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A Practical Approach to Corrosion Failure Analysis
Published in Richard B. Eckert, Torben Lund Skovhus, Failure Analysis of Microbiologically Influenced Corrosion, 2021
Corrosion of steel under abiotic conditions produces iron oxides and oxyhydroxides, such as magnetite (Fe3O4), goethite (FeOOH) hematite (Fe2O3), maghemite (γ-Fe2O3), and lepidocrocite (FeOOH). In fresh and marine waters, two-line ferrihydrite is produced by iron-oxidizing bacteria (IOB), e.g., Leptothrix and Gallionella; however, it is unstable and transforms into goethite and/or hematite upon air exposure. As described by McNeil and Little (1990), Mackinawite is a form of iron sulfide (FeS1- x) characteristically produced by SRB; however, it can be produced in some cases by abiotic conditions as well. Manganese oxide (MnO2) is a mineral characteristic of manganese oxidizing bacteria (MOB) that is more likely to be found under more aerobic conditions.
The pe Changes in a Stratified Lake During a Period of Summer Stagnation: An Example of a Redox Titration
Published in James F. Pankow, Aquatic Chemistry Concepts, 2018
Since the production of the dissolved S(−II)T will take place after essentially all of the Fe(III) is reduced to Fe(II), we finally ask if the S(−II)T will build up enough to allow FeS(s) to form. The common mineral form of FeS(s) is mackinawite. At 25°C/1 atm, the Ks0 for this metal sulfide is 10−18.0. Once the system has become sufficiently reducing for significant formation of S(−II)T to occur, all of the (am)Fe(OH)3(s) will have been reduced to Fe(II)T (with only trace levels of dissolved Fe(III)T remaining), and so Fe(II)Twill equal 8.953032 × 10−6M. Taking pH = 6.60 as an estimate for that point, α0Fe(II)will equal ˜1.00, and α2 for the H2S system will equal 1.13 × 10−8. Thus, since S(−II)Trepresents the total concentration of dissolved S(−II), FeS(s) will start to form once () S(−II)T=10−18.0(1.13×10−8)(1.00)(8.953032×10−6)=9.92×10−6M
Practical Cases
Published in Héctor A. Videla, Manual of Biocorrosion, 2018
The role of bacteria in cathodic depolarization has been minimized by King and Miller29 who attributed this effect to the iron sulfide. Thus, the role of SRB would be limited to the removal of hydrogen atoms linked to ferrous sulfide crystals, whereas the iron sulfide lattice would act as cathodes for the hydrogen reaction. Later publications30 seem to confirm the depolarizing effect of ferrous sulfide on the hydrogen evolution reaction. A weak point of the CDT is the lack of information on the role of sulfides in the stimulation of the anodic reaction. As the localized corrosion and breakdown process is strongly dependent on several experimental factors such as the type and concentration of aggressive anions present in the medium and the protective film characteristics, the effect of sulfur anions has been studied in a series of laboratory experiments using alkaline31 and neutral buffered32 solutions as well as SRB cultures in saline media33 under well defined experimental conditions. Given the results of these studies, a bioelectrochemical interpretation of the biocorrosion process of carbon steel in anaerobic environments may be summarized as follows:21Biogenic sulfides effects on carbon steel localized corrosion are similar to that of abiotic sulfides. The characteristics and intensity of sulfide effects on the corrosion behavior of carbon steel are closely related to the nature of the protective film already present on the metal surface.In neutral media, sulfide ions lead to the formation of a poorly protective film of mackinawite.The anodic breakdown of passivity would be the first stage of the corrosion process. Thus, the role of SRB may be indirect through the production of aggressive species either as final (sulfides, bisulfides, or hydrogen sulfide) or intermediate metabolic compounds (thiosulfates, polythionates). Physicochemical characteristiscs of the liquid environment (pH, ionic composition, oxygen levels) can modify the SRB effects which could eventually change from corrosive to passivating.Cathodic depolarization effects attributed to SRB hydrogenase activity or to iron sulfide films would be developed later than passivity breakdown while the corrosion process is in progress.The action of biogenic sulfides can be enhanced by other aggressive anions already present in the environment (e.g., chlorides)34 or through microbial consortia within biofilms on the metal surface.35–37
Effect of interaction between corrosion film and H2S/CO2 partial pressure ratio on the hydrogen permeation in X80 pipeline steel
Published in Corrosion Engineering, Science and Technology, 2020
Chengshuang Zhou, Bei Fang, Jing Wang, Shiyin Hu, Baoguo Ye, Yanming He, Jinyang Zheng, Lin Zhang
Figure 5 shows SEM photographs of the surface of specimens served in the hydrogen permeation test with different H2S/CO2 partial pressure ratios. Figure 6 is an XRD pattern for corrosion films formed on the permeation specimens. Figure 5(a) shows that the inner layer of corrosion products in 0.1 MPa pure H2S environment has a relatively dense film. There were unfixed crystal particles on the film. The XRD result in Figure 6 indicated that the corrosion product is FeS (Mackinawite). Figure 5(b) shows that the corrosion product film at a total pressure of 1 MPa and H2S/CO2 partial pressure ratio of 1/10 is similar to that in 0.1 MPa pure H2S environment. The unevenly sized loose powder was attached to the corrosion product film, and the corrosion product was confirmed to be Mackinawite by the XRD result. The corrosion product film in a total pressure of 1 MPa and a partial pressure ratio of H2S/CO2 of 1/100 was shown in Figure 5(c). The corrosion product film was partially peeled off without particles on the surface. The XRD result shows that the corrosion product is a mixture of FeCO3 and FeS. Figure 5(d) shows that the corrosion product film consists of fine crystals with high density at a total pressure of 1 MPa and a partial pressure ratio of H2S/CO2 of 1/1000. The film is confirmed to be FeCO3 by the XRD result.
Magnetic sorbents biomineralization on the basis of iron sulphides
Published in Environmental Technology, 2018
Jana Jencarova, Alena Luptakova, Nikola Vitkovska, Dalibor Matysek, Petr Jandacka
The exact progress of iron sulphides formation is still discussed. In sediments, the first step, which is usually quite fast, involves reaction of Fe2+ (produced during biological Fe3+ reduction) with pore water sulphide in the form of HS− and forming FeS. Next, iron monosulphide converts into mackinawite. Mackinawite can react with elemental sulphur to form greigite [40]. It is generally admitted that greigite forms, in anhydrous conditions, via a solid-state transformation involving only a rearrangement of Fe cations within the cubic close-packed S array of mackinawite [56]. So, through a series of transformations amorphous sulphide might transform to a crystal form [57]. We expected occurrence of similar processes in performed laboratory experiments during 10 months.