Influence of nano-scale twins (NT) structure on passive film formed on nickel

X-ray photoelectron spectroscopy (XPS), potential of zero free charge (PZFC) and double-log of current-time techniques were used to study the effect of nano-scale twins (NT) structure on the chemical component of the passive film, the adsorption behavior of chloride ions on the passive film, and the passivation formation process in the solution containing 0.02 M NaCl. The results indicated that the passive film formed on NT coating was more integrated and more compact than those on IE nickel; the content of Ni(OH)₂ was higher and distribution of various components was more homogeneous across the passive films. The negative and smaller value of ΔE (the difference between the corrosion potential and PZFC) was observed for NT specimen, indicating that the adsorption capability of chloride ions on the passive film on NT specimen was markedly attenuated in the solutions. This decreased the susceptibility of NT specimen to pitting corrosion and was consequently responsible for the higher pitting potential.     

Comparative study of copper behaviour in bicarbonate and phosphate aqueous solutions and effect of chloride ions

Copper oxidation in aqueous solutions of pH 8 showed some differences in the presence of bicarbonate and phosphate ions. The bicarbonate ions did not interfere with Cu₂O film formation but the Cu²⁺ ions were stabilized by the complexing action of CO _2– ³ anions. In phosphate solutions, copper dissolved in the range of potentials associated with the Cu(I) oxidation state and the Cu(II) compound on the surface resulted in an extensive passivation region. In both solutions, a higher ion concentration caused an increase in the anodic current, suggesting that the copper ions were stabilized by the complexing action of the electrolyte. The copper oxidation current in a bicarbonate solution was higher than that observed in a phosphate solution of the same concentration. The thickness of the Cu(II) film rather than the Cu(I) layer appears to be the important factor related to the stability of the passive layer on the copper surface. The shift in the breakdown potential toward more positive values indicates that both bicarbonate and phosphate ions inhibit localized corrosion due to the presence of chloride ions. Their protective effect depends on the concentration of each anion, although the concentration of chloride ions necessary for pitting is larger in phosphate solutions than in bicarbonate solutions. In both solutions, long-term immersion of copper under anodic polarization results in the precipitation of a protective coating.     

Localized corrosion of 1024 mild steel in slightly alkaline bicarbonate solution with Cl− ions

The passive film breakdown of 1024 mild steel induced by the presence of 0.05m chloride ions had been investigated in 0.075–0.75m bicarbonate solutions at pH8.9–9.7. A rotating disc electrode with a Kel-F holder was used in conjunction with a rotating ring-disc electrode. The resistance to localized attack is closely linked to the preanodization potential (Eox) applied in the absence of Cl- ions. For Eox below about 0.2–0.3V vs SCE, the resistance to localized attack provided by the passive film is independent of Eox; above the breakdown potential, the localized attack is manifested by the formation of pits at the mild steel surface. The breakdown potential increases linearly with NaHCO3 concentration and pH. Passive film breakdown for Eox below about 0.2–0.3V vs SCE most likely begins with a surface film dissolution prior to the penetration of the aggressive anions through the film. For Eox above about 0.3V vs SCE under the same conditions, no pitting is noticed and the potential associated with localized attack shifts considerably in the anodic direction due to interstitial (formation of crevices) corrosion at the mild steel/Kel-F interface.     

Localized corrosion of 1024 mild steel in slightly alkaline bicarbonate solution with Cl? ions

The passive film breakdown of 1024 mild steel induced by the presence of 0.05m chloride ions had been investigated in 0.075–0.75m bicarbonate solutions at pH8.9–9.7. A rotating disc electrode with a Kel-F holder was used in conjunction with a rotating ring-disc electrode. The resistance to localized attack is closely linked to the preanodization potential (Eox) applied in the absence of Cl- ions. For Eox below about 0.2–0.3V vs SCE, the resistance to localized attack provided by the passive film is independent of Eox; above the breakdown potential, the localized attack is manifested by the formation of pits at the mild steel surface. The breakdown potential increases linearly with NaHCO3 concentration and pH. Passive film breakdown for Eox below about 0.2–0.3V vs SCE most likely begins with a surface film dissolution prior to the penetration of the aggressive anions through the film. For Eox above about 0.3V vs SCE under the same conditions, no pitting is noticed and the potential associated with localized attack shifts considerably in the anodic direction due to interstitial (formation of crevices) corrosion at the mild steel/Kel-F interface.     

Influence of grain size on the corrosion behavior of a Ni-based superalloy nanocrystalline coating in NaCl acidic solution

The effects of grain size on the electrochemical corrosion behavior of a Ni-based superalloy nanocrystalline (NC) coating fabricated by a magnetron sputtering technique, has been investigated in 0.5 M NaCl + 0.05 M H₂SO₄ solution. Coatings with grain sizes 10 nm, 50 nm and 100 nm were fabricated on glass and the superalloy substrates. The results indicate that a passive film with porous property, n-type semiconductive property and incorporation of chloride ions formed on the NC coating with 100 nm grain size, which increased the susceptibility to pitting corrosion. The NC coatings with 10 nm and 50 nm grain size formed compact, non-porous and p-type passive films without chloride ions, which improved resistance to pitting corrosion. The smaller grain size of the material decrease the amount of chloride ions adsorbed on the surface and promoted the formation of compact passive film, which significantly increased the material's resistance to pitting corrosion in acidic solution.     

铝在含锂盐的碱性溶液中稳定性的研究

为了解铝在锂盐溶液中的钝化行为,通过失重法研究了溶液pH值、温度、浸泡时间及氯离子浓度等因素对钝化膜形成及稳定性的影响。结果表明,溶液pH值和温度对钝化膜的和稳定性影响最大。为获得稳定的钝化膜,锂离子的浓度应随pH值的增大而增大,含锂钝化膜对氯离子的局部腐蚀有较强的抑制作用。     

Investigation into designed current oscillations during anodic dissolution of Al in NaCl + NaNO2 solutions

We previously proposed that current oscillations occurred when there were both an active factor and a passive factor that depended on each other and influenced the anodic dissolution processes of metallic materials alternatively. In this study, an electrochemical system, Al|NaCl + NaNO₂, was designed to verify this proposal. The chloride ions are aggressive ions (active factor), assisting the dissolution of the oxide film, while nitrite ions are inhibitive ones (passive factor), assisting the formation of the oxide film. The dissolution and the formation of the oxide film on the surface of the Al electrode occurred alternatively, and the current oscillations were observed to occur in this system, which proved the above point. The Al|NaCl + NaNO₂ system is a new electrochemical oscillator, in which hydrogen evolves periodically from the surface of the electrode during the current oscillations. The results were discussed in terms of the formation and the dissolution of the oxide film. The current oscillations were induced by pitting corrosion of Al in chloride ions containing solutions. It is expected that more oscillatory systems can be found and further studies into the nonlinear dynamic behaviour of metallic materials can be conducted in the light of the proposal.     

Characterization of passivity and pitting corrosion of 3003 aluminum alloy in ethylene glycol–water solutions

In this work, the passivity and pitting corrosion behavior of 3003 aluminum (Al) alloy in ethylene glycol–water solutions was investigated using various electrochemical measurements, Mott–Schottky analysis and surface analysis techniques. Results demonstrate that the passive film formed on Al alloy contains both Al oxide and Al alcohol, showing an n-type semiconductor in nature. There is an enhanced corrosion resistance of the Al-alcohol film, which is resistant to adsorption of chloride ions. The pitting corrosion of 3003 Al alloy occurs in the solutions containing a low concentration of ethylene glycol only, where the formed film is dominated by Al oxide. Chloride ions attack and replace the oxygen vacancies in the film, resulting in a local detachment of the film from the Al alloy. A galvanic effect exists between Al alloy substrate and the adjacent second phase particles. Pits form when Al alloy substrate is dissolved away and the second phase particles drop off from the substrate.     

Electronic structure and pitting behavior of 3003 aluminum alloy passivated under various conditions

Passivity of aluminum (Al) alloy 3003 in air and in aqueous solutions without and with chloride ions was characterized by electrochemical measurements, including cyclic polarization, electrochemical impedance spectroscopy (EIS), localized EIS and potential of zero charge, Mott-Schottky analysis and secondary ion mass spectroscopy (SIMS) technique. Stability, pitting susceptibility and repassivation ability of Al alloy 3003 under various film-forming conditions were determined. Results demonstrated that passive films formed on 3003 Al alloy in air and in Na₂SO₄ solution without and with NaCl addition show an n-type semiconductor in nature. The passive film formed in chloride-free solution is most stable, and that formed in chloride-containing solution is most unstable, with the film formed in air in between. Pitting of Al alloy 3003 passivated both in air and in aqueous solutions is inevitable in the presence of chloride ions. There is the strongest capability for the air-passivated Al alloy 3003 to repassivate, and the weakest repassivating capability for Al alloy 3003 passivated in chloride-containing solution. The resistance of the passivated Al alloy 3003 to pitting corrosion is dependent on the competitive effects of pitting (breakdown of passive film) and repassivation (repair of passive film). According to the differences between corrosion potential and potential of zero charge, passive film formed in air has the strongest capability to adsorb chloride ions, while the film formed in chloride-containing solution the least. Chloride ions causing pitting of passivated Al alloy 3003 in air and in chloride-free solution come from the test solution, while those resulting in pitting of passivated Al alloy 3003 in chloride-containing solution mainly exist in the film during film-forming stage.     

The breakdown of passive films on active metal anodes by halide ions in oxidizing molten salts

The various effects of halide ions on calcium, zinc and magnesium anodes in oxidizing molten salts can be related to a corrosion model involving a nonstoichiometric passive film containing an excess of metal ions. Competitive adsorption between passivating and aggressive anions attracted to the positively charged surface determines the stability of the film. The addition of chloride ions in molten LiNO₃ leads to pitting corrosion of the calcium anode and improvement of the open-circuit potential by as much as 1.3 V. In molten NaNO₃ and KNO₃, the formation of passivating peroxide and Superoxide anions greatly diminishes the effects of added chloride ions on the calcium anode. In molten LiClO₄ and NaClO₃, breakdown of the passive film occurs spontaneously due to the direct reaction of calcium with the molten oxyhalide salt to produce sufficient chloride ions to activate the anode. The best performance of the calcium anode is obtained in the oxyhalide molten salts.     

Mechanistic approach to electrochemical processes in the passive and pitting corrosion regions of carbon steel in dilute NaOH solutions containing Na2SO4

Passive film growth, electrodissolution and pitting corrosion of prepassivated carbon steel in dilute NaOH solutions containing Na₂SO₄ are studied by using potentiostatic and potentiodynamic techniques. Two kinetic reaction models implying different passive film growth mechanisms are proposed to describe the passive film growth, the electrodissolution process through the passive film and pitting corrosion. Current transients at constant potential recorded in the passive and pitting region can be satisfactorily reproduced by assuming the occurrence of simultaneous processes. The physical interpretation of adjusting parameters derived from the two models is consistent with a duplex structure for the passive film and with the nucleation and growth of pits when the applied potential exceeds the breakdown potential although both mechanisms for the passive layer growth seem to be equally probable.     

Influence of nanocrystallization on passive behavior of Ni-based superalloy in acidic solutions

The electrochemical corrosion behaviors of Ni-based superalloy nanocrystalline coating (NC) fabricated by a magnetron sputtering technique have been investigated in comparison with cast alloy in 0.25 M Na₂SO₄ + 0.05 M H₂SO₄ and 0.5 M NaCl + 0.05 M H₂SO₄ solution, respectively. Compared with cast alloy, the NC coating had a little higher passive current density in Na₂SO₄ acidic solution, while it had superior resistance to pitting corrosion in NaCl acidic solution. The semiconductive type of passive film of the NC coating was p-type in both acidic solutions, while, that of cast alloy changed from p-type in Na₂SO₄ acidic solution to n-type in NaCl acidic solution. XPS results indicated that Cr₂O₃ was the main component for the passive films of the NC coating as well as those of the cast alloy. No chloride ion was found in the passive film of NC coating while it was in the passive film of cast alloy. The chloride ions adsorbing on the surface of cast alloy incorporated into the passive film, which induced the formation of n-type oxide film. The nanocrystallization of Ni-base superalloy obviously weakened the adsorption of chloride ions on surface, which decreased the susceptibility of pitting corrosion in acidic solution.     

An investigation on general corrosion and pitting of iron with the in-line digital holography

In the anodic processes of the iron electrode in both neutral and acidic solutions, general corrosion and pitting dynamical processes in the presence of chloride ions were observed in situ with the in-line digital holography. The dynamic processes such as formation and dissolution of the passive film, initiation and propagation of pitting have been studied. During the general corrosion, not only is the temporal structure in order, evidenced by the regular change of current with time, but also the spatial structure, indicated by the uniform fringes in the holograms at the electrode/electrolyte interface. However, during the pitting processes, the order of the spatial structure is destroyed, which is indicated by the wrinkled fringes in the holograms; the temporal order is broken as well evidenced by the irregular change of current with time. The experimental result shows that there is synergistic effect between H⁺ and Cl⁻ on both the initiation stage and the propagation stage. With the presence of chloride ions, pitting occurs much more easily in acidic solution than in neutral solution.     

The role of chloride ions and pH in the corrosion and pitting of Al–Si alloys

The role of chloride ions in the pitting corrosion of some Al–Si alloys was investigated by chemical, polarization and EIS measurements, as well as SEM studies. Differences in corrosion rates of pure aluminium and the alloys are discussed. The capacitive behaviour of the oxide covered surface is replaced by resistive behaviour as immersion time increases in HCl solutions. At neutral pH corrosion currents increase then decrease with chloride ion concentrations. Pitting by chloride ions initiates more readily in acidic media.     

氯离子对催化裂化分馏塔顶冷却系统腐蚀的研究

针对延安炼油厂年产量200万t催化裂化装置分馏塔顶空冷器内侧腐蚀问题,进行现场取样检测,配制模拟溶液,研究氯离子单一因素的变化对腐蚀结果的影响,选用了空冷管束常用的10钢、20钢和304不锈钢三种材料进行腐蚀试验。通过对试验的极化曲线和电化学阻抗的分析,得到氯离子对10#钢和20#钢的腐蚀机理相同;三种材料都会随着氯离子的加入,出现局部腐蚀点蚀,且随着氯离子浓度的增大都有腐蚀加剧的趋势;304钢随着氯离子浓度的变大,点蚀电位下降不明显,钝化膜变的不稳定。综合对比,304钢抗腐蚀性表现优于10#钢,10#钢优于20#钢,但10#钢对于氯离子变化更敏感。     

On the role of NO2 ions in passivity breakdown of Zn in deaerated neutral sodium nitrite solutions and the effect of some inorganic inhibitors: Potentiodynamic polarization, cyclic voltammetry, SEM and EDX studies

As a first step towards studying pitting corrosion of Zn in deaerated neutral sodium nitrite solutions (pH 6.9), we have reported the results of potentiodynamic polarization and cyclic voltammetry measurements on the passivity and passivity breakdown of Zn in these solutions. Measurements were conducted under the influence of various experimental conditions, complemented by ex situ scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) examinations of the electrode surface. The voltammograms involve active/passive transition prior to the initiation of pitting corrosion as a result of breakdown of the passive film by NO₂⁻ ions. The active region displays one anodic peak due to the formation of ZnO passive film on the anode surface. SEM examinations confirmed the existence of pits on the electrode surface. The potential at which pits initiated (E_pit) was determined, together with a pit transition potential (E_ptp) that appeared as an abrupt current discontinuity on the reverse potential scan (hysteresis loop), and a protection potential (E_prot) that appeared at the end of the hysteresis loop. The value of E_pit shifted negatively as either C_nitrite or temperature was increased, while it increased with the increase in potential scan rate. The effect of adding some environmentally acceptable inorganic inhibitors, as tungstates, molybdates and silicates (water glass), on the pitting corrosion behaviour of Zn in nitrite solutions has also been studied. The mechanism of inhibition was discussed.     

Nickel-free manganese bearing stainless steel in alkaline media—Electrochemistry and surface chemistry

The use of austenitic nickel-containing stainless steels as concrete reinforcement offers excellent corrosion protection for concrete structures in harsh chloride bearing environments but is often limited due to the very high costs of these materials. Manganese bearing nickel-free stainless steels can be a cost-effective alternative for corrosion resistant reinforcements. Little, however, is known about the electrochemistry and even less on surface chemistry of these materials in alkaline media simulating concrete pore solutions. In this work a combined electrochemical (ocp = open circuit potential) and XPS (X-ray photoelectron spectroscopy) surface analytical investigation on the austenitic manganese bearing DIN 1.4456 (X8CrMnMoN18-18-2) stainless steel immersed into 0.1 M NaOH and more complex alkaline concrete pore solutions was performed. The results show that the passive film composition changes with immersion time, being progressively enriched in chromium oxy-hydroxide becoming similar to the conventional nickel-containing stainless steels. The composition of the metal interface beneath the passive film is strongly depleted in manganese and enriched in iron; chromium has nearly the nominal composition. The results are discussed regarding the film growth mechanism (ageing) of the new nickel-free stainless steel in alkaline solutions compared to traditional austenitic steels. Combining the results from pitting potential measurements with the composition of the passive film and the underlying metal interface, it can be concluded that the resistance against localized corrosion of the new nickel-free stainless steel relies on the strong chromium(III) and molybdenum (VI) oxy-hydroxide enrichment in the passive film.     

Passivity and passivity breakdown of a zinc electrode in aerated neutral sodium nitrate solutions

The passivation and pitting corrosion behaviour of a zinc electrode in aerated neutral sodium nitrate solutions was investigated by cyclic voltammetry and chronopotentiometry techniques, complemented by ex situ scanning electron microscopy (SEM), X-ray diffraction (XRD) and energy dispersive X-ray (EDX) examinations of the electrode surface. Measurements were conducted under different experimental conditions. The potentiodynamic anodic polarization curves do not exhibit active dissolution region due to spontaneous passivation. The passivity is due to the presence of thin film of ZnO on the anode surface. The passive region is followed by pitting corrosion as a result of breakdown of the passive film. SEM images confirmed the existence of pits on the electrode surface. The breakdown potential decreases with an increase in NO₃⁻ concentration and temperature, but increases with increasing potential scan rate. Addition of SO₄²⁻ ions to the nitrate solution accelerates pitting corrosion, while addition of WO₄²⁻ and MoO₄²⁻ ions inhibits pitting corrosion. The chronopotentiometry measurements show that the incubation time for pitting initiation decreases with increasing NO₃⁻ concentration, temperature and applied anodic current density. Addition of SO₄²⁻ ions decreases the rate of passive film growth and the incubation time, while the reverse changes produced by addition of either WO₄²⁻ or MoO₄²⁻ ions.     

Electrochemical behaviour of heat-treated AlZnMg alloys in chloride solutions containing sulphate

The electrochemical corrosion and passivation of Al5Zn1.7Mg0.23Cu0.053Nb alloys, submitted to different heat treatments (cold-rolled, annealed, quenched and aged, and quenched in two steps and aged), in sulphate-containing chloride solutions, has been studied by means of cyclic polarization, electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM), energy-dispersive X-ray (EDX), and X-ray photoelectron spectroscopy (XPS). The cyclic polarization curves showed that sulphate addition to the chloride solution produced a poor reproducible shift of the breakdown potential to more positive potentials. The repassivation potentials, much more reproducible, and practically separating the passive from the pitting potential region, were slightly displaced in the negative direction with that addition. When the alloys were potentiodynamically polarized in the passive potential region, sulphate was incorporated in the oxide film, thus precluding chloride ingress. In addition, Zn depletion was favoured, whereas Mg losses were avoided. Different equivalent circuits corresponding to different alloys and potentials in the passive and pitting regions were employed to account for the electrochemical processes taking place in each condition. This work shows that sulphate makes these alloys more sensitive to corrosion, increasing the fracture properties of the surface layer and favouring the pitting attack over greater areas than chloride alone.     

Electrochemical impedance spectroscopy study of the passive films of alloy 22 in low pH nitrate and chloride environments

Utilizing electrochemical impedance spectroscopy (EIS), we characterize the passive film properties of alloy 22 during immersion in low pH nitrate and chloride solutions. In pure HCl, the passive film grows thinner with increasing acid concentration. In contrast, in HNO₃, the passive film corrosion protection properties are enhanced, which leads to low corrosion rates, even at pH < −0.5. The combined influence of both HCl and HNO₃ in contact simultaneously with the alloy 22 surface shows multiple phases in the passive film properties depending on the pH. EIS results show that the passive film changes either thickness and/or composition as the system is driven chemically through different corrosion states, including: active, passive, active/passive and transpassive.