Gildes model studies of aqueous chemistry. II. The corrosion of zinc in gaseous exposure chambers

The GILDES model has been used to perform the first theoretical mechanistic study of the atmospheric corrosion of zinc in a controlled environment. Detailed comparisons are made of model results with laboratory data for short-term (0–1000 min) and long-term (0–680 h) exposures of zinc to SO₂, NO₂ and O₃ at high relative humidities. The agreement of theory and experiment is excellent, indicating that the model has captured the principal processes (especially ligand-promoted dissolution) involved in the corrosion of zinc under these conditions.     

Gildes model studies of aqueous chemistry. I. Formulation and potential applications of the multi-regime model

A six-regime computer model (Gas, the Interface between gas and liquid, the Liquid, the Deposition layer, the Electrodic region near the surface (for conducting and semiconducting solids), and the Solid) has been developed for the exploration of the chemistry of metal or metal oxide surfaces covered by a layer of water and exposed to the atmosphere. Aspects of relevant physicochemical processes are discussed for each of the regimes, with special attention given to kinetics. The applicability of the model to the following situations is discussed: indoor and outdoor corrosion of metal surfaces, thin film electrochemistry, metal chemistry in ocean photic zones, metal chemistry in lakes and rivers, and the chemistry of ice-coated surfaces.     

Initial NaCl-particle induced atmospheric corrosion of zinc—Effect of CO2 and SO2

Initial corrosion and secondary spreading effects during NaCl particle induced corrosion on zinc was explored using in situ and ex situ FTIR microspectroscopy, optical microscopy, and SEM/EDAX. The secondary spreading effect which occurs upon introduction of humid air on NaCl deposited zinc surfaces was strongly dependent on the CO₂ and SO₂ content of the introduced air. Ambient level of CO₂ (350 ppm) resulted in a relatively low spreading effect, whereas the lower level of CO₂ (<5 ppm) caused a much faster spreading over a larger area. In the presence of SO₂, the secondary spreading effect was absent which could limit the cathodic process in this case. At <5 ppm CO₂, the corrosion is more localized, with the formation of simonkolleite (Zn₅(OH)₈Cl₂ · H₂O), zincite (ZnO) and sodium carbonate (Na₂CO₃), and a larger effective cathodic area. At 350 ppm CO₂, the corrosion is more general and formation of simonkolleite, hydrozincite (Zn₅(OH)₆(CO₃)₂) and sodium carbonate was observed. Sodium carbonate was mainly formed in more alkaline areas, in the inner edge of the electrolyte droplet and in the secondary spreading area. Oxidation of sulphur and concomitant sulphate formation was enhanced in the presence of NaCl particles, due to the formation of a droplet, the separation of the anodic and cathodic areas and the accompanying differences in chemical composition and pH in the surface electrolyte.     

Effect of unusually elevated SO2 atmospheric content on the corrosion of high power electrical conductors - Part 3. Pure copper

This research work belongs to a series of studies simultaneously performed with two previous publications in this journal as Part I. Al and 6201 Al alloy and Part 2. Pure copper. The aim of the project was to have a comparative picture of the joint effect of marine and industrial atmospheric pollutants on the corrosion resistance of wire metals employed for high power electric transmission. This one is also based on the pure Cu behaviour, but limited to six marine-industrial atmospheres with extremely high SO₂ contents. The interest in this study was triggered by unusual results considered appropriate to investigate. Weight loss after 4 and 11 months exposure was determined and morphology of the attack was analysed through SEM-ESEM-EDX. Polarisation of samples after exposure to all the test sites as compared to bare Cu clarified the effect of unusually high SO₂ pollutant contents in these atmospheres on the high protectiveness of the corrosion products formed.     

Effect of atmospheric pollutants on the corrosion of high power electrical conductors - Part 2. Pure copper

The research work performed during this study was simultaneously followed with another one published in this journal as Part I. A1 and 6201 A1 alloy. Its aim was to reveal a comparative picture of the joint effect of marine and industrial atmospheric pollutants on the corrosion resistance of wire metals employed for electric transmission conductors. Weight loss after 4, 11, 16 and 24 months exposure was determined and morphology of the attack analysed through SEM-ESEM-EDX. Cu corrosion products showed higher protectiveness than those of Al in marine sites for the lowest [Cl⁻] and in marine-industrial atmospheres even for the highest SO₂ contents. Respect to marine sites where [Cl⁻] was higher than [SO₂] Cu was more susceptible than A1.     

The chemistry of copper patination

The chemistry of copper patination was investigated by two series of experiments. The chemistry of an aqueous copper-sulphate solution was studied at concentrations and pH values near those predicted in an electrolyte on copper exposed to the atmosphere. The electrochemical reactions in an electrolyte in contact with cuprite were investigated in a reaction vessel which used cuprite powder in artificial rainwater to study the electrochemistry of the atmospheric corrosion and patination of copper. Typical sulphate concentrations in rainwater are sufficient to precipitate posnjakite (Cu₄SO₄ (OH)₆2H₂O)), a possible precursor to brochantite, within an hour of wetting a cuprite surface. Brochantite (Cu₄SO₄ (OH)₆), the most commonly found copper salt in natural patinas is responsible for their green appearance. Precipitation of brochantite from the electrolyte resulted from an increase in pH due to the cathodic reduction of oxygen and an increase in cupric ion concentrations by cuprite oxidation.     

Inverse Gaussian process-based corrosion growth model for energy pipelines considering the sizing error in inspection data

This paper describes an inverse Gaussian process-based model to characterize the growth of the depth of corrosion defects on underground energy pipelines based on inspection data. The model is formulated in a hierarchical Bayesian framework, which allows consideration of uncertainties from different sources. The Markov Chain Monte Carlo (MCMC) simulation techniques are used to evaluate the probabilistic characteristics of the model parameters by incorporating the defect depths reported by multiple in-line inspections (ILIs) as well as the prior knowledge about these parameters. The bias and random scattering error associated with the ILI tool as well as the correlation between the random scattering errors associated with different ILI tools are considered in the analysis. An example involving real ILI data collected from an in-service pipeline is employed to illustrate the application of the growth model. The results indicate that the model in general can predict the growth of corrosion defects reasonably well. The proposed model can be used to facilitate the development and application of reliability-based pipeline corrosion management.     

Long-term atmospheric corrosion of mild steel

A great deal of information is available on the atmospheric corrosion of mild steel in the short, mid and even long term, but studies of the structure and morphology of corrosion layers are less abundant and generally deal with those formed in just a few years. The present study assesses the structure and morphology of corrosion product layers formed on mild steel after 13 years of exposure in five Spanish atmospheres of different types: rural, urban, industrial and marine (mild and severe). The corrosion layers have been characterised by X-ray diffraction (XRD) and scanning electron microscopy/energy dispersive X-ray spectroscopy (SEM/EDS). Long-term corrosion is seen to be more severe in the industrial and marine atmospheres, and less so in the rural and urban atmospheres. In all cases the corrosion rate is seen to decrease with exposure time, stabilising after the first 4–6 years of exposure. The most relevant aspects to be noted are (a) the great compaction of the rust layers formed in the rural and urban atmospheres, (b) the formation of hematite and ferrihydrite phases (not commonly found) in the industrial and marine atmospheres, respectively and (c) identification of the typical morphological structures of lepidocrocite (sandy crystals and flowery plates), goethite (cotton balls structures) and akaganeite (cotton balls structures and cigar-shaped crystals).     

Accelerated corrosion of MoO3-deposited copper

The accelerated oxidation kinetics of MoO₃-deposited copper were studied in the temperature range of 480–700 °C in air. The accelerated oxidation followed the parabolic-rate law, indicating that the process was diffusion-controlled. Oxygen diffusion along liquid channels in the oxide scale was inferred to be the rate-limiting step in the overall mechanism. The rate constant increased from 9.2 × 10⁻⁶ to 3.8 × 10⁻⁵ kg² m⁻⁴ s⁻¹ with increasing the deposit mass from 0.3 to 0.9 kg m⁻² at 700 °C.     

High-temperature SO2-gas corrosion of TiN–Ti5Si3 composites prepared by polymer pyrolysis

By pyrolyzing a mixture of Si-containing pre-ceramic polymers and TiH₂ powders in a N₂ atmosphere, a TiN–Ti₅Si₃ composite was synthesized. The composite was then corroded between 700 °C and 1000 °C for 20 h in an Ar–0.2% SO₂ atmosphere. TiN was mainly oxidized to rutile TiO₂. Ti₅Si₃ was oxidized to TiO₂ supersaturated with Si ions, and sulfidized to Ti₂S supersaturated with Si ions. At initial stage of corrosion, oxidation dominated sulfidation. As corrosion proceeded, sulfidation progressively occurred underneath the oxide scale based on the decreased oxygen potential and increased sulfur potential near the scale/matrix interface.     

Field studies of corrosion behaviour of copper alloys in natural seawater

Eight copper alloys were tested in a one-year field deployment in the North Atlantic Ocean. The corrosion behaviour was characterized by weight loss, optical and electronic microscopy analyses. The biofouling performance was quantified in terms of the biomass accumulation. The testing program included specimens in tensioned and untensioned configurations, as well as a set for seasonal deployments. The seasonal corrosion rates were 140% higher, and the rates of tensioned specimens were 39% higher than those of the untensioned specimens after 12 months of deployment. Good biofouling resistance was observed for all but one alloy, which exhibited heavy fouling by barnacles.     

Applicability of constant dew point corrosion tests for evaluating atmospheric corrosion of aluminium alloys

Field exposure tests of aluminium alloys were conducted at three sites in Japan. Meteorological data indicated that the dew point of the ambient atmosphere and aluminium panels remained constant for the short-term. Constant dew point corrosion tests were employed to reproduce atmospheric corrosion of aluminium alloys in the laboratory. The corrosion rates, corrosion morphology and corrosion product composition after 7 days of tests in the laboratory were similar to those formed after 3 months of exposure at coastal sites. Not only did the constant dew point corrosion test effectively reproduce the atmospheric corrosion of aluminium alloys, it also accelerated it.     

Copper corrosion inhibition in O2-saturated H2SO4 solutions

Corrosion inhibition of copper in O₂-saturated 0.50 M H₂SO₄ solutions by four selected amino acids, namely glycine (Gly), alanine (Ala), valine (Val), or tyrosine (Tyr), was studied using Tafel polarization, linear polarization, impedance, and electrochemical frequency modulation (EFM) at 30 °C. Protection efficiencies of almost 98% and 91% were obtained with 50 mM Tyr and Gly, respectively. On the other hand, Ala and Val reached only about 75%. Corrosion rates determined by the Tafel extrapolation method were in good agreement with those obtained by EFM and an independent chemical (i.e., non-electrochemical) method. The chemical method of confirmation of the corrosion rates involved determination of the dissolved Cu²⁺, using ICP-AES (inductively coupled plasma atomic emission spectrometry) method of chemical analysis. Nyquist plots exhibited a high frequency depressed semicircle followed by a straight line portion (Warburg diffusion tail) in the low-frequency region. The impedance data were interpreted according to two suitable equivalent circuits. The kinetics of dissolved O₂ reduction and hydrogen evolution reactions on copper surface were also studied in O₂-saturated 0.50 M H₂SO₄ solutions using polarization measurements combined with the rotating disc electrode (RDE). The Koutecky-Levich plot indicated that the dissolved O₂ reduction at the copper electrode was an apparent 4-electron process.     

Hydrogen evolution in aqueous solutions containing dissolved CO2: Quantitative contribution of the buffering effect

The hydrogen evolution reaction (HER) occurring on steel in an oxygen-free aqueous solution containing dissolved CO₂ was investigated. This reaction was modelled by taking into account the two dissociation reactions of dissolved CO₂. The mathematical problem was solved numerically using a finite element method (FEM). A fair agreement between the measurements performed on a steel rotating disc electrode and the theoretical calculations was obtained. Thus, the cathodic behaviour of steel in CO₂-containing solutions can be fully explained by the buffering effect induced by the presence of CO₂. Some interfacial pH measurements performed on a gold electrode also support this conclusion.     

Quantitative determination of corrosion products and adsorbed water on copper in humid air containing SO2 by IR-RAS measurements

The time dependency of the amounts of corrosion products and co-existing adsorbed water on copper in humid air containing SO₂ was estimated from a series of in situ time-resolved IR-RAS spectra on the basis of the relations between the band intensities and the mass changes of the corrosion products, which were determined by simultaneous measurement of IR-RAS and QCM. The amounts of both corrosion products increased slowly at the initial stage and later increased rapidly. Although the relative humidity was kept constant, the amount of adsorbed water increased nearly the same behavior as that of corrosion products in the stage of relatively small amounts of corrosion products and later increased rapidly when the amounts of corrosion products increased. In humid air without SO₂, sulfite gradually decomposed and some of it changed into sulfate.     

A general model for the repassivation potential as a function of multiple aqueous species. 2. Effect of oxyanions on localized corrosion of Fe–Ni–Cr–Mo–W–N alloys

A recently developed model for predicting the repassivation potential has been applied to stainless steels and nickel-base alloys in aqueous environments containing chlorides and various inhibiting anions. The model accounts for the effects of solution chemistry and temperature on the repassivation of localized corrosion by considering competitive dissolution, adsorption, and oxide formation processes at the interface between the metal and the occluded site solution. An extensive database of repassivation potentials has been established for six alloys (UNS 31603, N06600, N06690, S31254, S32205, and UNS S41425) in contact with solutions that combine chlorides with hydroxides, molybdates, vanadates, sulfates, nitrates, and nitrites at various concentrations and temperatures. Also, repassivation potentials are reported for four alloys (UNS N08367, N08800, N06625, and N10276) in chloride solutions. The database has been used to establish the parameters of the model and verify its accuracy. The model quantitatively predicts the transition between concentrations at which localized corrosion is possible and those at which inhibition is expected. It is capable of predicting the repassivation potential over wide ranges of experimental conditions using parameters that can be generated from a limited number of experimental data. The parameters of the model have been generalized as a function of alloy composition, thus making it possible to predict the repassivation potential for alloys that have not been experimentally investigated.     

Effect of direct current electric field on atmospheric corrosion behavior of copper under thin electrolyte layer

A thin layer electrochemical cell was successfully developed to study the atmospheric corrosion behavior of copper film in printed circuit board (PCB-Cu) under thin electrolyte layer (TEL) and direct current electric field (DCEF) by electrochemical impedance and electrochemical noise analysis. The electrochemical measurements and SEM morphologies after corrosion test indicate that DCEF decreases the corrosion of PCB-Cu under TEL. The corrosion rate and probability of pitting corrosion of PCB-Cu under DCEF decrease due to the electric migration of aggressive Cl⁻ ion out of working electrode surface.     

A cellular automaton model for predicting intergranular corrosion

The cellular automata (CA) methodology is applied to the case of intergranular corrosion. Appropriate CA rules are generated which can reproduce and predict the advance of a corrosion front. The proposed model shows qualitative and quantitative agreement with experimental intergranular corrosion data obtained from an aluminium AA2024 alloy in chloride solutions.     

The effect of molybdenum on the corrosion behaviour of the high-entropy alloys Co1.5CrFeNi1.5Ti0.5Mox in aqueous environments

The purpose of this study is to investigate the electrochemical properties of the Co_1.5CrFeNi_1.5Ti_0.5Mo_x high-entropy alloys in three aqueous environments which simulate acidic, marine, and basic environments at ambient temperature (∼25 °C). The potentiodynamic polarisation curves of the Co_1.5CrFeNi_1.5Ti_0.5Mo_x alloys, obtained in aqueous solutions of H₂SO₄ and NaOH, clearly revealed that the corrosion resistance of the Mo-free alloy was superior to that of the Mo-containing alloys. On the other hand, the lack of hysteresis in cyclic polarisation tests and SEM micrographs confirmed that the Mo-containing alloys are not susceptible to pitting corrosion in NaCl solution.