The corrosion of copper pipes in high chloride-low carbonate mains water

Thermodynamic and electrochemical methods were used to derive fundamental information about the likely corrosion processes of copper pipes in high chloride-low carbonate mains water under conditions of varying temperature and solution composition. The thermodynamic aspects consider the possible reactions and the stability of the resulting products at 25–100°C by means of potential-pH and stability diagrams, based on the calculations of the free energy change, ΔG_T⁰, of the reaction considered. These diagrams were constructed at ionic concentrations of chloride and bicarbonate ions corresponding to those found in the mains water in Perth, Western Australia. The reactions and products suggested by the potential-pH diagrams were verified experimentally, where possible, by cyclic voltammetry and potentiodynamic polarization. Further confirmation was made by analyzing some of the products formed, chemically or electrochemically, by an X-ray diffraction technique.     

The predictability of stress corrosion cracking susceptibility of steels in acetate solutions from potentiodynamic polarization curves

Stress corrosion cracking susceptibilities of mild and low alloy steels in acetate solutions, assessed using slow strain-rate testing techniques, correlate well with those predicted on the basis of data from fast and slow sweep rate potentiodynamic polarization curves. Accurate prediction of cracking susceptibility necessitates allowances being made for changes of solution pH which occur during stress corrosion and polarization tests. A predictive technique which allows for these pH changes has been developed, and when implemented yields polarization data that indicates the influence of potential, steel composition and solution temperature on cracking susceptibility. The stress corrosion cracking of steels in acetate solutions is intergranular and occurs only when the electrochemical conditions correspond to those of a predicted potential-pH domain that is associated with the Fe²⁺/Fe₃O₄ transition.     

Electrochemical studies on the effect of (2E)‐3‐amino‐2‐phenylazo‐but‐2‐enenitrile and its derivative on the behaviour of copper in nitric acid

The objective of this work is to provide additional insight on the influence of (2E)‐3‐amino‐2‐phenylazo‐but‐2‐enenitrile and its derivative as corrosion inhibitors for copper in 0.5 M HNO₃. Electrochemical techniques (potentiodynamic polarization, polarization resistance and impedance spectroscopy) as well as weight loss measurements have been employed to study the corrosion inhibition. The investigated compounds have shown inhibition efficiency in 0.5 M HNO₃. Inhibition efficiency of these compounds has been found to vary with the concentrations of the compounds. The adsorption of these compounds on the copper surface from the acid solution has been found to obey Langmuir adsorption isotherm. The results revealed that the compounds are mixed type inhibitors. The effect of temperature on the inhibition efficiency was studied.     

The corrosion inhibition of copper in hydrochloric acid solutions by a tripeptide compound

The efficiency of glutathione as a non-toxic corrosion inhibitor for copper in 0.5 M HCl has been studied by using the weight-loss technique, cyclic voltammetry, electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization. Maximum protection efficiency reaches about 92.7% for glutathione at 10 mM concentration level. Results obtained from potentiodynamic polarization and impedance measurements are in good agreement. The adsorption of glutathione on copper surface follows Langmuir isotherm. The adsorption free energy of glutathione on copper (−32 kJ mol⁻¹) reveals a strong physical adsorption of the inhibition on the metal surface.     

Electrochemical behavior of nickel in HNO<Subscript>3</Subscript> and the effect of chloride ions

The electrochemical behavior of nickel in HNO₃ solutions of varying concentrations was examined using the cyclic voltammetry and potentiodynamic anodic polarization techniques. The anodic branch of the cyclic voltammogram is characterized by one anodic dissolution peak and a passivation region before oxygen evolution. The cathodic branch shows only one cathodic reduction peak corresponding to the reduction of HNO₃. Analysis of the anodic polarization data shows features of both reversible and irreversible reactions pointing to the complexity of the system. CT⁻ ions enhance the active dissolution of nickel in HNO₃ due to the adsorption on the bare metal surface and cause destruction of the passive film and initiation of pitting corrosion.     

On the Characteristic Potentials of Pitting Corrosion of Compact and Powder Steel

The influence of chloride concentration and current density on the characteristic potentials of pitting corrosion found during potentiodynamic E _po ^pd and galvanostatic E _po ^cr polarization and E_rp repassivation of the PC process of 10Х17Н13М2Т and 12Х18Н10Т cast steels and 316L and 316L + 3% Сu 304HLD powder steels with addition of 10 and 15% Cu in a neutral chloride solution was studied. The porosity of the powder steel significantly decreases the pitting resistance. Addition of 3% Сu increases the pitting resistance, but does not allow achieving the pitting resistance level of compact molybdenum steel; neither does addition of 10 and 15% copper do so for 12Х18Н10Т steel.     

Electrochemical Corrosion of HVOF-Sprayed NiCoCrAlY Coatings in CO<Subscript>2</Subscript>-Saturated Brine

The effect of pre-oxidation treatment and surface preparation of optimized NiCoCrAlY coatings deposited by high-velocity oxygen fuel (HVOF) spraying and exposed to a low-temperature corrosive environment is reported herein. Coatings with two surface finish conditions (as-sprayed and ground) were heat treated under two different oxygen partial pressures (air and argon). The electrochemical corrosion behavior was evaluated in CO₂-saturated brine via potentiodynamic polarization, polarization resistance, and electrochemical impedance measurements. The results show that the grinding process and pre-oxidation treatment in argon enhanced growth and formation of α-Al₂O₃ scale. The potentiodynamic polarization results show that both pre-oxidation and surface treatment had a positive influence on the corrosion resistance of the coating. The reduction of the porosity and the formation of a dense, uniform, and adherent oxide scale through pre-oxidation treatment led to an increase of the corrosion resistance due to a decrease in active sites and blocking of diffusion of reactive species into the coating. However, according to the results, complete transformation from metastable alumina phases to α-Al₂O₃ in addition to formation and growth of dense α-Al₂O₃ is required to ensure full protection of the coating and base material over long periods.     

A Black Phosphate Conversion Coating on Steel Surface Using Antimony(III)-Tartrate as an Additive

A novel black phosphate conversion coating was formed on steel surface through a Zn-Mn phosphating bath containing mainly ZnO, H₃PO₄, Mn(H₂PO₄)₂, and Ca(NO₃)₂, where antimony(III)-tartrate was used as the blackening agent of phosphatization. The surface morphology and composition of the coating were characterized by scanning electron microscopy, energy dispersion spectroscopy, and x-ray photoelectron spectroscopy. Corrosion resistance of the coating was studied by potentiodynamic polarization curves and electrochemical impedance spectroscopy. The pH value of the solution had significant influence on the formation and corrosion resistance of the coating. The experimental results indicated that the Sb plays a vital role in the blackening of phosphate conversion coating. The optimal concentration of antimony(III)-tartrate in the phosphating bath used in this experiment was 1.0 g L^?1, as higher values reduced the corrosion resistance of the coating. In addition, by saponification and oil seals, the corrosion duration of the black phosphate coating in a copper sulfate spot test can be as long as 20 min.     

Copper Corrosion Under Non-uniform Magnetic Field in 0.5 M Hydrochloric Acid

The influence of a magnetic field on the electrochemical reactions taking place at the surface of a copper electrode immersed in a 0.5 M HCl solution at room temperature has been studied. The symmetry axis of the magnetic field was lined up in the same direction of the ion flow to minimize the Lorentz forces. Measurements of potentiodynamic polarization curves, electrochemical impedance spectroscopy and electrochemical noise allow concluding that the magnetic field significantly affects the cathodic reactions, with corrosion rates increasing under the presence of oxygen in acid media and decreasing when oxygen is eliminated.     

A comparison between the corrosion behavior of nanostructured copper thin films deposited on oxidized silicon and copper sheet in alkaline media

Copper thin films were deposited on oxidized silicon at a substrate temperature of 70 °C and 150 °C using EB-PVD technique. The morphology and crystal orientation of the deposited film were investigated by scanning electron microscopy (SEM) and X-ray diffraction (XRD), respectively. Corrosion behavior of films was studied through electrochemical impedance spectroscopy (EIS), potentiodynamic polarization, immersion test, and cathodic chronopotentiography. Additionally, the crystalline structure of corroded samples immediately after polarization was examined by XRD. Corrosion current density for copper deposits was higher than copper sheet by polarization tests, while the data obtained by the EIS technique emphasized higher corrosion current density for copper sheet. However there was a conflict between polarization and EIS data, the other results obtained by immersion and cathodic chronopotentiography tests proved that the corrosion resistance of copper deposits was higher than copper sheet in the same alkaline media, which can be attributed to chemical composition and higher thickness of the passive layer formed on copper deposits. On the other hand, breakdown potential (E_bp) for copper sheet was about 0.3 V_SCE, while a distinct E_bp was not found for copper deposits. This was a sign of higher stability of the passive layer formed on copper deposits. The XRD patterns of samples immediately after polarization showed a higher content of Cu(OH)₂ on copper deposits in comparison with copper sheet. The stable morphology formed on the surface of copper after polarization was monoclinic CuO, which is assumed to have a significant effect on copper protection in alkaline media. This morphology was more compact on copper deposits in comparison with copper sheet. This was due to higher ability of deposits to react with hydroxyl ions.     

The polarization behavior of the iron, 304 and 316 stainless steel electrodes in molten sodium carbonate under CO/CO2/H2/H2S atmospheres

The electrode polarization behavior of iron and austenitic stainless steels 304 and 316 was studied in molten sodium carbonate at 1000°C under an atmosphere of 24% CO, 24% CO₂, 49.3% H₂ and 2.7% H₂S at 1 atm. The empirical polarization data were fitted to a previously described analytical model incorporating the effects of electron transfer polarization, concentration polarization and ohmic loss. Three distinct anodic reactions were seen. Comparison of curve parameters with results from a previous study of the nickel electrode together with analyses of anodic scales and expected equilibria in the system indicate that these reactions, in order of increasing anodic overpotential, are the oxidation of iron to the Fe²⁺ state with the formation of FeO, the oxidation of iron and chromium to the 3+ state with the formation of the spinel oxide FeFe_2−xCr_xO₄, and the oxidation of CO₃²⁻ with formation of O₂. The only distinction in the behavior of the iron and stainless steel electrodes is in the composition of the spinel oxide and a Nernstian displacement of the reaction Fe = Fe²⁺ + 2e. In addition to these significant electrode reactions, carburization of iron was seen at cathodic potentials, with oxidation of the carbide at anodic potentials.     

Reactions at the CO,CO2/Ni electrode in molten sodium carbonate

Reactions at the nickel electrode in molten sodium carbonate at 1000°C under CO/CO₂ atmospheres were studied by electrode polarization. The polarization curves were analysed by means of a previously described computer model, which in turn was interpreted in terms of the absolute rate expressions for postulated reactions. In agreement with previous workers' observations for inert electrodes, the dominant anodic reactions were found to be oxidation of CO at low and intermediate anodic overpotentials, and oxidation of CO₃^2? at high anodic overpotentials. The cathodic reaction was found to be reduction of CO₃^2?. The form of the polarization curves was described by activation, concentration, and resistance polarization of these reactions; however, anomalous anodic behaviour was observed which was attributed to corrosion reactions at the electrode and accurately described through the use of additional anodic reactions displaying passivity.     

Effects of copper on the corrosion properties of low-alloy steel in an acid-chloride environment

The influence of Cu addition on the corrosion resistance of low-alloy steel in an acid-chloride solution was investigated by electrochemical methods, such as potentiodynamic polarization tests and an electrochemical impedance spectroscopy (EIS). The XPS analysis of the corroded surfaces indicated the formation of protective Cu₂O and Cu(OH)₂ layers on the surface. The formation of Cu products on the surface reduced the uniform corrosion rate of the steel, but promoted localized corrosion due to the galvanic interaction between the covered areas of copper oxide/hydroxide and the uncovered areas on the surface of steel.     

提高KF-AlF3-Al2O3熔体中Cu-Al基阳极的耐腐蚀性

采用恒电流和动电位极化技术研究经预氧化的和未经预氧化的Cu-Al基阳极(Cu-10Al和Cu-9.8Al-2Mn)在KF-AlF₃-Al₂O₃熔体中的阳极行为。将合金在700℃下进行短时间(8 h)氧化,然后在800℃下施以0.4 A/cm²的电流密度进行1 h恒电流极化。测定扫描速率为0.01 V/s的动电位曲线。对在阳极表面冻结的熔体样品进行XRD分析,并在实验后对阳极进行SEM分析,以研究合金表面形成的氧化皮的物相。所有阳极材料的稳态电位都在2.30~2.50 V(vs Al/AlF₃)范围内。根据动电位极化获得的数据计算阳极的腐蚀速率。结果表明,经预氧化的阳极比未经预氧化的阳极具有更低的腐蚀速率。     

Effects of NH4 +, Na+, and Mg2+ ions on the corrosion behavior of galvanized steel in wet–dry cyclic conditions

The effect of cations on the corrosion of galvanized steel (GS) is scarcely reported. In this study, a wet–dry cyclic test was conducted to study NH₄ ⁺, Na⁺, and Mg²⁺ cation effect on the corrosion behavior of GS available in Nepal. Fourteen wet–dry cycles (18 h wet and 6 h dry) were performed by exposing samples at 298 K with a relative humidity of 90% in a wet cycle and 50% in a dry cycle for 14 days. The cations strongly affect the corrosion rate of the GS sample estimated by weight loss and potentiodynamic polarization. The potentiodynamic polarization curves showed the inhibition of cathodic and anodic reactions by Mg²⁺ ion, while the NH₄ ⁺ ion only changed the cathodic reaction. Mg²⁺ ion was found to shift the corrosion potential to noble values compared with NH₄ ⁺ and Na⁺ ions. A compact and thin corrosion products layer was developed in Mg²⁺ salt solution in contrast to a thick and porous corrosion products layer in NH₄ ⁺ and Na⁺ salt solutions. Red rust due to corrosion of underlying steel appeared in the presence of NH₄ ⁺ and Na⁺ salt solutions. Finally, the weight loss data revealed that the corrosivity of cations for GS decreased in the order Na⁺ > NH₄ ⁺ > Mg²⁺.     

Fast etching of copper in thionyl chloride/acetonitrile solutions

We report fast etching of copper (Cu) in thionyl chloride (SOCl₂)/acetonitrile (CH₃CN) solutions. The etching rate can be tuned over a wide range by varying the concentration of the etchant, and the stirring rate of the liquid. The etching rate reaches 36 mg min⁻¹ cm⁻² in 1 mol L⁻¹ SOCl₂/CH₃CN under stirring at room temperature, which is much faster than any currently used etchant for Cu. With sonication, the etching rate reaches 320 mg min⁻¹ cm⁻². The chemical reactions involved are studied by X-ray photoelectron spectroscopy and Raman spectroscopy. The fast etching may find important applications in microelectronics.     

Electrochemical characterization of Ni47.7Ti37.8Nb14.5 shape memory alloy in artificial saliva

Electrochemical corrosion behaviour of the studied Ni_47.7Ti_37.8Nb_14.5 (NiTiNb) shape memory alloy was investigated for dental applications. An equiatomic NiTi alloy was used in some tests as reference material. Electrochemical techniques such as anodic potentiodynamic polarization, open circuit potential and electrochemical impedance spectroscopy (EIS) were employed. Experiments were carried out using artificial saliva. Very low passive current densities were obtained from the anodic polarization curve, indicating a typical passive behaviour for NiTiNb alloy. Over the surface of the NiTiNb alloy uniform corrosion appears, while in case of the NiTi alloy surface pitting corrosion is developed. The role that Nb plays as an alloying element is by increasing the resistance of NiTi alloy to localized corrosion. The EIS results exhibited high impedance values (order of 10⁶ Ω cm²) obtained from medium to low frequencies which are indicative of the formation of a highly stable passive film on NiTiNb alloy in the artificial saliva.     

Electrochemical behavior of anodized Mg alloy AZ91D in chloride containing aqueous solution

Electrochemical behavior in aerated 3.5 wt.% NaCl solution of Mg alloy AZ91D anodized or not has been investigated by using electrochemical impedance spectroscopy, potentiodynamic polarization and E_corr-t curve. Their microstructures before and after corrosion have been examined under scanning electron microscope. Testing results from E_corr-t and polarization curves indicate that the corrosion behavior of Mg alloy makes significant, characteristic changes due to anodization. Impedance spectra obtained show a regular evolution with exposure time revealing the development of corrosion damage. SEM micrographs confirm that there are pores, defects and microcracks in anodic film which determine the existence of film-vulnerable regions. Electrochemical data are combined with micrographs to explain protection mechanism of anodic film and corrosion mechanism of Mg alloy.     

Direct electrosynthesis of polyaniline–montmorrilonite nanocomposite coatings on aluminum alloy 3004 and their corrosion protection performance

Homogeneous and adherent polyaniline–montmorrilonite (MMT) nanocomposite coatings were electrosynthesized on aluminum (Al) alloy 3004 (AA 3004) by using the galvanostatic polarization method. The synthesized coatings were characterized by UV–Vis absorption spectrometry, Fourier transform infrared spectroscopy, X-ray diffraction patterns and scanning electron microscopy. The corrosion protection effect of the coatings was demonstrated by performing a series of electrochemical experiments of potentiodynamic and impedance measurements on Al in 3.5 wt% aqueous NaCl electrolytes. The corrosion current (i_corr) values decreased from 6.55 μA cm⁻² for uncoated Al to 0.102 μA cm⁻² for nanocomposite-coated Al under optimal conditions.