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Passivation of X65 steel in NaHCO 3 solution saturated with CO 2 using thin wire specimens
Author(s) -
Shang W. J.,
Xu L. N.,
Qiao L. J.,
Li J. X.
Publication year - 2017
Publication title -
materials and corrosion
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.487
H-Index - 55
eISSN - 1521-4176
pISSN - 0947-5117
DOI - 10.1002/maco.201609405
Subject(s) - passivation , materials science , electrochemistry , polarization (electrochemistry) , anode , porosity , electrode , metallurgy , corrosion , analytical chemistry (journal) , thin film , composite material , nanotechnology , chemistry , layer (electronics) , chromatography
The passivation of X65 steel in NaHCO 3 solution saturated with CO 2 was investigated using electrochemical and immersion tests as well as surface morphology and composition analysis. The tests were conducted using thin wire specimens at atmospheric pressure in NaHCO 3 solution with different concentrations and at different temperatures. The electrochemical properties of thin wire specimens and square specimens were compared. Thin wire specimens were immersed for a long period, during which the open circuit potential (OCP) was recorded. Anodic polarization was performed after the OCP was sufficiently high and stable. Electrochemical tests revealed that the electrochemical properties of the thin wire specimens were consistent with those of the square specimens. A sudden increase in the OCP of approximately 700 mV occurred after the specimens were immersed for a long period in the tested concentration and temperature. The time at which the OCP increase occurred decreased when the NaHCO 3 concentration or temperature were increased. After the OCP became stable, anodic polarization revealed favorable self‐passivation. Immersion tests on X65 steel demonstrated that the OCP increase may have been due to the filling of pores between FeCO 3 grains. Small tetrahedron grains formed in the pores of large hexahedral grains to lower the porosity of the film, thus making the film more compact. Consequently, the OCP increased and anodic polarization presented self‐passivation.