Mechanism of Cathodic Reactions in Acetic Acid Corrosion of Iron and Mild Steel

Kahyarian, Aria; Brown, Bruce; Nešić, Srdjan

doi:10.5006/2177

Cited by 34 publications

(19 citation statements)

References 28 publications

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“…The existence of the so-called "double wave" comes from the two independent cathodic reactions and their limiting currents. 20,38 Similar results were obtained at pH 4.0, see Figure 4(b), which shows the averages of the data collected from four repeated experiments. Data from the experiments conducted at pH 5.0 are presented in Figure 4(c), which shows the averages from experiments repeated six times.…”

Section: Resultssupporting

confidence: 80%

Verification of an Electrochemical Model for Aqueous Corrosion of Mild Steel for H₂S Partial Pressures up to 0.1 MPa

2017

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Hydrogen sulfide (H 2 S) corrosion of mild steel is a serious concern in the oil and gas industry. However, H 2 S corrosion mechanisms, specifically at high partial pressures of H 2 S (pH 2 S), have not been extensively studied because of experimental difficulties and associated safety issues. The current study was conducted under well-controlled conditions at pH 2 S of 0.05 MPa and 0.096 MPa. The pH range used was from pH 3.0 to pH 5.0, at temperatures of 30°C and 80°C, and with rotating cylinder speeds of 100 rpm and 1,000 rpm. Short-term exposures, lasting between 1.0 h and 1.5 h, were used to avoid formation of any protective iron sulfide layers. The experimental results were compared with a recent mechanistic model of sour corrosion developed by Zheng, et al. (2014). This model was based on corrosion experiments conducted at low pH 2 S (0.0001 kPa to 10 kPa) and is applicable only to conditions where protective iron sulfide layers do not form. The validity of the model at higher pH 2 S was examined, as it was uncertain if the mechanisms identified at lower pH 2 S were still valid. The comparison with the experimental results obtained in the present study indicated a good agreement between the model and the measurements. This confirmed that the physicochemical processes underlying H 2 S corrosion in the absence of protective iron sulfides are very similar across a wide range of H 2 S aqueous concentrations. It also demonstrated that the mechanistic corrosion model was reasonable when extrapolating from low to high pH 2 S.

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Section: Resultssupporting

confidence: 80%

Verification of an Electrochemical Model for Aqueous Corrosion of Mild Steel for H₂S Partial Pressures up to 0.1 MPa

2017

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“…While the reproducibility of the results obtained on a pure iron surface was slightly lower when compared to steel, the polarization curves showed that the pure iron surface is a significantly weaker catalyst for the reduction reactions, in agreement with previous reports. 25,36 Considering that the pure charge transfer controlled currents for H + reduction were not observed, the true difference in the electrocatalytic effect of the two surfaces cannot be properly distinguished here. Nevertheless, the observed difference even in this mixed mass transfer/charge transfer controlled regime signifies the importance of the substrate composition when discussing the electrochemical kinetics and mechanisms.…”

Section: Resultsmentioning

confidence: 99%

“…However, neither of the two competing ideas about the electrochemical activity of H 2 CO 3 appears to have sufficient experimental evidence in their support so far. As identified previously, 18,[25][26][27][28] the direct experimental evidence for electrochemical activity of a weak acid (such as H 2 CO 3 ) may be obtained by investigating the behavior of pure charge transfer controlled cathodic currents. If the reduction of H 2 CO 3 is significant, at a fixed pH, the charge transfer controlled currents would increase as pCO 2 increases-as a result of increased H 2 CO 3 concentration, and thus, increased rate of H 2 CO 3 reduction reaction.…”

Section: Fe 2þmentioning

confidence: 89%

“…The electrodes were polished and electrochemically treated according to the procedure discussed elsewhere. 25 The cathodic polarization measurements were initiated from open-circuit potential (OCP) toward the more negative values after a stable OCP was observed (< ±2 mV drift over 5 min). The steady-state voltammograms were obtained using staircase voltammetry at 0.5 mV/s scan rate and 1 s −1 sampling period.…”

Section: The Glass Cellmentioning

confidence: 99%

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Technical Note: Electrochemistry of CO2 Corrosion of Mild Steel: Effect of CO2 on Cathodic Currents

2018

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The common understanding of aqueous CO 2 corrosion mechanism considers carbonic acid as an electroactive species. The direct reduction of carbonic acid on a steel surface is believed to be the cause of the higher corrosion rates of mild steel, as compared to that observed in strong-acid solutions with the same pH. However, in-depth quantitative analyses based on comprehensive mechanistic models, developed in recent years, have challenged this idea. In an attempt to provide explicit experimental evidence for the significance of direct reduction of carbonic acid in CO 2 corrosion of mild steel, the charge transfer controlled cathodic currents in CO 2 saturated solutions were investigated in the present study. The experiments were conducted on three different surfaces: Type 316L stainless steel, pure iron, and API 5L X65 mild steel, in order to examine the possible effect of alloying impurities on the kinetics and the mechanism of cathodic currents. The experimental polarization curves showed that at a constant pH, the charge transfer controlled cathodic currents did not increase with increasing partial pressure of CO 2 from 0 bar to 5 bar. This confirmed that the direct carbonic acid reduction was not significant at the conditions covered in the present study, and its sole effect was to buffer the hydrogen ion concentration.

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“…[27][28][29][30][31] To date, most of the mechanistic corrosion rate predictive models [30][31][32][33] base the calculation of the cathodic current (rate of the HER) on studies 14,34,35 where the experimental conditions were significantly different from those encountered in the models' targeted applications. Considering the profound effect of pH, 36,37 electrode material and surface structure, 15,23,34,38,39 overpotential, 40 and solution composition 37 on the kinetics of the HER, a comprehensive understanding of the reaction mechanism and its kinetics is essential for accurate modeling of such systems.…”

Section: H366mentioning

confidence: 99%

Mechanism of the Hydrogen Evolution Reaction in Mildly Acidic Environments on Gold

Kahyarian

Brown

Nešić

2017

J. Electrochem. Soc.

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Despite numerous studies investigating the kinetics of the hydrogen evolution reaction (HER) on a gold surface in acidic solutions, the underlying mechanism of this reaction have remained controversial to date. In the present study, the existing mechanisms are reevaluated and found to be inadequate in explaining the steady state polarization behavior of the hydrogen evolution reaction in an extended cathodic potentials and mildly acidic pH range. It was shown that a mechanism including a surface diffusion step of H ads alongside the Volmer, Heyrovsky, and Tafel elementary steps, best describes the experimental data obtained in acidic perchlorate solutions up to pH 5, while the rate determining step changes both with pH and electrode potential. This overall HER mechanism was further verified using a comprehensive mathematical model based on the proposed elementary steps, where a satisfactory agreement with experimental results was obtained. The hydrogen evolution reaction (HER) has been the subject of numerous studies, either as a platform for investigating the theory of electrochemical processes, 1-9 or in terms of hydrogen production, energy storage, and energy conversion, 10-12 due to its significance in the alternative energy source framework. This trend had also include extensive investigations of the mechanism of the HER on gold in acidic solutions. 6,8,[13][14][15][16][17][18][19][20][21] However, a literature survey shows no general agreement on the underlying mechanism of this reaction to date. [13][14][15]17,18,20,21 Besides, the majority of the proposed mechanisms have been developed based on experimental results obtained in highly acidic environments, 6,8,13-21 but were not examined over an extended pH range.The experimental polarization curves obtained on gold in acidic solutions repeatedly reported to have two distinct Tafel slopes with values in the range of 50-70 mV at lower current densities and 100-130 mV at higher current densities. 3,6,16,18,21,22 A number of different explanations for the underlying mechanism based on these observed Tafel slopes have been proposed in the literature. In a study by Ives 20 in 0.1 N HCl solutions, the author reported polarization curves with an uncharacterized region at low current densities preceding to the 120 mV Tafel slope range. That uncharacterized section of the voltammograms had a significantly lower Tafel slope with values about 50-70 mV, which was extended to the cathodic currents up to about 1 A.m −2 and overpotentials up to about 150 mV. The author associated this lower Tafel slope with the interference of the hydrogen oxidation reaction. 20 However, considering the experimental conditions in that study, no significant interference of anodic currents due to hydrogen gas oxidation is expected, especially at the cathodic overpotentials as high as 150 mV.Bockris et al. 14,23 suggested that the apparent change of Tafel slope to ∼60 mV was caused by the change in potential drop across the diffusion double layer. This effect was believed to be most profoun...

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Mechanism of Cathodic Reactions in Acetic Acid Corrosion of Iron and Mild Steel

Cited by 34 publications

References 28 publications

Verification of an Electrochemical Model for Aqueous Corrosion of Mild Steel for H₂S Partial Pressures up to 0.1 MPa

Verification of an Electrochemical Model for Aqueous Corrosion of Mild Steel for H₂S Partial Pressures up to 0.1 MPa

Technical Note: Electrochemistry of CO2 Corrosion of Mild Steel: Effect of CO2 on Cathodic Currents

Mechanism of the Hydrogen Evolution Reaction in Mildly Acidic Environments on Gold

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Mechanism of Cathodic Reactions in Acetic Acid Corrosion of Iron and Mild Steel

Cited by 34 publications

References 28 publications

Verification of an Electrochemical Model for Aqueous Corrosion of Mild Steel for H2S Partial Pressures up to 0.1 MPa

Verification of an Electrochemical Model for Aqueous Corrosion of Mild Steel for H2S Partial Pressures up to 0.1 MPa

Technical Note: Electrochemistry of CO2 Corrosion of Mild Steel: Effect of CO2 on Cathodic Currents

Mechanism of the Hydrogen Evolution Reaction in Mildly Acidic Environments on Gold

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Verification of an Electrochemical Model for Aqueous Corrosion of Mild Steel for H₂S Partial Pressures up to 0.1 MPa

Verification of an Electrochemical Model for Aqueous Corrosion of Mild Steel for H₂S Partial Pressures up to 0.1 MPa