Passivity Breakdown Research Articles

Electrochemical measurements and atomistic simulations of Cl−-induced passivity breakdown on a Cu2O film

The mechanism of passivity breakdown on Cu2O films was studied. The thickness and components of the film were estimated by EIS, AES and XPS analyses. The structural relaxations, energies, electronic properties and diffusion coefficients were calculated by first-principles calculations. Both the experimental and calculated results demonstrate that the film thinning is due to the adsorption of Cl− on the surface instead of a penetration process. The inner point defects facilitate the adsorption of Cl−, and the introduction of Cl−, in turn, increases the transport rate of point defects. A theoretical model was proposed, which is also applicable to local breakdown.

Effect of amino acid on the passivation, corrosion and inhibition behavior of aluminum alloy in alkaline medium

The effect of L-methionine (L-Met) on the passivation and corrosion inhibition of aluminum alloy was investigated in carbonate medium in presence of chloride ions. This inhibitive action against the corrosion of aluminum in corrosive solution was investigated at 298 K using potentiodynamic polarization curves (PDP), cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The results obtained from the polarization curves reveal that the aluminum in alkaline medium exhibits a phenomenon of passivation with breakdown of passivity. Temperature effect on the corrosion behavior with the addition of (L-Met) studied in the range of temperature from 298 to 328 K. The inhibition efficiency decreases slightly with the increase in the temperature. Results show that L-Met is a good inhibitor and inhibition efficiency reach 87,23% at 10 −3 M. The electrochemical results are confirmed by scanning electron microscopy (SEM). The adsorption of this compound on aluminum surface obeys Langmuir’s adsorption isotherm. The kinetic and thermodynamic parameters were determined and discussed.

Corrosion resistance and mechanism of CeN, TiN and CeN/TiN bilayer composite film deposited by dual ion beam sputtering

Uranium (U) is an important engineering material in nuclear energy industry. Its environmental instability, however, posed challenges on its applications. Due to the active property and similar electronic configuration, Cerium (Ce) can be used as a reference metal to simulate the protection of uranium from corrosion. In order to improve the corrosion resistance of Ce, ceramic CeN, and ceramic TiN and CeN/TiN bilayer composite film were prepared by dual ion beam sputtering deposition system (DIBD). The crystal structure of films was identified by X-ray diffraction (XRD) and the chemical states of CeN film were characterized by the X-ray photoelectron spectroscopy (XPS). The Surface morphology and structure changes in atmospheric environment were examined by scanning electron microscopy (SEM) and XRD, The corrosion behavior was studied by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). The experimental results indicate the single film of CeN or TiN shows poor corrosion resistance, but the CeN/TiN bilayer composite film has better corrosion resistance. Based on the XPS, SEM and impedance analysis, we supposed that the loose of integrity and passivity breakdown on as deposited coating may be the corrosion inducement.

Passivity and its breakdown on low temperature plasma carburized AISI 204Cu stainless steel in chloride‐containing solution

The passivity and passivity breakdown of low temperature plasma carburized AISI 204Cu stainless steel were studied in borate buffer solution (pH 8.4) in the absence and presence of 150 mM KCl, performing potentiodynamic polarization, potentiostatic transients, and electrochemical impedance spectroscopy (EIS) measurements complemented with scanning electron microscopy (SEM). In the absence of chloride ions, the surface treatment exercise a beneficial role in the passivating characteristics of AISI 204Cu. Plasma carburizing significantly modifies the electrochemical response of 204Cu steel resulting in a more stable passive film. In the presence of chloride ions, both the untreated and plasma carburized specimen experience localized corrosion (pitting). However, plasma carburizing increases the breakdown potential and the extent of passivation domain, indicating improved resistance to initiation of pitting corrosion. Furthermore, EIS measurements performed at the breakdown state evidenced higher Rct and lower depression angle values for the carburized specimen compared to the untreated alloy, confirming its better localized corrosion behavior. The high amount of interstitial carbon is believed to be responsible for the enhanced protective function of passive film which exerts an effective inhibiting action towards the localized corrosion process.

Measuring and understanding the critical duration and amplitude of anodic transients

ABSTRACTAnodic transients are known to affect buried pipeline cathodic protection (CP) systems; however, their actual effects on pipeline corrosion have not been sufficiently quantified due to the lack of direct experimental evidences. In this work, a novel methodology developed based on an electrochemically integrated multi-electrode array has been used to visualise the dynamic effects of anodic transients on localised corrosion processes occurring on buried steel surfaces. It is shown that anodic transients do not necessarily cause steel corrosion, as long as their amplitude and duration are below critical values. The electrode array is able to determine these critical values accurately due to its ability to detect localised corrosion initiation, while the conventional coupon electrode is only able to estimate these values. The critical anodic transient duration has been explained as the incubation period for the breakdown of passivity formed on the steel surface exposed to CP-generated high pH conditions.

In situ imaging of corrosion processes in nuclear fuel cladding

ABSTRACTSpent nuclear fuel in the U.K. is stored within ponds dosed with NaOH in order to inhibit corrosion and, to ensure the efficiency of storage regimes, there is a need to define and quantify the corrosion processes involved during immersion of fuel cladding. In this project, state-of-the-art characterisation techniques were employed to image the corroding surfaces of two nuclear fuel cladding materials: stainless steel and Magnox. Advanced gas-cooled reactor fuel cladding consists of 20Cr-25Ni-Nb stabilised stainless steel and during irradiation the microstructure of the cladding undergoes significant changes, including grain boundary element depletion and segregation. High-speed atomic force microscopy with nanoscale resolution, enabled precipitates and pit initiation in stainless steel to be imaged. Magnox is a magnesium–aluminium alloy and during irradiation in a reactor the outer metal surface oxidises, forming an adherent passive layer which subsequently hydrates when exposed to water. Corrosion processes encompass breakdown of passivity and filiform-like corrosion, both of which were imaged in situ using the scanning vibrating electrode technique.

Spatial Heterogeneities and Onset of Passivation Breakdown at Lithium Anode Interfaces

Effective passivation of lithium metal surfaces, and prevention of battery-shorting lithium dendrite growth, are critical for implementing lithium-metal-anodes for batteries with increased power densities. Nanoscale surface heterogeneities can be "hot spots" where anode passivation breaks down. Motivated by the observation of lithium dendrites in pores and grain boundaries in all-solid batteries, we examine lithium metal surfaces covered with Li(2)O and/or LiF thin films with grain boundaries in them. Electronic structure calculations show that, at >0.25 V computed equilibrium overpotential, L(2)O grain boundaries with sufficiently large pores can accommodate Li(0) atoms which aid electron leakage and passivation breakdown. Strain often accompanies Li-insertion, applying a ~1.7% strain already lowers the computed overpotential to 0.1 V. Lithium metal nanostructures as thin as 12 Angstroms are thermodynamically favored inside cracks in Li(2)O films, becoming "incipient lithium filaments." LiF films are more resistant to lithium metal growth. The models used herein should in turn inform passivating strategies in all-solid-state batteries.

(Olin Palladium Award of the Electrochemical Society Address) Corrosion Mechanisms at the Atomic or Nanometric Scale

In this Award Lecture I will emphasize a surface science approach that allows to reach a deep understanding of the mechanisms of corrosion at the atomic or nanometric scale. I will show the link between atomic/nanometric scale mechanisms and the macroscopic corrosion manifestations. The lecture will include the combined experimental approaches using advanced surface analytical and electrochemical methods with theoretical approaches based on atomistic modeling. The high resolution techniques used in combination with classical electrochemical methods will be presented, high resolution meaning high space resolution, as achieved by near field microscopies (Scanning Tunneling Microscopy and Atomic Force Microscopy), high energy resolution in electron spectroscopy for chemical analysis, and high mass resolution for surface molecular analysis by Time-of-Flight Secondary Ions Mass Spectrometry.The formation of the metal-water interface occurring when a metal surface is exposed to water, which has been investigated by in situ Scanning Tunneling Microscopy, will be presented.A major part of this address will be devoted to passivity of metals and alloys, a central issue in corrosion science and engineering since the formation of ultra-thin surface oxide films is the best of all means for protection of metallic materials against corrosion. I will discuss the growth mechanisms, the nanostructure, and the electronic properties of passive films, as well as passivity breakdown and initiation of localized corrosion, with emphasis on atomic and nanoscale data. Cathodic reactions on oxidized metal surfaces will then be discussed, with a theoretical approach of the di-oxygen reduction on surface oxide films on Al surfaces using DFT.Finally I will mention recent work on corrosion inhibition by adsorbed organic molecules, an area in which progress has been recently achieved by combining quantum chemical calculations (DFT) with experiments.

Challenges in the Measurement of Passive Dissolution of Steel in Concrete

The corrosion rate of the steel reinforcement of concrete is measured and monitored in laboratory and civil structures by various techniques that include anodic or cathodic galvanostatic pulse, linear polarization resistance (using a given polarization rate), electrochemical impedance spectroscopy, etc. Considerable attention has been given to the suitability of those methods to measure the corrosion rate of steel in the active state, after passivity breakdown due to aggressive species contamination. However, fewer studies have evaluated the case of service in structures with required durability much in excess of one hundred years (as for example containment of radioactive waste) where the corrosion process is expected to remain in passive state, with anodic current densities typically lower than 10-8 A/cm2. The electrochemical measurement of such low corrosion rates is a challenging goal as it is difficult to separate polarization currents due to interfacial charge storage processes (which may be of actual or apparent non-Faradaic origin) to those related to the anodic, metal dissolution process itself. That separation often leads to the need for long duration of the measurements, which would make it impractical to monitor a large number of reinforcement locations in an actual structure. Understanding of the relevant measurement factors is needed to eventually develop more time efficient assessment methods for those systems.As part of developing that understanding, the objective of this work is the experimental and modeling analysis of steel in concrete in the passive state, in response to the application of cathodic cyclic polarization with polarization rates in the order of 0.001 mV/sec and polarization down to -300 mV with respect to the (passive) corrosion potential. This technique, implemented with higher polarization rates after appropriate adjustment as a refined form of Tafel extrapolation, is a possible candidate to monitor structures of interest. In order to interpret the passive corrosion process response to polarization excitation, a modified Randles interphase model analog was used. A novel feature of this study is the introduction of large amplitude time domain behavior of a constant phase angle element, which is then combined with the large amplitude response of the Faradaic current treated with a Butler-Volmer approach. The system steel/interface/concrete is described by a fractional order differential equation that is solved by the implementation of a finite differences aproach. Comparisons between the experimental results from multiple specimens at various scan rates and the response calculated by solution of the equations of the system were made, showing good agreement between both. Corrosion current densities obtained by numerically fitting the model to experimental results yielded values typically lower than 10-8 A/cm2 in agreement with other values reported in the literature for long term exposures of passive steel in concrete. Open issues on the applicability of these results for mechanistic interpretation of the processes at work on the rate of passive dissolution of steel in concrete are discussed.

Differential Kelvin Probe Potential Mapping of Concrete for Reinforcing Steel Corrosion Assessment

Chloride induced corrosion of steel reinforcement in concrete seriously limits civil infrastructure durability. Chloride ion intrusion through the concrete cover causes local passivity breakdown of the embedded reinforcement. Activation of the steel is manifested by a local open circuit potential drop reflecting increased polarization of the cathodic reaction , usually oxygen reduction, to match the increase in anodic current density. Local potential can be measured using a conventional Copper/Copper Sulfate reference electrode (CSE) with its wet junction tip physically contacting the external concrete surface at points on a grid pattern. The metallic terminal of the CSE is connected to the negative terminal of a high input impedance potential meter; the other terminal of the potential meter is connected to a point of the normally interconnected reinforcing steel (rebar) assembly, reached through a hole drilled in the reinforced concrete. The potentials measured at the grid are mapped revealing the locations of more negative readings, thus providing a diagnostic indication of where corrosion is occurring so local remedial action can be taken on an informed basis. While very useful, this type of survey can be time consuming. Delays occur because adequate contact between the moist CSE tip and the electrolyte in the concrete pore network may require some form of moisturizing surface preparation, and some time for stabilization of diffusional potentials that were altered by intrusion of newly introduced electrolyte in the pore network near the concrete surface. Such delays can become prohibitive in surveys that involve hundreds or thousands of m2 of highway bridge deck, especially if it becomes necessary to temporarily close traffic lanes. A radically new approach to conduct surface potential surveys in reinforced concrete uses a scanning array of mobile, macroscopic Kelvin probes. The Kelvin Probe (KP) uses a vibrating metallic capacitor disk hovering, but not touching, close to the concrete surface. In a metallic disk - metal surface system the KP yields the value of the difference of the Volta potential of both surfaces, obtained by finding the value of the potential difference that need to be applied in a connecting disk-metal surface circuit to null out the capacitive alternating current that would otherwise circulate there. On concrete, the probe provides the difference between the Volta potential of the metallic disk and an averaged, effective Volta potential of the heterogeneous concrete surface beneath the disk footprint. Because no surface preparation or electrolyte exchange is needed, the KP provides nearly instantaneous readings and obviates the need for stabilization delays thus opening the way for fast and practical surveying of large structures. Recent investigations [1, 2] have shown that the surface potential map obtained with an appropriately scaled macroscopic KP successfully reproduced the key features of the maps obtained with the conventional method, indicating that the spatial variations in the effective Volta potential of the concrete (and identification of corroding regions) can be used instead of those provided by the CSE survey, but at a much faster scanning speed. Until now KP operation was demonstrated only with wired contact to the rebar assembly. This investigation examines a differential mode, where anode identification is made without need for a trailing wire rebar contact, Potential measurements used a scanning array of two KPs 0.4 m from each other with galvanized steel sensing disks 0.1 m in diameter placed 0.01 m above the surface of an ~2.4x2.4 m reinforced concrete slab. The probes operated at a vibrating frequency of ~0.15 kHz with vibration amplitude > 1mm. The steel reinforcement in the slab was segmentally polarized via externally impressed currents to create temporarily anodic regions ~ 0.2x0.6 m on the external concrete surface. Differential operation was achieved over the entire concrete grid by means of an auxiliary temporary reference electrode that established periodic contact with the concrete surface, but serving only as a provisional link between contactless KP measurements thus keeping the overall scheme referenced to the metal disks. The results confirmed the suitability of the differential operation scheme and were contrasted against results of replicating conventional electrode measurements. Implications on deployment of this technique in highway applications and extension to larger KP arrays are discussed and presented. [1] Sagüés. A. and Walsh, M. “Kelvin Probe electrode for contactless potential measurement on concrete – Properties and corrosion profiling application”, Corrosion Science, Vol 56, pp 26-35, 2012. [2] Sagüés. A. and Emmenegger, L. “Contactless Electrode for Fast Survey of Concrete Reinforcement Corrosion” Final report, NCHRP IDEA Project 176, Transportation Research Board, National Research Council, Washington, DC, 2017 (In Press).

Passivity breakdown on 300 M and S280 ultra-high strength steels in borate buffer solutions containing chloride ion

Passivity breakdown and the pitting behavior of ultra-high strength 300M and S280 steels, which are commonly employed for aircraft landing gear, in the presence of chloride has been explored and compared, and the data were interpreted using the point defect model (PDM). The breakdown behavior was studied using cyclic potentiodynamic polarization while SEM and digital confocal microscopy were employed to explore the micro morphology and depth distribution of pits. The cumulative distributions in the breakdown voltage are near-normal, which are consistent with the PDM, assuming the distributions of potential breakdown sites in terms of the cation vacancy diffusivity for different concentrations of chloride are normal. Compared to 300M, S280 steel exhibits shallower pitting and is more resistant to breakdown. From the potential scan rate dependence of the breakdown potential, the critical areal cation vacancy concentration, ξ, resulting in passivity breakdown, is 8.6×1013 No.cm−2 for 300M and 2.4×1013 No.cm−2 for S280. These values are structurally in close agreement with the calculated results, considering the vacancy condensation is either on the cation sublattice of the barrier layer or on the steels lattice.

Atomic level characterization in corrosion studies.

Atomic level characterization brings fundamental insight into the mechanisms of self-protection against corrosion of metals and alloys by oxide passive films and into how localized corrosion is initiated on passivated metal surfaces. This is illustrated in this overview with selected data obtained at the subnanometre, i.e. atomic or molecular, scale and also at the nanometre scale on single-crystal copper, nickel, chromium and stainless steel surfaces passivated in well-controlled conditions and analysed in situ and/or ex situ by scanning tunnelling microscopy/spectroscopy and atomic force microscopy. A selected example of corrosion modelling by ab initio density functional theory is also presented. The discussed aspects include the surface reconstruction induced by hydroxide adsorption and formation of two-dimensional (hydr)oxide precursors, the atomic structure, orientation and surface hydroxylation of three-dimensional ultrathin oxide passive films, the effect of grain boundaries in polycrystalline passive films acting as preferential sites of passivity breakdown, the differences in local electronic properties measured at grain boundaries of passive films and the role of step edges at the exposed surface of oxide grains on the dissolution of the passive film.This article is part of the themed issue 'The challenges of hydrogen and metals'.

The Influence of Chloride Ion Concentration on Passivity Breakdown in Magnesium

An empirically derived dependence of an apparent breakdown potential (Eb) of magnesium (Mg) on chloride ion concentration is reported. In situations where spontaneous breakdown in the absence of external polarization is observed, leading to the subsequent propagation of localized corrosion, Eb can be determined by following time-dependent changes in free corrosion potential (Ecorr). Breakdown of temporary passivity is marked by a clear inflection in the time-dependent value of Ecorr, characterized by a sharp decrease in potential from a maximum value where Ecorr = Eb. Characterization of localized corrosion behavior by in situ scanning vibrating electrode studies, prior to and following the point of breakdown, is used to explain the observed Ecorr vs. time characteristics. Examples of typical behavior upon immersion in aqueous solutions containing different chloride ion concentrations ([Cl−]) are given for commercially pure Mg and an AZ31 alloy. For high purity Mg, which remains passive at pH 11 at all ch...

Threshold Chloride Concentrations and Passivity Breakdown of Rebar Steel in Real Concrete Solution at Different pH Conditions with the Addition of Glycerol

Addition of glycerol as a viscosity modifier in concrete is proposed to decrease the permeability of corrosion-inducing ions such as chloride and sulfate. In addition to controlling the permeability of concrete, glycerol could perform as an inhibitor of corrosion of rebar steel. Cyclic polarization studies were carried out on metallographically polished rebar steel specimens in actual concrete solutions at two different pH conditions (pH 12.5 and 9.0) and different chloride concentrations. The threshold concentration of chloride for passivity breakdown at pH 12.5 was greater than 50 × 10−3 mol/L in the absence of glycerol addition. The threshold increased to 81 × 10−3 mol/L upon addition of 2 wt% glycerol. The threshold chloride concentration for passivity breakdown in pH 9.0 cement solution was 0.2 × 10−3 mol/L without glycerol addition. No beneficial effect of glycerol was observed in the low pH condition. However, glycerol enhanced the passivation kinetics of the rebar steel in saturated cement solution, but did not affect the electronic properties of the passive layer. The passive layers exhibited n-type semiconductivity with a charge carrier density in the range of 2–7.5 × 1020 cm−3. Polarization of the specimens to potentials is higher than oxygen evolution potential, resulted in transition top-type semiconducting character due to an accumulation of holes. This phenomenon could be related to the passivity breakdown.

Threshold Chloride Concentration for Passivity Breakdown of Mg–Zn–Gd–Nd–Zr Alloy (EV31A) in Basic Solution

Mg–Zn–Gd–Nd–Zr alloy (EV31A) is a heat-treatable magnesium (Mg) cast alloy that can be used up to 200 °C for automobile and aerospace applications. This alloy has excellent mechanical properties (ultimate tensile strength: 280 MPa at room temperature, and ~230 MPa at 200 °C) and improved corrosion resistance. Electrochemical corrosion studies were conducted on this alloy under different heat treatment conditions in 0.1 M NaOH solution with the addition of 0–1000 ppm of chloride. The alloy showed excellent passivity in the 0.1 M NaOH solution. The passive potential range typically extended to more than 1.2 VAg/AgCl. The transpassive potential was observed to be dependent on heat treatment condition of the alloy. More than 80 ppm of chloride was required to induce passivity breakdown in any heat treatment condition. Peak aging at 200 °C for 16 h imparted better resistance for localized corrosion than other heat-treated conditions. The alloy in the as-received condition showed the highest passivation kinetics due to its smaller grain size that possibly increased the diffusion of reactive elements to form protective oxide. The passive film of the EV31A alloy showed n-type semiconductivity with a charge carrier density of ~2 × 1021 cm−3 with no chloride addition. The charge carrier density increased with chloride addition in the electrolyte which could be correlated with the susceptibility to localized corrosion.

Factors Influencing Passivity Breakdown on UNS N08800 in Neutral Chloride and Thiosulfate Solutions

In this work, the passivity degradation of UNS N08800 in solutions containing Cl− and S2O32− is studied by using polarization curve, electrochemical impedance spectroscopy (EIS), and X-ray photoelectron spectroscopy (XPS). Experimental results reveal that the passivity breakdown heavily depends on anodic potentials, concentration ratios of Cl− to S2O32−, and the composition of materials. A combined effect between Cl− and S2O32− on pitting corrosion is observed at high anodic potentials at which the passive film is broken down; in this situation, S2O32− ions can enter into the pits by electromigration, and they are reduced to Sads and S2−, stabilizing the metastable pits and accelerate the pit growth rate. However, there is no such combined effect at low anodic potentials when the passive film is intact, on the contrary, S2O32− is beneficial to passivity in chloride solutions. At low anodic potentials, the interaction of S2O32− with an intact passive layer is weak, and the adsorption of S2O32− would mitigate the detrimental effect of Cl− ions.

Electrochemical characterization of vascular bare-metal stents. A novel approach modifying the mini-cell system

Electrochemical characterization of stents can be seen as a key to assessing their biocompatibility. The aim of the present study was to investigate the electrochemical properties of bare-metal stent surfaces. The minicell system (MCS) was modified to record open circuit potential (OCP), cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) on NiTi, FeCrNi and CoCr stents using 1%NaCl, PBS and serum. Surfaces were examined by scanning electron microscopy (SEM) and energy-dispersive X-ray microanalysis (EDX) before and after electrochemical testing. CV showed passivity breakdown of FeCrNi and CoCr in 1%NaCl. Corrosion properties were inhomogeneous. Several surfaces of FeCrNi showed progressive activation and passivity breakdown while pitting was detected by SEM. EDX showed a decrease in Fe, Cr and Ni and an excessive presence of Cl. Corrosion rates (vcorr) were partially significantly different between the examined materials and electrolytes (e.g. using 1%NaCl: vcorr[FeCrNi]=2.08x10-2±1.14x10-2μm/y vs. [NiTi]=9.41x10 -3 ±1.87x10 -3 μm/y; p<0.001). EIS circuit diagrams indicated oxide films on passivated metal surfaces. The modified MCS is promising to assess the biocompatibility of stents via electrochemical analytics. Overall, the vcorr of all stents were below the required limit values.

Anodic dissolution behavior of zirconium in Bun4NBr-containing isopropanol solution

Anodic dissolution behavior of zirconium in Bun4NBr-contaning isopropanol solution was investigated using cyclic voltammetry, linear sweep voltammetry and chronoamperometry, complemented with a scanning electron microscope (SEM). The voltammograms did not exhibit active dissolution until the breakdown of passive layer induced by aggressive bromide anions. SEM images confirmed the existence of pits on zirconium surface. The depth and breadth of pits were intensified with increasing potential. The pitting potential shifted negatively as either temperature or Bun4NBr concentration was increased, while it increased with increasing scan rate. The corrosion current density increased with increasing temperature. The apparent activation energy of anodic dissolution of zirconium was 21.88 kJ/mol. The chronoamperometry revealed that increasing Bun4NBr concentration shortened the incubation time for passivity breakdown and accelerated the pit nucleation and growth. The experimental results were helpful to obtain the optimum conditions for electrosynthesis of zirconium isopropoxide.

(Keynote) Recent Progress in Nanoscale Understanding of Surface Oxide Film Formation, Properties and Breakdown on Metals and Alloys Using in Situ and Ex Situ Characterization Methods

After a short historical introduction in recognition to the pioneering work of Masahiro Seo, recent advances in the understanding at the nanoscale of the formation, properties and breakdown of oxide films on metals and alloys will be presented, with emphasis on data obtained using advanced in situ and ex situ surface analytical techniques such as Scanning Tunneling Microscopy (STM), Scanning Tunneling Spectroscopy (STS),Current-Sensing Atomic Force Microscopy (CS-AFM), X-ray Photoelectron Spectroscopy (XPS), and Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS), combined with electrochemical measurements, and complemented by atomistic modelling with Density Functional Theory (DFT). The following topics will be addressed: Nanostructured oxide layers formed by controlled thermal oxidation of copper single crystal surfacesPassive oxide films for corrosion protection of metals and alloys: crystallinity, oxide/metal epitaxy, effects of time of polarization on oxide crystallinity, compositional heterogeneity of surface oxides (in the case of stainless steel)Role of surface oxide defects in passivity breakdown and initiation of localized corrosion, investigated with high resolutionOxide layers deposited by ALD (Atomic Layer Deposition) for corrosion protection, and as model systems for the study of conversion-deconversion mechanisms in Li-ion batteriesAtomistic modelling of oxide layers on metals using density functional theory (DFT)

A Comparison of Potentiodynamic and Potentiostatic Electrochemical Test Methods for Resolving the Localized Corrosion Response of Heat Treated Al-Li-Cu Alloy 2099

The corrosion mechanisms for 3rd generation Al-Li-Cu alloy AA2099 were characterized based on the localized attack on the microstructure. Samples were subjected to a series of artificial heat treatments conducted at temperatures ranging from 120°C to 180°C for times ranging from 12 to 168 hours. The varying microstructures were analyzed using transmission electron microscopy (TEM) and electron diffraction spectroscopy (EDS), which characterized the secondary phase precipitates grown during artificial aging. The formation of the strengthening phase T1 (Al2CuLi) is of particular note due to its anodic behavior relative to the alloy matrix. This particle is prone to selective dissolution and dealloying and can dictate the morphology of localized corrosion depending on how it is distributed within the alloy. Localized corrosion was induced via individual immersion tests that utilized a highly oxidizing NaCl/H2O2 aqueous solution. The extent and morphology of the corrosion was assessed by optical microscopy. Results showed that pitting attack was apparent on samples aged at lower temperatures and/or for shorter times, when growth of secondary phase precipitates is hindered. Intergranular corrosion (IGC) was observed for the time-temperature combinations that promoted such precipitate growth. As revealed from TEM analysis, these samples showed T1 precipitates localized along grain boundaries. However, as samples continued to age and T1 formation became prevalent in the matrix, IGC was reduced. This is attributed to a smaller potential difference between grain boundary T1 and the surrounding area. Potentiodynamic experiments were then performed to identify any change in the localized breakdown potentials among the heat treated samples. It was shown that the specimens susceptible to IGC displayed a lower breakdown potential than those susceptible to only pitting. Additional electrochemical tests were performed to capture the transition from pitting to IGC and determine whether the transition is potential-dependent, time-dependent or a combination of both. Unlike other Al-Cu alloys scanned potentiodynamically through the region of passivity breakdown, AA2099 did not display a double breakdown potential that would have indicated separate breakdown events for pitting and IGC. However, potentiostatic tests conducted after the onset of pitting showed that this transition can be captured based on the total charge imparted on the alloy. Samples that exhibited the most severe IGC via the immersion tests required the smaller amount of imparted charge to initiate IGC from pits. This demonstrates that the progression from pitting to IGC is marked by a distinct temporal component.