TY - JOUR
T1 - Evolution of non-stoichiometric iron sulfide film formed by electrochemical oxidation of carbon steel in alkaline sour environment
AU - Sosa, E.
AU - Cabrera-Sierra, R.
AU - Rincón, Marina E.
AU - Oropeza, M. T.
AU - González, I.
N1 - Funding Information:
E. Sosa and R. Cabrera-Sierra are grateful to Conacyt and FIES for their postgraduate grant. The authors acknowledge the financial aid from Conacyt (project No. 32689 E) and FIES 98-13-II. SEM images were obtained by Luis Lartundo
PY - 2002/2/1
Y1 - 2002/2/1
N2 - Non-stoichiometric iron sulfide films (FexSy) were formed electrochemically on a 1018 carbon steel/1 M (NH4)2S, 500 ppm CN- interface, using cyclic chronoamperometry for different time intervals. The films showed great stability in medium typical of the catalytic plants of PEMEX Mexico (0.1 M (NH4)2S, 10 ppm CN- as NaCN, pH 8.8). Characterization of the films by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) show two different behaviors depending on the growth time. For films grown at times <15 min, oxidation of the film was continuous, while oxidation ability for the film formed at times >15 min was lower. Film characteristics were more clearly defined by EIS experiments, as the Nyquist diagrams show depressive loops with high, real impedance values (Zr>1 kΩ cm2) for films grown at longer times. Structural characterization by X-ray diffraction (XRD) and Scanning Electron Microscopy (SEM) correlated electrochemical behavior with topographical changes and chemical composition of the films formed. The abundance of sulfur and pyrrhotite is evident in the samples grown for increasing times, and is likely due to electrochemical/chemical oxidation of iron sulfides during film growth. The sulfur-rich layer is responsible for the passive character of these films. The equivalent electrical circuit describing the EIS spectra for films formed over longer times has fewer elements than that used to model EIS spectra for films grown at shorter times. In particular, diffusion of atomic hydrogen is not apparent in sulfur-enriched films, and the charge transfer is carried out at the metal/film interface with values that are insensitive to film thickness and chemical nature.
AB - Non-stoichiometric iron sulfide films (FexSy) were formed electrochemically on a 1018 carbon steel/1 M (NH4)2S, 500 ppm CN- interface, using cyclic chronoamperometry for different time intervals. The films showed great stability in medium typical of the catalytic plants of PEMEX Mexico (0.1 M (NH4)2S, 10 ppm CN- as NaCN, pH 8.8). Characterization of the films by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) show two different behaviors depending on the growth time. For films grown at times <15 min, oxidation of the film was continuous, while oxidation ability for the film formed at times >15 min was lower. Film characteristics were more clearly defined by EIS experiments, as the Nyquist diagrams show depressive loops with high, real impedance values (Zr>1 kΩ cm2) for films grown at longer times. Structural characterization by X-ray diffraction (XRD) and Scanning Electron Microscopy (SEM) correlated electrochemical behavior with topographical changes and chemical composition of the films formed. The abundance of sulfur and pyrrhotite is evident in the samples grown for increasing times, and is likely due to electrochemical/chemical oxidation of iron sulfides during film growth. The sulfur-rich layer is responsible for the passive character of these films. The equivalent electrical circuit describing the EIS spectra for films formed over longer times has fewer elements than that used to model EIS spectra for films grown at shorter times. In particular, diffusion of atomic hydrogen is not apparent in sulfur-enriched films, and the charge transfer is carried out at the metal/film interface with values that are insensitive to film thickness and chemical nature.
KW - Alkaline sour environment
KW - Carbon steel
KW - EIS
KW - Sulfide iron films characterization
KW - Sulfur
UR - http://www.scopus.com/inward/record.url?scp=0036472276&partnerID=8YFLogxK
U2 - 10.1016/S0013-4686(01)00851-9
DO - 10.1016/S0013-4686(01)00851-9
M3 - Artículo
SN - 0013-4686
VL - 47
SP - 1197
EP - 1208
JO - Electrochimica Acta
JF - Electrochimica Acta
IS - 8
ER -