Structure of corrosion film formed on copper exposed to controlled corrosive environment

This paper describes a transmission electron microscopy (TEM) investigation of copper coupons exposed to a corrosive mixed flowing gas environment (MFG). A focused ion beam (FIB) lift-out technique was used to extract electron transparent specimens for TEM investigation. A duplex corrosion film comprising cuprite (Cu₂O) and chalcocite (Cu₂S) developed on the copper substrate. The oxide demonstrated a dense morphology with evidence of chlorine in the oxide layer showing that chlorine plays an important role in the corrosion of copper transforming the protective Cu₂O layer to a non-protective layer. The outer layer of the Cu₂S demonstrated a porous morphology allowing easy penetration of water and gases.     

纯铝1060在中国南沙群岛严酷海洋大气中的腐蚀以及点蚀行为

通过质量损失测量、扫描电子显微术、能谱分析、X射线光电子能谱和电化学阻抗谱等技术研究纯铝1060在南沙群岛海洋大气环境中暴露34个月后的腐蚀行为以及点蚀行为.结果表明,在纯铝表面发生严重的点蚀,并且暴露13个月后的平均腐蚀速率达到1.28 g/(m2·a).X射线光电子能谱的测试结果表明主要的腐蚀产物为Al2O3、Al...     

Surface characterization and corrosion behavior of 70/30 Cu-Ni alloy in pristine and sulfide-containing simulated seawater

The corrosion behavior of the 70/30 Cu-Ni alloy in stagnant, aerated pristine and sulfide-containing simulated seawater as a function of exposure time was investigated with polarization curve measurement and electrochemical impedance spectroscopy (EIS). It was demonstrated that the compact protective oxide film formed on the 70/30 Cu-Ni alloy resulted in the decrease of corrosion rate in aerated pristine seawater; while the corrosion rate of 70/30 Cu-Ni alloy in aerated sulfide-containing seawater increased dramatically due to the catalysis of the sulfide ions or sulfide scale for both the cathodic and anodic reactions. The impedance spectra and the corresponding equivalent circuits confirmed that a duplex layer of a surface film was formed on the 70/30 Cu-Ni alloy in aerated pristine seawater after a period of time and that the inner layer was responsible for the good resistance of the alloy; while only a porous and non-protective corrosion product layer formed on the 70/30 Cu-Ni alloy in aerated sulfide-containing seawater, which made small values of charge transfer resistance (R_ct) to last for a abnormally long time by interfering with the growth of the protective oxide film. The composition of the surface film on the alloy in pristine and sulfide-containing seawater for different exposure times were investigated thoroughly by XPS. It was found that the duplex corrosion product layer formed on the alloy in pristine seawater was composed of an inner Cu₂O and an outer CuO layer. The porous and non-protective corrosion product layer formed on the alloy in aerated sulfide-containing seawater was a mixture of CuCl, Cu₂S, NiS, Cu₂O and NiO with trace amounts of CuO and Ni(OH)₂ and that the most significant component was Cu₂S. In addition, SEM was used to analyze the topography of the 70/30 Cu-Ni alloy in both solutions after different exposure times.     

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.     

Differences between corrosion products formed on copper exposed in Tokyo in summer and winter

We analyzed the copper corrosion products that formed during a month in summer and a month in winter at three sites in Tokyo using several analytical techniques. The X-ray diffraction patterns revealed that cuprite Cu₂O and posnjakite Cu₄SO₄(OH)₆·H₂O formed on copper exposed in summer. By contrast, only cuprite was found in winter exposed copper. The X-ray fluorescence results indicated that the amounts of sulfur and chlorine on the copper plates exposed in summer were much greater than those in winter. This could be explained by the change in particulate sulfate and sea salt concentrations. Depth profiling analysis by Auger electron spectroscopy revealed that the oxide layer formed in summer was thicker than that in winter. This difference in oxide layer thickness could have been due to the differences in temperature, relative humidity, and the amount of sulfur and chlorine on the copper plate.     

The Effect of Impurities on the Formation of the Inner Porous Layer in the Cu2O Scale During Copper Oxidation

The effect of impurities on the formation of the inner porous layer in the Cu₂O scale during copper oxidation was examined using 99.99 (4N), 99.9999% (6N) and floating-zone-refined (FZR, >99.9999) copper specimens at 800° C. Oxidation for 240 min shows that an inner porous layer was formed in the Cu₂O scale near the Cu₂O/Cu interface for 4N copper, but not for 6N and FZR copper. The results support that the inner porous layer in the oxide scale is related to impurities from the metal base.     

Effect of temperature on copper corrosion in high-level nuclear waste environment

The effect of temperature on the corrosion behavior of copper in simulated high-level nuclear waste environment was systematically studied. Electrochemical methods, including electrochemical impendence spectra, Mott–Schottky technology, cyclic polarization, and potentiostatic polarization, were employed to characterize the corrosion behavior of copper at different temperatures. Stereoscopic microscopy and scanning electron microscopy were used to examine the surface morphology, and X-ray photoelectron spectroscopy analysis was used to identify the composition of the passive film. The experimental results show that corrosion resistance of the passive film does not blindly decrease with the increase of temperature but increases at 60 °C owing to a compact outer layer; there is a potential for pitting corrosion, which decreases as the temperature increases. The main product of copper in an anaerobic aqueous sulfide solution is Cu₂S but the content of CuS increases at higher temperatures. The whole passivation range shows p-type semiconductor characteristics and the magnitude of the acceptor density is 10²³ cm^?3, which increases with increasing temperature.     

The Corrosion of Cu–Al Binary Alloys in H2/H2S/H2O Atmospheres at 400–900°C

The corrosion behavior of pure Cu and of three Cu–Al alloys containing 1, 5, and 10 wt.% Al was studied at 400–900°C in a H₂/H₂S/H₂O gas mixture. Both Cu–1Al and Cu–5Al alloys had the single-phase structure of α-Cu, while Cu–10Al was the intermetallic compound Cu₃Al. In general, the corrosion behavior of all the alloys followed the parabolic rate law, and the corrosion rate constants generally increased with increasing temperature but decreased with increasing Al content. The scale formed on pure Cu was an exclusive single layer of Cu₂S, while the scales formed on Cu–Al alloys were heterophasic and duplex, consisting of an outer layer of Cu₂S and an inner layer of Cu₂S and CuAlS₂. X-ray diffraction results showed no evidence of oxides and the amount of CuAlS₂ increased with increasing Al content. The formation of Cu₂S and CuAlS₂ on higher Al-content alloys resulted in a subsurface phase transformation from α-Cu (for Cu–5Al) or from Cu₃Al (for Cu–10Al) to Cu₃Al + Cu₉Al₄. The formation of CuAlS₂ in the inner layer of Cu–Al alloys was responsible for the reduction of corrosion rates, as compared to those of pure Cu.     

An investigation on the mechanisms of ant nest corrosion of copper tube in formic acid environment

Copper tubes used in air-conditioners and refrigerators often fail due to ant nest corrosion (ANC) in formic acid environment. In this paper, corrosion behavior and corrosion mechanisms of copper tubes in formic acid (HCOOH) were analyzed by vapor corrosion tests, optical microscopy (OM), scanning electron microscope (SEM), energy-dispersive X-ray spectrometry (EDS). The effects of the surface condition on ANC of copper tube were also investigated. Results showed that ANC of copper tube was a spontaneous process. The surface integrity of copper tube surface oxide layer is not the decisive factor of ANC. ANC originated from the dissolution of the surface oxide layer in HCOOH, which exposed fresh copper matrix. ANC is a special electrochemical corrosion, where the copper matrix acts as an anode and the undissolved surface oxide layer acts as a cathode due to the potential difference. The accumulation of corrosion products consisting of Cu(HCOO)₂ and Cu₂O can produce a wedge effect and generate many microcracks until to penetrate the copper tube wall. These findings would provide a deep understanding of the corrosion behavior of copper and copper alloys.     

Characterization of corrosion products formed on Ni 2.4 wt%–Cu 0.5 wt%–Cr 0.5 wt% weathering steel exposed in marine atmospheres

Weathering steel manufactured with high concentrations of copper (0.5 wt%), chromium (0.5 wt%) and nickel (2.4 wt%) was studied with the aim of furthering knowledge on corrosion product characterization and performance in marine environments. Specimens exposed for two years in a rural atmosphere and two marine environments were characterized by optical microscopy, SEM/EDS, XRD and Raman spectroscopy and corrosion rates measured. The main phases found were ferrihydrite, maghemite and goethite in the inner corrosion layer, and lepidocrocite in the outer layer. Cu and Ni were homogeneously distributed while Cr tended to be concentrated in the inner layer.     

Effect of minor addition of Zr on the oxidation behavior of Ti-Cu metallic glasses

The oxidation behavior of (TiCu)_100-XZr_X (x=3, 5, 7 at%) amorphous alloy during continuous heating up to 1073 K has been investigated. The weight-gain due to oxidation occurs in a two-step mode. The first-step oxidation (630~730 K) is associated with supercooled liquid region. The oxidation layer consists of intermixed TiO₂ + ZrO₂ layer at outer side and amorphous oxide layer at inner side. The oxidation rate at the second-step above 880 K becomes significantly different depending on the Zr content. In x=3 alloy, the oxidation layer consists of TiO₂ layer at outer side, intermixed TiO₂ + ZrO₂ layer, and Ti₃Cu₃O layer at inner side. As the fraction of ZrO₂ increases in x=5 and 7 alloys, the growth of oxide layer is accelerated due to provision of easier diffusion path in the intermixed oxide layer, forming intermixed multi-phase (TiO₂ + ZrO₂ + Ti₃Cu₃O + Cu₅₁Zr₁₄) oxide layer.     

Characterisation of corrosion products formed on copper exposed at indoor and outdoor sites with high H2S concentrations

Abstract

Corrosion products formed on copper exposed indoors and outdoors at sites with high hydrogen sulphide (H₂S) concentrations were characterised using several analytical techniques. The crystalline corrosion products that formed on the copper exposed indoors were chalcocite (Cu₂S) and cuprite (Cu₂O), while those that formed on the copper exposed outdoors were chalcocite, cuprite and basic copper sulphates. Surface analysis by X-ray photoelectron spectroscopy revealed differences between the copper exposed indoors and outdoors that are explained by the composition, localisation and oxidation of the corrosion products. The surface morphologies of the corrosion products also differed. Elemental depth profiling by glow discharge optical emission spectroscopy revealed that the corrosion products that formed indoors were mainly chalcocite with cuprite only at and near the surface. In contrast, the corrosion products that formed outdoors were a mixture of chalcocite and cuprite. These differences in corrosion products are attributed to the differences in relative humidity during exposure.     

Photoacoustic study on cathodic reduction of anodic oxide films formed on copper in borate solution

An in-situ photoacoustic (PAS) technique, using a piezoelectric detector with high sensitivity was applied to the study on duplex oxide films anodically formed on copper in pH 8.4 borate solution. The PAS signals from the copper electrode were produced by an irradiation of light beam with a wavelength of 514.5 nm. The PAS amplitude during cathodic reduction of the outer oxide layer to Cu₂O changed in the opposite direction, depending on the anodic potential of film formation and oxidation time. Assuming that the change in PAS amplitude is proportional to both optical absorption coefficient and film thickness, it was deduced from comparison of the estimated absorption coefficients for Cu (OH)₂, CuO and CuO_0.67 films that dehydration of the outer layer having an average composition of CuO_x (OH)_2?2x proceeded with increasing anodic potential of film formation and oxidation time during growth of the duplex oxide film. Moreover, it was found that the change in PAS amplitude during cathodic reduction of the total Cu₂O film involving the inner layer to metallic copper was proportional to the electric charge required for cathodic reduction, i.e., the film thickness, irrespective of anodic potential of film formation and oxidation time, which proved the validity of the above assumption.     

STUDY ON HOT CORROSION RESISTANCE OF A NEW DIRECTIONAL SOLIDIFICATION Ni–BASED SUPERALLOY

研究了新型定向凝固镍基高温合金DZ68的抗热腐蚀性能, 并与K438合金进行了比较. 结果表明: 热处理态DZ68合金组织中几乎没有(γ+γ') 共晶, 碳化物尺寸小,其整体组织比较均匀; 在热腐蚀过程中发生比较均匀的腐蚀, 其外腐蚀层的腐蚀产物主要是(Ni, Co)Cr₂O₄, 内腐蚀层的腐蚀产物主要是Al₂O₃. 热处理态K438合金组织中存在较多的 (γ+γ'共晶和数量较多、尺寸较大的长条状碳化物, 组织均 匀性较差; 在热腐蚀过程中发生不均匀腐蚀, 其外腐蚀层的腐蚀产物主要是NiO, 内腐蚀层的腐蚀产物主要是CrS.两种合金中Ti元素的偏析有促进其它元素偏析的倾向, 使合金组织的均匀性恶化,热腐蚀均匀性变差. 在本实验条件下, DZ68合金的抗热腐蚀性能略好于K438合金.     

Differential reflectometry of corrosion products of copper

The new technique of differential reflectometry was applied to study some fundamental corrosion processes for copper. Free corrosion in air for one day yielded differential reflectograms characteristic of mixed oxides of Cu₂O and CuO. With increasing time of exposure to air, the reflectograms evolved into typical CuO patterns. Similarly, free corrosion of copper in distilled water yielded mixed oxides of Cu₂O and CuO. Holding copper potentiostatically near the boundary between these two corrosion products as shown on the Pourbaix diagram always yielded at first a mixed oxide which turned into the stable species after several days of polarization. It was further found that copper held potentiostatically first in the CuO region and then in the Cu₂O region of the Pourbaix diagram does not lose the characteristic patterns of CuO. This suggests that the sudden shift in potential induces growth of Cu₂O under the existing CuO layer without dissolving the CuO.     

The nature of the copper sulfide film grown on copper in aqueous sulfide and chloride solutions

In this paper, the properties of copper sulfide films formed both anodically and naturally in deaerated/anoxic aqueous sulfide and chloride solutions were investigated using a series of electrochemical and surface analytical techniques. A combination of cyclic voltammetric, corrosion potential (E_corr), and cathodic stripping voltammetric experiments showed that the sulfide film growth kinetics and film morphologies were controlled by the supply of SH⁻ from the bulk solution to the copper surface. There was no passive barrier layer observed on the copper surface under either electrochemical or corrosion conditions. The film morphology was dependent on the type and concentration of anions (SH⁻, Cl⁻) present in the solution. Scanning electron microscopy on both surfaces and focused ion beam-cut cross-sections showed the growth of a thin, but porous, base layer of chalcocite (Cu₂S) after short immersion periods (up to 2 hr) and the continuous growth of a much thicker crystalline outer deposit over longer immersion periods (≥36 hr), suggesting a solution species transport-based film formation process and the formation of an ineffective thin “barrier-type” layer on copper.     

Laboratory scale investigation into the corrosion of copper in a sulphur-containing environment

The effect of temperature and gas composition on the corrosion rate and corrosion by-product of copper foil was studied by exposing it to sulphur (S₂), S₂ + hydrochloric acid (HCl) and hydrogen sulphide. The temperature was varied from 80 to 140 °C. Copper foil reacted with S₂ to form CuS, Cu₉S₈ and Cu_1.8S. Corrosion rates ranged from 9.6 μm/h at 110 °C to 0.5 μm/h at 140 °C. The presence of HCl caused pitting and enhanced the corrosion rate above 112 °C. Cu₂S formed when copper was exposed to hydrogen sulphide gas. Sulphide scale that formed was friable and non-adherent.     

Corrosion of copper and silver plates by volcanic gases

Corrosion products that had been formed on copper and silver plates exposed in Miyake Island, where suffered a volcanic eruption in 2000, were analyzed by X-ray techniques to get better understanding of copper and silver corrosion in harsh environment. The exposure experiment was carried out from September 2004 to April 2005. Many kinds of patina were found on copper such as cuprite (Cu₂O), posnjakite (Cu₄SO₄(OH)₆ · H₂O), brochantite (Cu₄SO₄(OH)₆), antlerite (Cu₃SO₄(OH)₄), and geerite (Cu₈S₅). For silver, silver chloride (AgCl) and silver sulfide (Ag₂S) were formed. Although the volcanic activity had greatly subsided, the atmospheric corrosion of copper and silver plates exposed on Miyake Island was mainly affected by volcanic gases, wet-dry cycles in the environment, and sea-salt aerosols.     

Sulphide-induced stress corrosion cracking and hydrogen absorption of copper in deoxygenated water at 90°C

Stress corrosion cracking (SCC) of oxygen-free phosphorous-alloyed copper was investigated in sulphide- and chloride-containing deoxygenated water at 90°C with sulphide concentrations of 0.001 and 0.00001 M. Several intergranular defects were found in the specimen exposed to the high sulphide environment. Similar defects were not found in the low sulphide environment, where only slight corrosion on grain boundaries and slip lines occurred. Hydrogen content measurements show an increase in hydrogen uptake of the plastically deformed specimens, which is dependent on the sulphide concentration and on plastic deformation of copper. However, the highest hydrogen content was measured in friction stir welds, welded in air without shielding gas, and tested in the high sulphide environment. The embedded oxide particles in the weld metal act as local hydrogen trapping sites and selectively react with the sulphide solution. A relatively thick air-formed oxide film covers the copper canisters when deposited, which transforms into a sulphide film in the repository conditions. Thus, some of the coupon specimens were pre-oxidised. The conversion of the pre-existing Cu₂O film into Cu₂S film occurs quickly and the transformation is almost 100% efficient. The structure and properties of the Cu₂S films, susceptibility of copper to sulphide-induced SCC and hydrogen uptake of copper in reducing, anoxic repository conditions are discussed.     

Hot corrosion studies of a salt-coated Ni-based superalloy under flowing wet air and sulfur vapor ambient

Corrosion of a salt-coated Ni-superalloy has been studied at 900°C under a wet air and sulfur vapor ambient. The corrosion thickness, after an incubation of ~60 hr, linearly increases with the corrosion time t and the onset of surface spallation occurred at t ≈ 60 hr. The corroded layer consists of a corrosion front dominated by Cr₃S₄ scales and linear precipitate structures, an inner corrosion layer dominated by Ni₃S₂ and NiO, and an outer corrosion layer dominated by Al₂O₃ networks surrounding the Ni₃S₂ and/or NiO scale structures. The corrosion mechanism is discussed based on the coexistence of H₂O, sulfur, and oxygen.