Near‐wall hydrodynamic effects related to flow‐induced localized corrosion

The relationship between near‐wall hydrodynamic conditions and flow‐induced localized corrosion of copper alloys was investigated. Flow‐induced localized corrosion tests for copper alloys were conducted in corrosive solutions using a jet‐in‐slit testing apparatus, in which various hydrodynamic conditions were reproduced. To evaluate local damage, the profiles of the specimens were measured using a surface roughness meter. In addition, the near‐wall hydrodynamic conditions on the material surface in the apparatus were measured by pressure gauges to determine the distribution of near‐wall velocities and velocity fluctuations. In the equation used to predict corrosion damage, three types of hydrodynamic conditions were applied as parameters related to the mass transfer coefficient in the film of corrosion products. The damage profiles calculated from the equation could be fitted to that obtained from the corrosion test.     

油气管道CO2腐蚀过程中弹状流的影响

通过分析弹状流近壁面处的动力边界层和扩散边界层及弹状流对管壁CO2腐蚀的影响,发现弹状流动特性对管壁的质量传递、动量交换、管壁处的电化学腐蚀以及腐蚀产物膜的形成和破坏有显著的影响作用。提出弹状流动形态和CO2腐蚀产物膜特性是管壁腐蚀速率和腐蚀形态的重要影响因素,弹单元内的壁面切应力变化特性、正应力变化特性、壁面传质变化特性以及电化学腐蚀特性的非线性耦合作用是油气管道内壁CO2腐蚀的重要影响因素。在此基础上阐述了CO2腐蚀产物膜的微观结构、力学特性以及膜内的传质特性对腐蚀产物膜的形成、破坏以及修复作用。     

Corrosion of an aluminum alloy chilled in flowing seawater and the effect of cathodic prevention

A new type of jet‐in‐slit testing apparatus for a specimen, chilled with a peltier element, was developed to investigate corrosion on the heat transfer surface of an aluminum alloy heat exchanger, in contact with a liquefaction gas at cryogenic temperature and in flowing seawater. The specimen can be chilled, even under flowing conditions, using this apparatus. Corrosion tests and polarization measurements of a specimen chilled by a peltier element were carried out in flowing seawater at various temperatures. The effect of chilling a specimen was equivalent to the effect achieved for a test in solution at a lower temperature. The process was dependent on a passive film, formed on the surface of the aluminum alloy specimen, as evidenced by polarization measurements. The extent of corrosion damage increased with increasing temperature of the solution, and showed maximum damage at high temperature. At high temperatures, erosion‐corrosion was found at the central part of the specimen, but the effect of flow was negligible at low temperature. Corrosion tests for a cathodically polarized specimen were conducted under flowing conditions. Corrosion damage was accelerated by cathodic polarization at lower temperatures.     

Experimental investigation on gas-liquid two-phase slug flow enhanced carbon dioxide corrosion in vertical upward pipeline

The carbon dioxide corrosion behavior of API N80 grade steel enhanced by gas-liquid two-phase vertical upward slug flow has been both mechanistically and experimentally investigated. It is found that the hydrodynamic characteristics of slug flow, such as the direction alternated wall shear stress, the fluctuation of wall normal stress, and the mass transfer near the wall, have significant effects on the carbon dioxide corrosion process. It is difficult to form dense, compact, and protective corrosion product film in the corrosion process, which is dominated by general corrosion, and can develop into pitting and mesa attack due to localized corrosion. An empirical correlation is suggested to predict slug flow enhanced carbon dioxide corrosion. It is found that the mass transfer in corrosion product film can be neglected and the slug flow enhanced carbon dioxide corrosion is dominantly controlled by mass transfer or by both of mass transfer and electrochemical corrosion reaction.     

Effect of passive film on the galvanic corrosion of titanium alloy Ti60 coupled to copper alloy H62

Ti alloys exhibit high potential because of the compact passive film. However, the effect of passive film on galvanic corrosion is not clear. On the one hand, the great potential difference can accelerate the galvanic corrosion of other metals with low potential. On the other hand, the passive film can hinder the electrochemical reactions, inhibiting the galvanic corrosion. To clarify this question, the galvanic corrosion of titanium alloy Ti60 coupled to copper alloy H62 was studied using zero‐resistance ammeter, scanning vibrating electrode technique, scanning electron microscopy, and potentiodynamic polarization measurements. The chemical composition and electrical properties of the passive film on Ti60 were detected using X‐ray photoelectron spectroscopy and Mott‐Schottky plots. The results indicate the galvanic corrosion of Ti60‐H62 coupling is ignorable in spite of the great galvanic potential difference between them. It can be attributed to the low electron donor density of passive film, which inhibits the electron charge transfer process at the film/solution interface, causing the slow cathodic reaction rate on Ti60.     

注多元热流体环境下流速对N80钢腐蚀行为的影响研究

目的 研究不同流速条件下N80钢在注多元热流体环境中的腐蚀特征,探究流速变化对N80钢腐蚀行为的影响规律及机理。方法 利用自制高温高压多相流冲刷腐蚀环路装置模拟不同流速(0、0.5、1.0、2.0 m/s)的注多元热流体环境,采用失重法计算不同流速下N80钢的平均腐蚀速率,并同时进行原位电化学测试。采用扫描电子显微镜(SEM)和X射线衍射仪(XRD)对不同流速条件下N80钢腐蚀后的腐蚀产物物相组成和表面微观形貌进行分析。结果 N80钢在注多元热流体环境中的平均腐蚀速率随着流速增加而增大。流速增加影响O2的扩散传质过程、近表面离子分布和壁面剪切力的大小,使腐蚀产物膜特征发生变化。0 m/s时,腐蚀产物主要由FeCO3和少量Fe2O3组成,为单层膜结构,腐蚀形态为均匀腐蚀。0.5~2.0 m/s范围内,腐蚀产物种类增加,主要由FeCO3、Fe2O3和少量FeO(OH)组成,呈双层膜结构,同时N80钢表面腐蚀产物膜出现鼓泡,且随流速增加鼓泡数量增加,去除腐蚀产物膜后发现鼓泡下方存在局部腐蚀。原位电化学测试结果表明:随着流速增加,塔菲尔极化曲线的阳极斜率增大,阴极斜率减小。电化学阻抗谱测试结果表明,N80钢表面外层腐蚀产物膜电阻Rf1、电荷转移电阻Rct和扩散电阻W随流速增加而减小。结论 流速增大加快了O2的扩散传质过程,使得腐蚀电化学控制步骤由阴极氧扩散过程转变为阳极溶解过程,且试样表面保护性FeCO3膜厚度减小,导致产物膜保护性降低。另外,Fe²⁺更容易被氧化形成Fe³⁺,局部FeCO3被氧化成为Fe2O3,破坏了内层膜的完整性,导致局部腐蚀发生。     

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 effect of hydrodynamic conditions on the rate of copper cathodic reduction from aqueous ethanol environments

The effect of hydrodynamic conditions on copper electroplating from aqueous ethanol CuSO₄ solutions is studied. Adding ethanol is found to result in a decrease in the ionic mass transfer rate in the solution. Experimental data are analyzed on the basis of the convective diffusion equation for a rotating disc electrode. Diffusivities of copper cations and kinetic current densities are estimated.     

Critical characteristics of corrosion product film obtained by fluid structure interaction

The critical characteristics of corrosion product film (CPF) were investigated, and the mechanism of flow‐accelerated corrosion (FAC) was discussed by improving the multiple reference frame method (MRF) using the space temporary coordinate system. The improved MRF was used to accomplish fluid structure interaction (FSI) numerical simulation for FAC testing machine with a pre‐filming specimen. The new numerical method for the simulation of the critical characteristics of the CPF was proposed by coupling FSI and contact analysis in COMSOL Multiphysics software based on Hertz theory, which was used to calculate the critical characteristics of the specimen. The results reveal that the deformation and stress of the CPF increased with increasing temperature and flow velocity. The critical flow velocity was higher than the pre‐filming flow velocity and increased with increasing temperature. The calculation results are consistent with those of the linear polarization experiment.     

Electrochemical characteristic of chemical-mechanical polishing of copper with oxide passive film

1　INTRODUCTIONThankstoitslowresistivityandhighelectromi grationresistance ,copperappearstobeaverypromisingsubstituteforaluminumininterconnec tions[1] .However ,copperisverydifficulttopattern ,andonlychemical mechanicalpolishing (CMP)tech nologycanresolvethisproblem[2 ] .CMPwasinitiallyinvestigatedandopenedoutfrom 1980soverseas[3] ,anditisthebestandonlyglobalplanarizationtech nologyatpresent ,butkeepsholdofbusinesssecretsallthetime .Fayolleetal[2 ] researchedCMPprocessofcopperwhereFe(…     

Flow-dependent corrosion – II. Ferrous materials in pure and particulate chloride solutions

The corrosion behaviour of non alloyed steel, cast iron, and 13% chromium steel has been investigated in chloride containing media without and with sand (one-phase and two-phase flow) at various flow velocities. In one-phase flow mass transfer determined corrosion prevails with the structure and composition of surface layer being the dominating factor. In two-phase flow mainly erosion corrosion is observed together with a strong influence of hydrodynamic parameters. Particular emphasis is given to the experimental techniques required for the investigation of flow dependent corrosion.     

Corrosion and Cavitation Erosion Behaviours of Cast Nickel Aluminium Bronze in 3.5% NaCl Solution with Different Sulphide Concentrations

The effect of sulphide(Na_2S) concentration(SC) on the corrosion and cavitation erosion behaviours of a cast nickel aluminium bronze(NAB) in 3.5% NaCl solution is investigated in this study.The results show that when the SC exceeds 50 ppm,the hydrogen evolution reaction dominates the cathodic process,and a limiting current region appears in the anodic branch of the polarisation curve due to the formation of a copper sulphide film,which is a diffusion-controlled process.After longterm immersion,the increased mass loss rate of NAB with the sulphide additions of 20 and 50 ppm is attributed to the less protective films,which contains a mixture of copper oxides and sulphides.Moreover,NAB undergoes severe localised corrosion(selective phase corrosion,SPC) at the β' phases and eutectoid microstructure α+κ_Ⅲ.By comparison,NAB undergoes general corrosion and a copper sulphide film is formed in 100 and 200 ppm sulphide solutions.Cavitation erosion greatly increases the corrosion rate of NAB in all solutions and causes a negative potential shift in 3.5% NaCl solution due to the film destruction.However,a positive potential shift occurs in the solutions with SC higher than 50 ppm due to the accelerated mass transfer of the cathodic process.The cavitation erosion mass loss rate of NAB increases with the increase of SC.The occurrence of severe SPC decreases the phase boundary cohesion and causes brittle fracture under the cavitation impact.The corrosion-enhanced erosion is the most predominant factor for the cavitation erosion damage when the SC exceeds 50 ppm.     

Study of the oxide scale integrity on Ni‐base alloy CMSX‐4 during isothermal and thermal‐cycling exposure

The excellent isothermal high‐temperature corrosion resistance of the single crystalline Ni‐base superalloy CMSX‐4, which is due to external alumina formation, is substantially reduced under thermal‐cycling conditions. Particularly, tapered edges exhibit a high cracking and spallation rate leading to premature onset of breakaway oxidation in combination with strong internal corrosion attack. To characterize these effects, specimens with different geometries were prepared, i.e., rectangular‐shaped and wedge‐shaped specimens. Measurements under isothermal and thermal‐cycling conditions at a temperature of 1100°C in air were carried out using a self‐designed thermobalance. By using wedge‐shaped specimens the conditions for spallation, Al depletion and eventually, breakaway oxidation in combination with internal corrosion (Al₂O₃, TiN and AlN) could be correlated with the change in thickness of the specimen and the duration of the high‐temperature dwell time. As compared to rectangular‐shaped specimens, wedge geometries revealed a much higher susceptibility to oxide spallation and consequently, a higher rate of aluminium depletion. An evaluation of the surface fraction affected by oxide spallation and an analysis of the spalled oxidation products were carried out in order to determine the role of dwell time duration as well as the effect of the number of thermal cycles.     

A novel process for copper protection in the simulated industrial cooling water based on click synthesis and self‐assembling method

The triazole inhibitor of 1‐(p‐tolylthio)‐1H‐1,2,3‐triazole‐4‐carboxylic acid (TTC) was synthesized via the Cu(I)‐catalyzed azide‐alkyne 1,3‐dipolar cycloaddition reaction. The self‐assembling method was performed to fabricate the self‐assembled film of TTC on the copper surface. The electrochemical measurement results indicate that the TTC film can efficiently protect the copper from corrosion in high concentrated industrial cooling water. The protection efficiency of TTC film for copper is 92.2%. Surface characterizations imply that the copper with TTC film after corrosion is covered with multiple protective layers. It probably contains Cu(I) and Cu(II) complexes mixed with nitrogenous compound, Cl^? and SO₄^2?. The result of quantum chemical calculation shows that the superior performance of TTC film is related to the adsorption of TTC molecules on copper surface horizontally. This kind of adsorption is mainly achieved via the adsorption centers of triazole ring and O atoms in TTC molecule.     

Long term corrosion behaviour of copper in soil: A study of archaeological analogues

The long term corrosion behaviour of copper in soil environment has been addressed by studying two archaeological copper samples. The microstructures of the material of construction of a Chalcolithic (2350BC‐1800BC) copper chisel from Balathal and an OCP period (2650BC‐800BC) Cu anthropomorphic object have been first characterized by microscopy and the features understood by stereological methods. The equiaxed grain size, coring effects in the grains and the relatively soft matrix of the OCP copper object indicated that it was manufactured by casting. The deformed grains near the surfaces and variation in the microhardness of the sample at different points suggests that the Chalcolithic copper chisel was processed by cold deformation after casting of the square cross section chisel. The surface patina on the two archaelogical copper objects has been characterized by X‐ray diffraction. In the case of OCP copper, the green surface patina was analyzed as a mixture composed mainly of cuprite, and minor amounts of malachite and brochantite. In the case of Chalcolithic copper, the patina was composed of sulfates and oxysulfates in the outer layers while the inner layers were rich in copper oxides. The electrochemical behaviour of both the archaeololgical coppers has been characterized and compared with that of a modern Cu sample by potentiodynamic polarization studies. The corrosion rate, determined by Tafel extrapolation technique in 3.5% NaCl solution, of Chalcolithic Cu was only marginally higher than that of modern and OCP Cu. The higher rates of corrosion in case of archaeological coppers have been attributed to the presence of second phase sulfide inclusions.     

Corrosion resistance of 3,4‐dihydroxyphenylalanine/octadecylamine complex coatings on copper substrate

Octadecylamine (ODA) film assisted with the preferential adhesion of poly‐DOPA was prepared on copper substrates by dip‐coating method. The DOPA self‐polymerized and adhered membrane was firmed to the copper substrate in mild aqueous alkaline environments. By immersing the substrate coated with poly‐DOPA in its absolute ethyl alcohol solution, ODA was adsorbed onto the substrate to give a hydrophobic surface. The formation and surface structure of the film were characterized by water contact angle measurement (DA), and scanning electron microscopy. The corrosion behavior of the functional hybrid films was evaluated by electrochemical impedance spectroscopy. Experimental results show that the impedance of the composite films reaches to 10⁶ Ω, enhancing anti‐corrosion property of copper surface greatly.     

Corrosion resistance of austenitic stainless steel separator for molten carbonate fuel cell

STS310S and SC-STS310S (simultaneously co-deposited chromium and aluminum onto 310S austenitic stainless steel substrate by pack-cementation process) were used as separator materials on the cathode side of a molten carbonate fuel cell. With the STS310S, corrosion proceeded via three steps; a formation step of unstable corrosion product, a protection step against corrosion until breakaway, and an advance step of corrosion after breakaway. The final corrosion product was LiFeO₂ and the loss of mass was 6.5 mg/cm² after a corrosion test of 480 hr at 650°C. The SC-STS310S showed more effective corrosion resistance, however, than did common STS310S. There was especially no corrosion loss on the SC-STS310S after the 480 hr corrosion test. It is anticipated that it will be very useful as an alternative separator on the cathode side off the MCFC in the future.     

Effect of extrusion wheel angular velocity on continuous extrusion forming process of copper concave bus bar

The continuous extrusion forming process for producing large section copper concave bus bar under different extrusion wheel angular velocities was studied by three-dimensional finite element technology based on software DEFORM-3D. The rigid-viscoplastic constitutive equation was employed in the model. The numerical simulation results show that the deformation body flow velocity in the die orifice increases gradually with the increase of the extrusion wheel angular velocity. But slippage between the rod and extrusion wheel occurs when the extrusion wheel angular velocity is high. The effective stress near the die orifice enhances gradually with increasing extrusion wheel angular velocity. High stress is concentrated in adjacent regions of the flash gap. The effective strain gradient is greater near the abutment than that near the die orifice. The effective strain of the product increases gradually with increasing extrusion wheel angular velocity. In the deformation process, the deformation body temperature increases remarkably due to friction and deformation. So the cooling is necessary in the region of the die and tools.     

2,3-二巯基丁二酸对铜的缓蚀性能研究

目的以马来酸为原料制备2,3-二巯基丁二酸(DMSA),研究DMSA对铜在0.5 mol/L NaOH溶液中的缓蚀作用。方法以马来酸为原料,通过加成、消去、加成再水解的方法制备2,3-二巯基丁二酸,利用红外光谱和质谱对其结构进行表征。通过静态腐蚀失重实验研究铜在添加不同含量DMSA的NaOH溶液中的腐蚀速度,采用极化曲线和交流阻抗谱技术研究铜在添加不同含量DMSA的NaOH溶液中电化学行为,并用电子扫描电镜观察铜表面腐蚀形貌。结果红外光谱和质谱结合证明,目标产物为DMSA。铜在DMSA质量浓度分别为0,2.5,5.0 g/L的NaOH溶液中的腐蚀速率分别为7.60,3.25,2.13μg/(cm2·h)。当NaOH溶液中DMSA的质量浓度为5.0 g/L时,缓蚀率可达到94.92%。结论 DMSA在铜表面的吸附能降低水分子的侵蚀,增大铜表面的腐蚀产物膜电阻和电荷转移电阻,属于阳极型缓蚀剂。     

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.