Investigation on inhibition of CrO4 2− and MoO4 2− ions on carbon steel pitting corrosion by electrochemical noise analysis

The inhibition effect of chromate (CrO₄ ^2–) and molybdate (MoO₄ ^2–) anions on the pitting corrosion of 16Mn carbon steel in 0.1 M NaCl containing bicarbonate solution was studied based on electrochemical noise analysis (ENA) and the potentiodynamic polarization method. The experimental results indicated that, once the pits occur on the surface of the carbon steel after 4–6 h of immersion, increasing the concentration of CrO₄ ^2– and MoO₄ ^2– ions accelerate the repassivation process, and attenuate the duration and the nucleation rate of metastable pits. Further analysis demonstrated that noise resistance R _n might not be suitable for the evaluation of the inhibition efficiency of CrO₄ ^2– and MoO₄ ^2– anions on pitting corrosion in the present system. However, the transient charge q _pit, which is an integral of all current transients during a certain period, can characterize the inhibition performance on pitting corrosion. A new definition of inhibition efficiency based on q _pit is given.     

硫酸盐还原菌诱导腐蚀的电化学噪声分析

基于电化学噪声(EN)和信号处理研究硫酸盐还原菌(SRB)对304不锈钢诱导的腐蚀。将304不锈钢电极分别置于硫酸盐还原菌接种前后的培养基中,利用电化学工作站分别对2种试样的腐蚀进程进行电化学噪声测量,将测得的噪声数据去除直流漂移,再对这些数据进行时域、频域和小波分析。结果表明:通过时域分析得到的标准偏差和噪声电阻可表征腐蚀速率,局部因子则可以区分腐蚀类型。通过频域分析得到的功率谱密度曲线,能表征304不锈钢腐蚀的程度。小波分析则能从不同尺度下分解信号,更加直观、清晰地表征腐蚀进程。利用电化学噪声技术能很好地监测SRB对不锈钢的腐蚀影响,根据不同的需求采用不同的分析方法进行电化学噪声数据分析,才能准确表征腐蚀类型、腐蚀速率以及腐蚀程度。     

Electrochemical behaviour of iron and copper in a culture solution for Spirulina platensis

Cyclic voltammograms of iron and copper electrodes were run in sodium hydroxide, carbonate–bicarbonate buffer and culture media for Spirulina platensis at 30°C. Potentiostatic steady state polarisation curves for both electrode surfaces in these electrolytes were performed in the presence and the absence of S. platensis at fixed temperature. Corrosion potential and corrosion current density values of iron and copper were obtained graphically from these curves. In all cases, the largest corrosion current density corresponded to the maximum biogenerated-oxygen concentrations, that is, illuminated culture media containing S. platensis. Corrosion potentials of iron electrodes shifted to positive values for increasing corrosion rates, whereas constant corrosion potentials were obtained for copper electrodes independently of the electrolyte.     

Application of electrochemical noise to evaluate outdoor atmospheric corrosion of copper after relatively short exposure periods

This study focused on the application of electrochemical noise to assess the protection level of corrosion products formed on copper during relatively short exposure time in different outdoor atmospheres. Electrochemical noise, cathodic reduction measurements and gravimetric (mass loss) analysis were applied to copper samples exposed at urban and rural/industrial areas in Cuba for 4 months. Measurements of Electrochemical current noise indicated that the poorest protective corrosion products were formed on samples exposed to atmospheres with high concentration of H₂S which agreed with the corrosion rate determined by mass loss and electrochemical chronopotentiometry (cathodic reduction). The electrochemical noise methodology proposed in this work showed acceptable and reproducible results by using an electrochemical cell in which the electrolyte was formed by a distilled-water wetted cloth in contact with the compounds present on a corroded metallic surface. This methodology indicated that the corrosion protection level of the corrosion products formed on copper is related to the corrosivity of the atmosphere.     

Electrochemical investigations of copper behaviour in different cupric complex solutions: Voltammetric study

The electrochemical behaviour of copper has been investigated in different cupric complex solutions by cyclic voltammetry. In pyridinic and picolinic solutions the reduction of cupric complex occurred in two stages leading to Cu(I) and Cu(0), respectively. The electrodeposited copper is oxidized in two steps leading to Cu(I) and Cu(II) as in ammoniacal cupric complex solutions. In glycine, alanine, sulfamic acid and ethylenediamine solutions, the cuprous complex is an intermediate in the cupric complex reduction but it is not detected during the oxidation of the electrodeposited copper in these solutions. In EDTA and triethanolamine solutions, the cuprous complex is not observed. The rate of copper etching was determined in pyridinic and ammoniacal cupric solutions and was shown to be faster in ammoniacal cupric solutions than in the pyridinic solutions.     

乙炔黑/双十六烷基磷酸复合膜传感器测定环境水样中痕量铜

报道了一种用乙炔黑(AB)/双十六烷基磷酸(DHP)复合膜修饰的电化学传感器,该传感器能高灵敏度测定水样中痕量的Cu~(2 )。在pH值为4.5的磷酸盐缓冲溶液中,于-0.08V(vs.SCE)处有一灵敏的氧化峰。该修饰电极测定Cu~(2 )的线性范围为8×10~(-9)～5×10~(-7)mol·L~(-1),富集300s检测限为3×10~(-10)mol·L~(-1)。用该修饰电极测定了环境水样中的Cu~(2 ),其结果与原子吸收测定值相符。     

Investigation of copper corrosion inhibition by STM and EQCM techniques

The mechanism of copper corrosion and its inhibition were studied using electrochemical techniques, in situ scanning tunneling microscopy (STM) and electrochemical quartz crystal microbalance (EQCM) methods. The morphological changes of Cu (111) were followed in 0.1 M Na₂SO₄ solution at pH 2.95. The adsorption of 5-mercapto-1-phenyl-tetrazole (5-McPhTT) at different concentrations was studied. The anodic dissolution of copper in 0.1 M Na₂SO₄ was clearly modified and hindered by the addition of 5-McPhTT. The anodic current density was reduced sharply due to the adsorption of the inhibitor on the metal surface thus providing protection. EQCM data revealed that the addition of the inhibitor to the aggressive solution did not cause a continuous increase in the electrode mass. This fact indicates that the inhibitor effect in hindering copper corrosion was due to the adsorption of a monolayer or even a submonolayer.     

Amperometric determination of thiourea in alkaline media on a copper oxide–copper electrode

A copper oxide–copper electrode was tested in alkaline media for the anodic electrochemical detection of thiourea (TU). The correlation between the history of the electrode and potential range for optimum sensing of the particular susceptible species was analysed by electrochemical and surface layer techniques. The chemical composition and morphology of surface layers were examined using the SEM/EDX technique. Electrochemical data were obtained by cyclic voltammetry (CV) and chronoamperometry (CA). The linear calibration plots for an amperometric detection of TU in a delimited potential range, using CV and CA, were obtained for the 1–8 mM concentration range. Some considerations on the correlation between TU, electrode formation and polarization conditions are proposed. A copper oxide–copper electrode can be used as an inexpensive alternative for amperometric determination of TU in alkaline media without fouling the electrode surface.     

The use of electrochemical noise measurements to detect bad copper electrorefining conditions

Additives like thiourea, gelatin and chloride are used during copper electrorefining to promote a smooth deposit. However, additives can also facilitate nodule formation when their ratios and/or concentrations are inadequate. A preliminary investigation was conducted to determine if electrochemical noise (EN) measurements could be used to monitor and detect inefficient copper electrorefining conditions due to improper ratios and/or concentrations of additives. EN measurements were carried out in the laboratory under simulated industrial conditions. Galvanostatic experiments were conducted using a synthetic electrolyte containing different concentrations of additives. A 316L SS cathode and industrial copper anodes were used. The effects of three different data acquisition frequencies were also investigated. EN signals obtained as potential time record series were studied using statistical analyses and frequency domain transforms. The different calculated parameters gave similar results for all conditions studied except when additives present in the electrolyte led to nodule formation. Results also showed that the data acquisition frequency must be at least 10 Hz to detect improper ratios and/or concentrations of additives.     

连续电解精炼阴极铜过程中添加剂的作用

采用循环伏安法研究了浓度不同的几种添加剂(硫脲、聚丙烯酰胺、明胶和骨胶)对铜电解精炼过程的影响。结果发现,与未加添加剂的空白电解液相比,加入单一添加剂后铜沉积电流峰值明显提高,表明单一添加剂的加入会促进阴极铜的沉积。当在电解液中加入3.0 mg/L硫脲和2.4 mg/L聚丙烯酰胺作为复合添加剂时,铜沉积电流峰值与加入单一硫脲与聚丙烯酰胺时相比分别提高了31.2%与5.1%,表明二者有协同作用。结合扫描电镜(SEM)、能谱(EDS)和X射线衍射(XRD)对阴极铜的微观形貌、元素组成与物相进行表征,发现使用上述复合添加剂时,阴极铜的表面形貌与纯度最理想。     

电化学测试技术在缓蚀剂缓蚀行为研究中的应用

对常规的电化学测试方法在缓蚀剂性能评价及作用机理研究方面的应用现状进行了综述,介绍了新兴电化学测试技术在缓蚀剂研究领域的应用进展。进一步指出发展适合缓蚀体系特点的测试技术和研究方法将成为缓蚀剂性能研究的重要内容之一。结合现代表面分析技术,电化学测试技术在未来缓蚀剂领域中具有广阔的发展应用前景。     

Protection of copper surface in acidic chloride solution by non-toxic thiadiazole derivative

This paper deals with electrochemical properties of copper in the presence of the non-toxic compound 2-amino- 5-ethyl- 1,3,4-thiadiazole (AETDA) in acidic chloride solution. Electrochemical techniques: open circuit potential measurements, linear potentiodynamic measurements, cyclic voltammetry measurements and chronoamperometric measurements in addition to SEM–EDS analysis were used during the work. Results show that inhibition efficiency of 2-amino-5-ethyl-1,3,4-thiadiazole depends on inhibitor concentration and immersion time of copper electrode in inhibitor solution. Cyclic voltammetry and linear potentiodynamic measurements beside chronoamperometric measurements indicate formation of protective layer on copper surface. Moreover, results obtained by electrochemical measurements point out that the stability of formed layer depends primarily on the concentration of inhibitor and of potential values at which protective film is formed. Also, potentiodynamic measurements show that AETDA in acidic chloride solutions acts as mixed-type inhibitor. Inhibition mechanism of 2-amino-5-ethyl-1,3,4-thiadiazole includes adsorption of inhibitor on active sites on electrode surface which was confirmed by SEM–EDS analysis of the electrode surface. Adsorption of the AETDA in HCl solution obeys Langmuir adsorption isotherm.     

海水及模拟海水介质中铜缓蚀剂缓蚀机理的研究进展

阐述海水及模拟海水介质中各种有机类铜缓蚀剂的国内外研究进展和对各种有机类铜缓蚀剂的缓蚀机理和协同作用机理,并展望铜缓蚀剂新的研究和发展方向.     

Effect of nickel on copper anode passivation in a copper sulfate solution by electrochemical impedance spectroscopy

Electrochemical Impedance Spectroscopy (EIS) was applied on Cu-Ni samples passivated in a specially designed flat electrochemical cell which was heated at 60 °C. The electrolyte consisted of 160 g l⁻¹H₂SO₄, 40 g l⁻¹ Cu²⁺ and 0, 10, 20, 30 or 40 g l⁻¹ Ni²⁺ and the copper anodes contained nickel ranging from 0 w% to 10 w%. The oxygen content of the anodes and the electrolyte was also measured. An AC excitation signal of 10 mV and of 1mHz 100 MHz frequency was applied at the open circuit potential as well as at a passivation potential, the latter having been determined previously. The results indicate that nickel ion additions to the electrolyte increased the resistance of the electrolyte and altered the porosity, thickness and constituents of the passivation layer formed. The equivalent circuit models generated from the data acquired during the EIS experiments and the values for the electrical components were in the predicted range. The results are supported by supplementary XRD and SEM findings.     

Inhibition of copper corrosion in aerated hydrochloric acid solution by amino-acid compounds

The effect of two amino-acid compounds, dl-alanine and dl-cysteine, on copper corrosion in an aerated 0.5 mol l⁻¹ HCl solution was studied by weight-loss measurements, potentiodynamic polarisation curves, and electrochemical impedance spectroscopy. A conventional benzotriazole (BTA) inhibitor was also tested for comparison. dl-cysteine was shown to be the most effective inhibitor among those tested inhibitors. Potentiodynamic polarisation results revealed that both the dl-alanine and dl-cysteine acted as an anodic inhibitor; however, dl-cysteine, in particular, was more effective, as it strongly suppressed anodic current densities. The improved inhibition efficiency of dl-cysteine in the 0.5 mol l⁻¹ HCl solution was due to its adsorption on the copper surface via the mercapto group in its molecular structure.     

添加剂对酒石酸盐镀铜的影响

研究了一种无氰碱性镀铜工艺.运用循环伏安法和扫描电子显微镜研究了配方中三乙醇胺(4 mL/L)、硝酸铵(1.5g/L)、亚胺类物质hg01(1 mL/L)和吡啶类物质hg02(0.5 g/L)等4种添加剂的作用.结果表明:三乙醇胺能改善低电流密度处镀层质量;硝酸铵与铜离子结合能在较宽电流密度范围内参与阴极还原反应,有效抑制析氢反应;hg01优先吸附在阴极高电流密度处与铜离子产生强配合作用,能提高镀液的分散能力,有利于产生细微晶粒;hg02能在电极表面吸附,增大了铜沉积过程的极化作用,有效改善了中电流密度区镀层的整平性和脆性.X射线衍射研究表明,该铜镀层表现出(111)晶面的择优取向.该工艺具有良好的镀液及镀层性能,镀层厚度中等,适合用于铁基片上打底.     

Study on the corrosion behavior of reinforcing steel in cement mortar by electrochemical noise measurements

The corrosion behavior of reinforcing steel in cement mortar has been studied by electrochemical noise (EN) compared with the electrochemical impedance spectroscopy (EIS). The wavelet transform, as well as the statistical methods including the standard deviation of current noise (σ_I) and noise resistance (R_n), has been employed to analyze the EN data of reinforcing steel in mortar. It is revealed that there exist three different corrosion stages of reinforcing steel in cement mortar, including a competition process between breakdown and repassivation of passive film, a pitting development and an active corrosion during the 20 cyclic immersion and drying tests. The energy distribution plot (EDP) is able to provide useful information about the dominant process for the different corrosion stages.     

The Influence of electrochemical surface modifications on naval steel corrosion

The corrosion behaviour of naval steels is characterized by cyclic voltammetric profiles, open-circuit potential decays and polarization curves in 0.5 M sodium nitrate and in 0.6 M sodium chloride at 20 °C. Naval steel surfaces can be modified by the application of periodic symmetric and/or asymmetric potential routines in strong alkaline solutions. These perturbations produce the formation of protective or non-protective surface oxides, which can be characterized by scanning electron microscopy and cyclic voltammetry. Corrosion parameters of the new surface oxides are evaluated by polarization curves after long-time exposures in electrolytes containing sodium chloride and sodium nitrate.     

Synthesis and electrochemical properties of redox active polyurethanes with ferrocene units in polyether soft segments

Electrochemical active segmented polyurethane with ferrocene units in polyether soft segments (PU‐S‐Fc) has been originally synthesized and identified by ¹H‐NMR spectra. Electrochemical behaviors of PU‐S‐Fc blending with lithium perchlorates were investigated by cyclic voltammetry. In N,N′‐dimethyl formide solution, PU‐S‐Fc exhibited normal cathodic and anodic peaks of the ferrocene/ferricinium (Fc/Fc⁺) couple. Compared with that of ferrocene molecules blended in ordinary polyurethane (PU‐B‐Fc), redox peaks of ferrocene units in PU‐S‐Fc were found to be broader, which may be ascribed to the weak adsorption of the polyurethane on the electrode surface. The influence of lithium perchlorate concentration on peak potentials indicated that supporting electrolytes played an important role in electrochemical redox of PU‐S‐Fc. In the solid state, PU‐S‐Fc/Li⁺ showed discernible redox peaks at temperatures higher than 60°C, and an exponential increase curve of electrochemical response with an increase of temperature was found. Temperature variations of the solid‐state ionic conductivity for PU‐S‐Fc/Li⁺ can be interpreted by the Arrhenius equation. The similarity between the temperature dependence of ionic conductivity and electrochemical response revealed that transport mechanism of ionic and redox species in the polyurethane matrix was controlled by the mobility of polyether chains. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 2674–2680, 1999     

Study of the copper anode passivation by electrochemical noise analysis using spectral and wavelet transforms

The passivation of copper anode in sulphuric acid industrial electrolyte at 65 °C was investigated by electrochemical noise (EN) technique using three imposed anodic currents 153, 180 and 210 mA cm⁻² (galvanostatic or chronopotentiometric technique). The wavelet transforms and power spectral density (PSD) analyses have been employed to analyse the EN data. It has been found that during active dissolution the electrode surface is dominated by long time scale process and the change of the position of the maximum relative energy from D7 to D8 could be an indication of future passivation. This is associated in fast Fourier transform analyses by the disappearance of the low frequency plateau (white noise). During anodic dissolution the electrode surface was mainly undertaking general corrosion and the relative energy distribution was concentrated on large timescale crystals (D7-D8) with range of scale between 25.6 and 12.6 s. During passivation the electrode surface was dominated by short time scale process (D3), and during trans-passivation by medium (D4) followed by short time scale process (D2) with range of scale between 0.8 and 0.4 s, 1.6 and 0.8 s and 0.4 and 0.2 s, respectively. Crystals D2 and D3 could be related to metastable pitting and crystal D4 to localized corrosion.