Many studies have been conducted on the action of corrosion inhibitors on corrosion product layers.
There are varying opinions: the inhibitor may preferentially interact with the metallic surface or the
existence of a corrosion scale enhances inhibitor adsorption. This paper will address the effect of the
type of corrosion inhibitor active on the growth of iron carbonate. Our paper1 presented at NACExpo
2008 explored the synergistic interaction a quaternized amine compound has with iron carbonate. This
work is a continuation and examines how imidazoline and phosphate ester compounds interact with
iron carbonate. Tests were performed using the Rotating Cylinder Electrode (RCE) technique in
conjunction with LPR (Linear Polarization Resistance), Tafel studies and EIS (Electrochemical
Impedance Spectroscopy). Test samples composed of 1018 carbon steel were exposed to a pH 6.5
CO2-purged brine environment for the duration of the test. SEM/EDS (Scanning Electron
Microscopy/Electron Dispersive Spectroscopy) were used in the analyses of the corrosion samples in
order to observe the morphology, thickness and crystal structure of the iron scale layer. This work will
provide insight on how various types of corrosion inhibitor actives affect the growth of iron carbonate.
KEYWORDS: corrosion inhibition, iron carbonate, imidazoline, phosphate ester, linear polarization
resistance, electrochemical impedance spectroscopy, potentiodynamic sweeps,
scanning electron microscopy