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Title: Effect of HCO 3 on electrochemical kinetics of carbon steel corrosion in CO 2-saturated brines

Abstract

The effect of HCO 3 (aq) on CO 2 corrosion of carbon steel was investigated in deaerated 3.5 wt% NaCl solutions at 30 °C from pH 3.96 to 7.15. In the CO 2-saturated solutions, the pH was adjusted with different HCO 3 (aq) concentrations, c[HCO 3 (aq)]. The corrosion rate decreased by a factor of 2 as the pH and c[HCO 3 (aq)] increased. The cathodic current density during polarization increased at higher pH with higher c[HCO 3 (aq)], indicating that HCO 3 (aq) acted as an additional hydrogen source for the hydrogen evolution reaction. As the pH increased, the active dissolution regions displayed similar anodic Tafel slopes and suggested a modified Bockris mechanism for the Fe oxidation reaction. The exchange current densities for the half reactions were calculated to study kinetics of the anodic and cathodic half reactions independently. The anodic exchange current density ( j0,a) increased by one order of magnitude in the presence of CO 2, indicating the involvement of CO 2(aq) in the Fe oxidation reaction. As the pH and c[HCO 3 (aq)] increased, the cathodic exchange current density ( j0,c) decreased by a factor of 50 because the increase in j0,c[HCO 3 (aq)] was notmore » high enough to compensate the decline from the other hydrogen sources, especially j0,c[H +(aq)]; and j0,a decreased by a factor of 2.4 because HCO 3 (aq) may have competed with CO 2(aq) for the surface coverage and the increase in j0,a[CO 2(aq)] could not compensate the decrease in j0,a[CO 2(aq)]. It suggests that the reaction rate constant of HCO 3 (aq) was smaller than CO 2(aq) for the anodic half reaction and was smaller than H +(aq) for the cathodic half reaction. The XPS results verified that the corrosion products transitioned from iron carbonate to hydroxide as the pH increased while iron carbonate remained the major product. As the pH increased with HCO 3 (aq), a second time constant was observed at lower frequencies of the electrochemical impedance spectroscopy (EIS) results.« less

Authors:
 [1];  [2];  [3];  [3];  [4]
  1. National Energy Technology Lab. (NETL), Pittsburgh, PA, (United States); AECOM, Pittsburgh, PA (United States)
  2. National Energy Technology Lab. (NETL), Pittsburgh, PA, (United States)
  3. National Energy Technology Lab. (NETL), Albany, OR (United States)
  4. National Energy Technology Lab. (NETL), Pittsburgh, PA, (United States); Carnegie Mellon Univ., Pittsburgh, PA (United States)
Publication Date:
Research Org.:
National Energy Technology Lab. (NETL), Albany, OR and Pittsburgh, PA (United States)
Sponsoring Org.:
FE; USDOE
OSTI Identifier:
1509718
Report Number(s):
NETL-PUB-22327
Journal ID: ISSN 0013-4686
Grant/Contract Number:  
FE0004000
Resource Type:
Accepted Manuscript
Journal Name:
Electrochimica Acta
Additional Journal Information:
Journal Volume: 290; Journal Issue: C; Journal ID: ISSN 0013-4686
Publisher:
Elsevier
Country of Publication:
United States
Language:
English
Subject:
Electrochemical corrosion; Kinetics; Bicarbonate ion; Half reactions; Tafel slopes

Citation Formats

Wright, Ruishu F., Brand, Edward R., Ziomek-Moroz, Margaret, Tylczak, Joseph H., and Ohodnicki, Jr., Paul R. Effect of HCO3− on electrochemical kinetics of carbon steel corrosion in CO2-saturated brines. United States: N. p., 2018. Web. doi:10.1016/j.electacta.2018.09.114.
Wright, Ruishu F., Brand, Edward R., Ziomek-Moroz, Margaret, Tylczak, Joseph H., & Ohodnicki, Jr., Paul R. Effect of HCO3− on electrochemical kinetics of carbon steel corrosion in CO2-saturated brines. United States. doi:10.1016/j.electacta.2018.09.114.
Wright, Ruishu F., Brand, Edward R., Ziomek-Moroz, Margaret, Tylczak, Joseph H., and Ohodnicki, Jr., Paul R. Wed . "Effect of HCO3− on electrochemical kinetics of carbon steel corrosion in CO2-saturated brines". United States. doi:10.1016/j.electacta.2018.09.114. https://www.osti.gov/servlets/purl/1509718.
@article{osti_1509718,
title = {Effect of HCO3− on electrochemical kinetics of carbon steel corrosion in CO2-saturated brines},
author = {Wright, Ruishu F. and Brand, Edward R. and Ziomek-Moroz, Margaret and Tylczak, Joseph H. and Ohodnicki, Jr., Paul R.},
abstractNote = {The effect of HCO3–(aq) on CO2 corrosion of carbon steel was investigated in deaerated 3.5 wt% NaCl solutions at 30 °C from pH 3.96 to 7.15. In the CO2-saturated solutions, the pH was adjusted with different HCO3–(aq) concentrations, c[HCO3–(aq)]. The corrosion rate decreased by a factor of 2 as the pH and c[HCO3–(aq)] increased. The cathodic current density during polarization increased at higher pH with higher c[HCO3–(aq)], indicating that HCO3–(aq) acted as an additional hydrogen source for the hydrogen evolution reaction. As the pH increased, the active dissolution regions displayed similar anodic Tafel slopes and suggested a modified Bockris mechanism for the Fe oxidation reaction. The exchange current densities for the half reactions were calculated to study kinetics of the anodic and cathodic half reactions independently. The anodic exchange current density (j0,a) increased by one order of magnitude in the presence of CO2, indicating the involvement of CO2(aq) in the Fe oxidation reaction. As the pH and c[HCO3–(aq)] increased, the cathodic exchange current density (j0,c) decreased by a factor of 50 because the increase in j0,c[HCO3–(aq)] was not high enough to compensate the decline from the other hydrogen sources, especially j0,c[H+(aq)]; and j0,a decreased by a factor of 2.4 because HCO3–(aq) may have competed with CO2(aq) for the surface coverage and the increase in j0,a[CO2(aq)] could not compensate the decrease in j0,a[CO2(aq)]. It suggests that the reaction rate constant of HCO3–(aq) was smaller than CO2(aq) for the anodic half reaction and was smaller than H+(aq) for the cathodic half reaction. The XPS results verified that the corrosion products transitioned from iron carbonate to hydroxide as the pH increased while iron carbonate remained the major product. As the pH increased with HCO3–(aq), a second time constant was observed at lower frequencies of the electrochemical impedance spectroscopy (EIS) results.},
doi = {10.1016/j.electacta.2018.09.114},
journal = {Electrochimica Acta},
number = C,
volume = 290,
place = {United States},
year = {2018},
month = {9}
}

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