Pit Growth Rate Research Articles

Crystallographic Pit Growth on Aluminum (100)

Crystallographic pits were grown on Al(100) at temperatures from 30 to 90°C, in solutions of Pits grew during a galvanostatic anodic pulse for 5-100 ms that was preceded by a galvanostatic cathodic pulse of 50 ms. The anodic potential has a small peak for 1-2 ms and then remains constant. The cathodic pulse causes rapid pit nucleation so most pits nucleate within 5 ms, and pit passivation and pit growth are the dominant processes at longer times. It was determined that a substantial fraction of pits passivates during the pulse, so growth rates were calculated from the increase in largest pit size with pulse duration. The growth rate is constant at each temperature and follows an Arrhenius temperature dependence with an activation energy of There are significant differences between the growth of pits and the growth of etch tunnels. The activation energy for pit growth is one-half that for tunnel growth, and pit growth rates are greater than tunnel growth rates. It is proposed that the chemisorbed chloride complex postulated to be an intermediary for Al dissolution changes from one structure during pit growth to another, more stable, structure during tunnel growth. © 2004 The Electrochemical Society. All rights reserved.

Stochastic approach to the pit growth kinetics of Inconel alloy 600 in Cl − ion-containing thiosulphate solution at temperatures 25–150 °C by analysis of the potentiostatic current transients

The pit growth kinetics of Inconel alloy 600 in aqueous 0.1 M Na 2S 2O 3 + 0.1 M NaCl solutions was investigated as a function of solution temperature by analysis of the potentiostatic current transient, based upon a stochastic theory. Potentiostatic current transients revealed that time necessary for pit embryo formation, t pit,form decreased with increasing solution temperature. Analysis of the statistical distribution of t pit,form demonstrated that the pit embryo formation rate function at higher solution temperature exhibits a weaker dependence on exposure time compared with that at lower solution temperature. This is attributable to the increase in the active sites necessary for pit embryo formation due to the increase of the defects in oxide film grown at higher solution temperature. Moreover, it was found that the rate of pit growth decreased with increasing solution temperature over the whole applied potential range. Based upon the experimental findings, the kinetics of pit growth with respect to solution temperature is discussed in terms of the changes of the shape parameter derived from the stochastic theory, the pit growth rate parameter determined from the logarithmic potentiostatic current transient and fractal dimension of the pits formed on the electrode surface.

Pitting Corrosion Control of Aluminum 2024 Using Protective Biofilms That Secrete Corrosion Inhibitors

Abstract The corrosion behavior of Al 2024-T3 (UNS A92024) exposed to artificial seawater (AS) and Luria Bertani (LB) medium has been studied using electrochemical impedance spectroscopy (EIS). Tests were performed in sterile media and in the presence of three different biofilm-forming bacteria: a Bacillus subtilis biofilm that was genetically engineered to produce either polyaspartate or polyglutamate, a Bacillus licheniformis bacterial biofilm that naturally produces γ-polyglutamate, and an Escherichia coli biofilm that was genetically engineered to produce polyphosphate. A significant reduction in active pit growth rates and an ennoblement of the corrosion potential (Ecorr) were observed in both media in the presence of these biofilms, which produce corrosion inhibitors. The lowest corrosion rates of Al 2024 exposed to the LB medium were observed in the presence of the B. subtilis bacterial biofilm-producing polyaspartate and the E. coli bacterial biofilm that produced polyphosphate. In the presence of...

Corrosion Control Using Regenerative Biofilms on Aluminum 2024 and Brass in Different Media

The corrosion behavior of Al 2024-T3 and C26000 brass exposed to artificial seawater and Luria Bertani medium has been studied using electrochemical impedance spectroscopy. Tests were performed in sterile media and in the presence of three strains of bacteria. A Bacillus subtilis biofilm was genetically engineered to produce polyaspartate or polyglutamate, a B. licheniformis biofilm naturally produced the anionic polymer γ-polyglutamate, and E. coli was genetically engineered to produce polyphosphate. A significant reduction of active pit growth rates and an ennoblement of the corrosion potential were observed for Al 2024 in both media in the presence of the biofilms. The lowest corrosion rates of Al 2024 exposed to LB medium were observed in the presence of the B. subtilis bacterial biofilms producing polyaspartate and the E. coli bacterial biofilm producing polyphosphate in which was more positive by about 400 mV than in the sterile solution. A significant reduction of corrosion rates and an ennoblement of were also observed for brass in both media in the presence of the biofilms. Samples exposed in the presence of biofilms remained untarnished and unattacked for time periods exceeding one week, while samples exposed in the sterile solutions were covered with a dark film of corrosion products. © 2002 The Electrochemical Society. All rights reserved.

The aspect ratio of surface grooves and metastable pitting of stainless steel

The metastable pitting behavior of 316L stainless steel with different surface roughness in 0.01 M NaCl solution was studied using potentiostatic and potentiodynamic polarization methods and statistical treatments. As surface roughness decreased, the nucleation rate of metastable pits decreased. The peak current of metastable pits also decreased, but the average growth rate of metastable pits showed a slight increase. The aspect ratio of surface groove, w/ d, was suggested to characterize the openness of surface grooves, in which w is the width of the groove at the opening and d the depth of the groove. Bigger w/ d value indicates more smooth surface, and it is more difficult for micro-pit to nucleate. Under certain conditions of solution and potential, there is a critical w/ d value. Metastable pits may nucleate only on those surfaces whose w/ d values are less than the critical value. As the aspect ratio w/ d increases, the nucleation rate of metastable pits decreases linearly, and both metastable pitting potential E m and pitting potential E p move in the positive direction.

Kinetics of C−NO and C−N2O Reactions

Apparent turnover frequency (TOF) rates for the C−NO reaction were calculated on the basis of overall rates measured for three graphite samples with different dimensions at various temperatures (500−750 °C) and partial pressures. These TOF rates were rates per edge site on the edges of the crystals. The TOF rates were also determined for one of these graphites for the C−N2O reaction. Temperature breaks on the Arrhenius plots were observed for the C−NO reaction while no such temperature break was observed in TOF rates measured by directly following the etch pit growth rates (using STM). The temperature break phenomenon is attributed to pitting (and the ensuing pit growth) by O atoms dissociated from NO. The TOF rates appeared to be inversely proportional to the basal plane crystal size. This result was attributed to the steps and defects that also contributed significantly to the overall rates.

Nanometer-Size Monolayer and Multilayer Molecule Corrals on HOPG: A Depth-Resolved Mechanistic Study by STM

Surface defects on highly oriented pyrolytic graphite (HOPG) were controllably produced by bombardment with Cs+ ions at various incident kinetic energies ranging from 0.3 to 10 keV and at various dose densities. Defects in the HOPG created by Cs+ ion impacts were subsequently oxidized at 650 °C in air to produce nanometer-size monolayer and multilayer molecule corrals (pits). The controlled production of both monolayer and multilayer pits on HOPG bombarded with energetic Cs+ ions was realized and studied by scanning tunneling microscopy (STM). The pit density, pit yield, pit diameter, and pit depth can be well controlled by varying the experimental conditions. Multilayer pits can be controllably produced using Cs+ ion bombardment at higher kinetic energies, and monolayer pits can be produced using low-energy Cs+ ion bombardment. The presence of both monolayer and multilayer pits on the same HOPG samples makes the direct comparison of pit growth rates possible under exactly the same conditions. The measure...

Development of a Method for Corrosion Fatigue Life Prediction of Structurally Loaded Bearing Steels

In this study a simplified method to predict corrosion fatigue properties for the Cr-alloyed bearing steel 100CrMnMo8 is proposed. With this method corrosion pits are assumed to act as defects, which could initiate fatigue cracks. A linear elastic fracture mechanics (LEFM) model was used to evaluate the critical corrosion pit size when mechanical fatigue crack propagation occurred. The unknown parameters in the prediction model were corrosion pit growth rate and the threshold stress intensity factor (ΔKth) for fatigue crack growth. In this study corrosion pit growth rate was determined for 100CrMnMo8 in a chloride-containing water solution by aid of a statistical method. Corrosion pit growth rate was found to be approximately proportional to the square root of time. The time dependence of corrosion pit growth led also to the conclusion that characterization of corrosion fatigue strength must be made with respect to both exposure time in a corrosive environment and the number of cycles to a runout level. ΔKth for fatigue crack growth was estimated from interrupted rotating bending fatigue tests in the corrosive environment in question. Since only the corrosion pit growth rate and ΔKth are needed as input in the proposed corrosion fatigue prediction model, much effort can be saved since this can reduce the amount of fatigue testing. Corrosion pit growth rate can be determined on unloaded test coupons in the desired environment. Hence, for materials selection, exposure tests followed by a corrosion pit size analysis can indicate the corrosion fatigue performance in a given environment.

Effects of Hydrogen on Disorder of Passive Films and Pitting Susceptibility of Type 310 Stainless Steel

The effects of hydrogen in type 310 stainless steel on the disorder of passive films and pitting susceptibility have been investigated. It is found that hydrogen decreases the breakdown potential, facilitates the pitting initiation and increases the pit density and growth rate. The passive films are found to exhibit n-type semiconductivity. Observed hysteresis in the capacitance-potential curve and Urbach tail in the photocurrent spectra indicate that the passive films are highly defective. Hydrogen increases the disorder of the passive films, which is one of the reasons that hydrogen increases the pitting susceptibility. © 2000 The Electrochemical Society. All rights reserved.

Activation of pure Al in an indium-containing electrolyte — an electrochemical noise and impedance study

The activation of aluminium in an acidic indium-containing electrolyte has been studied using electrochemical noise measurements. The average pit-growth rate, measured under freely corroding conditions, was comparable in the presence and absence of indium. However, pit growth times were considerably higher in the presence of indium. The initial breakdown process followed a pseudo-first order process with a rate constant almost a factor of two greater in the case of the indium-containing solution. Analyses of the current–noise data in the frequency domain yielded spectral noise plots, which agreed well with impedance spectra measured under similar conditions. Good agreement was also obtained between R n , which is defined as the ratio of the standard deviation in the potential noise signal to the standard deviation of the current noise signal, and the zero frequency limit of the impedance.

Effects of sulphate ion additives on the pitting corrosion of pure aluminium in 0.01 M NaCl solution

Effects of sulphate (SO 4 2−) ion additives on the pitting corrosion of pure aluminium (Al) have been investigated in aqueous 0.01 M NaCl solution as a function of SO 4 2− ion concentration using potentiodynamic polarisation experiment, ac impedance spectroscopy, electrochemical quartz crystal microbalance technique and abrading electrode technique. The addition of SO 4 2− ions to NaCl solution raised the pitting potential ( E pit) of pure Al in value and simultaneously the anodic current density at potentials much higher than the E pit on the polarisation curves. This implies that SO 4 2− ions impede the initiation of pit on pure Al surface below the E pit, but enhance the growth of pre-existing pits, which is validated by optical microscopy. It was found that the values of the Cl − ion-incorporated outer film resistance R out,ox in SO 4 2− ion-containing chloride solutions were much lower than those in SO 4 2− ion-free solution, obtained from the impedance spectra measured at potentials below the E pit. The chloride peak disappeared from the Auger spectra in SO 4 2− ion-containing solutions. The mass decay rate and pit growth rate b were observed to increase in values once the pits were formed in SO 4 2− ion-containing chloride solutions. Based upon the above experimental results, it is suggested that SO 4 2− ions retard the oxide film breakdown by Cl − ion incorporation into the film, while they accelerate the Al metal dissolution through the instantaneous formation of tunnels at the bottom of the pre-existing pits after the exposure of bare surface above the E pit.

Spectral analysis of electrochemical noise with different transient shapes

The noise spectra under different transient shapes were calculated and the relationship between the spectral parameters (roll-off slope and roll-off frequency) in the frequency domain and the transient variables in the time domain were analyzed. The influence of corrosion types on noise spectra was considered. It is shown that a ‘white’ noise always appears in the low-frequency range of the noise spectrum and the roll-off slope of the spectrum in the high-frequency range depends on the transient shape, not the corrosion type. During pitting, the roll-off frequency of the noise spectrum is directly related to the time constant of the exponential function contained in the noise transient in the time domain and reflects the repassivation or growth rate of the metastable pits. For the triangular- and delta-shaped transients generally generated during passivity or general corrosion, the roll-off frequency is related to the time interval of the current transient during the current rise or drop stage. Although spectral analyses can extract useful information from the noise transients, the spectra cannot display the difference of any two transients that are symmetrical in shape in the time domain.

Pit Growth Study in Al Alloys by the Foil Penetration Technique

The foil penetration technique was used to study pit growth in AA1100-O and AA2024-T3. Preliminary work on AA1100-O foils of different thicknesses indicated that the pit growth rate increased with increasing applied potential, suggesting that pit growth was not under transport control. Foil penetration experiments were also carried out on AA2024-T3 foils of a given thickness, at open circuit as well as anodic potentials. Dichromate ions and other oxidizing agents were added to some test solutions. Dichromate ions were shown to have little influence on the pit growth rate at controlled anodic potentials, even when added in large concentrations. However, dichromate ions effectively inhibited pitting at open circuit when present in very small amounts. Polarization curves of AA2024-T3 in 1 M NaCl with various additives show a large effect of dichromate ions in the cathodic region and no effect in the anodic region. These observations suggest that chromate (or its reduction product) acts as a cathodic inhibitor. Examination of penetrated samples was performed by optical and scanning electron microscopies, as well as by microradiography. © 2000 The Electrochemical Society. All rights reserved.

Effects of applied potential and solution temperature on the pitting corrosion of pure aluminium in sulphate ion-containing chloride solution

Effects of applied potential and solution temperatureT s on the pitting corrosion of pure aluminium (Al) were investigated in 0.01 M NaCl solutions containing various sulphate (SO4 2-) ion concentrations using a potentiodynamic polarisation experiment, the potentiostatic current transient technique, ac impedance spectroscopy and atomic force microscopy (AFM). The potentiodynamic polarisation curves showed a rise in the pitting potentialE pir values and a simultaneous increase in anodic current density at potentials much higher than theE pit value as the SO42~ ion concentration increases. This implies that (SO4 2-) ions impede pit initiation at potentials belowE pit but enhance pit growth aboveE pit. This was confirmed from the larger pit growth rate parameterb values of pure Al exposed to (SO4 2-) ion-containing chloride solutions during the abrading action than those exposed to (SO4 2-) ion-free chloride solution. Furthermore, at 7s=25°C, the charge densityQ values for the Al metal dissolution in the presence of (SO4 2-) ions were smaller than the value in its absence. By contrast, as validated by the capacitance values and the AFM images of the re-anodized specimens, an enhanced metal dissolution was observed in (SO4 2-) ion-containing chloride solutions at 7s=60° and 80°C. From the experimental findings, it is suggested that (SO4 2-) ions act as inhibitors of pitting corrosion on pure Al belowE pit and at 7s=25°C, whereas they act as promoters at 7s=60 ° and 80°C. This originates from the accelerated dissolution of the bare metal extensively exposed to the temperature-sensitive Cl ion attack, which occurs at potentials aboveE pit

Kinetics of Graphite Oxidation: Monolayer and Multilayer Etch Pits in HOPG Studied by STM

Oxidation experiments using a particular grade of highly oriented pyrolytic graphite have allowed observation of large numbers of both monolayer and multilayer etch pits on the same samples, formed under identical conditions. Scanning tunneling microscopy was used to measure pits produced after various etch times, temperatures, and O2 pressures. From these data pit growth rates, activation energies, and reaction orders were derived. Although multilayer pits were observed to grow over 3 times faster than monolayer pits in air, both types of pits had the same activation energy. Multilayer etch pits were sometimes observed to form at screw dislocations in the graphite but were also seen in the absence of such defects. The experimentally determined reaction rates and activation energies were not consistent with a direct reaction of edge-carbon atoms with atmospheric oxygen, but instead suggest a chain reaction or preequilibrium process. A mechanism for oxidation of multilayer pits involving reaction of partia...

Pitting in Aluminum Thin Films: Supersaturation and Effects of Dichromate Ions

The growth of pits in 209 nm thick Al films in chloride solutions with and without dichromate ions was examined using image analysis of the growing pits to determine pit current density. In pure chloride solutions, the pit current density decreased at high potentials after reaching a maximum value, and then was almost independent of applied potential. A hysteresis in the pit current density‐potential behavior was observed during downward stepping of the potential from high values. This is a result of a combination of supersaturation of the pit electrolyte followed by salt film formation, and changes in mass transport from hydrogen bubbles that increase convection and lift the remnant passive film away from the dissolving surface. In solutions containing dichromate ions, the corrosion and repassivation potentials shifted in the noble direction, and rather large metastable pits formed at the open circuit. A large concentration of dichromate ions was needed to inhibit pit growth. In dichromate solutions, subsequent pit growth at higher potentials often initiated at the edge of the open‐circuit pits. The rate of pit growth was lower for these pits because the remnant passive film layer was not easily lifted up at these sites, and thus created a barrier for mass transport away from the dissolving pit edge.

Deterministic Prediction of Pit Depth Distribution

Abstract In this paper, the deterministic predition of damage via damage function analysis (DFA), which provides a robust technology for estimating the damage function at future times, is described. General analytical expressions for calculating the damage functions that can be used with arbitrary dependencies of pit nucleation rate, pit growth rate, and repassivation rate on the system parameters have been obtained. The application of DFA to prediction of pitting damage is illustrated by reference to the pitting corrosion of iron in neutral chloride-containing solutions.

A probability model for the growth of corrosion pits in aluminum alloys induced by constituent particles

Localized corrosion in the form of pitting in certain classes of aluminum alloys, e.g. 2024-T3 and 7075-T6, is recognized as one of the degradation mechanisms that affect the durability and integrity of structures, and it is a concern for commercial transport and military aircraft. Pitting has been shown to initiate at constituent particles, which are either anodic or cathodic relative to the matrix, and involves complex electrochemical processes. Furthermore, local interactions between particles and the matrix enhance the rate of pit growth. Probabilistic modeling for the growth of corrosion pits in aluminum alloys in aqueous environments in presented. The focus of the growth process is specifically the role of clustered particles. The purpose of the effort is to estimate the cumulative distribution function ( cdf) for the size of corrosion pits at a given time for use in multi-site damage and crack growth analyses. The model incorporates the evolution of local damage at each particle and the corrosion pit growth involving interactions with neighboring particles. Some of the key random variables included are the size, density and location of both the anodic and cathodic particles. Statistical estimates for the distribution functions of the underlying random variables are based on experimental observations.

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Stress corrosion cracking (SCC) of solution-treated Al-Zn-Mg alloy was mainly examined in 0.2N-H2SO4+7.2×10-3M-NaCl (Solution-A) and 0.4N-H2SO4+2.4 x 10-3M-NaCl (Solution-B) solutions in relation to pitting potential, crack initiation sites and crack morphology. Pitting potentials (Vc) obtained from current-time curves under various potentials were at-0.78V in solution-A, and at -0.68V in solution-B. The time to fracture decreased with an increase of applied potential in both solutions. It seems that the critical potential for SCC corresponds to the pitting potential under stress (V'c σ). Transgranular SCC was observed in both solutions. The crack directly initiates on the surface in the range of V'cσ-Vc, and initiates at the bottom of pits in the range of Vc-Vc* (potential which crack growth rate equals to pit growth rate). Mechanical fracture occurred in the potential above Vc*. Cracks initiating from the bottom of pit stops growing below the protective potential (ER). Therefore, it is necessary for SCC that dissolving pits be present. The crack path is at the grain boundary at pH=3.3 depending on the pH, however, crack and pitting potential does not exist at pH=5.8.

A simplified method for estimating corrosion cavity growth rates

A simplified method is proposed for calculating corrosion cavity propagation rates. This method is based on an assumption that if the rate of an electrode reaction depends (in an explicit form) only on the potential, the pit growth rate depends only on the concentration of those species that determine the potential distribution near the metal within the cavity. The advantage of this method is that it permits one to predict the rates of cavity propagation without knowing various parameters, such as the equilibrium constants of some chemical reactions and diffusion coefficients of species that are present at relatively low concentrations near the electrode surface. The analytical expressions for calculating propagation rates of cylindrical and hemispherical pits are compared with available experimental data. The influence of aggressive anions on the pit propagation rate has been investigated. It is shown that transport processes in the internal environment do, in the general case, influence the kinetics of metal corrosion.