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The Mechanism of the Oxygen Reduction on Rust-covered Metal Substrates
Abstract
Oxygen reduction is a major cathodic partial reaction during the corrosion of iron. The reaction is greater than the H+ reduction reaction for pH values >4. In the same pH range the iron surface is covered by insoluble oxide layers like rust scales. As rust scales are reduced in the potential range of the oxygen reduction, it was the aim of this study to analyse the relation between the kinetics of the oxygen reduction and the reduction of the rust layer. The results presented in this paper show that oxygen is predominantly reduced within the rust scale and not at the metal/electrolyte phase boundary. In order to allow any oxygen reduction, the rust layers have to be reduced. Oxidized rust scales, which are nearly free of Fe2+ states, inhibit the reduction of oxygen completely.
... The consideration of processes within the oxide film suggests (e.g. Stratmann and Müller, 1994) Stratmann and Müller (1994) reported that oxygen is predominantly reduced within the oxide film and not at the metal/electrolyte interface. The enhancement of nitrate reduction in Fe 0 -H 2 O systems by addition of external Fe 2+ (Zhang and Huang, 2006) confirms the results of Stratmann and Müller (1994) and their general relevance for ...
... The consideration of processes within the oxide film suggests (e.g. Stratmann and Müller, 1994) Stratmann and Müller (1994) reported that oxygen is predominantly reduced within the oxide film and not at the metal/electrolyte interface. The enhancement of nitrate reduction in Fe 0 -H 2 O systems by addition of external Fe 2+ (Zhang and Huang, 2006) confirms the results of Stratmann and Müller (1994) and their general relevance for ...
... Stratmann and Müller, 1994) Stratmann and Müller (1994) reported that oxygen is predominantly reduced within the oxide film and not at the metal/electrolyte interface. The enhancement of nitrate reduction in Fe 0 -H 2 O systems by addition of external Fe 2+ (Zhang and Huang, 2006) confirms the results of Stratmann and Müller (1994) and their general relevance for ...
The reactivity of elemental iron, Fe0 is widely investigated for use in permeable
reactive barriers. Fe0 is known for its efficient removal of a wide range of contaminants, like organic and inorganic substances, heavy metals and viruses.
Beside its efficacy, Fe0 is unexpensive and available in quantities huge enough for
the use in permeable reactive barriers. Aqueous decontamination by Fe0 (e.g., in Fe0-H2O systems) may proceed by (i) contaminant adsorption onto Fe0, aged and nascentFe0 corrosion products, (ii) contaminant co-precipitation with nascent Fe0
corrosion products, (iii) contaminant reduction by Fe0 (direct reduction), and (iv) contaminant reduction by FeII and atomic or molecular hydrogen (indirect reduction). Investigations for the efficacy of Fe0 are abundantly performed under shaken conditions.
In this work the influence of shaking intensities on the decontamination in “Fe0-H2O” systems was investigated. Methylene blue (MB) was used as a model contaminant for the characterization of the removal efficiency of Fe0. MB is both
easy in handling and inexpensive and its adsorption behavior is comparable with
several organic contaminants. Besides, it is a contaminant of the textile industry
itself. MnO2 and GAC were added as comparable systems to the “Fe0-H2O” system
for a better understanding of proceeding processes in this system. Investigations were performed under non-shaken, mild and violent shaken conditions. Shaking duration was either one day, three or five days.
It could be shown, that shaking intensity as well as shaking duration has a significant influence on the discoloration of MB and thus decontamination. The generation of corrosion products was accelerated and the contaminant removal, which is mainly due to adsorption and co-precipitation on in-situ generated corrosion products, increased significantly. Furthermore, the pattern of discoloration, i.e. decontamination, under shaken conditions differed strongly from the pattern seen in the undisturbed experiments.
Data obtained by this work indicate, that experiments performed under shaken conditions might be difficult in transfer to reality and when compared with each other. Therefore, investigation of decontamination efficiency or removal mechanisms should be performed under undisturbed (non-shaken) conditions
... In previous works [21][22][23] the contribution of the rust layer in the atmospheric corrosion mechanism of iron and carbon steel was investigated. The corrosion rate increases during drying due an enhancement of oxygen diffusion and thinning of the electrolyte layer [22,23], reaching a maximum value right before the complete drying out of the surface. ...
... In previous works [21][22][23] the contribution of the rust layer in the atmospheric corrosion mechanism of iron and carbon steel was investigated. The corrosion rate increases during drying due an enhancement of oxygen diffusion and thinning of the electrolyte layer [22,23], reaching a maximum value right before the complete drying out of the surface. The composition of a rust layer changes periodically from an oxidized state Fe 3+ to a Fe 2+ enriched reduced state. ...
... The composition of a rust layer changes periodically from an oxidized state Fe 3+ to a Fe 2+ enriched reduced state. The rust formed on the steel is reduced at potentials more negative than 0 V vs SHE during wetting, and Fe 2+ species are created within the lattice of the lepidocrocite (ƴ-FeOOH) [21,22]. As result, an increase of the n-type semiconducting oxide conductivity is produced. ...
... Electron transfer to any adsorbed species only occurs if there is no conduction barrier at the Fe 0 surface (Landolt 2007, Nesic 2007, Lazzari 2008, Groysman 2010. It is well-known that, at pH > 4.5, an oxide scale forms on the Fe 0 surface and shields it from dissolved species, including dissolved O2 (Stratmann andMüller 1994, Lazzari 2008). For the EE concept to be applicable, it means that the universal oxide scale on Fe 0 should be electronically conductive, which is not the case in Fe 0 /H2O systems (Noubactep 2014, Noubactep 2016. Figure The electrochemical reaction for aqueous iron corrosion is depicted in Equation 1: shift to lower values is not typically envisaged such that a pH increase occurs as a rule (Lipczynska-Kochany et al. 1994, Matheson and Tratnyek 1994, Schreier and Reinhard 1994, Hu et al. 2021). ...
... In other words, the oxide scale, acting as diffusion barrier for contaminants and dissolved O2, also represents a conductive barrier for electrons from Fe 0 . For this reason, electrons from the metal body cannot (quantitatively) reduce any initially dissolved species (contaminants and O2) ( Figure 1) (Stratmann and Müller 1994, Jiao et al. 2009, Noubactep 2013, Noubactep 2019. Clearly, the EE concept is built on a thinking mistake. ...
... However, there are two more intriguing facts: (i) Fe 0 oxidation by water is not discussed, and (ii) water is just considered as a proton source for reaction after Eq. 3. The presentation of the authors textually reads, alkyl halides "can also be reduced by iron. In the presence of a proton donor like water, they typically undergo reductive dehalogenation" This means that the seminal work of Whitney (1903) was ignored as well as thousands of works describing corrosion as resulting from the presence of water, including impurities in natural oil (Brondel et al. 1994) and atmospheric humidity (Stratmann and Müller 1994). Moreover, the is no iron corrosion in dry (H2O free) chlorinated solvents (Rhodes andCarty 1925, Archer 1979). ...
The suitability of remediation systems using metallic iron (Fe0) has been extensively discussed during the past 3 decades. It has been established that aqueous Fe0 oxidative dissolution is not caused by the presence of any contaminant. Instead, the reductive transformation of contaminants is a consequence of Fe0 oxidation. Yet researchers are still maintaining that electrons from the metal body are involved in the process of contaminant reduction. According to the electron efficiency concept, electrons from Fe0 should be redistributed to: i) contaminants of concern (COCs), ii) natural reducing agents (e.g., H2O, O2), and/or iii) reducible co-contaminants (e.g. NO3-). The electron efficiency is defined as the fraction of electrons from Fe0 oxidation which is utilized for the reductive transformations of COCs. This concept is in frontal contradiction with the view that Fe0 is not directly involved in the process of contaminant reduction. This communication recalls the universality of the concept that reductive processes observed in remediation Fe0/H2O systems are mediated by primary (e.g., FeII, H/H2) and secondary (e.g., Fe3O4, green rusts) products of aqueous iron corrosion. The critical evaluation of the electron efficiency concept suggests that it should be abandoned. Instead, research efforts should be directed towards tackling the real challenges for the design of sustainable Fe0-based water treatment systems based on fundamental mechanisms of iron corrosion.
... Below the E corr , the cathodic reduction reaction is evidenced. This behavior is associated with the oxygen reduction reaction (O 2 + 2H 2 O + 4e − → 4OH − ), which is the most common reaction carried out in chloride solutions and near-neutral pH media [39]. Additionally, a mixed activation-diffusion control is evidenced. ...
... Below the Ecorr, the cathodic reduction reaction is evidenced. This behavior is associated with the oxygen reduction reaction (O2 + 2H2O + 4e − → 4OH − ), which is the most common reaction carried out in chloride solutions and near-neutral pH media [39]. Additionally, a mixed activation-diffusion control is evidenced. ...
Advanced high-strength steels (AHSSs) are designed for meeting strict requirements, especially in the automotive industry, as a means to directly influence the reduction in the carbon footprint. As rotary friction welding (RFW) has many important advantages over other welding technologies, it plays an important role in the automotive sector. On the above basis, in this work, combinations of the first (complex phase (CP)), second (TWIP (TW)), and third (quenched and partitioned (Q&P)) generations of similar and dissimilar high-alloyed advanced steels have been joined by the RFW process. Having a specific microstructure, rods of CP/CP, Q&P/Q&P, CP/TW, and Q&P/TW steels were welded by employing a homemade adaptation machine under fixed parameters. Microstructural characterization has allowed us to corroborate the metallic bonding of all the tested advanced steels and to identify the different zones formed after welding. Results indicate that the welding zone widens in the center of the workpiece, and under the current friction action, the intermixing region shows the redistribution of solute elements, mostly in the dissimilarly welded steels. Furthermore, because of their complex chemistry and the different mechanical properties of the used steels, dissimilarly welded steels present the most noticeable differences in hardness. The TWIP steel has the lower hardness values, whilst the CP and Q&P steels have the higher ones. As a direct effect of the viscoplastic behavior of the steels established by the thermomechanical processing, interlayers and oxidation products were identified, as well as some typical RFW defects. The electrochemical response of the welded steels has shown that the compositional and microstructural condition mostly affect the corrosion trend. This means that the dissimilarly welded steels are more susceptible to corrosion, especially at the TWIP–steel interface, which is attributed to the energy that is stored in the distorted microstructure of each steel plate as a consequence of the thermomechanical processing during RFW.
... Resulted Fe 3+ acts as an oxidant, also for Fe 0 . The generated ions (Fe 2+ and Fe 3+ ) react with water and form hydroxides, which after many series of reactions form oxides (Table 1) (Stratmann and Müller 1994). ...
... Depending on the film permeability structure, the contamination migrates because of molecular diffusion and electromigration (van der Kamp et al. 1996, Nordsveen et al. 2003. The process of iron corrosion (1) produces Fe 2+ ions (Stratmann and Müller 1994), (2) exhaust O2, H + ions, in addition to the contamination near the surface of Fe 0 , and (3) causes a change in concentration between the contaminants and particles crossways the oxide film and create the molecular diffusion (Noubactep 2008b, 2009a, Noubactep 2009b, Noubactep et al 2009b, Noubactep et al 2009c, Noubactep 2010b, Gunawardana et al. 2011, Noubactep 2012b. The oxide film is considered as an electron conductor, through which electrons are transferred from Fe 0 surface to the bulk solution and contaminants. ...
The concept that metallic iron (Fe0) is a reducing agent under environmental conditions has urged the large-scale application of Fe0 filters for environmental remediation and water treatment. During the past two decades, some 3,000 scientific articles have widely discussed the importance of processes yielding water treatment in Fe0/H2O systems. The current state-of-the-art knowledge is that Fe0 is the generator of (i) contaminant scavengers (iron hydroxides/oxides), and (ii) reducing agents (e.g. H/H2, FeII, green rusts, Fe3O4). In other words, contaminant reductive transformation in the presence of Fe0 is not mediated by electrons from the metal body (direct reduction).
The realization that Fe0 is not the reducing agent in Fe0/H2O systems has redirected fundamental researches on the operating mode of Fe0 filters. In this effort, a cationic azo dye (methylene blue, MB) has been presented as reactivity indicator to characterize changes in Fe0/H2O systems. The present study investigates the impact of contact time on the efficiency of Fe0/H2O systems. The research questions are "is there any direct relationship between experimental duration and system's efficiency?" If yes, how is the efficiency modified in the presence of natural additives such as manganese oxides (MnO2) and sand? Both research questions are justified by the evidence that the Fe0 surface is constantly shielded by an oxide scale which has been reported to mediate a 'reactivity loss' of Fe0 materials.
The methodology consists of (i) varying the experimental duration, and (ii) modifying the Fe0/H2O system by amending it with various amounts of MnO2 and sand. The efficiency of Fe0/sand/MnO2 systems for water treatment is characterized using methylene blue (MB) as reactivity indicator. Batch experiments using various weight ratios of Fe0 and the two additives were performed for up to six weeks (47 days). The impact of the intrinsic reactivity of MnO2 was characterized by using different types of MnO2. The MB discoloration process was investigated both under shaking and non-disturbed conditions.
The results clearly demonstrate the impact of increased contact time on the extent of MB discoloration in all tested systems (Fe0, Fe0/sand, Fe0/MnO2 and Fe0/sand/MnO2). As a rule, MB discoloration was improved by increased experimental duration. It was noted that the extent of MB discoloration is influenced by the diffusive (or advective) transport of MB from the solution to the reactive materials at the bottom of the test tubes. Without shaking, more time is needed for the transport of MB to the particles of tested materials. For experiments lasting for longer times, sand addition prevented Fe0 particles from compaction (cementation) at the bottom of the test-tubes. This enabled the long-term generation of iron hydroxides (new iron corrosion products) for the discoloration of MB by adsorption and co-precipitation. The same observation was made for Fe0/MnO2 systems. In other words, the addition of non-expansive materials (e.g. MnO2, sand) is necessary to sustain the efficiency of Fe0 filters. Shaking the test tubes increased the extent of MB discoloration by two different mechanisms: (i) speeding up the mass transport of MB solution towards the adsorptive materials, and (ii) speeding up the kinetics of Fe0 corrosion, creating new corrosion products. Discoloration processes occur due to MB diffusion and advection which are accelerated during the shaking operation. The results clearly delineate the complexity of the Fe0/MnO2/sand system and suggest that varying the experimental conditions will give more opportunities to discuss the efficiency of Fe0/H2O systems.
... Combined X and neutron imaging - Letters a, b, c, d, e, f, g and h refer to the location and scale of measurement, as defined in Fig. 1 Parentheses () indicate that the method may potentially be applicable under certain conditions but lacks well-documented evidence Endash ''-'' indicates that the method is not applicable [13] and reduction of Fe(III)-rich phases to Fe(II)-rich phases on mill scale/rust layers [5] Materials and Structures (2022) 55:124 Fe(III)-rich phases (which are generally insulating) and the lack of an electrolyte needed for the electrochemical reactions to occur at an appreciable rate [14]. When concrete is saturated, the Fe(III)-rich phases can be reduced to Fe(II) compounds, and this generates a cathodic current (in addition to the oxygen reduction reaction) to sustain anodic reactions [14,15] in the crevice. ...
... Combined X and neutron imaging - Letters a, b, c, d, e, f, g and h refer to the location and scale of measurement, as defined in Fig. 1 Parentheses () indicate that the method may potentially be applicable under certain conditions but lacks well-documented evidence Endash ''-'' indicates that the method is not applicable [13] and reduction of Fe(III)-rich phases to Fe(II)-rich phases on mill scale/rust layers [5] Materials and Structures (2022) 55:124 Fe(III)-rich phases (which are generally insulating) and the lack of an electrolyte needed for the electrochemical reactions to occur at an appreciable rate [14]. When concrete is saturated, the Fe(III)-rich phases can be reduced to Fe(II) compounds, and this generates a cathodic current (in addition to the oxygen reduction reaction) to sustain anodic reactions [14,15] in the crevice. As a result, the presence of rust layers (and potentially mill scale) may have a catalysing effect on the corrosion process, as illustrated in Fig. 2. ...
The steel–concrete interface (SCI) is a complex, multi-phase and multi-scale system. It is widely known to influence the performance and long-term durability of concrete structures. However, a fundamental understanding of its properties and effects on corrosion initiation of embedded reinforcing steel remains elusive. This is attributed to its complicated heterogeneity and time-dependent nature, exacerbated by the lack of suitable techniques for systematic and detailed characterisation. This paper, prepared by members of the RILEM Technical Committee 262-SCI, critically reviews available information regarding current methods (laboratory or field-based) for characterising local properties of the SCI that have been identified as governing factors affecting corrosion initiation. These properties include characteristics of the steel such as mill scale and rust layers, and characteristics of the concrete such as interfacial voids, microstructure and moisture content. We evaluated over twenty methods and summarised their advantages, applications and limitations. The findings show a severe lack of well established, non-destructive techniques that are suitable for direct monitoring of the SCI at a representative scale with sufficiently high resolution (spatial, temporal), particularly for moisture related aspects. Several promising novel techniques with significant potential for further development and application were identified and discussed. Finally, we provide several recommendations for future research needs that are required to advance this critically important topic.
... The detection of magnesium hydroxide indicates that anodic and cathodic areas were strongly separated on the corroding surface. Cathodic sites are supposed to be alkali under atmospheric exposure conditions [40]. The corrosion products formed on the steel surfaces were studied more in detail with XRD, focusing on the two higher salt loading densities. ...
... The detection of magnesium hydroxide indicates that anodic and cathodic areas were strongly separated on the corroding surface. Cathodic sites are supposed to be alkali under atmospheric exposure conditions [40]. (Figure 8). ...
Atmospheric corrosion is one of the major sources of hydrogen in a high-strength-steel product in service. Even low concentrations of absorbed hydrogen can cause a hydrogen embrittlement-related material degradation. The extent of atmospheric corrosion and thus the related hydrogen entry is highly dependent on the environmental parameters, such as the relative humidity. The present work focused on the hydrogen entry at low relative humidity, where atmospheric corrosion rates are expected to be low. Hydrogen insertion and distribution in CP1000 steel induced by corrosion under dried and rewetted single droplets of aqueous NaCl and MgCl2 solution were studied using the Scanning Kelvin Probe (SKP) and the resulting amounts of diffusible hydrogen were analyzed using thermal desorption mass spectrometry (TDMS). Corrosion product analyses were carried out with SEM/EDX, XRD, and Mössbauer spectroscopy. The results revealed the strong impact of salt type and concentration on the hydrogen entry into steel. The hygroscopic effect of MgCl2 and the formed corrosion products were responsible for the prolonged insertion of hydrogen into the steel even at very low levels of relative humidity.
... Next to O 2 , also Fe(III) can be electrochemically reduced forming magnetite (Sarin et al., 2004b). Electrons may be conducted through minerals in the corrosion scale (such as magnetite) (Cornell & Schwertmann, 1996) or through Fe 2+ adsorbed to Fe(III) minerals such as goethite and lepidocrocite (Stratmann & Müller, 1994). All these mineral phases were detected in our tubercles. ...
The extent of how complex natural microbial communities contribute to metal corrosion is still not fully resolved, especially not for freshwater environments. In order to elucidate the key processes, we investigated rust tubercles forming massively on sheet piles along the river Havel (Germany) applying a complementary set of techniques. In-situ microsensor profiling revealed steep gradients of O2 , redox potential and pH within the tubercle. Micro-computed tomography and scanning electron microscopy showed a multi-layered inner structure with chambers and channels and various organisms embedded in the mineral matrix. Using Mössbauer spectroscopy we identified typical corrosion products including electrically conductive iron (Fe) minerals. Determination of bacterial gene copy numbers and sequencing of 16S rRNA and 18S rRNA amplicons supported a densely populated tubercle matrix with a phylogenetically and metabolically diverse microbial community. Based on our results and previous models of physic(electro)chemical reactions, we propose here a comprehensive concept of tubercle formation highlighting the crucial reactions and microorganisms involved (such as phototrophs, fermenting bacteria, dissimilatory sulphate and Fe(III) reducers) in metal corrosion in freshwaters.
... [7][8][9][10] The two principal reduction reactions of interest in aqueous solutions are oxygen reduction and hydrogen evolution. Stratman and Muller 11 showed that oxygen reduction principally occurs at Fe 2+ sites within the oxide. A study by Le Bozec and colleagues, 12 which examined the effect of surface treatments on the cathodic polarization behavior of stainless steels, showed that reduction of iron species in the oxide improved the overall oxygen reduction reaction (ORR) capability of the oxide. ...
The cathodic polarization behavior of UNS S13800 in NaCl solutions, ranging from dilute to saturated, and across a range of temperature values was studied using potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), and x-ray photoelectron spectroscopy (XPS). Analysis of the data indicated that the concentration of the solutions affected the ability of the oxide to catalyze reduction reactions. Dilute-to-low concentration solutions exhibited different Tafel slopes at low and high cathodic potentials while middle-to-high concentration solutions exhibited a single Tafel slope. The XPS data showed the oxides formed in low chloride solutions had a higher Fe2O3 concentration while the oxides formed in the high chloride solution had a higher Cr2O3 concentration. The EIS data showed the oxides had a similar thickness, but the oxide formed in the low chloride solution had a higher charge-transfer resistance while the oxide formed in the high chloride solution had a higher oxide resistance. A method for analyzing cathodic polarization curves on stainless steels is described and a framework for predicting the cathodic polarization response for UNS S13800 is developed, including a model for the diffusivity of dissolved oxygen as a function of chloride concentration and temperature.
... The cathodic branch is associated with the oxygen reduction reaction. According to Strattman et al. [44], this reduction reaction is the most prominent in neutral and aerated NaCl solutions. The alloy composition and the process route of the steel samples (P1 or P2 routes) modify the reaction kinetics of the system. ...
The objective of this research work is to obtain the hot ductility behavior, and the structural, microstructural and mechanical characteristics of one of the latest generation of AHSS steels, a complex phase (CP) steel microalloyed with boron (0.006 wt.%), processed by hot and cold rolling operations and heat-treated using two different quenching and partitioning (Q&P) treatments, a one-step partitioning (quenching to 420 °C) and the other a two-step partitioning (quenching to 420 °C and reheated to 600 °C). The results show that boron has a marked effect on the solidification process of the CP steel, refining the austenitic grain size. Due to its refinement, the boron-containing steel had better ductility throughout the temperature range examined (700–900 °C), i.e., the hot ductility trough. Thus, the minimum percentage of reduction in area (%RA) value occurring at 800 °C was 43% for the boron-free steel, compared with 58% for the boron-containing steel. Hence, cracking would not be a problem when straightening the strand on continuous casting. The benefit of boron addition on the room temperature properties was found to be very marked for the higher temperature two-step partitioning treatment, giving a yield stress of 1200 MPa, a UTS (ultimate tensile strength) of 1590 MPa and a total elongation above 11%. The final Q&P microstructure, in both one- and two-step partitioning conditions, consisted of retained austenite (RA-γ), martensite and ferrite islands in a bainitic matrix. Furthermore, the boron treated steel on quenching produced a greater amount of RA-γ, which accounted for its better room temperature ductility and produced a martensitic matrix rather than a bainitic one, giving it greater strength. The addition of boron improved the corrosion resistance of this type of third generation AHSS steel.
... Oxidation is the process where a metal loses electrons to oxygen and other substances in the air or water. As oxygen is reduced, an oxide layer is formed on the metal [1]. This process can damage the overall integrity of the metal. ...
... So further work we could focus on extracting more sensitive features which will help to identify corrosion more clearly. According to Stratmann et al. atmospheric corrosion mechanism could be separated into three stages: Wetting of the dry surface [40], Wet surface [41] and Drying out of the surface. Where maximum metal loss occurs in wet-dry cycle which predominantly take place in stage three, at this point rate of corrosion top. ...
As the most widely used material, metal has been applied to social and industrial
infrastructures. Asthe corrosion causes mechanical failure costing a huge amount of money
every year. So, detection of Corrosion for the safety of both society and industry is
significantly important. For solution a plenty of nondestructive testing and evaluation
(NDT&E) techniques were adopted. Such as ultrasonic testing (UT), eddy-current testing
(ECT), radiographic testing (RT) and electromagnetic methods. In comparison with other
methodologies, Magnetic Barkhausen Noise (MBN) is a novel NDT&E technique which
provides an opportunity for efficient nondestructive testing and has been applied to detect
defect and characterization for ferromagnetic materials.
In this paper an approach for surface corrosion detection using MBN is introduced as
NDT&E method. During this study 6 sheets of steel has been used for inspection, half of
them kept under water to expose these to have corrosion and other halves were kept on safe
environment for 1, 6 & 12 months respectively, giving 3 sets of data each containing
measurements with corrosion and without. MBN method was employed to have
measurement data form the specimens using an oscilloscope. These data then processed,
characterized, analyzed and finally corroded specimen’s data are compared with the non�corroded specimens to build up a relationship between MBN and corrosion.
At the end of this study the result showed a very complex characteristics in terms of
corrosion. A very few features of MBN were found sensitive and others were random.
Which will lead us to improve the method and work on the limitation that has been
encountered during this study.
Keywords: Non-destructive testing, Magnetic Barkhausen Noise, surface corrosion, defect
detection
... On the one hand, increasing the concentration of the solution will lead to an increase in the conductivity of the solution, accelerating the corrosion process; on the other hand, the solution concentration continues to increase but will reduce the content of dissolved oxygen and lead to an increase in the concentration of Fe 2+ near the anode, thereby increasing the resistance to electron transfer, inhibiting the reaction, and resulting in a reduction in the corrosion rate. Later, surface corrosion products were gradually generated by accumulation, but due to the presence of Cl − , pitting corrosion was easily triggered, reducing the area of the protective corrosion product layer; the reduction in the amount of corrosion products is gradually involved in the corrosion process, causing corrosion to occur further, thus increasing the corrosion rate [19,20]. ...
This paper analyzed the corrosion behavior and corrosion performance of ER8 wheel steel through a full immersion test. The average corrosion rate of the ER8 wheel specimen in 2.0% NaCl solution shows a gradual increase over the whole corrosion cycle. Although the corrosion rate showed fluctuations at 3.5% and 5.0% concentration before 576 h, the corrosion rate also showed a steady increase after 576 h. The corrosion rates of specimens at different concentrations after 2160 h were over 0.12 mm/year. With increasing immersion times or concentrations of NaCl solution, the coverage area of the corrosion products dominated by iron oxides gradually increased, and the corrosion products on the surface became denser. The corrosion products were primarily γ-FeOOH, α-FeOOH and Fe3O4. As the density of the surface corrosion products increased, cracks and holes appeared on the surface of the rust layers, which made the rust layer unable to protect the substrate from further corrosion. After removing the corrosion products, pitting corrosion appeared on the surface of the substrate. The radius of the capacitive reactance arc gradually decreased with the increasing immersion time. The impedance modulus in the low-frequency region decreases and then increases with increasing NaCl solution concentration, which is the highest in 3.5% NaCl solution. Icorr increased with an increasing Cl− concentration, which was similar to the mechanism of catalytic electrolysis due to Cl−. The specimens with rust layers have worse corrosion resistance when the immersion time is extended. The corrosion product did not protect the substrate but accelerated the corrosion process.
... Malgré cela, les vitesses de corrosion à l'état passif mesurées restent équivalentes avec ou sans défaut d'interface et inférieures à 0,6 μA/an (0,05 μA/cm 2 ). En ce qui concerne la corrosion par carbonatation, l'étude montre clairement que les courants de corrosion galvaniques pouvant se développer entre différentes zones de ferraillage peuvent être extrêmement importants notamment en présence de défaut d'interface acier-béton.Abderrahmane SOUFI.[26] L'objectif principal de ce travail est de réaliser une analyse performancielle sur des mortiers de réparation industriels et de proposer un meilleur choix quant à l'utilisation de ces matériaux dans un milieu marin. ...
est une recherche scientifique d'étudier Influence des conditions
environnementales sur la corrosion des
bétons armés à base de granulats de
baryte
... Malgré cela, les vitesses de corrosion à l'état passif mesurées restent équivalentes avec ou sans défaut d'interface et inférieures à 0,6 μA/an (0,05 μA/cm 2 ). En ce qui concerne la corrosion par carbonatation, l'étude montre clairement que les courants de corrosion galvaniques pouvant se développer entre différentes zones de ferraillage peuvent être extrêmement importants notamment en présence de défaut d'interface acier-béton.Abderrahmane SOUFI.[26] L'objectif principal de ce travail est de réaliser une analyse performancielle sur des mortiers de réparation industriels et de proposer un meilleur choix quant à l'utilisation de ces matériaux dans un milieu marin. ...
est une recherche scientifique d'étudier Influence des conditions
environnementales sur la corrosion des
bétons armés à base de granulats de
baryte
... Iron (Fe) Fe-NPs are frequently applied for enhanced reduction of Cr(VI) because of their strong reducing ability, outstanding performance, low cost, and ease of availability (Bruton et al., 2015;Lv et al., 2017;Ponder et al., 2000). Zero-valent iron (ZVI) can react with water and oxygen in which iron provides electrons to water and Fe(II) delivers electrons to O 2 (Stratmann and Müller, 1994). Ions such as Cr (VI) can rapidly take electrons and fall to lower oxidation states (Fiúza et al., 2010). ...
... The corrosion of CS is influenced by the buildup of insoluble rust layers on the surface, which can inhibit O 2 reduction if they are composed of Fe III phases. 37 With a 10:1 Cu:CS area ratio, in the absence of bentonite, the build-up of corrosion products caused the gradual decrease in E g by blocking surface reactivity while the Cu functioned effectively as an inert O 2 reduction electrode. The abundant corrosion product found on the CS was composed primarily of Fe III phases: maghemite, goethite, and lepidocrocite. ...
The long-term containment plan for Canada’s used nuclear fuel employs copper-coated carbon steel (CS) containers encased in compacted bentonite clay buffer boxes. In the hypothetical case of a through-coating defect, galvanic interactions between the Cu coating and the CS vessel are dependent on the conditions at the container surface. A zero-resistance ammeter was used to measure the galvanic current between Cu and CS electrodes at various area ratios in the presence of aerated 1 M NaCl and obstructive layers of bentonite slurry. The presence of bentonite resulted in an order of magnitude decrease in the corrosion rate of the steel. Through scanning electron microscopy with energy dispersive X-ray analysis and Raman spectroscopy, we showed that in the presence of bentonite slurry, the extent of steel corrosion decreased significantly, favoring mild surface etching over oxide growth. Electrochemical impedance spectroscopy measurements showed that the total impedance on carbon steel generally increased with bentonite layer thickness, but the total impedance on Cu plateaued when the layer exceeded 6 mm, consistent with trends in galvanic current density on carbon steel. The benign conditions produced by the bentonite slurry are attributed to the slightly alkaline pH and the hindrance of O2 diffusion.
... Iron (Fe) Fe-NPs are frequently applied for enhanced reduction of Cr(VI) because of their strong reducing ability, outstanding performance, low cost, and ease of availability (Bruton et al., 2015;Lv et al., 2017;Ponder et al., 2000). Zero-valent iron (ZVI) can react with water and oxygen in which iron provides electrons to water and Fe(II) delivers electrons to O 2 (Stratmann and Müller, 1994). Ions such as Cr (VI) can rapidly take electrons and fall to lower oxidation states (Fiúza et al., 2010). ...
The ever increasing concentration of toxic and carcinogenic hexavalent chromium (Cr (VI)) in various environmental mediums including water-bodies due to anthropogenic activities with rapid civilization and industrialization have become the major issue throughout the globe during last few decades. Therefore, developing new strategies for the treatment of Cr(VI) contaminated wastewaters are in great demand and have become a topical issue in academia and industry. To date, various techniques have been used for the remediation of Cr(VI) contaminated wastewaters including solvent extraction, adsorption, catalytic reduction, membrane filtration, biological treatment, coagulation, ion exchange and photo-catalytic reduction. Among these methods, the transformation of highly toxic Cr(VI) to benign Cr(III) catalyzed by metallic nanoparticles (M-NPs) with reductant has gained increasing attention in the past few years, and is considered to be an effective approach due to the superior catalytic performance of M-NPs. Thus, it is a timely topic to review this emerging technique for Cr(VI) reduction. Herein, recent development in synthesis of M-NPs based non-supported, supported, mono-, bi- and ternary M-NPs catalysts, their characterization and performance for the reduction of Cr(VI) to Cr(III) are reviewed. The role of supporting host to stabilize the M-NPs and leading to enhance the reduction of Cr(VI) are discussed. The Cr(VI) reduction mechanism, kinetics, and factors affecting the kinetics are overviewed to collect the wealthy kinetics data. Finally, the challenges and perspective in Cr(VI) reduction catalyzed by M-NPs are proposed. We believe that this review will assist the researchers who are working to develop novel M-NPs catalysts for the reduction of Cr(VI).
... Because of the surface inhomogeneity and hydrogen ion concentration of the solution, hydrogen evolution may occur in locally acidified regions, such as corrosion pits, grain boundaries, and other stress concentration sites, which is consistent with some previous reports [41][42][43]. This result explains the increase in the corrosion current after the addition of NaHSO 3 . ...
21Cr2NiMo steel is widely used to stabilize offshore oil platforms; however, it suffers from stress-corrosion cracking (SCC). Herein, we studied the SCC behavior of 21Cr2NiMo steel in SO2-polluted coastal atmospheres. Electrochemical tests revealed that the addition of SO2 increased the corrosion current. Rust characterization showed that SO2 addition densfied the corrosion products and promoted pitting. Furthermore, slow strain rate tests demonstrated a high susceptibility to SCC in high SO2 contents. Fracture morphologies revealed that the stress-corrosion cracks initiated at corrosion pits and the crack propagation showed transgranular and intergranular cracking modes. In conclusion, SCC is mix-controlled by anodic dissolution and hydrogen embrittlement mechanisms.
... They have important applications in oxygen reduction reactions (ORRs) due to their remarkable electrocatalytic characteristics [4]. These reactions play a significant role in corrosion [5], water electrolysis [6], electrochemical energy conversion [7], diverse industrial processes [8], etc. Their strong catalytic abilities are used, for example, in direct methanol fuel cells (DMFCs) for the conversion of fuel at the anode and the reduction of oxygen at the cathode [9]. ...
Our work presents, for the first time, a comprehensive study of the synthesis of fully metallic platinum nanoparticles (Pt-NPs) involving the ablation process in double distilled water using a KrF excimer laser. To obtain detailed information on Pt-NP morphology and optical properties, prepared colloids were characterized using High Resolution Scanning Transmission Electron Microscopy (HR-STEM) with advanced capabilities for Energy Dispersive X-ray Analysis (EDX), UV/Vis optical spectroscopy, and Direct Analysis in Real Time—Mass Spectrometry (DART-MS). The influence of the applied laser fluence and laser repetition rate (RR) values on the characteristics of the obtained Pt-NPs and the ablation process, respectively, were also analyzed. Spherical and spherical-like nanoparticles exhibiting aggregation were produced. The Pt-NP mean size values were between 2.2 - 1.2 nm and 4.0 - 1.0 nm, while their interplanar distance measurements showed a face-centered cubic (FFC) Pt lattice (111), as revealed by HR–STEM measurements, for all investigated samples. The smallest mean size of 2.2 nm of the Pt-NPs was obtained using a 2.3 J cm2 laser fluence at a 10 Hz RR, and the narrowest size distribution of the NPs was obtained with a 2.3 J cm2 laser fluence at a 40 Hz RR. A linear dependence of the Pt-NP diameters versus the laser repetition rate was found at a constant fluence of 2.3 J cm2. The proposed eco-friendly synthesis route of Pt-NPs, because of its relative simplicity, has the potential for use in industrial production.
... The reaction shown in Equation 2.1 is the stoichiometrically dominant reaction under anoxic conditions (O2 free). However, even under oxic conditions, Equation 2.1 is the sole path for iron corrosion because the in-situ generated oxide film acts as a diffusion barrier for dissolved species (including O2) (Whitney 1903, Stratmann andMüller 1994) and a conduction barrier for electrons from the metal body (Hu et al. 2019a, Noubactep 2022). In the recent remediation literature, it has been largely considered that reducible contaminants compete with water for Fe 0 oxidation (Liu et al. 2013, Qui et al. 2018, He et al. 2020, Hu et al. 2021b). ...
In rural and peri-urban regions of the developing world, many tube wells used as drinking water sources are microbially and chemically polluted. Consequently, hundreds of millions of people lack access to “safe” drinking water worldwide. People drinking tube well water may suffer from preventable water-borne diseases including diarrhea, skin lesions, and cancer. To address this problem, the United Nations have launched the Sustainable Development Goals (UN SDGs) which are regarded as a global urgent call for action by all countries, in a global partnership. The UN SDGs for safe drinking water (Goal 6) aims to achieve universal water supply by 2030. This goal can only be achieved if affordable and efficient water treatment technologies are made available for households and small communities for simultaneous removal of chemicals and pathogens. Ideally, such systems should be constructed using locally available materials and labor. Filtration on metallic iron (Fe0) based beds has been identified as such an appropriate technology and steel wool (SW) a universally available material. Moreover, Fe0-based filters have been designed and disseminated in some parts of the world but have not yet reached global applicability.
A critical review on the abundant literature on using Fe0-based filters for safe drinking water provision revealed that existing devices were not designed on the knowledge basis of the science of aqueous iron corrosion (corrosion science). Iron corrosion induces generation of solid iron corrosion products (FeCPs) which are well-documented contaminant scavengers. FeCPs consisting of Fe-oxide hydroxides are formed in the vicinity of the Fe0 surface and act as a diffusion barrier for dissolved species. Iron corrosion is additionally a volumetric expansive process because the volume of each oxide or hydroxide is at least twice larger than that of iron metal (Fe0). These two main characteristics imply that (i) the efficiency of each Fe0-based filter depends on the kinetics of production of FeCPs (reactivity loss), and (ii) Fe0- based filters will experience porosity loss with increasing service life (permeability loss). In other words, reactivity loss and permeability loss are inherent characteristics of Fe0-based filters which should be addressed in the design stage. Moreover, designed systems should be tested for months or years, given the incertitude on the kinetics of iron corrosion.
The objective of the present work was to design a science-based household filter and to test it for one year in the coastal city of Douala (Cameroon). The work started with a systematic review of available designs and a presentation of two main potentially durable designs. The one with a Fe0/sand filter sandwiched between two biological sand filters (BSFs) was tested with polluted well water from Logpom (Douala, Cameroon) using 300 g of a commercial SW (grade 000; d = 50 m) as Fe0 source. Previous works using Fe0 SW in water filters revealed
that grade 00 (d = 25 m) was depleted after some 6 months. The used well water was slightly turbid, polluted with pathogens (total coliforms = 1950 UFC mL−1), and contaminated with nitrate ([NO3−] = 24.0 mg L−1). The following parameters were monitored twice per month for one year in the influent and effluent water of the filter unit: (i) nitrate concentration, (ii) coliform level, (iii) pH value, and (iv) turbidity. The iron concentration and the hydraulic conductivity (permeability) were also determined. Prior to pilot testing, the impact of chloride ions (Cl-) on the efficiency of Fe0 filters was characterized in laboratory column experiments, using the methylene blue discoloration method.
Results of laboratory column experiments revealed that the chloride concentrations expected in well waters in Douala would not negatively impact the efficiency of Fe0 filters. The tested design could produce safe drinking water for at least one year. Coliforms (> 99% decrease), nitrate (> 99%) and turbidity (> 96%) were nearly quantitatively removed over the whole testing period and well below the recommended limits of the World Health Organization (WHO). The effluent pH increased continuously from 6.6 to 8.4. The effluent iron concentration was constantly lower than 0.2 mg L−1. These values are within the WHO drinking water quality standards. The initial flow velocity of 20 L h-1 decreased to ~8.33 L h–1 after one year, corresponding to a permeability loss of nearly 41.5 %. At the end, the filter was still producing 200 L of drinking water
These results confirmed the suitability of commercial Fe0 SW as efficient material to construct durable water filters for households. It appears that the success of the design relied on the low ratio of Fe0 SW (10 vol %) dispersed in the matrix of sand (90 vol %). The tested design can be immediately be applied practically, provide that appropriate construction materials are found. Future research should include (i) testing lower Fe0 SW ratios (same grade), (ii) testing other grades of Fe0 SW in parallel experiments (1 year or more); (iii) testing the same systems for the removal of arsenic and uranium which are the most widespread natural pollutants. Fe0 SW based water filters can be considered as one of the best tools for the achievement of Goal 6 of the United Nations sustainable development goals (SDGs), despite the threat of COVID-19.
... This is because the oxide scale on Fe(0) acts both as (i) a conductive barrier for electrons from the metal body and (ii) a physical barrier for the migration of O2 to the vicinity of Fe(0). (Stratmann and Müller 1994). Clearly, before the advent of the Fe(0) remediation technology, it was obvious to corrosion scientists that water is the sole oxidizing agent for Fe(0) under aqueous environmental conditions (pH > 4.5). ...
Over the past three decades, groundwater remediation using permeable reactive barriers (PRBs) has proven to be effective. The majority of installed PRBs uses metallic iron (Fe(0)) as a reactive material. However, the success of implemented Fe(0) PRBs is yet to be rationalized as Fe(0) is a generator of iron oxides (contaminant scavengers) and secondary reducing agents (e.g. Fe(II), Fe3O4, H2, green rust), This communication demonstrates that Fe(0) is not an environmental reducing agent. Therefore, more science-based investigations are needed to optimize the operation of Fe(0) PRBs. In particular, Fe(0) PRBs and Fe(0)-based water filters should be regarded as particular cases of "metal corrosion in porous media". A key feature of such systems is that the extent of Fe 0 corrosion temporally depends on the residual porosity (capillarity). Thus, the functionality of any Fe 0 PRB should be monitored in a way that the time-dependent variation of the kinetic of iron corrosion is discussed.
... It is very important to notice that the reaction in Eq. 3 is also not possible because the Fe (0) surface is shielded by an oxide scale, which acts as a diffusion barrier to O2 (Stratmann and Müller, 1994). Clearly, Whitney (1903) had already demonstrated that the electrochemical relationship between Fe(0) and H + is the root cause of rusting, despite the presence of CO2 (H2CO3), O2 and other oxidizing agents like nitrate. ...
The global effort to mitigate the impact of environmental pollution has led to the use of various types of metallic iron (Fe(0)) in the remediation of soil and groundwater as well as in the treatment of industrial and municipal effluents. During the past three decades, hundreds of scientific publications have controversially discussed the mechanism of contaminant removal in Fe(0)/H2O systems, with the large majority considering Fe(0) to be oxidized by contaminants of concern. This view assumes that contaminant reduction is the cathodic reaction occurring simultaneously with Fe 0 oxidative dissolution (anodic reaction). This view contradicts the century old theory of the electrochemical nature of aqueous iron corrosion and hinders progress in designing efficient and sustainable remediation Fe(0)/H2O systems. The aim of the present communication is to demonstrate the fallacy of the current prevailing view based on articles published before 1910. It is shown that properly reviewing the literature would have avoided the mistake. Going back to the roots is recommended as the way forward and should be considered first while designing laboratory experiments.
Water pollution is calling for a sustainable remediation method such as the use of metallic iron (Fe ⁰ ) to reduce and filter some pollutants, yet the reactivity and hydraulic conductivity of iron filters decline over time under field conditions. Here we review iron filters with focus on metallic corrosion in porous media, flaws in designing iron filters, next-generation filters and perspectives such as safe drinking water supply, iron for anaemia control and coping with a reactive material. We argue that assumptions sustaining the design of current Fe ⁰ filters are not valid because proposed solutions address the issues of declining iron reactivity and hydraulic conductivity separately. Alternatively, a recent approach suggest that each individual Fe ⁰ atom corroding within a filter contributes to both reactivity and permeability loss. This approach applies well to alternative iron materials such as bimetallics, composites, hybrid aggregates, e.g. Fe ⁰ /sand, and nano-Fe ⁰ . Characterizing the intrinsic reactivity of individual Fe ⁰ materials is a prerequisite to designing sustainable filters. Indeed, Fe ⁰ ratio, Fe ⁰ type, Fe ⁰ shape, initial porosity, e.g. pore size and pore size distribution, and nature and size of admixing aggregates, e.g. pumice, pyrite and sand, are interrelated parameters which all influence the generation and accumulation of iron corrosion products. Fe ⁰ should be characterized in long-term experiments, e.g. 12 months or longer, for Fe dissolution, H 2 generation and removal of contaminants in three media, i.e., tap water, spring water and saline water, to allow reactivity comparison and designing field-scale filters.
Metallic iron (Fe0) is readily available worldwide and it has shown promise for water treatment in filtration systems. Fe0 filters remove physical contamination (e.g. colloids, suspended particles), pathogens (e.g. bacteria, viruses), and micro-pollutants (e.g. arsenic, nitrate, pesticides, pharmaceuticals) from polluted waters. Accordingly, Fe0 filters can be used for water treatment applications where other materials (e.g. activated carbon, biochar, bone char) are economically or logistically infeasible. Therefore, Fe0 filters are a good candidate to help low-income communities in their efforts to achieve universal access to safe drinking water by 2030. The objective of this chapter is to summarize available knowledge on the design of Fe0 filters in order to booster their large scale application at household and small community levels. Optimal conditions for Fe0 filters include the rational choice of the used materials building the reactive zone (Fe0 and other aggregates), the Fe0 ratio in the reactive zone, the Fe0 mass (e.g. size of the filter or number of filters in series), and the contact time (flow velocity). The proper combination of these design parameters is discussed. Results show that: (i) all reactive Fe0 can be used for efficient water filters, (ii) only porous Fe0 materials are suitable for sustainable water filters, (iii) well-designed hybrid Fe0/aggregate systems are also sustainable, (iv) the major limitation of Fe0 filters is the lack of knowledge on the long-term corrosion rate. Future research efforts should last for months or years.
Advances in Drinking Water Purification
Small Systems and Emerging Issues
1st Edition - January 17, 2024
Editor: Sibdas Bandyopadhyay
Paperback ISBN: 9780323917339
9 7 8 - 0 - 3 2 3 - 9 1 7 3 3 - 9
eBook ISBN: 9780323972024
Description
Advances in Drinking Water Purification: Small Systems and Emerging Issues captures the knowledge and impact on the performance of various types of water purification technologies and identities the need for further development with a view to carry forward the SDG global targets of achieving safe and affordable drinking water. The book bridges the knowledge gap between various types of treatability options which is essential for selection of suitable treatment systems and augmentation in the desirable levels of specific contaminants. It focuses on providing the scope of selecting location specific technology options by presenting multiple approaches for treatment of most crucial toxic contaminants/pathogens.
In addition, it provides insights into the effect of nature of impurities and selection of treatment options on the global quality of drinking water, comprising its possible impacts on the efficiency of the techniques used and thus on the safety of drinking water. This information is indispensable in identifying the appropriate technology depending on the socioeconomic conditions to address the problem of decontamination in drinking water.
The breakdown of materials, typically metals, is due to a chemical environmental response that causes a functional breakdown of the components. A reverse extractive metallurgy process called corrosion relies on temperature, stress, erosion, and environmental concentration. It produces significant economic losses that range between 1% and 5% of Gross National Product (GNP) annually for any nation. In addition, rust not only raises the costs of components, but is also accountable for fatalities and safety risks. Thus, the purpose of this review is to provide a general overview of the various types of corrosion and related preventative strategies. Consequently, corrective action can be taken to reduce the impact of corrosion-related issues.
Pitting corrosion is one of the most dangerous forms of corrosion, leading to sudden catastrophic failures in engineering systems. Once initiated, pit propagation rates are largely dependent on the magnitude of the supporting cathodic current available from the oxygen reduction reaction (ORR) occurring on the external passive film. Here the ORR kinetics on conventional and high Cr content FeCr alloys made by arc-melter were investigated by experimental and computational methods. Density functional theory calculations suggested that the overpotentials for the ORR on FeCr oxides are in the order Cr2O3 > Fe3O4 > Fe2O3 > FeCr2O4, which was experimentally confirmed on the FeCr alloys by rotating disc electrode experiments in both O2 saturated 0.1 M NaOH and 3.5 wt% NaCl. Koutecky-Levich analysis demonstrated that ORR follows a 4-electron pathway on all surfaces investigated. Moreover, the investigation of the Pourbaix diagrams of FeCr revealed that at potentials where pitting corrosion initiates the main constituents of the passive films should be a mixture of Fe2O3 and Cr2O3, rather than FeCr2O4, which is proved to be a good ORR catalyst. The results support the postulation that one role Cr additions play in the prevention of pitting corrosion is to suppress the ORR reaction.
Aqueous electrolyte traditionally used for electrochemical characterization of soil‐related corrosion in laboratories fails to represent the soil physical features, such as pore structure, soil heterogeneity, soil compaction, and saturation levels, in the diffusion‐controlled corrosion process. This article introduces a semi‐solid agar system to reproduce the physical structure of soil for corrosion study. For feasibility validation of the agar system, direct comparison regarding electrochemical activity, diffusion characteristics, and corrosion mechanisms has been performed on pipeline steel in aqueous sodium chloride (NaCl) solution (5 g L⁻¹), 5 g L⁻¹ NaCl‐containing agar, and 5 g L⁻¹ NaCl in sand, respectively. The results indicates that oxygen diffusion in agar and sand media is similar, which significantly weakens the cathodic activity of steel specimens, but leads to distinct corrosion characteristics from those identified in aqueous NaCl solution counterparts. The high diffusion rate of chloride ions in aqueous solution also accelerates corrosion of pipeline steel in NaCl solution through extensive attack at defect sites, but the limited chloride ion movement and the diminished driving force for anodic corrosion activity reduce such attack in their agar and sand equivalents. The solid nature of agar outperforms aqueous electrolytes as soil replicate to explore soil‐related corrosion responses at laboratory scale.
The corrosion behaviors of self-designed Ni-containing low-alloy steels with Mo addition in tropical marine atmosphere was investigated by surface analysis and electrochemical methods. The results showed that with the increase of Ni content, the weight gain rates of low-alloy steels gradually decreased and the composition phases of inner product films changed from γ-FeOOH to α-FeOOH. The synergistic effect of Ni and Mo on the corrosion resistance of low-alloy steel was related to the Ni content in the steel matrix. The corrosion resistance can be significantly improved by adding Mo when the Ni content was in the range of 1.72 to 2.87 wt.%. The enhanced synergistic effect of Ni and Mo could further promote the formation of more protective corrosion products, such as α-FeOOH, NiFe2O4 and Mo6+.
Effect of pre-tension deformation on the rusting behavior of S450EW weathering steel was studied through electrochemical measurements and characterizations on rust layer. The rust layers are no longer stratified and become porous on the deformed samples. Simultaneously, the occlusion effect beneath the rust layer is alleviated. Owing to the above both aspects, the rust layer keeps a composition of approximately 7 wt.% γ-FeOOH, 20 wt% α-FeOOH, and 73 wt.% Fe3O4/γ-Fe2O3 under each deformation degree. The deformation increases the defects in the incipient passive film, thereby promoting rust generation but leaving inadequate time for the evolution of the rust layer.
Oxygen reduction reaction (ORR) has been disclosed in recent studies as a significant secondary cathodic process during magnesium corrosion. This work elaborates on the contribution of ORR to the total corrosion process of pure Mg at different impurity levels in NaCl electrolyte with the assistance of local techniques. A finite element based numerical model taking into account the contribution of ORR during the corrosion of the Mg test materials has been designed in this study considering the local oxygen concentration. Respective computational simulations were calibrated based on the experimental data and evaluated accordingly. Finally, the simultaneous monitoring of local concentration of H2 and O2, and the combined modeling study reveal the relation between ORR and hydrogen evolution reaction.
Corrosion is one of the primary causes for failures of underground metal pipes. The literatures on corrosion of pipes indicate that the effect of corrosion on the mechanical properties of pipe materials is highly harmful and needs prevention. However, very few research work is available on corrosion effect related to various corrosion related failures. The aim of this paper is to present a comprehensive investigation on various corrosion induced failure, synthesized corrosion inhibitor and corrosion resistance coatings for reduction this environmental impact. In this paper, the mechanism of corrosion in concrete structures is studied and analysed. In addition, kinetics of corrosion, and reactions of the concrete structures that resulted in corrosion failure are discussed. Further, the study also encompasses boiler corrosion, types and preventive measures for minimizing corrosion and preventing catastrophic failure.
KeywordsCorrosionOxidationOxygen corrosionCarbonic acid corrosionBoilerStress corrosion crackingPrevention
In this paper, the effect of elements such as Ni, Al, and Si in gray cast iron on the atmospheric corrosion resistance of gray cast iron was studied by using corrosion weight gain, salt spray test, electrochemistry, and X‐ray diffraction. The results show that the corrosion behavior of gray cast iron can be divided into two stages. The later stage of corrosion resistance of gray cast iron with Ni element is better than the early stage of corrosion resistance, while the reverse is true for gray cast iron with Al element. There is no significant effect of increasing the Si content on the corrosion behavior of gray cast iron. The corrosion products of each specimen are all composed of Fe2O3, α‐FeOOH, γ‐FeOOH, and Fe3O4. After the comparison test, it can be concluded that the Ni element is seen to be conducive to the formation of protective rust layer with higher α‐FeOOH content. In addition, the rust layer of gray cast iron containing Al is loose and scaly, while the rust layer of gray cast iron containing Ni is dense and spongy. The addition of Ni element can make gray cast iron stable to improve the self‐corrosion potential and reduce the self‐corrosion current density, thus reducing the corrosion rate of gray cast iron. We investigated the effects of alloying elements Ni, Al, and Si on the salt spray corrosion resistance of gray cast iron and revealed the electrochemical properties of the corrosion products and the metal matrix. It was investigated whether the corrosion resistance of gray cast iron could be improved by adding different alloying elements or changing the content of alloying elements.
In the present work, we examined the structure and protectiveness of rust layers formed on friction stir welded (FSWed) high phosphorus carbon steels, compared with those on SMA490AW and COR-TEN weathering steels. Rust layers were grown on base materials and FSWed materials under a wet/dry cyclic corrosion test. XRD revealed that the rust layers on all the materials consisted of Fe3O4 (magnetite), α-FeOOH (goethite), β-FeOOH (akaganeite), and γ-FeOOH (lepidocrocite), and main constituents of the rust layers were goethite and magnetite. On the base materials, the fraction of protective goethite increased with increasing P concentration in steel when the fraction was compared among SMA490AW, COR-TEN, and 0.1C-0.1P specimen, whereas for 0.1C-0.3P, 0.3C-0.1P, and 0.3C-0.3P specimens, the fraction decreased compared with that on 0.1C-0.1P specimen. The corrosion current of rusted base materials decreased with increasing P concentration when compared among SMA490AW, COR-TEN, and 0.1C-0.1P specimen. In contrast, the corrosion current of 0.1C-0.3P, 0.3C-0.1P, and 0.3C-0.3P specimens was comparable to that of 0.1C-0.1P specimen, indicating the improved protectiveness of rust layers formed on high phosphorus carbon steel. In addition, the protectiveness of rust layers on the FSWed materials was comparable to, or higher than that on the base materials, in particular, the protectiveness was apparently higher, independent of the fraction of goethite when the materials were subjected to the FSW below A1. The improved protectiveness for the FSWed specimens demonstrates that FSW does not deteriorate the corrosion resistance of rusted high phosphorus carbon steels.
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The corrosion of Fe(0) in the presence of O2 in nature can lead to the oxidation of organic compounds, but the efficiency is very limited. Herein, attempts were made to establish a galvanic system that separates the anodic Fe(0) oxidation reaction and the cathodic O2 reduction reaction using an air-breathing cathode. Compared with the chemical Fe(0)/O2 system, it exhibited a substantially higher capability of destroying a variety of pollutants, such as organic dyes (12 types), phenol, nitrobenzene, acetaminophen, phenol, and ethylenediaminetetraacetic acid. The degradation rate constant of a model dye (i.e., Rhodamine B) increased from 0.047 min⁻¹ (chemical) to 1.412 min⁻¹ (galvanic) under the passive air-breathing condition. The electric circuit design promoted Fe(0) dissolution to Fe(II) and triggered electron transfer that drives O2 reduction to H2O2, two important species responsible for the generation of HO• at high abundance. In addition, the galvanic Fe(0)/O2 system produces electricity while destroying pollutants. Tests with real Ni plating wastewater further demonstrated the capability of the system to oxidize complexed organics and phosphite. This study provides a new strategy for boosting the oxidative capacity of the Fe(0)/O2 system, which shows promise for acid wastewater treatment.
The oxidation behavior of corrosion products that form on Ni-containing low alloy steel was investigated by electrochemical polarization curves, scanning electron microscopy, electron probe micro-analyzer, X-ray diffraction, transmission electron microscopy, and X-ray photoelectron spectroscopy. The corrosion products were oxidized to Green Rust containing Cl⁻ (Green Rust(Cl⁻)) and an amorphous substance, which were produced in an ordinary- and negative-pressure environment, respectively. The enrichment of Ni in the corrosion product could inhibit two oxidation reactions of the corrosion product, especially inhibiting the formation of amorphous substances. In addition, oxygen reduction could be also suppressed via the enrichment of Ni.
Metallic iron (Fe0) has been increasingly used to remove toxics from water over the past three decades. However, the idea that metallic iron (Fe0) is not an environmental reducing agent has been vigorously refuted. Researchers presenting their findings in a scientific journal have to accept the burden of proving that their argumentation has any validity. This 30-year-lasting discussion within the Fe0 remediation community is alien to electro-chemists, as it is a century-old-knowledge. Nevertheless, the peer reviewed literature on "remediation using Fe0" seems to be dominated by evaluators thinking that Fe0 is a reducing agent. This communication challenges the view that Fe0 donates any electron to any dissolved species. The sole goal is to reconcile a proven efficient technology with its scientific roots, and enable the design of better Fe0 remediation systems.
The discharge of excessive phosphate from wastewater sources into the aquatic environment has been identified as a major environmental threat responsible for eutrophication. It has become essential to develop efficient but affordable techniques to remove excess phosphate from wastewater before discharging into freshwater bodies. The use of metallic iron (Fe0) as a reactive agent for aqueous phosphate removal has received a wide attention. Fe0 in-situ generates positively charged iron corrosion products (FeCPs) at pH > 4.5, with high binding affinity for anionic phosphate. This study critically reviews the literature that focuses on the utilization of Fe0-based materials for aqueous phosphate removal. The fundamental science of aqueous iron corrosion and historical background of the application of Fe0 for phosphate removal are elucidated. The main mechanisms for phosphate removal are identified and extensively discussed based on the chemistry of the Fe0/H2O system. This critical evaluation confirms that the removal process is highly influenced by several operational factors including contact time, Fe0 type, influent geochemistry, initial phosphate concentration, mixing conditions, and pH value. The difficulty in comparing independent results owing to diverse experimental conditions is highlighted. Moreover, contemporary research in progress including Fe0/oxidant systems, nano-Fe0 application, Fe0 material selection, desorption studies, and proper design of Fe0-based systems for improved phosphate removal have been discussed. Finally, potential strategies to close the loop in Fe0-based phosphate remediation systems are discussed. This review presents a science-based guide to optimize the efficient design of Fe0-based systems for phosphate removal.
Previously it was suggested that in the bi-modal model for corrosion loss as a function of exposure period the instantaneous corrosion rate increases by a factor of about 4 through the transition phase from Mode 1 to Mode 2. Recent experimental observations (from Part 1) and other experimental observations covering a range of corrosion influencing parameters closely support this value. The reason for it is examined through a model of the development of corrosion through the transition zone, based on interpretations of the data presented in Part 1. It is shown that pitting plays a crucial role in lowering local pH conditions and permitting transitioning of the corrosion process from oxygen reduction (in Mode 1) to the hydrogen evolution (in Mode 2) as the thermodynamically possible cathodic reaction. In both cases the rates of corrosion are controlled by diffusion considerations, not electrochemical kinetics. This also permits a theoretical basis for the observed ratio of around 4. Further, eventual long-term corrosion, usually observed as close to a linear trend in time, is proposed as representable a system in quasi-static equilibrium, involving both the hydrogen evolution reaction at the corrosion interface and loss of ferrous ions from the external face of the rust layers.
The aim to produce highly active, selective, and long-lived electrocatalysts by design drives major research efforts toward gaining fundamental understanding of the relationship between material properties and their catalytic performance. Surface characterization tools enable to assess atomic scale information on the complexity of electrocatalyst materials. Advancing electrochemical methodologies to adequately characterize such systems was less of a research focus point. In this Review, we shed light on the ability to gain fundamental insights into electrocatalysis from a complementary perspective and establish corresponding design strategies. These may rely on adopting the perceptions and models of other subareas of electrochemistry, such as corrosion, battery research, or electrodeposition. Concepts on how to account for and improve mass transport, manage gas bubble release, or exploit magnetic fields are highlighted in this respect. Particular attention is paid to deriving design strategies for nanoelectrocatalysts, which is often impeded, as structural and physical material properties are buried in electrochemical data of whole electrodes or even devices. Thus, a second major approach focuses on overcoming this difference in the considered level of complexity by methods of single-entity electrochemistry. The gained understanding of intrinsic catalyst performance may allow to rationally advance design concepts with increased complexity, such as three-dimensional electrode architectures. Many materials undergo structural changes upon formation of the working catalyst. Accordingly, developing “precatalysts” with low hindrance of the electrochemical transformation to the active catalyst is suggested as a final design strategy.
The mechanism behind corrosion rate increase of anodised iron under illumination has been studied by comparing photocurrents with corrosion currents from polarisation curves under controlled convection. Under illumination with photon energies larger than the iron oxide band gap of ∼2 eV, corrosion current densities increased by maximum 30%, triggered largely by hole annihilation through cation dissolution. Thermal effects in the oxide also play a role. Photocurrent measurements indicate little upward band bending, with fluctuations, in the n-type oxide at open circuit. The contributions of different mechanisms to the photocorrosion rate have been quantified, relevant for steels and photoelectrochemical water splitting.
Elektrochemische Reduktion von Sauerstoff an rotierenden Scheibenelektroden. Berechnung und Messung der durch den Antransport bedingten Grenzstromdichten. Analytische Ermittlung der Korrosionsgeschwindigkeiten bei Versuchen ohne Bildung von Rostschichten. Electrochemical reduction of oxygen on rotating disc electrodes. Calculation and measurement of current densities limited by the transport of oxygen. Analytical testing of corrosion rates on specimens without rust layers. Réduction électrochimique de l'oxygène sur électrodes rotatives en disques. Calcul et mesure des densités de courant limitées par l'apport de l'oxygène. Détermination analytique des vitesses de corrosion sur éprouvettes sans couches de rouille.
Einfluß der haftenden Rostschichten auf die Geschwindigkeit der elektrolytischen Sauerstoffkorrosion des Eisens bei Messungen mit der rotierenden Scheibenelektrode. Abhängigkeiten von der Temperatur, der Strömung und der Zusammensetzung des Elektrolyten. Influence of the adherent rust layers on the rate of electrolytic oxygen corrosion of iron in measurements with the rotating disc electrode. Dependences on temperature, flow, and composition of the electrolyte. Influence des couches de rouille adhérantes sur la vitesse de la corrosion à oxygène électrolytique du fer lors des mesures à l'aide de l'électrode à disque rotatif. Dépendances de la température, du courant et de la composition de l'électrolyte.
The oxygen corrosion of unalloyed and low alloy steel by cathodic reduction of oxygen is limited by the supply of oxygen. Experiments with rotating disc electrodes confirmed that the limiting current densities of the oxygen reduction, which increase with the square root of the angular speed, remain nearly independent of temperature up to 60 C. Corrosion experiments with steel specimens showed that the limiting current densities can only be obtained with acidified solutions; under these conditions no rust layer is observed. In an almost neutral citrate solution, also without formation of rust layers, the corrosion rates at room temperature and increased revolutions of the disk electrode were, however, lower by more than a factor of 2. The limiting values depending on oxygen supply were just reached at 60 C.
The kinetics of oxygen reduction were studied on iron in borate and bicarbonate buffered solutions, pH 9.8, using the rotating disk-ring method. Under these conditions O2 reduction occurs both on the oxidized surface and on the oxide-free one, depending on potential. On the oxidized surface the series mechanism was found to be operative. On the oxide-free surface the four-electron reduction was observed, but, due to the very small rate of H2O2 formation with respect to the total reduction current, a reliable distinction between the parallel and series mechanism could not be made. All the rate constants of the O2 and H2O2 reactions on the Fe surface were determined. No catalytic decomposition of H2O2 was found. The kinetics of the O2 reduction reaction is slower on more oxidized surfaces.
The development of a new ring–disc electrode technique is described in which a bismuth ring electrode is used as a potentiometric detector of changes in pH produced by reactions taking place on the disc electrode. The convective-diffusion equation for the system is solved and theoretical results are presented for the ‘detection efficiency’, which compares the change in pH at the ring electrode with that at the disc-electrode surface. The effects of buffers are considered. Provided that CO2 is excluded, experimental results are found that are in excellent agreement with the theoretical predictions. Results are presented for the generation of H+ and OH– on nickel, gold and thionine-modified electrodes. The technique is shown to be very sensitive in that fluxes as low as 10–12 mol cm–2 s–1 and changes in coverage of fractions of a monolayer can be measured.
Atmospheric corrosion of iron in an SO2-containing atmosphere with saturated humidity leads to the formation of Fe(OH)3 which transforms to crystalline FeOOH with amorphous FeOOH as a transition product. In an aqueous 0.2 M Na2SO4 electrolyte FeOOH is reduced at least to Fe3O4, and α-FeOOH at the most negative potential. By air exposure Fe3O4 is not re-oxidized in any appreciable amount. Therefore, it is proposed to replace Fe3O4 by Fe(OH)2 as the reduced state in the Evans model of atmospheric corrosion.
Electrochemically induced phase transformations of isolated rust layers have been investigated in situ by transmission Möβbauer spectroscopy. It has been found that oxidized rust films can be reduced in several stages. At potentials between −0.2 and −0.4 V(SHE) γ-FeOOH is partly reduced within the given crystal structure: Fe3+ ions are reduced to Fe21 and simultaneously O2 ions are protonized by diffusion of H+ into the lattice of γ-FeOOH. At potentials between −0.3 and −0.4 V the lattice of γ-FeOOH is transformed into the one of Fe3O4 and at potentials below −0.4 V α-FeOOH can also be reduced within the given crystal structure. After re-oxidation the reduced FeOOH phases are oxidized reversibly, whereas Fe3O4 can only be oxidized within the spinel structure to Fe3−δO4. Simultaneously to these redox reactions extremely small () α-FeOOH crystals are transformed into larger crystals (Ostwald-ripening), and to a certain extent γ-FeOOH is transformed into the lattice of α-FeOOH. The importance of these phase transformations for understanding a number of corrosion processes is discussed.
Isolated rust layers have been investigated by electrochemical methods to find out whether their reduction and re-oxidation can affect the atmospheric corrosion of iron. At potentials below 0 mV, first a thin Fe2+-containing surface layer is formed on top of the γ-FeOOH. This reduced surface layer can dissolve into the cell electrolyte at acid pH, or at lower potentials the Fe2+-ions can react with γ-FeOOH to Fe3O4. The formation of magnetite could be followed by in-situ magnetic measurements. The reduced surface layer can easily be oxidized back to γ-FeOOH, magnetite can partly be oxidized to γ-Fe2O3.
The pathways and rate-determining steps of oxygen reduction on iron in neutral pH range have been investigated. The various mechanistic criteria are obtained as a function of the nature of the electrode surface: bare iron and passive iron. The oxygen reduction on bare iron proceeds through 4e** minus pathways with little hydrogen peroxide as an intermediate and formation of superoxide radical in the rds. On passive iron, oxygen reduction proceeds through a 2e** minus pathway with the formation of hydrogen peroxide as a reaction product. An rds involving chemisorption of oxygen is suggested.
The electrochemical reduction of α‐, γ‐, δ‐, and amorphous was investigated. These oxides were applied as pastes to weathering steel substrates and galvanostatically reduced in solutions of . Raman and infrared spectroscopy were used to monitor the reaction products. Amorphous, were reduced to magnetite, , under the experimental conditions of this investigation; however, was not reduced under these conditions. The atmospheric corrosion product formed on a weathering steel light standard was entirely reduced to and had a galvanostatic reduction curve similar to those for .
An equivalent circuit for the ring-disk electrode is proposed and tested. The model assumes that the resistance between the auxiliary electrode and the disk (or ring) electrode is the series combination of two resistances. One resistance is shared by both the disk and the ring electrodes, whereas the other is characteristic of the disk (or the ring) electrode. Changing the position of the Luggin capillary tip produces different uncompensated ohmic potential drops. The IR drops can be interpreted by assuming that the tip of the Luggin capillary is being located somewhere on these resistances.
Während der kathodischen Reduktion des Sauerstoffs können sich in Ni2+ -haltigen Lösungen dünne Ni(OH)2-Deckschichten bilden. Diese Deckschichten inhibieren die Elektrodenreaktion. Im stationären Zustand entspricht die Stromdichte der Diffusionsgrenzstromdichte der Hydroniumionen, die zur Stabilisierung der Deckschicht im ungesättigten Elektrolyten notwendig ist.
Die Dicke der Deckschicht kann mit dem Faraday-Gesetz berechnet werden.
Inhibition of oxygen reduction by thin Ni(OH)2 films
During the cathodic reduction of oxygen in Ni2+-contending solutions thin Ni(OH)2-layers can be precipitated. These layers inhibit the electrode reaction. During stationary measurements the current density is equal to the limiting diffusion current density of the hydronium ions, which is necessary for the stabilization of the layer in the non-saturated electrolyte.
The thickness of the layers can be calculated with Faraday's law.
The anodic deposition of FeOOH·x H2O layers on gold electrodes at pH 7.2 yields a sandwich-type oxide film consisting of an inner n-type semiconducting layer of γ-FeOOH and an outer layer of FeOOH·x H2O. The outer layer is electronically insulating, but conducting for small ions, e.g. H+ and OH−. Reaction sites at the oxide surface and the inner surface of γ-FeOOH can be distinguished by the different influence of film thickness and electrode potential on electrode capacity and the rate of various electron-transfer reactions. Reactions with a current density depending strongly on the film thickness d but not on the potential, for example, the oxidation of [Fe(CN)6]4− and Fe2+, are explained as reactions limited by the diffusion of the species through the outer FeOOH·x H2O film. Other reactions, such as charging of the electrode capacity, the anodic oxygen evolution, the cathodic film reduction and the oxidation of incorporated [Fe(CN)6]4− ions, take place at the surface of the inner γ-FeOOH layer.
Der Einfluß des Gefügezustandes des Eisens und eines niedriglegierten Stahles auf die Wasserstoffpermeation bei Raumtemperatur wird mit Hilfe der elektrochemischen Permeationsmethode untersucht. Die Transportvorgänge im Werkstoff während der Wasserstoffbeladung oder -effusion werden durch die Gefügeelemente und den Wasserstoffgehalt beeinflußt. Die in Abhängigkeit vom Werkstoffzustand ermittelten Diffusionskoeffizienten überstreichen bis zu fünf Zehnerpotenzen. Bei instationärer Diffusion bewirken Versetzungen und Phasengrenzen einen Abfall des effektiven Diffusionskoeffizienten auf Werte zwischen 10−7 und 10−9 cm2/s. Bei stationärer Permeation werden Diffusionskoeffizienten zwischen 10−5 and 10−4 cm2/s erreicht.
Investigations on the influence of microstructure of steels on unsteady state hydrogen permeation
The effect of microstructure of iron and a low alloyed steel on hydrogen permeation at room temperature is studied by means of the electrochemical permeation method. Hydrogen transport through these materials during charging or effusion processes is affected by microstructural heterogeneities and hydrogen content. The diffusivity as a function of the state of the materials ranges over about five orders of magnitude. In course of non-steady state diffusion dislocations and interfaces decrease the effective diffusivity to values between 10−7 and 10−9 cm2/s. At steady state permeation the diffusivity reaches the values of 10−5 to 10−4 cm2/s.
A comparison has been made of the galvanostatic reduction of iron oxide films formed by deposition on platinum and by anodic
or air oxidation of iron. The major reduction process is that of Fe+++ ion to Fe++ ion in solution. Some ferrous ion is adsorbed on the unreduced oxide. There is no evidence for reduction to an intermediate
solid phase. The results indicate that the two waves observed in the cathodic reduction of anodically formed (or air‐formed)
films are due to the presence of the two “phases”
and
in the as‐formed films.
Die Kinetik und Katalyse der kathodischen Sauerstoffreduktion wurden an glatten Pd-, Ag-, Au-, Fe-, Co und Ni-Elektroden in alkalischen (KOH), an Pd auch in schwefelsauren Elektrolyten untersucht. Die kathodische Reaktionsordnung (RO) bezüglich des Partialdruckes von Sauerstoff beträgt an Pd, Ag und Au + 1 an Fe, Co und Ni dagegen + 0,5. Daraus folgt, daß im ersten Fall die Reduktion des Sauerstoffes im Durchtrittsbereich direkt zu Hydroxidionen bzw. Wasser führt, wahrend im zweiten Fall (RO = +0,5) ausschließlich Peroxid bzw. Perhydroxylanion gebildet wird. — Hinsichtlich der Hydroxidionenkonzentration werden — mit Ausnahme von Ni — negative kathodische R.O. gefunden; dies wird auf die zunehmende spezifische Adsorption von OH⁻ -lonen mit wachsender Alkalität zurück-geführt. Ferner ist die mit steigender Elektrolytkonzentration abnehmende Löslichkeit des Sauerstoffes zu berücksichtigen. — Die elektrokatalytische Aktivität der Elektrodensubstrate nimmt in der Reihenfolge Fe < Ni < Au < Ag < Co(Pd) < Pd(Co) zu.
In this review the physico-chemical fundamentals of the atmospheric corrosion of iron are discussed, as they result from a number of electrochemical and spectroscopic techniques, which have been applied in order to analyze the corrosion mechanism of the atmospheric corrosion during wet-dry-wet transitions. - After wetting a dry corroded metal surface the cathodic partial reaction of the corrosion process is given by the reduction of Fe3+- to Fe2+-states within the lattice of γ-FeOOH. If the corrosion potential is rather negative, then also magnetite is formed. As a consequence of the formation of Fe2+ states the electronic conductivity of oxide crystals close to the metal/oxide interface is increased. This results in an acceleration of the kinetics of the oxygen reduction.
Bei Laborversuchen zur atmosphärischen Korrosion von Reineisen wurde der Metallabtrag eines dünnen Bleches über magnetische Messungen und der Sauerstoffverbrauch gasvolumetrisch bestimmt. Die Meßwerte zeigten, daß nach einer kurzen Befeuchtung zuerst eine Auflösung des Eisens unter Reduktion der Rostschicht abläuft. Die Korrosionsstromdichte beträgt dabei kurzfristig bis zu 500 m̈/cm2, fällt aber zeitlich rasch ab. Neben dieser Korrosion unter Rostreduktion spielt die Korrosion bei kritischer Befeuchtung der Metalloberfläche während des Austrocknens des Korrosionssystems eine dominierende Rolle. Die Korrosionsstromdichte erreicht hier Werte bis zu 1 mA/cm2.
Investigations towards understanding of the atmospheric corrosion processes of pure iron
In an investigation of the atmospheric corrosion of pure iron the metal loss of a foil was determined by magnetic measurements and the oxygen consumption gasvolumetrically. The results showed that in the period immediately following short wetting iron dissolution takes place with reduction of the rust layer. The corrosion current density thereby reaches a value of 500 m̈A/cm2 temporarily falling rapidly with time. Apart from this the corrosion under conditions of critical humidity of the metal surface during the drying-out of the corrosion system plays a dominant role. The corrosion current density reaches here values up to 1 mA/cm2.
Die auf Fe-Basislegierungen gebildeten Rostschichten sind elektronisch sehr reaktiv. Durch Polarisation dieser Oxidschichten werden Festkörperreaktionen ermöglicht, die zur Reduktion der 3-wertigen Oxidhydrate führen. Diese Redox-Reaktionen erlauben eine Eisenauflösung ohne Reduktion von Sauerstoff und erhöhen damit den Metallabtrag insbesonders bei periodisch variierenden Korrosionsbedingungen und bei polymerbeschichteten Werkstoffoberflächen. Durch die Oxidreduktion werden elektronenleitende Oxide gebildet, die die Kinetik von Sauerstoffreduktion bestimmen. Schließlich ändert sich bei der Reduktion der Rostschicht die Rostmorphologie. Dies führt zu einem Haftungsverlust bei polymerbeschichteten oxidbelegten Metalloberflächen.
Influence of rust layers on corrosion reactions of low alloy steels
Rust layers formed on iron base alloys are electrochemically highly reactive. Due to a polarisation of these oxide scales solid state reactions are induced, by which the 3-valent iron oxides are reduced. These redox reactions allow the dissolution of iron without the reduction of oxygen and therefore increase the corrosion rate, if the corrosion conditions vary periodically or if the material is coated by a polymer layer. Due to the oxide reduction electron-conducting oxides are formed, which determine the rate of the oxygen reduction. This causes the loss of adhesion for polymer coated and oxide covered iron substrates.
A l'aide d'une lectrode disque tournant en acier au carbone, on a effectu des tracs potentiostatiques de courbes courant-potentiel cathodiques et des mesures de rsistance de polarisation, dans une solution 3% are et agite de chlorure de sodium. On montre de cette faon que le contrle de la corrosion, purement diffusionnel dans le domaine des vitesses de rotation relativement basses de l'lectrode, devient mixte, c'est--dire d'activation-diffusion, aux vitesses plus leves. Il s'ensuit que, dans le premier cas, l'intensit de corrosion peut tre donc considre comme gale au courant limite de diffusion de l'oxygne dissous; par contre, dans le second cas, les vitesses de corrosion dtermines par extrapolation au potentiel de corrosion des droites de Tafel corriges de la diffusion sont en bon accord avec celles obtenues par d'autres mthodes, en particulier une mthode de mesure directe (dosage du fer pass en solution).Plotting of steady-state cathodic polarization curves and polarization resistance measurements was carried out in an aerated and stirred 3 wt% NaCl solution using a carbon steel rotating disc electrode. Under these conditions, it is shown that the corrosion process which is controlled only by convective diffusion at relatively low rotation speeds, attains mixed kinetics, i.e. activation-diffusion control, at higher rotation speeds. In the first case, the corrosion rate can be considered equal to the limiting diffusion current of dissolved oxygen; in the second case, the corrosion rates determined by extrapolation to the corrosion potential of the diffusion corrected Tafel line are in good agreement with those determined by other methods, particularly by titration of dissolved iron.
In this study for the first time a circuit is presented which allows the measurement of polarisation curves on metal surfaces which are covered by electrolyte layers as thin as 2 μm. The circuit does not need any Luggin capillary but uses a Kelvin probe as a reference electrode which does not touch the surface under investigation. Results are discussed which have been obtained with platinum and iron as working electrodes. On iron electrodes, during drying the rate of the oxygen reduction is accelerated due to a faster transport of oxygen through the thin electrolyte layer. The surface is passivated either due to the precipitation of corrosion products or due to pH-changes inside the thin electrolyte layer. This confirms the model of the atmospheric corrosion of iron and steel presented in part 2 of this paper.
The reduction of oxygen on passive iron in alkaline solutions has been studied. The reaction orders with respect to O2 and OH− are and −1 respectively. The proposed reduction mechanism involves the mediation of surface [Fe(II)] sites formed by reduction of the passive film which act as adsorption centres. It is suggested that the formation of adsorbed peroxo species under Temkin conditions accounts for the O2 reaction order whereas the acid-base properties of the passive films are responsible for the OH− reaction order. At potentials around −0.4 to −0.5 V vs. SHE, an unusual decrease in current with increasing rotation rate is observed, which is related to the desorption of adsorbed peroxide.
In this study, the corrosion properties of iron and the alloys Fe-0.5Cu and Fe-3.4Cu are investigated during several wet/dry transitions. The corrosion potential is measured with a Kelvin probe without touching the surface under investigation, the corrosion rate is followed by the decay of the partial-pressure of oxygen in a closed volume. It could be shown that the corrosion rate of pure iron during drying is determined by three competing reactions: the acceleration of the diffusion limited oxygen reduction in the beginning, the passivation of the surface as drying continues and the decrease of the rate of the oxygen reduction during the last stage of drying. The latter process is coupled to the re-oxidation of the previously reduced Fe3+ and therefore with Fe2+ enriched oxyhydroxides, as oxygen is reduced on these Fe2+ doped semiconducting iron oxyhydroxides. In opposite to pure iron the two FeCu alloys show low corrosion rates during drying, but the reason of this is quite different for both alloys. The alloy Fe-0.5Cu shows rather negative corrosion potentials during drying, which is interpreted by a slow kinetics of the oxygen reduction on the oxide scale formed on this alloy. In contrast to this, the corrosion potentials of the alloy Fe-3.4Cu are shifted anodically after several wet/dry cycles, the surface being passivated. No activation is observed, even if the surface is covered by thick electrolyte layers. Activation occurs only, if again SO2 is adsorbed onto the metal surface.
The reduction and re-oxidation kinetics of iron oxide scales on steel, formed either during corrosion in water or synthetically prepared, have been studied by using electrochemical methods and oxygen consumption techniques. Reduction of these scales during stagnation periods in water distribution systems and re-oxidation of the reduced scales by dissolved oxygen are discussed on the basis of an electrochemical and an oxygen transfer model.
Electrochemical methods for the investigation of metal-hydro gen systems are superior to other techniques, e.g., gas-volumetric, because of their simple procedure and their flexibility towards variation of experimental conditions. Moreover, these techniques allow measurements at very low hydrogen equilibrium pressures which occur, for instance, in the V(a)-metal-hydrogen systems in the concentration range of ideal dilute solutions at normal temperatures.The removal of surface layers, which retard the hydrogen passage from the electrolyte into the metal and vice versa, is a necessary condition for electrochemical methods to be applicable. Using ultra-high-vacuum techniques, surface hindrances on base metals like V, Nb, Ta, Ti, and others, can be eliminated. Thus, it is possible to study diffusion, permeation, and solubility of hydrogen (isotopes), in these metals as well as in precious metals such as palladium and its alloys.Various electrochemical hydrogen-diffusion and permeation methods are presented and compared. Their applicability and the limits of application are demonstrated for pre-selected systems.A recently developed electrochemical technique for measuring hydrogen (isotope) solubility in transition metals is described. By means of this method, pressure-concentration equilibrium isotherms of V, Nb, and TaH systems have been obtained recently, at ordinary temperatures, from vanishingly low hydrogen concentrations, corresponding to extremely low equilibrium pressures, up to atomic ratios H/Me of 0.5.