为. 研究结果表明,304不锈钢在模拟海洋大气环境下的点蚀行为分为钝化、亚稳态点蚀和稳态点蚀三个阶段. 在钝化阶段,电位电流噪声信号出现少量的同步异向波动,腐蚀事件发生频率高,平均电量低;在亚稳态点蚀阶段,电位电流噪声信号出现大量的同步同向波动,腐蚀事件发生频率降低,平均电量上升,通过扫描电镜观察蚀点;在稳态点蚀阶段,电位电流噪声信号不仅存在大量的同步同向波动,还出现了同步异向波动,腐蚀事件发生频率较低,平均电量大幅度上升,通过扫描电镜观察到电极表面出现小而浅的蚀点. 而动电位极化法可以证实304不锈钢点蚀的发生. 两种分析方法所得结果具有较好的一致性,证明该监测系统很好地实现了对模拟海洋大气环境下304不锈钢点蚀行为的连续监测,并能判断点蚀的发生.     

Anodic treatment of steel 40Kh in a 35-% sulfuric acid electrolyte containing chloride ions

Anodic dissolution of steel 40Kh in a sulfuric acid electrolyte containing Cl^– ions is studied by analyzing the experimental dependence of anodic current on the specimen potential. The dependences of the critical passivation current, anodic current at –0.15 to 0.55 V (Ag/AgCl), and passivation current on the concentration of Cl^– ions (c) are determined. The maximum value of c for the passivation at 0.55–1.6 V (Ag/AgCl) is refined. The dependence of the specimens steady-state potential on c is determined and its decrease is related to an abrupt increase in the anodic current at the passivation potentials.Translated from Elektrokhimiya, Vol. 41, No. 3, 2005, pp. 371–374.Original Russian Text Copyright © 2005 by Ivashkin.     

Characterization of surface composition on Alloy 22 in neutral chloride solutions

The composition of anodically grown oxide films on Alloy 22, a Ni‐Cr‐Mo(W) alloy, has been investigated in 5 mol l^?1 NaCl at room temperature using X‐ray photoelectron spectroscopy and time‐of‐flight secondary ion mass spectrometry. For applied potentials up to 0.2 V (vs Ag/AgCl (saturated KCl solution)), a Cr(III) oxide barrier layer develops at the alloy/oxide interface accounting for the excellent passivity demonstrated to prevail in this potential region by previous electrochemical impedance spectroscopy measurements. At higher potentials, this layer is destroyed by defect injection as Cr(III) is oxidized to the more soluble Cr(VI). The overall oxide/hydroxide film thickness is, however, increased as Mo(VI)/W(VI) species accumulate at the oxide solution interface. The potential of 0.2 V at which the barrier layer switches from growth to destruction coincides with the previously demonstrated threshold potential for the initiation of crevice corrosion. Copyright © 2012 John Wiley & Sons, Ltd.     

Studies on the repassivation behavior of aluminum and aluminum alloy exposed to chromate solutions

This study explores the repassivation ability of a scratch in a chromate conversion coating (CCC) on aluminum alloy, AA2024‐T3, and hence evaluates the theory of migration of hexavalent chromium ions from the protected surface of the aluminum alloy to the exposed surface. To confirm that protection was indeed restored by hexavalent chromium ions, the repassivation of a scratch on pure aluminum exposed to a dichromate solution was studied. This forms the simplest subsystem model of the CCC on the alloy in which the CCC is replaced by pure hexavalent chromium and alloy with pure aluminum. Open‐circuit potential measurements, synchrotron infrared microspectroscopy (SIRMS) and secondary ion mass spectroscopy (SIMS) have been used judiciously to evaluate the repassivation behavior. Results indicate that the dichromate ions have high mobility. The slow migration of Cr(VI) ions from the protected surface to the scratch is observed to result in repassivation, as seen from the steady increase in the potential in 0.05 M NaCl solution. The results obtained from SIMS and SIRMS confirm the migration of the oxyanions from the protected region to the metal surface exposed by the scratch. The SIRMS results indicate the formation of an Al(III)–Cr(VI) complex, proposed and shown to be formed in the pits. Copyright © 2003 John Wiley & Sons, Ltd.     

Pitting behavior on super 13Cr stainless steel in 3.5% NaCl solution in the presence of acetic acid

The pitting behavior was investigated on super 13Cr stainless steels in 3.5% NaCl solution in the presence of HAc. The electrochemical measurements including potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), and chronoamperometric experiments were carried out, as well as the SEM surface analysis. The parameters such as E _corr and I _corr were obtained by fitting technique. Moreover, the equivalent circuit model was applied in the analysis of Nyquist plots, and ZsimWin software was used to analyze the EIS data. The results indicate that the pitting corrosion is accelerated with increasing the amounts of HAc. In addition, pitting nucleation and growth mechanisms were described in this work.     

Corrosion resistance in chloride solution of the AlSi10Mg alloy obtained by means of LPBF

The paper deals with the corrosion resistance in chloride solutions of an AlSi10Mg alloy obtained by laser powder bed fusion (LPBF) process. The potentiodynamic tests were carried out in solutions having different chloride contents. The results emphasize the role of chloride concentration on localized corrosion. The increase of concentration reduces pitting potential. In addition, the influence of the post-processing heat treatment temperature was recognized. Penetrating attacks occurred either on after low temperatures stress relieving or specimens without any treatment, promoted by selective dissolution of the α-Al phase stimulated by galvanic coupling with noble silicon precipitates at the border of the melt pool. Such penetrating morphology was not observed after heat treatments at high temperature.     

Corrosion and adsorption properties of electrochemical manganese dioxide in the acidic and weakly alkaline sulfate solutions

Corrosion and adsorption properties of manganese dioxide, which was anodically deposited on platinum, its powder, and compacted tablets of manganese dioxide in the solutions with various pH values are studied using various experimental methods. It is shown that the corrosion rate of manganese dioxide decreases with increasing pH of solution, and the process proceeds by the electrochemical mechanism with conjugate chemical reactions of the formation and decomposition of the product of transition stage. The adsorption properties of manganese dioxide powder with respect to copper ions increase with increasing pH of solution, whereas the amount of manganese ions passing to the solution almost vanishes at pH 9.     

The influence of Ce3+ ions on the corrosion rate of stainless steel in acidic solutions of different pH-values

The corrosion resistance of AISI 420 stainless steel in 0.1 mol L^?1 H₂SO₄ + 0.1 mol L^?1 Na₂SO₄ solutions at different pH-values and the inhibiting effect of Ce³⁺ ions was studied using electrochemical polarization methods. The results reveal decreasing of the corrosion rate with an increasing the pH of the solution, which demonstrates the progressive protective character of the inhibitor used. At pH lower than 3.33, the corrosion inhibition was most probably a result of the competitive adsorption of Ce³⁺ with H⁺ ions on the cathodic sites of the electrode surface, and it was found to be dependent on the relative concentration of H⁺/Ce³⁺. The peroxide generated from the oxygen reduction reaction at pH 3.33 was found to be capable oxidize trivalent cerium (Ce) to the tetravalent state. As obtained hydroxide precipitates act as diffusion barrier hindering the corrosion processes, whereafter a spontaneous passivity occurs on the steel surface at this pH.     

Inhibitive action of ethanol extracts from Nauclea latifolia on the corrosion of mild steel in H2SO4 solutions and their adsorption characteristics

The inhibitive action of ethanol extracts from leaves (LV), bark (BK) and roots (RT) of Nauclea latifolia on mild steel corrosion in H₂SO₄ solutions at 30–60 °C was studied using weight loss and gasometric techniques. The extracts were found to inhibit the corrosion of mild steel in H₂SO₄ solutions and the inhibition efficiencies of the extracts follow the trend: RT > LV > BK. The inhibition efficiency increased with the extracts concentration but decreased with temperature rise. Physical adsorption of the phytochemical components of the plant on the metal surface is proposed as the mechanism of inhibition. The adsorption characteristics of the inhibitor were approximated by the thermodynamic-kinetic model of El-Awady et al.     

烯胺阻锈剂对钢筋在模拟碳化混凝土孔隙液中的点蚀抑制

通过电化学噪声(ECN)、电化学阻抗(EIS)及极化曲线研究了四乙烯五胺(TEPA)在碳化模拟混凝土孔隙液中对Q345B碳钢点蚀的抑制机理. 结果表明: 通过吸附成膜和隔离Cl^-离子对钝化膜的侵蚀, TEPA浓度升高导致碳钢点蚀电位正移. 低浓度的TEPA会造成亚稳态蚀点形核速率略微增加, 但会降低其寿命. 随着TEPA浓度增加, 噪声电阻上升, 而亚稳态蚀点寿命和平均点蚀电量则迅速下降, 表明其明显加速了亚稳态蚀点修复, 当TEPA浓度达0.10 mol·L^-1时, 噪声峰消失, 基底电流趋于零, 蚀点全面钝化. TEPA不仅能抑制Cl^-离子引起的亚稳态和稳态蚀点生长, 还可吸附于钝化膜表面, 抑制膜的均匀溶解. 形貌观察表明, 亚稳态蚀点主要在稳态蚀点周围形核和生长, 并不断为稳态蚀点所吞并, 造成碳钢表面蚀坑一般沿平面而不是垂直方式扩展.     

Rapid relaxation pathway of the excited state of linear merocyanines in solutions

Excited‐state relaxation of linear merocyanine dyes in solution is investigated using time‐resolved spectroscopy techniques and quantum chemical calculations. The merocyanine L‐Mero4 and phenyl‐substituted P‐L‐Mero4 have a S‐trans and S‐cis structure, respectively, consisting of indole moiety as the donor, indandione as the acceptor, and the tetramethine as the bridge. The time‐correlated single‐photon counting (TCSPC) picosecond measurements after excitation at wavelength 515 nm to the ππ* state yield emission curves with a short component τ₁ in the range of 27–160 ps and a second component τ₂ of 200–780 ps for L‐Mero4. In P‐L‐Mero4, τ₁ lies in the range of 18–150 ps and τ₂ 220–520 ps. The subfemtosecond transient absorption measurements yield a short component around 0.4–1.4 ps, and the second/third components are similar to those in the TCPSC measurements. The analysis of the experimental data demonstrates that the ground state recovery exhibits a biexponential rise and rapidly indicates that the conversion back to the electronic ground state provides a fast, nonradiative pathway. Quantum chemical calculations on the electronic structures and their dependence on the molecular confirmation are performed. We identify the excited states and the relaxation path along the twist of the center double bonds in tetramethine that might be the nonradiative pathway. The C=C double bond is weakened in the ππ* state. The phenyl substitution in the conjugated double bond weakens this C=C bond, lowers the isomerization barrier, increases the nonradiative rate, and reduces the emission quantum yield. In polar solvents, the energy of the perpendicular conformer along the trans–cis isomerization path is increased to achieve less coupling to the ground state surface. Because of the small barrier to the trans form, these two conformers establish an equilibrium condition. The trans form, which lies at a lower energy, gains more population and thus has a higher emission yield.     

Experimental and theoretical studies on the inhibition potentials of some derivatives of cyclopenta‐1,3‐diene for the corrosion of mild steel in HCl solutions

The inhibition of the corrosion of mild steel in HCl by some cyclopentadiene‐1,3‐diene derivatives, namely, 1‐(thiophen‐2‐yl)ethanone (2APT), 1‐(1H‐pyrrol‐2‐yl)ethanone (2AP), and (E)‐2‐(1‐hydrazonoethyl)‐1H‐pyrrole (2APH)), was studied experimentally using weight loss and hydrogen gas evolution measurements. The theoretical aspect was studied using the density functional theory and quantitative structure activity relation (QSAR) methods. The results obtained indicated that the studied compounds are good inhibitors for the corrosion of mild steel in HCl. The adsorption of the inhibitor on mild steel surface was found to be spontaneous, exothermic, and obeyed the Langmuir adsorption isotherm model. A good correlation was found between experimental inhibition efficiencies and some calculated quantum chemical parameters and also with the theoretical inhibition efficiencies obtained from QSAR modeling. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011     

The effect of phase composition of Ti-20 at % Cr alloy on its anodic activation in the chloride and bromide solutions

The effect of phase composition of Ti-20 at % Cr alloy on its anodic behavior in the solutions containing aggressive Cl⁻ and Br⁻ anions and, for comparison, non-aggressive SO₄²⁻ anion is studied. Different phase compositions of the alloy were obtained by using different modes of heat treatment. The features of anodic behavior of alloys with various phase compositions are related to the electrochemical properties of titanium and chromium, their tendency to passivation and breakdown of passivity in the presence of various anions.     

The role of migration mass transfer in the electrodeposition of nickel from sulfate-chloride and chloride solutions containing succinic acid

The electrodeposition of nickel from 0.5 M sulfate-succinate-chloride (I) and 0.3 and 0.5 M chloride-cuccinate (II) solutions at a temperature of 50°C is studied. It is found that, depending on the pH₀ of solution and the concentration of succinic acid and nickel, the maximum cathodic current density for producing high-quality nickel deposits is to 35 A/dm² in electrolytes I and to 60 A/dm² in electrolytes II. This corresponds to the metal deposition rates to 23 and 48 A/dm², respectively. It is shown experimentally that high buffer properties of solutions (succinate buffer) are one of the reasons for high permissible current densities of nickel electrodeposition. The computer-calculated data showed that the intensification of nickel electrodeposition is caused also by the acceleration of mass transfer due to the presence of a considerable fraction of nickel in the form of positively charged complexes and a high concentration of components stabilizing pH_S in the near-cathode layer.     

In‐situ characterization of the early stage of pipeline steel corrosion in bicarbonate solutions by electrochemical atomic force microscopy

An electrochemical atomic force microscope was used to characterize the early stage of corrosion of an X100 pipeline steel in bicarbonate solutions with varied concentrations by synchronous measurements of electrochemical potential of the steel and its topographic evolution with time. Upon immersion of the steel in 0.01 M NaHCO₃ solution, both electrochemical potential and topographic profile are associated with the dissolution of air‐formed oxides present on the steel surface. The potential drops and the surface roughness increases rapidly. When corrosion of the steel occurs, the potential further drops and the surface roughness of the steel increases gradually. As the steel corrosion achieves a steady state, the generation of corrosion products reaches a dynamic equilibrium state. The surface roughness maintain an approximately stable value. In solutions containing increased bicarbonate concentrations, such as 0.1 M and 0.5 M NaHCO₃, the steel can be passivated. The formed passive film can eliminate some surface features and improves the surface roughness. The topographic profile of the steel surface in 0.5 M NaHCO₃ solution is smoother than that in 0.1 M solution. The surface features within 20 nm become eliminated after 4500 s of immersion in 0.1 M NaHCO₃ solution, while larger features within 50 nm in size are eliminated in 0.5 M NaHCO₃ solution in the same time period. Copyright © 2016 John Wiley & Sons, Ltd.     

On the mechanism initiating bursting oscillatory patterns during the pitting corrosion of a passive rotating iron-disc electrode in halide-containing sulphuric acid solutions

Bursting current oscillations (trains of current spikes interrupted by a steady-state passive current) were found to occur during the iron anodic polarization in halide-containing sulphuric acid solutions. These oscillations occur at potentials located within a partially passive state of the iron. The partially passive state appears at potentials more positive than the unstable passive-active transition region of the current-potential curve of the Fe|2 M H₂SO₄ system for halide concentrations approximately ranged between 20 and 50 mM. The bursting oscillations appear after a certain induction period which ranged from minutes to several hours. Experiments were conducted in which an external resistance was connected in series between the ground and the working electrode for the Fe|2 M H₂SO₄ + 30 mM Br⁻ system. The results demonstrate that the appearance of oscillations is closely related to an IR-drop mechanism operating during the pitting corrosion of Fe induced by halides. When an appropriate value of the external resistance was imposed in the system the induction period was entirely eliminated. Bursting oscillations appear at once after setting the potential at the desired value. These results provide strong evidence that during the anodic electrodissolution of iron in halide-containing sulphuric acid solutions bursting current oscillations will be induced even though the electrode seems to be in the partially passive state. This is expected to occur after the passage of an induction period during which the system acquires a critical value of the ohmic potential drop. Received: 20 October 1997 / Accepted: 2 January 1998     

XPS investigations of the electrochemical double layer on silver in alkaline chloride solutions

The electrochemical double layer on Ag in alkaline NaCl solutions was examined ex situ with X-ray photoelectron spectroscopy (XPS). The specimens were removed from the electrolyte with hydrophobic surfaces and under potential control. The potential dependent surface concentrations of the adsorbed anions (Cl⁻, OH⁻), cations (Na⁺), the surface excess charge and the amount of adsorbed water were determined and compared to the results obtained for acidic NaCl solutions. The distinct differeness found between both electrolytes were discussed in terms of a specific adsorption of hydroxide ions in the basic Cl⁻-electrolyte; i.e., the OH⁻-surface concentration has to be considered for a proper determination of the cationic excess charge and the potential of zero charge. In addition, the initial stages of silver (1) oxide formation were examined with XPS.     

电化学方法研究ZnAl,ZnAlRE合金在NaCl溶液中的腐蚀行为

用电化学方法研究了锌中掺入不同量Al、RE的锌合金在NaCl溶液中的耐蚀性能、硬度以及电化学行为的变化,并试图从合金结构上给予解释。