Multianalytical in-situ investigations of the early stages of corrosion of copper, zinc and binary copper/zinc alloys

A new experimental infrared reflection absorption spectroscopy (IRRAS) set-up for in-situ investigation of corrosion phenomena occurring in the metal–atmosphere interface was developed. It was applied in combination with in-situ tapping-mode atomic force microscopy (TM-AFM) and phase detection imaging (PDI) to study the early stages of corrosion of pure copper and pure zinc as well as to determine the influence of increasing zinc contents in brass. Additionally, ex-situ secondary ion mass spectrometry (SIMS) investigations were carried out on the samples after exposure.The investigations were accomplished in synthetic air with 80% relative humidity (RH) and synthetic air with 80% RH and 250 ppb SO₂. The experiments showed that an increase of the zinc content in the brass alloy yields to an increase of the dimension of the corrosion features formed on the metal surface during weathering. Large features on top of smaller features were observed with TM-AFM on the surfaces exposed to SO₂-containing humidified air, which could be identified by IRRAS as metal sulphur compounds. Furthermore, an increased amount of physisorbed water on the metal surfaces was determined with IRRAS in dependence of the increasing zinc content in the brass samples.     

Electro magnetic interference shielding characteristic of silver coated copper powder

The present investigation deals with the synthesis of silver coated copper powder for potential application as filler material in conductive polymers for electro magnetic interference (EMI) shielding. Copper powders were obtained by the reaction of cuprous oxide and, hydrazine in a mixed solvent (H₂O:ethanol) at various reaction conditions. The cuprous oxide powder was produced by the reaction of CuSO₄, NaOH and D-glucose. The synthesized copper powder was silver coated by its reaction with (NH₄)₂SO₄, C₄H₄O₆KNa and AgNO₃. The prepared powders were characterized by XRD, SEM, TGA and XPS. The coaxial transmission line method was used to measure the EMI shielding effectiveness of the powders. The silver coated copper powders exhibited an improved oxidation resistance and higher EMI shielding effectiveness as compared to the uncoated copper powders.     

Corrosion products of tin in humid air containing sulfur dioxide and nitrogen dioxide at room temperature

To obtain a fundamental understanding of the corrosion behavior of tin in corrosive gas environments, in situ infrared reflection absorption spectroscopy measurements were carried out on tin in humid air containing SO₂ and NO₂ at room temperature. A series of time-resolved in situ IR spectra in air of 90% relative humidity (RH) containing 10-22 ppm SO₂ suggested that the oxide films on tin specimens had a protective effect and that no significant corrosion occurred. The corrosion products in air of 80-90% RH containing 10-22 ppm NO₂ were SnO₂, SnO, nitrate and hyponitrite. The synergistic effect of SO₂ and NO₂ on corrosion of tin was not observed in humid air (RH of 90%) containing 0.84 ppm SO₂ and 1.8 ppm NO₂.     

Corrosion evaluation and surface characterization of the corrosion product layer formed on Cu-6Sn bronze in aqueous Na2SO4 solution

The binary bronze alloy Cu-6Sn corrosion, and formation and properties of corrosion product layer (patinas) during 12 days of exposure to 15 mM Na₂SO₄ aqueous solution were investigated by a range of diverse experimental techniques. For the reasons of comparison, some techniques were applied, in parallel, to copper. Gravimetric measurements revealed lower corrosion rates of bronze than those of copper, probably caused by the presence of tin compounds in the corrosion product layer. Cyclic voltammetry results showed that the oxidation processes on bronze are affected by the formation of tin oxide species. Electrochemical impedance spectroscopy showed that, as opposed to copper which produced only two time constants, bronze corrosion resistance was dominated by the additional high-frequency time constant representing redox processes occurring at the corrosion product surface. SEM, ATR FTIR and PIXE results suggest that Cu-6Sn bronze corrosion in 15 mM Na₂SO₄ solution was impeded by the formation of two-layered structure of corrosion products that formed due to selective dissolution of copper at the layer/solution interface, leaving the outer layer enriched in highly corrosion resistant Sn oxi/hydrohide species.     

Surface composition of electropolished CuNi alloys—An application of AES and XPS

The surface composition of CuNi alloys that were electropolished in a mixed acid (H₂SO₄ : H₃PO₄ : H₂O = 170 : 546 : 308 vol. ratio) were examined by means of Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS). Analysis by AES revealed that surface content ratio of nickel to copper on the electropolished surfaces was almost the same as the bulk one; the surface electropolished at the transpassive region was slightly enriched with copper. Chemical species of the surface were revealed by XPS to be Ni₂O₃ and copper oxide (Cu₂O and/or CuO).     

The oxidation of cupronickel alloys—I. XPS study of inter-diffusion

The outer surface of thick oxides formed on the high copper-cupronickel alloys is invariably copper oxide, yet at room temperature the oxide film is entirely nickel oxide. The ESCA (or XPS) technique has been used to determine the temperature at which overgrowth of the initial nickel oxide by cuprous oxide takes place on a alloy. By means of interrupted oxidation runs on a heated probe in the ESCA spectrometer, the physical and chemical displacement of Cu₂O by NiO has been followed. It is concluded that the diffusion step in this displacement reatcion is probably rate controlling during oxidation of the alloy at temperatures up to 650°C.The XPS spectra have been interpreted quantitatively and excellent agreement is found between the calculated stoichiometry and the chemical shifts of the Auger spectra.     

Application of automated electrical resistance sensors for measurement of corrosion rate of copper,bronze and iron in model indoor atmospheres containing short-chain volatile carboxylic acids

The corrosion rate of copper and bronze Cu-8 wt.%Sn increased rapidly when the concentration of formic or acetic acid in air reached about 300 ppb at 80% relative humidity (RH) and a temperature of 20 °C. It decreased slowly during the several days after pollutant removal due to the slow rate of pollutant desorption from the metal surfaces. Corrosion of these metals was barely affected by the acids at RH up to 60%. For iron, the critical concentration of formic acid in air which led to surface activation at 80% RH was between 1000 and 1590 ppb.     

Mechanism of dissolution of a Cu-13Sn alloy in low aggressive conditions

Corrosion of a synthetic Cu-13Sn alloy with a dendritic structure was investigated in a low aggressive medium (0.01 M Na₂SO₄ aqueous solution). The corrosion rate was accelerated through anodic polarization of the alloy in a potential range close to the open-circuit potential. The composition of the corrosion layer was followed as a function of the polarization time, using scanning electron microscopy and energy dispersive spectrometry methods. The results clearly showed that bronze corrosion in these experimental conditions proceeds by decuprification. Selective copper dissolution leads to corrosion layers enriched in tin compounds. It was concluded that bronze is partially passivated through the presence of a tin oxide layer, which slows down copper dissolution rate, compared to pure copper.     

Numerical simulation of corrosion process with two-step charge transfer mechanism in the Cu/CuSO4 + H2SO4 system

The corrosion process in the Cu/CuSO₄ + H₂SO₄ system is considered as the sum of two coupled single-electron electrochemical reactions that occur simultaneously and independently on the surface of the copper electrode. Our numerical model incorporates diffusion and migration of solution species including cuprous ions, as well as the chemical equilibria for copper sulphate and sulphuric acid dissociation. Numerical simulations are compared with the trends discovered during experimental investigation of copper corrosion in similar systems.     

Influence of surface treatment on the photoelectrochemical behaviour of Y-Ba-Cu-O thin films

Y-Ba-Cu-O films with different surface treatments have been studied by photoelectrochemical and XPS measurements. The influence of etching by bromine in ethanol of these films has been followed by means of the electrochemical oxidation of ferrocene in an aprotic electrolyte. From the dependence of dark and photocurrent on etching time it is concluded that Y-Ba-Cu-O thin films on LaAlO₃ are covered by a 1, 1nm thick nonstoichiometric surface layer. The cathodic polarization of Y-Ba-Cu-O at -0,9 V vs. Ag/AgCl in acetonitrile/0,1 M lithium perchlorate leads to the formation of a lithium-containing, oxygen-enriched surface layer. The photoelectrochemical response of the reduced films is similar to that of cuprous oxide and passive layers on copper.     

A correlation between electrochemical behaviour, composition and semiconducting properties of naturally grown oxide films on copper

Copper(I) oxide films formed under open-circuit potential in neutral aqueous solutions have been characterized, using coulometry, photocurrent spectroscopy and X-ray photo-electron spectroscopy (XPS). The reduction potential of the oxide layer was found to depend on the presence in the electrolyte of chloride ions, Cu(II) or Cu(I) ionic species or of a corrosion inhibitor. XPS analyses were performed on these oxide layers, and showed in some cases an evolution of the oxidation state of copper from + 2 to + 1 state throughout the film. Different conducting properties of the cuprous oxides could be demonstrated through photo-electrochemical measurements, and the formation of a duplex Cu₂O layer with two semiconducting components of different stoichiometries was discussed.     

Inhibition of copper sulphidation by boron implantation

Pure polycrystalline copper and copper implanted with boron ions at a dose of 3.0 × 10¹⁷ ions cm^?2 at 25–150 keV have been exposed to hydrogen sulphide in moist air. The rate of growth of a sulphide film on the boron-implanted copper is lower than on pure copper by at least a factor of four after 18 h under the exposure conditions ([H₂S] = 3.0 ppm, T = 22.5°C, RH = 85%). The resistance of the implanted copper to sulphide corrosion is ascribed to inhibition of copper diffusion through the surface oxide layer.     

Surface pretreatment of austenitic stainless steel and copper by chemical, plasma electrolytic or CO2 cryoblasting techniques for sol-gel coating

The surface pretreatments of the austenitic stainless steel and copper surfaces for the sol-gel coating were carried out by chemical, plasma electrolytic or CO₂ cryoblasting techniques. With the austenitic stainless steel the smoothest surfaces were obtained with plasma electrolytic cleaning, after which the measured contact angles of water were clearly decreased revealing improved hydrophilicity. As well with the copper samples the smooth surface and improved hydrophilicity was obtained with the plasma electrolytic cleaning, but oxide layer formed to the copper surface immediately after the treatment. CO₂ cryoblasting provided rough surface with wetting properties close to the original surface both for austenitic stainless steel and copper surfaces. CO₂ cryoblasting provided best appearance for the copper surface because no oxidation happened with that treatment. XPS and SIMS studies showed that with the plasma electrolytic treatment the surface layer of the austenitic stainless steel enriched of chromium and the oxide layer formed on the surface was less than 10 nm thick. With the chemical cleaning and CO₂ cryoblasting, the chromium enrichment to the stainless steel surface was less. However XPS and SIMS studies showed that chemical treatment provided thinner oxide layer to copper surface than plasma electrolytic treatment.     

Quantitative determination of corrosion products and adsorbed water on copper in humid air containing SO2 by IR-RAS measurements

The time dependency of the amounts of corrosion products and co-existing adsorbed water on copper in humid air containing SO₂ was estimated from a series of in situ time-resolved IR-RAS spectra on the basis of the relations between the band intensities and the mass changes of the corrosion products, which were determined by simultaneous measurement of IR-RAS and QCM. The amounts of both corrosion products increased slowly at the initial stage and later increased rapidly. Although the relative humidity was kept constant, the amount of adsorbed water increased nearly the same behavior as that of corrosion products in the stage of relatively small amounts of corrosion products and later increased rapidly when the amounts of corrosion products increased. In humid air without SO₂, sulfite gradually decomposed and some of it changed into sulfate.     

Interfacial reactions of chalcopyrite in ammonia–ammonium chloride solution

The interfacial reactions of chalcopyrite in ammonia–ammonium chloride solution were investigated. The chalcopyrite surface was examined by scanning electron microscopy and X-ray photoelectron spectroscopy (XPS) techniques. It was found that interfacial passivation layers of chalcopyrite were formed from an iron oxide layer on top of a copper sulfide layer overlaying the bulk chalcopyrite, whereas CuFe_1–xS₂ or copper sulfides were formed via the preferential dissolution of Fe. The copper sulfide layer formed a new passivation layer, whereas the iron oxide layer peeled off spontaneously and partially from the chalcopyrite surface. The state of the copper sulfide layer was discussed after being deduced from the appearance of S^2–, S^2?₂, S^2?_n, S⁰ and SO^2?₄. A mechanism for the oxidation and passivation of chalcopyrite under different pH values and redox potentials was proposed. Accordingly, a model of the interfacial reaction on the chalcopyrite surface was constructed using a three-step reaction pathway, which demonstrated the formation and transformation of passivation layers under the present experimental conditions.     

The Mechanism of Dezincification and the Effect of Arsenic. I.

Abstract

Copper formed by dezincification of brass shows, in microsections, a dense layer at the surface roughly proportional in thickness to the depth of dezincificatton. The underlying copper frequently shows growth rings of alternate, more or less dense copper layers, sometimes incorporating bands of cuprous oxide, and a narrow band of dense copper is usually observed adjacent to the advancing corrosion front. These features are explained, and have been reproduced in laboratory experiments, on the basis of a redeposition theory of dezincification.

The first step in either dezincification or pitting corrosion of brass is dissolution of both copper and zinc, the copper forming cuprous chloride. In pitting corrosion the cuprous chloride is precipitated and subsequently hydrolysed or oxidised to secondary corrosion products. In dezincification, it is reduced to copper close to the point at which it first forms.

Beta- and non-arsenical alpha-brass both reduce cuprous chloride to copper (the beta much more readily), but arsenical alpha does not. These differences between the three types of brass are reflected in their relative susceptibility to dezincification. The reasons for these differences will be reported in Part II of the paper.     

Inhibition action of tween‐80 on the corrosion of cold rolled steel in sulfuric acid

The inhibition action of a nonionic surfactant of tween‐80 on the corrosion of cold rolled steel (CRS) in sulfuric acid (H₂SO₄) has been investigated by weight loss and potentiodynamic polarization methods. Atomic force microscope (AFM) provided the CRS surface conditions. The results show that tween‐80 is a good inhibitor in 1.0 M H₂SO₄, and its adsorption obeys Langmuir adsorption isotherm. Effects of temperature (20–50 °C) and acid concentration (0.5–7.0 M) on the inhibition action were investigated. Polarization curves show that tween‐80 is a mixed‐type inhibitor in sulfuric acid, but prominently inhibits the cathodic reaction. The results obtained from weight loss and potentiodynamic polarization are consistent, and the inhibition action could also be evidenced by AFM images.     

青铜器加速腐蚀的多孔氧电极研究

用具有适当空隙的电镀Cu-Sn-Pb三元合金作为青铜器模拟试片.应用腐蚀膏试验和微电极测试,研究了氯化亚铜(CuCl)、碱式氯化铜［Cu2Cl(OH)3］和碱式碳酸铜［Cu2(OH)2CO3］等腐蚀产物对氧的去极化反应的影响.以上述铜盐为活性物质制备出多孔氧电极,与青铜试片在3％NaCl溶液中组成腐蚀原电池,进行了阴极极化曲线测试,并进行以CuCl为活性物质的氧电极的恒电流放电和恒电阻放电测试.结果表明CuCl使试片的腐蚀速度高出其它二价铜盐两个数量级,对氧的去极化反应催化活性最高,氧电极的放电性能稳定并且模拟了被称为“粉状锈”主要成分的Cu2Cl(OH)3的生成过程 .提出了加速青铜器小孔腐蚀的多孔氧电极机理.     

The Atmospheric corrosion of statue bronzes exposed to SO2 and NO2

We report on the atmospheric corrosion of different cast statue bronzes in humid air containing ppb levels of SO₂ and SO₂+NO₂. In addition, copper, tin, zinc, and lead samples were studied in these environments. The samples were exposed to synthetic atmospheres with careful control of pollutant concentrations, relative humidity and flow conditions. Deposition of SO₂ was studied using on-line gas analysis. The weight gain was registered after four weeks exposure, and corrosion products were analysed by Electron Probe Micro Analyser (EPMA), X-ray diffraction (XRD), and Fourier Transform Infrared spectroscopy (FTIR). The synergistic effect of SO₂ and NO₂ was remarkable on all bronze materials examined. The weight gain was correlated to alloy composition. Thus, high zinc and low lead content resulted in the greatest weight gain, while high tin content favoured a low weight increase. Lead exhibited a rapid deposition of SO₂ followed by zinc and copper, while tin was unreactive towards SO₂. There was no measurable indication that microstructure influenced corrosion. The corrosion product morphology found in SO₂+NO₂ environment indicated a localised type of attack. The anodic sites were covered by a tin-rich corrosion product close to the metal. Oxidation of soluble divalent tin by O₂ at the anodic sites to form insoluble SnO₂ – xH₂O, is suggested to explain the corrosion protection afforded by alloying with tin. Tin was enriched in the corrosion products while no lead was found. The zinc/copper relation was higher in the corrosion products than in the alloy composition.     

The corrosion of copper by atmospheric sulphurous gases

The sulfurization of copper by atmospheric gases is widely recognized, but the importance of the potential causative agents of sulfurization and the mechanisms involved have remained unresolved. In this work, polycrystalline copper has been exposed to the atmospheric gases hydrogen sulfide (H₂S), carbonyl sulfide (OCS), carbon disulfide (CS₂), and sulfur dioxide (SO₂) in humidified air under carefully controlled laboratory conditions. At room temperature, the rates of sulfurization by H₂S and OCS are comparable, and are some two orders of magnitude greater than those by CS₂ and SO₂. Given the atmospheric concentrations of these gases, it is clear that OCS is the principal cause of atmospheric sulfurization of copper except near sources of the gases where high concentrations may render H₂S (and possibly SO₂) important. At constant absolute humidity, the sulfurization rate of copper by OCS is found to be inversely proportional to temperature over the range 21–80°C, a property attributed to reduced quantities of surface water at high temperatures and the subsequent decrease in the rate of hydrolytic transformation of OCS into a reactive form. In a final series of experiments, the initial sulfurization of copper by 2.2 ± 0.2 ppm H₂S in humidified air at 22°C has been studied in detail. The first stages of sulfurization involve rapid attack by H₂S at surface defect sites. As these corrosive mounds spread and merge, diffusion of copper to the surface is impeded and the fraction of H₂S molecules striking the surface that become incorporated into the corrosion film drops sharply from ～ 5 × 10^?5 (at t = 5 s) to ～ 8 × 10^?7 (at t = 72 h).