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Abstract: The effect of the presence of dissolved ferrous ion (Fe2+(aq)) on surface oxide film growth and conversion on carbon steel in pH 8.4 borate solutions was studied as a function of potential. The results of electrochemical measurements and surface analyses provide a consistent picture of oxide growth and conversion behaviour and the role of Fe2+(aq) on the oxidation. At potentials<−0.4VSCE the presence of Fe2+(aq) in solution somewhat suppresses the dissolution of FeII, thus reducing the net rate of anodic oxidation, while at potentials>−0.4VSCE the presence of Fe2+(aq) at 0.1mM can substantially increase the rate of formation of γ-FeOOH on the carbon steel surface via oxidation of Fe2+(aq). [Copyright &y& Elsevier]

Abstract: Surface oxide film growth and conversion on carbon steel at pH25°C 10.6 was studied as a function of temperature in a range of 25–80°C. The current behaviour observed as a function of various cyclic voltammetry scan conditions and the current and EIS spectra as a function of time during 7-d potentiostatic experiments all present consistent pictures of an oxide growth and conversion mechanism that depends mainly on electrode potential. At pH25°C 10.6 where the solubilities of both FeII and FeIII species are low, the chemical and phase composition of the oxide film formed on carbon steel depends on the electrode potential, but is independent of temperature. For the type of film formed, three potential regions can be defined: formation of a uniform and compact magnetite-like layer at potentials <−0.6VSCE, a uniform and compact maghemite-like layer in the range from −0.6 to 0.0VSCE, and small crystallites of γ-FeOOH on a compact layer at potentials >0.0VSCE. Although temperature influences the rates of thermal processes such as dissolution and charge transport through the oxide phase, and the Schikorr reaction at temperatures >70°C, these thermal processes do not influence the oxide composition, but instead influence only the thickness of the oxide film at pH25°C 10.6. [Copyright &y& Elsevier]

Abstract: The effect of γ-radiation on the kinetics of carbon steel corrosion has been investigated by characterizing the oxide films formed on steel coupons at 150°C and at two pH values. Results show that continuous irradiation enhances surface oxide formation with the type of oxide formed dependant on the solution pH. For experiments at 150°C and a [OH−] equivalent to that for pH25°C =10.6, the surface oxide on carbon steel after γ-irradiation was non-porous and uniform, and no localized corrosion was observed. This oxide, however, appears to be susceptible to brittle fracture during cooling. Raman spectroscopy of the surface film indicates that it is a mixture of the phases of Fe3O4 and γ-Fe2O3. In contrast, at 150°C with [OH−] equivalent to neutral pH25°C, metal dissolution is significant and the surface oxide film is very porous. Raman spectra show that this oxide film is also composed of a mixture of Fe3O4 and γ-Fe2O3. The results from this work combined with previously reported electrochemical studies of the same system as a function of pH and temperature can be used to deconvolute the effects of radiation, pH and temperature on the nature of the corrosion process. [ABSTRACT FROM AUTHOR]

The effect of ionizing radiation on steel corrosion is an important materials issue in nuclear reactors. In the presence of ionizing radiation water decomposes into both oxidizing and reducing species (e.g., OH, H2O2, O2−) whose net interactions with steels are not fully understood. The effect of radiation on the corrosion kinetics of carbon steel has been studied at pH 10.6 and room temperature, using electrochemical and chemical speciation analyses. The present study investigates the effect of γ-radiation on carbon steel corrosion and compares it with that of chemically added H2O2, which is considered to be the key radiolytically produced oxidant at room temperature. Various oxide films were pre-grown potentiostatically on carbon steel electrodes, and then exposed to either γ-radiation at a dose rate of ∼6.8 kGy h−1 or to H2O2 in a concentration range of 10−6 to 10−2 M. The corrosion kinetics were studied by monitoring the corrosion potential (ECORR), and periodically performing linear polarization (LP) and electrochemical impedance spectroscopy (EIS) measurements. [Copyright &y& Elsevier]

Abstract: Surface oxide film growth and conversion processes on carbon steel were studied using a range of electrochemical techniques and ex situ surface analyses. The electrochemical study included (i) cyclic voltammetry as a function of various scan conditions and (ii) 7-day potentiostatic oxidation at a range of potentials while periodically performing Electrochemical Impedance Spectroscopy. Carbon steel surfaces at various stages of electrochemical oxidation were examined by SEM, Raman and X-ray photoelectron spectroscopy (XPS). These studies yield a consistent picture of film formation/conversion processes on carbon steel at pH 10.6, which is different to that reported for basic solutions (pH>13). Oxide film formation/conversion mechanisms for three potential regions are proposed. In region I (≤−0.6V vs SCE), the main oxide formed is Fe3O4 which grows via a solid-state process; in region II (−0.5V≤ E (vs SCE)≤−0.2V), continuous growth of the Fe3O4 layer is accompanied by its anodic conversion to a more maghemite (γ-Fe2O3)-like phase near, or at, the oxide/solution interface by a similar solid-state mechanism to that described for region I; in region III (0.0V< E (vs SCE)<0.4V), the anodic conversion of this Fe3O4/γ-Fe2O3 oxide to γ-FeOOH leads to a significant structural change, which can lead to film fracture and the introduction of enhanced transport pathways in the film. [Copyright &y& Elsevier]