Corrosion behavior of Cu/Al casting-rolled clad plates in different alkaline solution

The effect of pH value and different kinds of anions on the corrosion behavior of Cu/Al casting-rolled clad plates in the alkaline solution was evaluated by means of scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), weight loss analysis, 3D confocal laser scanning microscopy (CLSM) and electrochemical test. Results show the corrosion mainly occurs on the aluminum side. The corrosion resistance of the Cu/Al decreases as the pH value increases. When pH≥12, the dissolution of the film layer is faster than the passivation process. The addition of Cl⁻ ions reduces the corrosion resistance of the Cu/Al clad plates, which leads to pitting corrosion. The higher the concentration of Cl⁻ ions, the more prone the pitting to occur. The addition of SO₄²⁻ ions causes the denudation of the samples. The corrosion resistance of the Cu/Al is better in the alkaline solution containing NO₃⁻ ions than that in the solution containing Cl⁻ ions or SO₄²⁻ ions. When adding SO₄²⁻, NO₃⁻ and Cl⁻ to the pure alkaline solution, the corrosion resistance of the Cu/Al clad plates decreases.

     

Corrosion behavior of 2205 stainless steel in simulated flue gas condensate with different chloride concentrations in a waste incineration power plant

The effect of Cl⁻ on the initial corrosion behavior of 2205 duplex stainless steel (2205 DSS) in simulated flue gas condensate from a waste incineration power plant was investigated using Mott–Schottky plot, micro-area electrochemical methods, and microscopic surface morphology observation. The results show that at 150°C, the carrier concentration of the 2205 DSS passive film was maintained at a small value and changed little when the Cl⁻ concentration is less than 25 g/L, indicating that it has good pitting resistance. When the Cl⁻ concentration reaches 30 g/L and above, the carrier concentration of the passive film increases remarkably, and pitting corrosion appears on the 2205 DSS surface. At 180°C, there is no obvious pitting on the surface when the Cl⁻ concentration is not more than 15 g/L. When the Cl⁻ concentration is 20 g/L or above, the carrier concentration of the passive film significantly increases, and pitting corrosion appears on the surface. When the Cl⁻ concentration reaches 30 g/L, the carrier concentration of the passive film increases sharply. The passive film on a 2205 DSS surface is seriously damaged and accompanied by the occurrence of uniform corrosion.     

Review of micro-scale and atomic-scale corrosion mechanisms of second phases in aluminum alloys

Localized corrosion of aluminum (Al) alloys, such as pitting corrosion, intergranular corrosion, and stress corrosion cracking is closely related to the micro-galvanic corrosion between the second phase and the Al matrix. Using high-resolution transmission electron microscopy and first principles calculations, the factors that affect corrosion mechanisms of the second phase in Al alloys at micro-scale and atomic-scale were examined, including the composition and structure of second phase, pH of the environment, stress and adsorption behavior of adsorbates (such as Cl⁻, H₂O, OH⁻ and O²⁻).     

Effects of coolant chemistry on corrosion of 3003 aluminum alloy in automotive cooling system

In this work, effects of coolant chemistry, including concentrations of chloride ions and ethylene glycol and addition of various ions, on corrosion of 3003 Al alloy were investigated by electrochemical impedance spectroscopy measurements and scanning electron microscopy characterization. In chloride‐free, ethylene glycol–water solution, a layer of Al‐alcohol film is proposed to form on the electrode surface. With the increase of ethylene glycol concentration, more Al‐alcohol film is formed, resulting in the increase in film resistance and charge‐transfer resistance. In the presence of Cl^? ions, they would be involved in the film formation, decreasing the stability of the film. In 50% ethylene glycol–water solution, the threshold value of Cl^? concentration for pitting initiation is within the range of 100 ppm to 0.01 M. When the ethylene glycol concentration increases to 70%, the threshold Cl^? concentration for pitting is from 0.01 to 0.1 M. In 100% ethylene glycol, there is no pitting of 3003 Al alloy even at 0.1 M of Cl^?. Even a trace amount of impurity cation could affect significantly the corrosion behavior of 3003 Al alloy in ethylene glycol–water solution. Addition of Zn²⁺ is capable of increasing the corrosion resistance of Al alloy electrode, while Cu²⁺ ions containing in the solution would enhance corrosion, especially pitting corrosion, of Al alloy. The effect of Mg²⁺ on Al alloy corrosion is only slight.     

Role of alloyed copper on corrosion resistance of austenitic stainless steel in H2S–Cl− environment

Corrosion test, surface analysis and thermodynamic calculation were carried out in the H₂S–Cl⁻ environments to clarify the role of alloyed Cu on the corrosion resistance of austenitic alloys. The alloyed Cu improved pitting corrosion resistance in the H₂S–Cl⁻ environment. The surface film of Cu-containing alloy indicated double layer consists of copper sulfide and chromium oxide, and the copper sulfide was able to exist stably compared to iron sulfide and nickel sulfide. It is concluded that the copper sulfide would enhance the formation of chromium oxide film which improve the pitting corrosion resistance in the H₂S–Cl⁻ environment.     

Atmospheric corrosion monitoring of a weathering steel under an electrolyte film in cyclic wet–dry condition

Electrochemical Impedance Spectroscopy (EIS) and film thickness measurements have been employed to study the corrosion monitoring of steel under an electrolyte film in wet–dry cycles simulating a coastal atmosphere. The results indicate that within each cycle, the corrosion rate increases during drying process due to an increase in Cl⁻ concentration and an enhancement of oxygen diffusion by thinning out of the electrolyte. As corrosion process proceeds, the corrosion rate increases greatly and reaches a maximum. During subsequent corrosion stage, the corrosion rate decreases greatly and keeps at a low value due to the formation of a stable rust layer.     

Mg-15Li合金在碱性NaCl溶液中的腐蚀行为

    用电化学方法研究了Mg-15Li合金在碱性NaCl溶液中的腐蚀行为.结果表明：在强碱性pH=13及扫描电镜环境下,当Cl^-浓度低于0.4 mol/L时,合金表面形成稳定的钝化膜;随Cl^-浓度增加,点蚀电位逐渐降低.     

Galvanic corrosion behaviour of iron coupled to aluminium in NaCl solution by scanning eectrochemical microscopy

Scanning electrochemical microscopy (SECM) was used to sense the concentration of ions in 0.1M NaCl aqueous solution at the iron-aluminium couple. The SECM measured the concentration of ions relevant to the corrosion processes. The electrochemical behaviour of galvanic Fe/Al coupling was investigated as a function of time using SECM microelectrode tip. SECM amperometric line scan curves were obtained over the Fe/Al at a constant distance. In the first case the chemical species participating in the corrosion reactions at the sample are detected at the SECM-tip by applying appropriate potential values to the microelectrode. The release of Al³⁺ into the solution from local anodic surface, as well as the consumption of dissolved oxygen at the corresponding cathodic surface was successfully monitored. The results revealed that the galvanic couple where Fe/Al is close to each other will show lower corrosion rate due to the formation of corrosion products on the metal surface with further increase in exposure times.     

油气开采环境下管道的协同腐蚀及防护研究进展*

服役于高温高压 CO₂ / H₂S 环境下的管道腐蚀是油气田中急需解决的重要问题。CO₂、H₂S 及 Cl^- 是油气田管道中常见的腐蚀介质，其与温度、压力、pH值、含水率、流速等外界因素间的协同腐蚀作用会导致管道严重腐蚀，研究这些腐蚀介质与外界因素的协同腐蚀机制以及减缓管道腐蚀的措施有着重要的科学意义和经济价值。针对油气开采过程中金属管道的腐蚀问题，综述了 CO₂、H₂S 及 Cl^- 在协同腐蚀过程中起到的作用，讨论了温度、压力、pH 值、含水率及流速等实际工况条件下外界因素对腐蚀过程的影响。论述了现有管道腐蚀防护技术与工艺的特点：合金元素的掺杂可以改善腐蚀形貌，提高腐蚀产物层的致密性，等离子体扩渗与镀膜技术能够制备一层致密的保护层来吸收部分腐蚀介质并减缓腐蚀速率，缓蚀剂的添加可以减缓管道的阴极或阳极反应或形成减缓腐蚀速率的吸附层。最后展望了未来油气田管道防护技术的发展方向：为了有效地对油气开采环境下的管道进行保护，需要进一步研究腐蚀介质和外界因素间的协同腐蚀作用，模拟实际工况下的腐蚀环境， 对等离子体扩渗与镀膜技术、缓蚀剂等现有的防护技术进行系统的试验测试。     

Evaluation of atmospheric galvanic aluminum corrosion in electrical transmission towers at different sites in the Valparaíso region,Chile. Wire-on-Bolt Test (CLIMAT)

This study evaluates environmental aggressiveness and atmospheric galvanic corrosivity categories in Chile (Classification of Industrial and Marine ATmospheres test) by installing bolts in electrical transmission towers in the Valparaiso region across four exposure sites: Playa Ancha, San Sebastián, Las Vegas, and San Felipe. Classifications of marine corrosion index (MCI), industrial corrosion index (ICI), and atmospheric corrosion index (ACI) used different galvanic couples: aluminum/steel for MCI, aluminum/copper for ICI, and aluminum/polyethylene for ACI. Corrosion indices varied by season (summer, autumn, winter, and spring), for which couples were exchanged every 3 months. Intraseason variation depended mainly on the meteorochemical variables of the zone, the Cl⁻/SO₂ ratio, and the presence of general and pitting corrosion in the aluminum. The results indicate that, regardless of environmental condition, the aluminum in Al/steel (MCI) and Al/copper (ICI) couples presented a higher corrosion rate than when not forming a galvanic couple (ACI). Moreover, under higher environmental chloride, these differences increase. The Playa Ancha station presented the highest ACI.     

H2S and O2 influence on the corrosion of carbon steel immersed in a solution containing 3 M diethanolamine

Aqueous solutions with 3 mol L⁻¹ (M) diethanolamine (DEA) concentration are extensively used in the gas processing industry to remove acid gases. However, the degradation of the DEA and the formation of heat-stable salts (HSS) lead to severe corrosion problems. Even worse, equipment corrosion can be magnified by the unavoidable presence of sulphide acid and dissolved oxygen as a result of hydrocarbon (natural gases and crude oil) processing. The aim of this work is to study the combined corrosion effects of DEA, sulphide acid and oxygen on carbon steel. Electrochemical methods revealed that in the 3 M DEA medium without oxygen, corrosion processes are modulated by adsorbed DEA film formation. Furthermore, it was shown that the addition of oxygen and 15 × 10⁻³ mol L⁻¹ (15 mM) H₂S produced the formation of an adherent film on the carbon steel surface. Chemical analyses by EDAX revealed a homogeneous film of corrosion products composed of iron oxide and sulphide formed in DEA solution containing O₂ and H₂S, respectively. Equivalent circuits were used to estimate the parameters associated with ion diffusion through the formed corrosion films. The results showed that the presence of H₂S induced the formation of thin iron sulphide films that provide protective properties to the metal. It is concluded that the presence of oxygen in a sweetening plant should be avoided as DEA degradation can be produced with the subsequent decrease in chelating process efficiency and the increase in corrosion problems.     

Effect of 6-thioguanine,as an electrolyte additive,on the electrochemical behavior of an Al–air battery

In this study, the electrochemical behavior of an Al–air battery is improved by mixing 6-thioguanine into 4.0 M NaOH electrolyte. The electrochemical performance of the Al electrodes is analyzed using potentiodynamic polarization, potentiostatic oxidation, and electrochemical impedance spectroscopy. The surface morphology of the Al electrodes after discharging for 1,000 s is characterized using scanning electron microscopy coupled with X-ray elemental mapping for Al, O, C, N, and S. Furthermore, the utilization efficiencies of these samples are also determined. The results show that the corrosion resistance of the Al electrodes initially increases and then decreases with an increase in 6-thioguanine concentration. The presence of 6-thioguanine enhances the corrosion resistance to the maximum, with a corrosion current density (I_corr) of 6.170 mA/cm², and corrosion inhibition efficiency (η) of 36.56%, at 0.5 mM of 6-thioguanine.     

Corrosion behavior of ultra-fine grained industrial pure Al fabricated by ECAP

Corrosion behavior of ultra-fine grained(UFG) industrial Al fabricated by equal channel angular pressing(ECAP) for 16 pass times was investigated by potentiodynamic polarization test, potentiostatic polarization test, electrochemical impedance spectroscopy(EIS) measurement, immersion test and surface analyses (OM and SEM). The microstructures including grain size, grain boundaries and dislocations were also observed by TEM. The results show that the UFG industrial pure Al has more positive pitting potential, less corrosion current density and five times larger passive film resistance compared with the coarse grained(CG) one. It was found that the increased pitting resistance is profited from the more stable passive film kept in the Cl⁻ aggressive solution due to more grain boundaries, larger fraction of non-equilibrium grain boundaries and residual stress of the UFG industrial pure Al.     

中性水介质中铝的腐蚀行为

针对中性水介质中金属铝的腐蚀问题,采用旋转挂片腐蚀试验和电化学方法对模拟水样中铝的腐蚀行为进行研究。试验结果表明,流速、温度和溶液浓缩倍率均对铝的腐蚀有影响。随着流速和温度的升高,溶液中溶解氧的扩散速度加快,电荷传递电阻减小,导致铝的腐蚀速率加快;溶液浓缩倍率增大,溶液中离子浓度增大,很容易破坏铝表面的氧化膜而产生腐蚀,因此导致金属铝腐蚀速率增大。     

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.     

Microstructure,microhardness and corrosion resistance of laser cladding Ni–WC coating on AlSi5Cu1Mg alloy

The microstructure, microhardness, and corrosion resistance of laser cladding Ni–WC coating on the surface of AlSi5Cu1Mg alloy were investigated by scanning electron microscopy, X-ray diffraction, microhardness testing, immersion corrosion testing, and electrochemical measurement. The results show that a smooth coating containing NiAl, Ni₃Al, M₇C₃, M₂₃C₆ phases (M=Ni, Al, Cr, W, Fe) and WC particles is prepared by laser cladding. Under a laser scanning speed of 120 mm/min, the microhardness of the cladding coating is 9–11 times that of AlSi5Cu1Mg, due to the synergistic effect of excellent metallurgical bond and newly formed carbides. The Ni–WC coating shows higher corrosion potential (−318.09 mV) and lower corrosion current density (12.33 μA/cm²) compared with the matrix. The crack-free, dense cladding coating obviously inhibits the penetration of Cl⁻ and H⁺, leading to the remarkedly improved corrosion resistance of cladding coating.     

Influence of regulated modification of nitride layer by oxygen on the electrochemical behavior of Ti–6Al–4V alloy in the Ringer's solution

The corrosion behavior of oxynitrided Ti–6Al–4V alloy was investigated in the Ringer's solution (simulated body fluid) at a temperature of 37°C. The oxynitriding of the alloy was carried out by leaking controlled oxygen‐containing medium into the reaction chamber at the final stage of the nitride formation. It was determined that oxynitriding improved corrosion resistance of Ti–6Al–4V alloy as it provided lower corrosion current density by 1.3–1.5 times and higher corrosion potential. In this paper, we analyzed that the resistance of the double layer had increased with the increase of the oxygen content in titanium oxynitride. Its value was higher compared with untreated alloy, indicating higher corrosion resistance of the oxynitrided one.     

Influence of hot water conditioning on the corrosion behavior of carbon steel

The effect of hot water conditioning on the corrosion behavior of carbon steel in aqueous solutions of sodium chloride has been examined. In particularly, it has been examined the effect of water conditioning in the presence of octadecylamine = ODA on the corrosion and passivation of carbon steel, which was a major point in this research because of the big interest in the improvement of the hot water corrosion situation in electric and heating power stations of development countries, where a lot of damage is produced on the walls of the heat exchangers. It has been tried to determine which conditioning methods are working to improve the corrosion resistance and also to remove the deposits. Because it is known that ODA = Octadecylamine improves the corrosion resistance (it does not allow the formation of thick layers and also removes the deposits), it has been tried to develop a method of hot water conditioning by using ODA. For examining the corrosion behavior and the resistance of these materials electrochemical techniques have been used: DC – Potentiodynamic scanning AC – Electrochemical Impedance Spectroscopy (EIS) Scanning Electron Microscopy (SEM) was applied to determine the morphology of the oxide layers. Additionally, the electrolytes after hot water conditioning were analyzed for dissolved iron. The most important results are: 1. Hydrazine conditioning reveals in pure hot water much lower corrosion than oxygen conditioning. 2. ODA addition retards the corrosion much more in the case of hydrazine conditioning, than in the case of oxygen conditioning. 3. Hot water conditioning in the case of carbon steel does not form protective oxide layers resistant to 0.01 m Cl⁻‐solution (low polarization resistance, no passive range). 4. ODA showed no beneficial effect on the anodic branch of the polarization curve in 0.01 m Cl⁻‐solution, but it reduced the cathodic currents.     

The effects of Cl ion concentration and relative humidity on atmospheric corrosion behaviour of PCB-Cu under adsorbed thin electrolyte layer

The effects of Cl⁻ ion concentration and relative humidity on atmospheric corrosion behaviour of PCB-Cu under adsorbed thin electrolyte layer were investigated by cathodic polarization curves and electrochemical impedance spectroscopy. Results indicated that the cathodic process of PCB-Cu corrosion was dominated by the reduction of oxygen and corrosion products. The cathodic current density increased with increasing relative humidity and Cl⁻ ion concentration. The corrosion rate was initially dominated by oxygen reduction, but at the later stage of corrosion, the anodic process began to affect the corrosion rate due to the accumulation of corrosion products.     

Crevice corrosion monitoring of titanium and its alloys using microelectrodes

Crevice corrosion of titanium and its alloys in 10% sodium chloride was investigated at 100°C with the aid of microelectrodes. Potential, pH and chloride ion concentration inside the crevice were monitored using an Ag/AgCl electrode, a tungsten microelectrode and a Ag/AgCl chloride ion selective microelectrode, respectively. The pH and Cl^? concentrations within the crevice were calculated from the standard potential‐pH and potential‐log[Cl^?] calibration curves. The effect of Mo on the crevice corrosion of titanium was also studied. The passivation behavior on the titanium and Ti‐15%Mo alloy was studied using electrochemical impedance studies. There was no apparent change in pH and Cl^? ion activity inside the crevice for the alloy at 100°C, whereas a marginal decrease in pH and increase in Cl^? ion concentration were observed for pure titanium. Thus pure titanium is susceptible to crevice corrosion in hot 10% NaCl solutions at 100°C. The chloride ion activity was found to be reduced for the alloy so that the pH inside the crevice increased. The corrosion reaction resistance (R_t) was found to increase with the addition of Mo as an alloying element. It also increases with externally applied anodic potential. Hence, Mo is an effective alloying element, which enhances the crevice corrosion resistance of titanium.