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Title: Effect of HCO3- on electrochemical kinetics of carbon steel corrosion in CO2-saturated brines

Journal Article · · Electrochimica Acta
 [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)

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.

Research Organization:
National Energy Technology Laboratory (NETL), Pittsburgh, PA, Morgantown, WV, and Albany, OR (United States)
Sponsoring Organization:
FE; USDOE
Grant/Contract Number:
FE0004000
OSTI ID:
1509718
Alternate ID(s):
OSTI ID: 1635818
Report Number(s):
NETL-PUB-22327
Journal Information:
Electrochimica Acta, Vol. 290, Issue C; ISSN 0013-4686
Publisher:
ElsevierCopyright Statement
Country of Publication:
United States
Language:
English
Citation Metrics:
Cited by: 53 works
Citation information provided by
Web of Science

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Figures / Tables (12)