As-grown oxide layers on copper in aerated 0.1M sodium acetate and 0.5M sodium chloride solutions, with and without benzotriazole, are studied using photoelectrochemical techniques. In the sodium acetate solution, BTA does not basically modify the semi-conducting properties of the oxide layers. Moreover in this electrolyte, the oxide film shows simultaneously, at the rest potential, p-and n-type behaviours associated with different energy gaps. In the sodium chloride solution, a p-type behaviour is observed for short immersion times, but for longer immersion times, an additional anodic component appears in the higher wavelength range. In presence of BTA, the oxide layer shows the same semi-conducting behaviour in sodium chloride than in sodium acetate solutions.

The electrochemical behavior and the chemical composition of passive films formed on the Alloy 690 at room temperature in borate buffer solution (pH = 9.0) was studied with different techniques for two surface finishings. XPS and quantum yield measurements showed the presence of Ni and Cr oxides and hydroxides for passive films formed on both the as received and the mechanically polished one, whereas the presence of mixed spinel type Ni(1-x)FexCr2O4 was only observed on the as received material. Additionally, Electrochemical Impedance Spectroscopy (EIS) highlighted a higher corrosion resistance for the as received alloy in comparison with the mechanically polished alloy, which was linked to the chemical composition of the oxide film. Electrochemical measurements were performed before, during, and after oxidation of the Alloy 690 of Steam Generator (SG) tube of Pressurized Water Reactor (PWR) at high temperature and high pressure in the simulated primary circuit of PWR. At high temperature, the interface becomes electrochemically active yielding the precipitation of the corrosion products which form a few tens of nm thick diffusion barrier for the released metal cations. This overlayer is built on the top of a few nm thick, Cr-rich inner-layer at the alloy/oxide interface which was found to behave similarly to that initially formed at ambient temperature. It is concluded that high temperature oxidation in the static condition of an autoclave at 325 degrees C does not promote a better passivation state than the one already existing initially. (c) 2019 Elsevier Ltd. All rights reserved.

Oxygen pollution in hydrogen sulfide (H2S) saturated test solutions can compromise the results of standardized tests, which guide materials selection in safety-critical components. To examine the temporal evolution of such contamination, we have used the electrochemical methods of impedance spectroscopy and hydrogen permeation to study the corrosion of iron exposed to oxygen-polluted H2S-saturated solutions. EIS analyses were performed with a previously developed model, which explicitly accounts for the contribution of a conductive and porous iron sulfide overlayer. A good correlation is found between corrosion estimates from EIS and weight loss, measured to be higher than the O-2-free case. Hydrogen permeation studies across the iron membrane were conducted to qualitatively evaluate the impact of dissolved 02 on hydrogen entry. We observe that O-2 contamination was found to significantly reduce hydrogen charging into the metal.

Mildly acidic water containing dissolved H2S presents a strong risk in the cracking of low-carbon steels. Several studies on H2S cracking mechanisms have shown that the main driving force is linked to the ability of H2S to promote hydrogen entry into the bulk material. Standard test methods have been developed and published as NACE technical standards (e.g. NACE TM0284 and NACE TM0177) to aid materials selection in the oil and gas sector. Though it is recognized that oxygen pollution should be avoided during H2S cracking tests, there is a lack of experimental data to illustrate the effects of a small oxygen pollution. Dissolved oxygen concentrations greater than the recommended upper limit (50 parts per billion) can easily be obtained in the case of poor laboratory practices. This paper will focus on the interactions between oxygen and H2S on electrochemical behavior of unalloyed steel. A continuous O2 injection at a level corresponding to 500 ppb is applied, together with H2S bubbling in our test solutions, for periods lasting the same order as SSC standard tests. Steel surface reaction phenomena/corrosion rates in H2S saturated solution, with or without oxygen pollution, are studied using electrochemical impedance spectroscopy. The evolution of corrosion rates obtained from impedance analysis was compared to two other independent methods: i/ weight loss measurements and, ii/ hydrogen permeation. Without O2 pollution, a permeation efficiency of 100% was obtained, as expected. Permeation current density was thus found to match precisely with the corrosion current density determined by impedance analysis at different times. On the other hand, when a continuous O2 pollution was added in the system, significantly higher corrosion rates were observed, associated with test solution acidification. At the same time, permeation efficiency was decreased by up to one order of magnitude.

Materials selection in the oil and gas industry relies on engineering standards, such as NACE TM0177 and NACE TM0284, which stipulate that oxygen contamination should be avoided during materials testing in H2S-containing media. In this second paper, as part of a series of articles that evaluates how traces of oxygen modify the corrosion of pure iron and hydrogen permeation across iron membranes in H2S-containing solutions, the impact of changing the H2S partial pressure from 100 kPa to 0.1 kPa was investigated. It was found that bulk solution chemistry for all H2S partial pressures changes with time, due to the formation of H2S-O-2 reaction products (sulfates, sulfites, and thiosulfates), which results in bulk solution acidification. Electrochemical and weight-loss measurements confirm that Fe corrosion rates in baseline well-deaerated H2S-containing solutions decrease with decreasing H2S partial pressure, although these are observed to be much higher under continuous oxygen contamination. With decreasing H2S partial pressure, hydrogen uptake in Fe also decreases, due to lower and lower concentrations of dissolved H2S and the associated increase in pH. However, even at 1 kPa and 0.1 kPa H2S, permeation effciencies remain close to 100% when no O-2 contamination is present. The hydrogen uptake is always relatively lower in Fe exposed to oxygen-polluted H2S solutions. Permeation efficiencies decrease continuously. From electrochemical data and surface characterization, these observations at lower H2S partial pressures are attributed to the disruptive effect of oxygen on the nature of sulfide corrosion products, and hydrogen entry promotion, along with the contribution of an additional cathodic reaction that does not result in hydrogen entry into the metal.

Corrosion of iron exposed to H2S saturated solution at pH 4 was studied by electrochemical impedance spectroscopy, weight loss coupons and surface analysis. Hydrogen permeation was also used as indirect means of evaluating the intensity of the proton reduction reaction leading to hydrogen entry into the metal. Since corrosion in this type of test solution results in the rapid build-up of a conductive and highly porous iron sulfide scale, a specific contribution of the film has to be considered. An impedance model was thus proposed. The faradaic anodic impedance consists of a two-step reaction with charge transfer and adsorption - desorption. An additional contribution, associated with the conductive and highly porous iron sulfide film was added in parallel. This contribution, mostly visible in the low frequency domain, presents a 45 degrees tail associated with a porous electrode behavior. This model was well adapted to describe impedance diagrams measured at various exposure times, up to 620 h. Charge transfer resistance determined from impedance analysis allowed calculating the evolution with time of the corrosion current density. A very good correlation was found between this corrosion current density and the hydrogen permeation current density. As expected in our experimental conditions, a permeation efficiency close to 100% is demonstrated. Corrosion rate of 490 mu m/year was measured by weight-loss specimens, confirming the validity of the impedance analysis, which resulted in a calculated corrosion rate of 530 mu m/year. (C) 2018 Elsevier Ltd. All rights reserved.

This paper examines the influence of traces of oxygen on corrosion and hydrogen charging of steel in an H2S containing environment. It is well known that H2S promotes hydrogen entry into steels, th ...

Materials selection in the oil and gas industry relies on engineering standards, such as NACE TM0177 and NACE TM0284, which stipulate that oxygen pollution should be avoided during materials testing in H2S-containing media. In this paper, we explore the manner in which traces of oxygen can modify the test solution chemistry and the corrosion of/hydrogen permeation across iron membranes in H2S-containing solutions. Oxygen pollution is shown to strongly influence solution chemistry, through the introduction of sulfur-oxygen reaction products resulting in bulk acidification. Weight loss, electrochemical methods, and solution chemistry measurements conclude that iron corrosion rates in the presence of oxygen pollution are doubled, when compared against the control system (without oxygen pollution). Unexpectedly, despite a lower pH and higher corrosion rates in the oxygen-polluted H2S-containing solutions, the hydrogen permeation rate decreases monotonically, relative to the control. We discuss how this observation is most likely related to a disruption of sulfur adsorbates involved in hydrogen entry promotion.

This paper examines the influence of traces of oxygen on corrosion and hydrogen charging of steel in an H2S containing environment. It is well known that H2S promotes hydrogen entry into steels, that may result in many types of steel failures such as Hydrogen Induced Cracking (HIC), Sulfide Stress Cracking (SSC), and Stress-Oriented Hydrogen Induced Cracking (SOHIC). Since it is a huge concern for oil and gas industries, standard test methods have been developed and published as NACE technical methods (e.g. NACE TM0284 and NACE TM0177). Though it is recognized that oxygen pollution should be avoided during H2S cracking tests, there is still a lack of experimental data to illustrate the potential impacts of a small oxygen pollution. The aim of the present study is to check if oxygen traces can modify the mechanisms of corrosion and hydrogen charging of steel in H2S containing medium. Experiments consisted of hydrogen permeation measurements through a thin pure iron membrane. They were performed at free potential circuit in order to ensure more realistic environmental conditions. The corrosion rate was also evaluated and test solutions analyzed.

The modification of photo-generated charge transport properties in aligned titanium dioxide nanotubes (TiO2-NTs) regarding the anatase/rutile ratio was studied by photo-electrochemical methods. TiO2-NTs obtained by anodization were thermally treated under air flux at different temperatures to significantly modify the proportion of TiO2 anatase and rutile phases in the tubular structure. Material characterisation methods (XRD, SEM, UV-visible spectroscopy) were used to determine the characteristics of the different TiO2-NT electrodes in terms of dimensions, proportion of each phase and optical properties. The solar to chemical energy conversion efficiency of these electrodes during an oxidation process was investigated in basic aqueous solution, using methanol as a sacrificial agent, by cyclic voltametry and Incident Photon to Current conversion Efficiency (IPCE) measurements. TiO2-NTs with a high rutile content absorb photons of higher wavelengths, but despite this red shifted optical band gap, they exhibit the lowest photo-electrochemical conversion efficiency. To further investigate the transport properties in these photoelectrodes, Intensity-Modulated Photocurrent Spectroscopy (IMPS) was used with two different irradiation wavelengths to determine the transport and recombination properties of anatase and rutile separately. The results obtained by this set of experiments indicate that the presence of the rutile at the bottom of the nanotubes is the major factor limiting the photo-generated electron transfer.

Electrochemical methods (cyclic voltammetry (CV), potential steps, and electrochemical impedance spectroscopy) were successfully combined with in situ reflectometry measurements for a detailed analysis of the passive layer evolution as a function of the electrode potential. Interestingly, both EIS and surface reflectivity allowed a film thickness in the nanometer range to be readily determined. In addition, transient analyses of the reflectivity simultaneously recorded with CVs show the formation of both Fe2O3 and Fe3O4 oxides. The image analysis showed that the steel surface reactivity is heterogeneous and presents micrometric islands coated with a thicker oxide layer than the surrounding surface. The in situ combination of these techniques thus offers a powerful analytical description of the interface on a local scale and its transient response to a perturbation.

Steady-state polarization curves, X-ray photoelectron spectroscopy, and impedance spectroscopy were used to explore the electrochemical properties for carbon steel in alkaline electrolytes. The complex-capacitance representation allowed determination of a capacitance value at high frequency, from which the oxide film thickness could be estimated. These results are in good agreement with values obtained using the power-law model, providing a single mathematical model that is shown to apply in both the anodic and cathodic domains for the characterization of an oxide layer.

This paper examines the influence of oxygen traces on corrosion and hydrogen charging of steel in H2S containing environment. It is well known that H2S is the driving force for many types of steel ...

The corrosion of steel in concrete is an important phenomenon of degradation of reinforced concrete structures, which starts with the breakdown of the passive layer on steel surface. Reinforcing steel in concrete is usually passivated due to the formation of a protective oxide layer that remains stable in the high alkaline surrounding pore solution. However, carbonation and contamination with chlorides induce passive film breakdown and pitting corrosion initiation. Thus, corrosion inhibitors can be added to fresh concrete as admixtures. A new eco-friendly bio-admixture (BA) produced with extra-cellular substances from a Gram-negative bacteria (Pseudomonas) was tested as inhibitor of corrosion. BA was added at concentration of 10 v/v % to various simulated electrolytes representative of concrete pore solutions (CPS) extracted from different concrete mixtures (CEM I, CEM II and CEM III; w/c = 0.45). The objectives were to study the influence of (1) the chemical composition of CPS and (2) the bio-admixture on the electrochemical behaviour and the surface chemical composition of C15 carbon steel, used for reinforcement of building concrete. Electrochemical measurements: corrosion potential Ecorr as a function of time, polarization curves, electrochemical impedance spectroscopy were performed first in 0.1 M NaOH reference solution to understand the electrochemical behaviour of C15 mild steel by and then compared to those obtained in simulated CPS without or with BA. The pH of the synthetic CPS was adjusted to 13. The electrochemical results were combined to surface reflectivity. Experiments were also carried out in chlorides solution in order to study the effect of BA in localized corrosion conditions. The estimation of the oxide layer thickness using the Cole-Cole approach confirmed the presence of an oxide layer in an extended cathodic potential range in presence of BA.

Phénomène complexe, la corrosion atmosphérique définie comme l’interaction entre un matériau et les facteurs climatiques, ne peut se modéliser facilement. Il faut pourtant lutter contre ce fléau qui ronge nos ponts métalliques et modifie la conductivité des composants électroniques !