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Role of climatic conditions on corrosion characteristics of structural steels
Abstract
Corrosion behaviour of low alloy (LASS) and plain carbon (PCSS) structural steels exposed in different types of climatic conditions and nature of rust formed on their surfaces have been studied after 2years of exposures. The test sites were chosen to represent four types of environments who strongly influence the corrosion of metals and alloys. They include (a) humid–saline, (b) humid–saline–urban (c) humid–industrial and (d) plain dry–urban environments. Mass loss, Raman spectroscopy, scanning electron microscopy and electrochemical impedance spectroscopic studies have been performed to study the corrosion behaviour and characterise the nature of rusts formed on these steels. Mass loss measurement technique has been used to determine the loss of thickness of steels during their atmospheric and salt spray exposures. Results indicate that the corrosion rate of steels is strongly influenced by the climatic conditions prevailing at the exposure sites. The presence of SO2 and salinity in the environments change the structure and protective properties of rust formed on the steels’ surface. Electrochemical impedance and cyclic polarisation studies of the steels in simulated environments have been performed to understand the mechanism of corrosion in different climatic conditions.
... Iron is highly corrosive when exposed to the environment because it occurs as iron oxide and not a pure metal in its raw state (Singh et al. 2008;Stansburg and Buchanan 2009). The process of Fe-based materials returning to their original form by interaction with the environment is rusting, a corrosion process. ...
... Various tests are done to evaluate the corrosion behaviour of steels (Kubzova et al. 2019;Melchers 2018;Singh et al. 2008;Suleiman et al. 2013;Zou et al. 2011). The immersion test is the most basic technique whereby the corrosion rate is taken as a function of the weight and thickness of material lost. ...
... The immersion test is the most basic technique whereby the corrosion rate is taken as a function of the weight and thickness of material lost. The electrochemical techniques are more complex and rooted in electrochemistry (Singh et al. 2008;Zou et al. 2011). These are mainly used to assess the corrosion rate and corrosion behaviour of the materials based. ...
An overview of the characterisation of rust by colour is presented. Each distinct rust colour is caused by atmospheric impurities, high or low moisture content and high or low oxygen environment over time. Yellow rust is mainly due to the high moisture environment over a period of time, which drips. Brown rust is dry, crusty and due to water and oxygen contact with localised patches on component surfaces. Black rust, the most stable form, occurs in low moisture and low oxygen environment. The rust residue shows where the reaction started, especially in contact with chlorides. The causative factors of red rust are atmospheric and similar to black rust in a chloride-containing environment. The effect of packaging, manufacturing and environmental factors on rust colour is briefly discussed. Visual characterization of rust could pre-empt root causes and analytical tools for validation. The limitations of these concepts are mentioned and directions for future research highlighted.
... However, as the CCT progressed up to 120 CCT, the number of a-FeOOH peaks increased, indicating a stable rust layer formation. The latter observation was also reported in several other studies (Ref [10][11][12]. The protective ability index (PAI) of steel has been related to the a/c ratio ( Ref 8,10,11,30). ...
... A slight decrease at 120 CCT was probably due to the cracking and reformation of the rust layer. The GI-XRD results indicated that at higher CCT, c-FeOOH phase fraction decreased and that of a-FeOOH increased due to the former getting converted to more stable a-FeOOH (Ref [10][11][12]25). Hence, at higher CCT, the rust layer becomes more stable and compact due to the predominance of a-FeOOH. ...
The surface rust layer of ASTM A572 grade 50 high-strength low-alloy structural steel was examined under laboratory wet/dry cyclic corrosion test (CCT) conditions in a simulated polluted marine environment. According to the corrosion kinetics study, the entire corrosion process in the sample occurred in four stages, which were identified by the power law exponent, evolved phases, and electrochemical behavior of the rust layer at various stages. During the early stages of corrosion, the reduction of rust layer phases and the anodic dissolution of the steel substrate accelerated the overall corrosion rate. Variations in the corrosion rate were observed as the composition of the rust layer stabilized with increasing CCT cycle due to cracking and self-repairing of the rust layer. At higher CCT, the composition of the rust layer gradually changed from a conductive γ-FeOOH phase to a stable α-FeOOH phase. The electrochemical impedance analysis also revealed an increase in rust layer resistance as well as charge transfer resistance of side reactions such as hydrogen evolution reaction (HER). As a result, as CCT increased, corrosion resistance and thus the protective ability index increased (PAI). The defect density in the semiconducting rust layer formed at higher CCT was lower, indicating a higher level of protection. Based on the findings, a plausible mechanism of growth of the protective rust layer on the steel sample was proposed.
... According to some authors ( Ref 8,14,[29][30][31], the chemical reactions that explain the mechanism of the corrosion reaction in a simulated industrial environment is cyclic processes that can generate H 2 SO 4 , accelerating the rusting process. The reactions that take place in water with dissolved oxygen are cathodic and anodic: The corrosive process can be accelerated when the corrosive environment has a pH drop due to the presence of SO 2 in the atmosphere. ...
... The reactions that take place in water with dissolved oxygen are cathodic and anodic: The corrosive process can be accelerated when the corrosive environment has a pH drop due to the presence of SO 2 in the atmosphere. In this environment, the reduction in SO 2 prevails instead of O 2 , and corrosion is catalyzed, where SO 2 becomes H 2 SO 4 (Ref 8,14,29). Under a thin solution layer, sulfuric acid accelerates iron dissolution, facilitating the formation of FeOOH ( Ref 29,32). ...
The effect on the corrosive behavior of three new-type Si-based weathering steel and the addition of Ni, Mo, and Mn was investigated. Carbon steel was used for comparison. For this purpose, wet/dry cyclic corrosion tests for 6, 15, 30, 45, and 60 cycles, each cycle lasting seven days, were conducted in simulated industrial environments. Mass loss measurements estimated the corrosion rate. The oxide layer was analyzed by electrochemical impedance spectroscopy (EIS), and rust formation was investigated by SEM microscopy. X-ray diffraction (XRD) was used to determine the crystalline structure of corrosion products produced after exposure. The weathering steel with a higher amount of Si and the one with the addition of Ni, Mn, and Mo had the lowest corrosion rates and presented similar corrosion performance after 15 cycles. The rust layer formed in the simulated industrial environment is rich in the α-FeOOH phase, and its amount increases with exposure time.
... These rust corrosion products in the form of oxides appear as an adherent film which can be seen under suitable SEM magnification. It is well known that iron corrosion in the atmosphere proceeds by hydrated oxides formation [40,52,59]. The half-cell reactions can be expressed by the following Equations It has been reported earlier that a stable film on iron surface forms via ( ) -2 OH under an alkaline environment which tends to protect the surface of rebar [2,[60][61][62][63]. ...
... Dissolution results in the formation of γ-FeO(OH) which can transform into ferric oxy-hydroxide like α-FeO(OH) or Fe 3 O 4 followed by further transformation into Fe 3 O 4 to γ-Fe 2 O 3 [2,75]. It has been reported in the earlier studies that the phase transformation of γ-FeO(OH) to α-FeO(OH) caused by the saline environment causes a net lowering of the corrosion rate in the case of carbon steel which is well evident in the present research, as in the case of 3.5% NaCl solution lower corrosion behaviour is observed for both plain and epoxy coated rebar samples [55,59,65]. In this context, the following equations exhibit the cathodic and anodic reactions: It can be seen from figure 11 that for the ECR samples, XRD profiles primarily reveal the occurrence of iron chloride hydroxide [Fe 2 (OH) 3 [53,76]. ...
Corrosion of steel rebars and susceptibility of reinforcement steel to chloride ion attacks are the two major problems for the construction industries and thereby a huge amount of money is spent to repair it. Epoxy coating on the steel rebars can be one cost-effective solution to alleviate the detrimental effects of corrosion in concrete structures. In the present research, plain and epoxy coated rebar (ECR) samples were chosen to study the correlation between microstructure, hardness and corrosion performance. The microstructures of the investigated thermomechanically treated (TMT) rebars primarily reveal tempered martensitic rings at the outer surface followed by a narrow bainitic transition zone in between along with a ferrite-pearlite microstructure at the inner core. The corrosion resistance of plain and epoxy-coated rebars in naturally aerated 3.5% NaCl and 1% HCl solutions were studied using gravimetric test, open circuit potential (OCP) test, and linear polarization monitoring techniques. It has been witnessed that the corrosion current (icorr) has been shifted towards lower values and polarization resistance (Rp) values are higher for ECR samples which is a clear indication of higher corrosion resistance of the ECRs than the plain rebars. Energy dispersive spectroscopy (EDS) analysis reveals the presence of iron hydroxides and iron oxides. However, x-Ray diffraction (XRD) analysis indicates the existence of various types of oxides, hydroxides, and oxy-hydroxides like iron chloride hydroxide [Fe2(OH)3Cl], goethite (α-FeO(OH)), lepidocrocite (γ-FeO(OH)), magnetite (Fe3O4) and bernalite [Fe(OH)3(H2O)0.25] in the epoxy coated rebar samples whereas, plain rebars indicate the presence of goethite (α-FeO(OH)), maghemite (γ-Fe2O3), magnetite (Fe3O4), hydrogoethite (Fe2O3.H2O), lepidocrocite (γ-FeO(OH)) and iron oxide (Fe21.34O32). All the experimental results confirm that ECR samples are more corrosion resistant under both acidic and saline environments.
... [1] Automobiles, bridges, buildings, and especially power systems rely on many different metallic materials; however, corrosion in these systems is a major problem. [2] The main factors affecting atmospheric corrosion are temperature, [3] humidity, [4] light, and wind speed, [5] in addition to chemical pollutants such as chlorides and sulfides. [6] The corrosion kinetics of carbon steel conform to the power exponential equation. ...
... The most polluting gas in the industrial atmosphere is SO 2 , [10] which produces sulfuric acid when dissolved in water, resulting in acidic corrosion. [4] Moreover, SO 2 promotes the production of α-FeOOH. [9c] With the expansion of industries, the atmosphere of coastal cities has transformed into a coastal-industrial atmosphere. ...
The synergistic effect of chloride ions and industrial corrosive gases in the atmosphere intensifies metal corrosion. Therefore, the study of this corrosive behavior and its effects on metals in complex environments is crucial. In this study, the wet/dry cyclic corrosion test, under a constant deposited salt, was used to simulate atmospheric corrosion conditions. In addition, the methods of corrosion weight gain, dynamic potential polarization curves, electrochemical impedance spectroscopy, and other analyses were used to explore the mechanism and law of Q235 steel with different corrosion times in different coastal‐industrial atmospheric environments. The corrosion pattern of Q235 steel and the composition of the rust layer were further investigated through X‐Ray Diffractometer analysis and Scanning Electron Microscope observations. The results show that the content of Fe3O4 decreases at higher chloride ion concentrations and the content of α‐FeOOH increases in later stages of corrosion.
... (The experimental equipment for simulating the corrosion environment of the marine splash zone is patented as ZL 2020 2 1337994.3) The samples were subjected to cyclic corrosion for 24,72,168,288,432, and 600 h in dry/immersion environments. Each dry-wet cycle included a 10-minute immersion stage and a 50-minute drying stage. ...
... γ-FeOOH is a semiconductor. In addition to its special anion selectivity, it also has strong electrochemical activity [23][24][25], which makes the stability of the rust layer very poor, and corrosive ions can easily pass through the rust layer and act on the matrix. In the middle period of corrosion, in the rust layer, there appears a small amount of iron-manganese oxide (Fe,Mn) x O y ), which will not only reduce the denseness of the outer rust layer so that ions to the inner layer diffuse but also adsorb anions in the medium. ...
The corrosion behavior of a medium-Mn steel in a simulated marine splash zone was studied by a dry–wet cyclic corrosion experiment and electrochemical experiment. The corrosion products were characterized by corrosion rate calculation, composition detection, morphology observation, element distribution detection, valence analysis, polarization curve, and electrochemical impedance test. The results show that the corrosion products of the sample mainly include γ-FeOOH, FexOy, MnxOy, and a small amount of (Fe,Mn)xOy, and the valence state of iron compounds and manganese compounds in different corrosion stages changed obviously. In the initial corrosion products, Mn is enriched significantly and facilitates the electrochemical reaction of corrosion process. The content of Ni in the inner rust layer is high. The semi-quantitative analysis of the corrosion product elements shows that the atomic concentrations of Cr and Mo increase significantly in later corrosion products, indicating that the dense isolation layer formed by alloy element compounds in the corroded layer is the main factor to improve the protection ability of the rust layer at the end corrosion stage of the sample. With the corrosion durations, the corrosion current density of the sample with the corrosion product film first increases and then decreases, and the corrosion potential first moves negative and then shifts in a positive direction subsequently, indicating that the protective effect of the corrosion product film is gradually significant.
... RH is relevant because corrosion only occurs when an electrolyte is present on the metal surface. T affects the corrosion rate because it influences the mobility of atoms [45], so the number of electrochemical reactions, and corrosive agents can increase reactivity [46], create strongly hygroscopic surfaces [47] or increase conductivity [12]. However, complex interactions between these environmental factors make their actual effect ambiguous. ...
... Meanwhile, it should be noted that the SO 2 -polluted seawater can be easily acidified by the sulphates via the acid regeneration mechanism [57,58]: ...
In this work, the effects of Nb micro-alloying on the stress corrosion cracking (SCC) behaviors of the heat-affected zone (HAZ) of high-strength low-alloy (HSLA) steel exposed to SO2-polluted seawater were investigated using electrochemical measurements, static load U-bend immersion tests and slow strain rate tensile experiments combined with fractographic observations. Results indicated that Nb existed in solute status in the coarse-grained HAZ (CGHAZ) while simultaneously in the form of solute status and NbC precipitate in the fine-grained HAZ (FGHAZ) and inter-critical HAZ (ICHAZ). With reduced prior austenite grain sizes, Nb micro-alloying refined the lath bainite in the CGHAZ as well as induced the formation of acicular ferrite in the FGHAZ and granular bainite in the ICHAZ. Moreover, the three types of HAZ microstructures had a high SCC susceptibility in SO2-polluted seawater in the increasing order of ICHAZ < FGHAZ < CGHAZ under the combined mechanism of anodic dissolution and hydrogen embrittlement. Nevertheless, attributing to the variations of microstructural constituents and the presence of NbC precipitates, Nb micro-alloying was capable to enhance the SCC resistance of HAZ microstructures by inhibiting the initiation and propagation of SCC cracks, with the SCC susceptibility decreased by ~ 5%, ~ 28% and 24% for CGHAZ, FGHAZ and ICHAZ, respectively.
... the oxidant in the rust layer [54]. The γ-FeOOH reduction process is as follows: ...
This study investigates the corrosion behavior of dissimilar gas tungsten arc (GTA) welded joints between super duplex stainless steel (sDSS 2507) and pipeline steel (X-70) using electrochemical and immersion corrosion tests. The GTA welds were fabricated using ER2594 and ER309L filler metals. The study examined the electrochemical characteristics and continuous corrosion behavior of samples extracted from various zones of the weldments in a 3.5 wt.% NaCl solution, employing electrochemical impedance spectroscopy, potentiodynamic polarization methods, and an immersion corrosion test. EIS and immersion investigations revealed pitting corrosion in the X-70 base metal/X-70 heat-affected zone, indicating inferior overall corrosion resistance due to galvanic coupling. The corrosion byproducts identified in complete immersion comprised α-FeOOH, γ-FeOOH, Fe3O4, and Fe2O3, whereas γ-FeOOH and Fe3O4 were predominant in dry/wet cyclic conditions. Corrosion escalated with dry/wet cycle conditions while maintaining a lower level in complete immersion. The corrosion mechanism involves three wet surface stages in dry/wet cycles and typical oxygen absorption during complete immersion. Proposed corrosion models highlight the influence of Cl⁻, O2, and rust layers.
... During the wetting process, the anode mainly dissolves the steel, and the cathode mainly dissolves the O 2 . During the drying process, conversion between corrosion products mainly occurs [32]. ...
... The corrosion process initiates with the formation of Fe(OH) 2 , which evolves into more stable phases such as lepidocrocite, goethite, Fe 3 O 4 , and α-Fe 2 O 3 [59]. Dissolved oxygen, along with γ-FeO(OH), plays a role in the rust layer's oxidation [66]. The reduction process of γ-FeO(OH) is involved in the corrosion mechanism: ...
This study explores the microstructure and corrosion resistance of dissimilar gas tungsten arc (GTA) welds between super duplex stainless steel (sDSS 2507) and nitronic steel (N50) using ER2594 and ER70S-2 filler metals. Scanning electron microscopy (SEM) was utilized for microstructural, compositional, and corroded surface analysis, including rust layer examination. Corrosion resistance was assessed through cyclic potentiodynamic polarization, electrochemical impedance spectroscopy, and continuous immersion in a 3.5 wt% NaCl solution. Results indicate that ER2594 demonstrates superior resistance to pitting, which is attributed to a substantial difference in pitting resistance equivalent number. Pitting initiation on the N50/sDSS 2507 base metal side with ER70S2 filler suggests galvanic coupling-induced general corrosion. Weight-loss measurements indicate hindered oxygen diffusion during continuous immersion, controlled by the electrochemical activity of the inner rust layer. Electrochemical tests demonstrate an oxygen-dependent cathodic reduction process, while complete immersion corrosion produces primary corrosion products such as β-FeO(OH), Fe3O4, Fe2O3, and γ-FeO(OH). The corrosion model reveals an oxygen-absorbing mechanism with non-protective rust layers and O2 diffusion control, emphasizing Cl⁻, O2, and rust layer interactions. This study highlights complex interactions between alloy composition, microstructure, and corrosion resistance to enhance performance, offering significant insights for tubing-couple assembly design in deep-water environments.
... The XRD results in Figure 10 and Table 5 further support that within one year of atmospheric corrosion, the corrosion products were mainly γ-FeOOH, followed by α-FeOOH. SO 2 is generally considered to be the most corrosive gas in the atmosphere [76] and contributes to the formation of α-FeOOH [77,78]. ...
The corrosion mechanism and characteristics of steel in typical atmospheric environments directly affect the rationality of corrosion protection methods. This study investigates the corrosion evolution law of Q235 steel that has been exposed to the urban industrial atmosphere for seven years. The mass loss is used for corrosion dynamics analysis. The rust layers have been characterized by SEM, EDS, and XRD. Finally, the corrosion mechanism was analyzed through a combination of electrochemical methods, corrosion kinetics, and rust layer characteristics. The mass loss results indicate that a two-stage corrosion power function law can still effectively describe the corrosion rate of a seven-year exposure that complies with the power function law. The short-term corrosion results fail to fully reflect the corrosion performance of Q235 steel. The typical morphological structures of γ-FeOOH and α-FeOOH are identified, and the rust layers change from a loose and flat form to a granular and, finally, compact into a smooth surface. The crystalline phases of the rust layers include α-FeOOH, γ-FeOOH, Fe3O4/γ-Fe2O3 and α-Fe2O3. Corrosion products in the initial period are mainly γ-FeOOH, followed by α-FeOOH, and a small amount of Fe3O4/γ-Fe2O3. With the increase in exposure time, α-FeOOH and Fe3O4/γ-Fe2O3 in the rust layer increase. SO2 and Fe3O4/γ-Fe2O3 are the primary factors accelerating steel corrosion. During the first three years of atmospheric corrosion, the primary corrosion mechanism was governed by the acid cycle reaction mechanism. However, from the fifth year of atmospheric corrosion, oxygen-absorbing corrosion began to gradually dominate, specifically oxygen-absorbing corrosion.
... At present, the tannic acid and phosphoric acid are mostly used in the water-borne rust conversion coatings on the market. [19][20][21] Singh et al. [22] used tannic acid as a rust conversion agent to prepare an epoxy zinc-rich rust conversion coating. Raman experiments show that tannic acid can effectively convert rust components, and the zinc powder filler contained in the zinc-rich coating acts as an anode sacrificial, which can provide cathodic protection to keep the coating for 200 h in the case of electrochemical corrosion. ...
In this study, the rust conversion coating that acts directly on the surface of rust layer, was studied from the preparation of rust conversion agents gallic acid (GA), 2‐hydroxyphosphonyl acetic acid (HPAA), and their compound (GA/HPAA), rust conversion effect and anticorrosive mechanism. Results show that 1) when GA and HPAA were combined to form GA/HPAA with a mass ratio of 2:1, the strengthening effect of rust conversion was observed, and a more complete, dense, and smooth covering film was generated on the rust surface. In this case, the corrosion current of GA/HPAA was reduced to 4.10 × 10⁻⁷ A cm⁻², while the GA was 2.35 × 10⁻⁶ A cm⁻² and HPAA was 2.16 × 10⁻⁶ A cm⁻². 2) The mechanism of rust conversion and corrosion resistance can be expressed as that the chelation reaction can occur between the rust and rust conversion agent, which can generate new coordination covalent bonds O–Fe–O, P–O–Fe, and C–Fe–O. In this case, they can firmly lock the rust and prevent it from spreading further. Meanwhile, a highly cross‐linked dense anticorrosion protective film can be formed. Due to the presence of these chelating products, they can act as obstacles, prolonging the diffusion path of corrosive medium and slowing down the interaction with the metal matrix.
... In the primary stage of corrosion, the main electrochemical reactions of AISI 4135 steel are the AD of iron and cathodic oxygen reduction, resulting in the formation of Fe(OH) 2 43-45 . The initial corrosion product, Fe(OH) 2 , is unstable and can be easily transformed into iron oxyhydroxides (FeOOH) in the presence of oxygen 46 . During the immersion stage, i.e. when the steel sample is immersed in seawater, the corrosion of steel occurs via a typical oxygen-absorbing corrosion mechanism 5,47 . ...
High-strength steels are widely used in marine engineering; however, they suffer from the risks of corrosion, hydrogen permeation, and stress corrosion cracking (SCC) in wet–dry cyclic marine environments. In this study, the corrosion, hydrogen permeation, and SCC behaviours of AISI 4135 steel in the tidal zone were investigated using electrochemical corrosion, electrochemical hydrogen permeation, and slow strain rate tests, respectively, via field exposure. The results showed that the AISI 4135 steel sample placed at the high tide level had high SCC susceptibility because of severe pitting corrosion and hydrogen permeation, whereas the steel samples placed at the middle and low tide levels had low SCC susceptibilities. The dry/wet time ratio was crucial in determining the SCC behaviour and mechanism of the steel in the tidal zone. With increasing time ratio, the SCC mechanism changed from micro-void coalescence control to localised anodic dissolution and hydrogen embrittlement in tandem.
... In the primary stage of corrosion, the main electrochemical reactions of AISI 4135 steel are the AD of iron and cathodic oxygen reduction, resulting in the formation of Fe(OH) 2 43-45 . The initial corrosion product, Fe(OH) 2 , is unstable and can be easily transformed into iron oxyhydroxides (FeOOH) in the presence of oxygen 46 . During the immersion stage, i.e. when the steel sample is immersed in seawater, the corrosion of steel occurs via a typical oxygen-absorbing corrosion mechanism 5,47 . ...
... , and a small amount of iron and manganese oxide (Fe,Mn) x O y and Nickel-Molybdenum oxide(NiMoO 4 ). γ-FeOOH is a semiconductor with strong electrochemical activity [22][23][24], it is easy to be reduced to some intermediate substance in corrosive medium and then oxidized again , which promotes the corrosion process. Due to γ-FeOOH special anion selectivity [25,26], Cl − can promote γ-FeOOH formation. ...
The corrosion behavior of a high manganese steel in simulated marine splash zone environment was studied by dry-wet cyclic corrosion experiment and electrochemical experiment. Corrosion kinetics, composition, surface morphology, cross-section morphology, element distribution, valence state, polarization curve and electrochemical impedance spectroscopy were analyzed with the aim of characterizing the characteristics of corrosion product films. The results show that in chloride-containing environment, in the initial corrosion products, Mn oxides with porous structure lead to higher corrosion rate. As corrosion extends, the formation of alloy element oxides in corrosion products changes the corrosion properties of rust layers at different stages. Mo oxides form a stable passivation film, which reduces the influence of chloride ion on corrosion. Ni oxides in the inner rust layer facilitate the transformation of goethite, and Cr oxides in the outer rust layer increase the densification of the rust layer. The stability and compactness of Fe 3 O 4 , α-FeOOH and FeCr 2 O 4 in the later corrosion products inhibit the corrosion action of manganese iron oxides and slow down the corrosion rate. With the corrosion durations, the corrosion current density of the sample with the corrosion product film first increases and then decreases, and the corrosion potential first moves negative and then shifts in a positive direction subsequently, indicating that the protective effect of the corrosion product film is gradually significant.
... It is suggested that SO 2 emitted by the Mathura refinery and the local industries in and around Agra and Firozabad, when combines with moisture in the atmosphere, forms sulphuric acid and causes "acid rain" which has corrosive effect on the gleaming white marble forming a fungus (Gorbushina et al. 1993). This theory and attribution for the deteriorating effect on the marbles of the Taj Mahal, however, need more investigation, especially in view of the fact that the corrosion rate of steel exposed at Agra experiences almost similar rate of corrosion as recorded at the other distant places considered to be free from the industrial pollution (Singh et al. 2008). The corrosion rate of steels is more affected due to the acid rain caused due to SO 2 pollution. ...
Deterioration of metallic and non-metallic structures and monuments is largely controlled by their surrounding environment. The Taj Mahal, a UNESCO (United Nations Educational, Scientific and Cultural Organization) world heritage situated in Agra of India built in seventeenth century using white marbles, is famous for its aesthetic look. Gradual yellowing and blackening of the monument are matter of great concern, and if not controlled, the heritage structure may lose its glaze and beauty. Extensive studies available on deteriorating effect of the monument miss a vital point related to the pollutants coming from severely polluted River Yamuna which flows very close to the Taj Mahal. To ascertain the possible effects of the pollutants carbon steel, copper and zinc samples were exposed for four years at the premise of Taj Mahal. The surface characterization of the exposed metals with electrochemical impedance spectroscopy, Raman spectroscopy and X-ray diffraction reveals the formation of respective sulphides of the studied metals. The findings suggest that the hydrogen sulphide from the polluted Yamuna River had damaging effect. The wind rose diagram developed at site of exposure further supports the above findings. The corrosion rate of copper was found to be 2.46 µm/year. This observation as well as identification of corrosion products formed on the metal surface (strong peaks of copper sulphide) provided strong evidences that the hydrogen sulphide evolved from the polluted river accelerated the deterioration of the metal.
... The service life difference caused by different environments is obvious. [1][2][3][4] Since the beginning of the 20th century, foreign countries began to study the atmospheric exposure corrosion of steel, and accumulated a large number of atmospheric corrosion data. [5][6][7][8] However, there are few data of similar studies in China. ...
China has the largest and most complex power grid in the world. But at the same time, the power grid is also facing severe challenges from the natural environment, so its security and reliability are particularly important. In this paper, Q235 carbon steel was used for exposure test. 81 experimental sites were set up in five cities of Southern Hebei Province. And the data of two years were collected and sorted out, and the map of atmospheric corrosion grade in Southern Hebei Province was drawn.
... The results presented in Figure 7, based on a Mössbauer analysis of the outermost layer, indicate lepidocrocite and goethite as the main constituents in the corrosion product of both steels exposed at the Tocumen test site. Lepidocrocite is usually formed in the early stages of atmospheric corrosion, but as the exposure time increases it is transformed into goethite [34]. According to Misawa et al. [35], the transformation takes place via the formation of an amorphous ferric oxyhydroxide, which is subsequently transformed into goethite by a solid-state process. ...
The mild carbon steel (CS) A-36 and weathering steel A-588 were exposed to the outdoor atmosphere at two different locations in tropical Panama. After a 10-year exposure, the results indicate that the chloride deposition rate and the type of steel play an important role in the corrosion behaviour of tested steels. Both types of steel mainly contain lepidocrocite and goethite as corrosion products at the urban site, while the corrosion products of steels exposed to a moderate marine atmosphere consisted of lepidocrocite, goethite and maghemite. The large fractions of maghemite in the corrosion products of steel A-36 suggest that this phase is interrelated to the higher corrosion rate of CS in the moderate atmospheric environment.
... The alkaline conditions of the medium, in turn, contribute to the growth of a passive film of protective oxides that prevent corrosion on the surface of iron [30]. The level of SO 2 in the atmosphere is an important factor influencing the structure of corrosion products and corrosion intensity of steels [31]. The concentration of sulphur dioxide in the atmosphere varies significantly depending on the region, season, etc. ...
This review aims to provide a general view on anti-corrosion coatings for the protection of steel railway structures exposed to atmospheric environments. The article describes the specific features of the operation of railway structures with steel elements, including culverts and bridge structures (bridges, viaducts, flyovers, overpasses), track and catenary. The structural, metallurgical and environmental factors influencing the nature and corrosion rate of these structures are summarized and discussed. The mechanisms of electrochemical processes of atmospheric corrosion of steels, corrosion products and layers are analyzed. The types of the most widely used anti-corrosion coatings for steel railway structures, their main components, and characteristics are depicted. The protective mechanisms of such coatings, as well as the processes leading to their degradation and destruction, are investigated. In conclusion, the article highlights key bottlenecks and areas for further research in this area in the context of increasing environmental compliance requirements, lower operating costs, and improved performance of anti-corrosion coatings for steel railway structures.
The corrosion behavior of high manganese steel in 0.01mol/L NaHSO3 solution and 3.5wt.% NaCl solution was studied by cyclic immersion test and electrochemical test. The results show that with the increase of immersion time, the corrosion rate of high manganese steel in both solutions shows a decreasing trend. The Fe2O3 and γ-FeOOH in the rust layer gradually change into stable and dense Fe3O4 and α-FeOOH, and the ratio of α/γ* increases continuously. The corrosion potential (Ecorr) of the rusted sample is continuously positive shifted, and the corrosion current density (Icorr) is continuously reduced, indicating that the protective effect of the rust layer on the steel substrate is gradually enhanced. Compared with 3.5wt.% NaCl solution, the rust layer of high manganese steel in 0.01mol/L NaHSO3 solution is more compact and the corrosion resistance is stronger.
In the normal operational environment, reboiler tubes are exposed to high temperatures, high saline contents, and dissolved oxygen, making them susceptible to stress corrosion cracking (SCC), which can lead to premature failure. To explore the SCC mechanisms in reboiler tubes, C-ring samples were prepared for a series of experiments, which include electrochemical impedance spectroscopy (EIS), potentiodynamic polarization, and cyclic voltammetry, to assess the SCC behavior of 2205 duplex stainless steel (DSS). An increase in both dissolved oxygen and applied stress contributes to a reduction in impedance values, facilitating chloride ion transport across the metal–electrolyte interface double layer and subsequently promoting passive film degradation. This degradation significantly impairs the passive film integrity; chloride ions reside at anionic sites in the passivation film's metal oxide. Furthermore, stress-induced dislocations augment the migration of cation vacancies within the passive film/2205DSS matrix, culminating in passive film rupture.
The corrosion behavior of carbon steel covered with coating films containing Al 2 (SO 4 ) 3 , CaO, and BaO was examined under a sulfuric acid mist environment containing chloride. CaSO 4 ･2H 2 O and BaSO 4 were formed as the corrosion products in the coating film and prevented the penetration of corrosives, in particular BaSO 4 was highly effective. Furthermore, the rust layer containing CaCO 3 adhered to the carbon steel substrate suppressed the penetration of chloride. The formation of these corrosion products suppressed the anodic reaction, resulting in higher corrosion resistance of the carbon steel in the chloride‐containing acid environment.
In this work, the outdoor corrosion behavior of AZ31B magnesium alloy in the Antarctic atmospheric environment was investigated. The surface corrosion state of the specimens exposed to the Antarctic atmosphere for 1 month and 24 months differ significantly. The corrosion rate after 1 month during the summer season was 19.82 g/m2·year and it decreased to 13.87 g/m2·year after two years’ exposure. Corrosion is initiated with pitting corrosion and then evolved to uniform corrosion with prolonging exposure time. The skyward surface exhibited a much severe corrosion than that of the groundward surface, attributed to the long-term existence of the adsorbed electrolyte layer. The corrosion products formed on the alloy exposed in Antarctica environment were MgCO3·3H2O, MgCO3·5H2O and Mg2CO3(OH)2·0.5H2O, with the MgCO3·3H2O as the dominant phase in the initial stage and the Mg2CO3(OH)2·0.5H2O as the dominant phase after long-term exposure.
Electrochemical corrosion and stress corrosion cracking (SCC) behavior of X80 steel in the sulfurated marine environment at open circuit potential and −850 mVSCE are investigated. The results show that SCC is controlled by both anodic dissolution and hydrogen evolution, which is attributed to the HSO3− acceleration of the anodic and cathodic current density. Localized anodic dissolution leads to pits, which induce stress that promotes the initiation of stress corrosion cracks. Under a cathodic potential of −850 mVSCE, the effect of dissolution is limited, and SCC susceptibility increases because of the synergistic effect of the high HSO3−concentration and cathodic potential.
A comparative study on the corrosion behavior of CoCrNi medium-entropy alloy (MEA) with CoCrFeMnNi high-entropy alloy (HEA) in SO2-polluted marine environment was investigated by a series of tests. Results indicate that CoCrNi MEA possesses smaller passive current density, larger polarization resistance and lower corrosion rate compared with those of CoCrFeMnNi HEA, which demonstrates that the MEA possesses better anti-corrosion performance than the HEA. This could be ascribed to the detail difference in the microstructure and passive film of the two alloys. Compared with the MEA, the smaller grain size and the larger number of oxides reduce the anti-corrosion performance of the HEA. Moreover, the oxide and matrix constitute the micro-galvanic corrosion cell, which promotes the generation of pits.
While the uncertainty from COVID-19 persists throughout the globe, the impact it triggered is not only limited to physical health issues. The pandemic forced people to adapt in many aspects. People’s behaviours and perceptions has shifted throughout the pandemic. Though, inhabitants of distinct culture perceive and react to things differently. There are findings that culture strongly influences both individuals and society perception of events and this pandemic is not an exception. Leisure is one of an autonomous way to express culture. This research is intended to spot global connection patterns in hobby interest and learn how the patterns has changed by the occurrence of COVID-19 with network graphs visualization. In the last decade, Google Trends has been proven to be a promising tool in behavioural
science studies. It allows researchers to draw summarized time-series data from the sample size of global Google users for free. One of its tools accumulates different search queries that belong to the same topic in different synonyms and languages as a topic which is essentially useful. This research has collected scaled data of ten selected hobbies, in fifty top GDP (2020) countries from January 1st, 2018 thru March 31st, 2021 with Google Trends topics. This work marks the period before March 11th,2020 as pre-pandemic and the period from this date as post-pandemic according to the World Health Organization’s announcement. This paper then calculate correlation matrices and visualize with network graphs. The analysis shows significant adjustments in global relationship patterns affected by the pandemic in most search topics.
Transparent and robust titanium dioxide (TiO2) coatings were prepared by the facile aerosol-assisted chemical vapor deposition (AACVD) method. The effects of deposition temperature and precursor concentration on the crystal growth and optical properties of TiO2 coating were investigated. It is found that the obtained TiO2 coating has strong adhesion to the substrate, which can effectively avoid mechanical scratches and wear by sharp objects, adhesive tape and steel wool. Besides, in the marine corrosion protection test, both the open circuit potential and electrochemical impedance of TiO2 coating immersed in artificial seawater for different times are greater than those of the bare S420 steel substrate. Particularly, the high-frequency phase angle of the TiO2 coating increases, and the impedance value at low frequency of 0.10 Hz is about 2 orders of magnitude higher than that of the bare S420 substrate. In addition, the significant decrease of corrosion products on the surface further proves that the deposited TiO2 coating exhibits better corrosion inhibition and excellent anticorrosion properties, which is expected in application of the surface coating protection of the marine exploration lens.
The environmentally assisted stress corrosion cracking (SCC) behaviours of low alloy E690 steel in SO2-containing NaCl solution are investigated. The result shows that the corrosion on the metal surface becomes serious with the addition of NaHSO3, which mainly exhibits pitting corrosion. When the NaHSO3 concentration increases to 0.01 mol/L, the static load enhances the local AD resulting in the pits, and the stress concentrations around the pits leads to the initiation and propagation of the crack. And the SCC exhibits the transgranular cracking controlled by a combined mechanism of anodic dissolution (AD) and hydrogen embrittlement (HE). With the addition of NaHSO3, the corrosion potential on the surface of metal changes the crack growth rate through altering the pH and electrochemistry at the crack tip. Compared to the static load, the dynamic load promotes the dislocation accumulation, increases the electrochemical activity at the crack tip, which facilitates the HE and further accelerates the crack growth.
Corrosion behaviors of low-alloy steel were investigated in the simulated tidal zones using stereoscopic microscope, field emission scanning electron microscope, X-ray diffraction, open circuit potential, and electrochemical impedance spectroscopy. The result shows that the corrosion in various tidal zones is much more severe than that of the immersion (IM) zone, and more severe corrosion takes place in the low tide (LT) and middle tide (MT) zones compared with the high tide (HT) zone. In the present test-time scale, uniform corrosion predominantly occurs in the IM and LT zones, and non-uniform corrosion occurs in the MT and HT zones. The main corrosion products in the LT and MT zones are Fe3O4 while α-FeOOH dominates the composition of rust layers in the HT zone.
The effects of different contents of rare earth (RE) elements Ce and La on the corrosion behavior of weathering steel Q355NHq were investigates with alternate immersion tests and electrochemical measurements. The corrosion rates were lowest with the rusted steels containing 170 ppm rare earth elements. Aspex analysis showed that steels with the rare earth elements content of 170 ppm had the greatest percentage of inclusions with high content of rare earth elements. The immersion tests showed modified inclusions with a high percentage of (RE)xOy exhibited a better corrosion resistance than CaS-Al2O3 inclusion. Compared with steels containing no more than 90 ppm RE, the rust layers of steels containing 170 ppm rare earth elements were compact, and contained high amounts of -FeOOH and low amounts of γ-FeOOH. Based on the results obtained, the influence of the different contents of rare earth elements in weathering steel corrosion is discussed.
Q345B carbon steel as well as Q450NQR1 and S500AW weathering steels were subjected to outdoor exposure corrosion tests in coal environments and indoor periodic immersion accelerated corrosion tests with a simulated coal leaching solution. The corrosion kinetics were studied by the weight loss method, and the corrosion morphology and corrosion product composition were observed and analyzed by scanning electron microscopy, energy-dispersive spectroscopy and X-ray diffraction. Afterward, correlation analysis of the indoor and outdoor tests was carried out by the gray correlation analysis method. The results show that the relationship between the corrosion weight loss and corrosion time of the three steels conforms to follow the exponent power law. In particular, Q450NQR1 steel has the best corrosion resistance. The types of corrosion products and the distribution of elements in the rust layer of the three steels are similar in the indoor and outdoor tests. The gray correlation degrees of the three steels in the indoor and outdoor tests are all greater than 0.6; thus, the two corrosion tests have a good correlation. Based on this, the accelerated simulation test method of the coal leaching solution is determined, and life prediction models of three steels in coal leaching solution are established to simulate the corrosion of the bottom board and side board.
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.
The effect of hydrogen charging on the corrosion behavior of E690 steel in 3.5 wt.% NaCl solution was investigated. The corrosion behaviors of the charged and uncharged steel were characterized using scanning electron microscopy, x-ray diffraction, Raman spectroscopy and x-ray photoelectron spectroscopy. The results showed that hydrogen charging promoted the precipitation of corrosion products on the surface of E690 steel, with the corrosion products mainly consisting of α-Fe2O3, α-FeOOH and γ-FeOOH. The relative content of α-FeOOH reached maximum when the hydrogen charging current density was 20 mA/cm2, and two different corrosion product layers were formed on the surface. And the hydrogen charged current density at 20 and 50 mA/cm2, the potentiodynamic polarization curves also displayed passivation regions.
The rusting behaviors of S450EW weathering steel under exposure conditions of continuous spray and wet/dry cycling were comparatively studied through electrochemical tests and characterizations on rust layers. Wet/dry cycling promotes the formation of γ-FeOOH and its transformation to α-FeOOH rather than to Fe3O4, inducing a lower content of Fe3O4/γ-Fe2O3 than that under continuous spray. The rust layer formed under wet/dry cycling presents less compositional segregation and structural stratification. Wet/dry cycles promote the diffusion of oxygen and ions and make rust formation and evolution proceed more equally at any thickness of the rust layer through the migration of the air/electrolyte interface.
Weathering steel (WS) has an extensive use in steel bridge construction thanks to its satisfactory atmospheric corrosion resistance, low life cycle cost and good mechanical properties. In this paper, cyclic immersion corrosion experiment was carried out in simulated industrial atmospheric environment. The corrosion weight loss, macro morphology, rusting coat section, XRD and electrochemical characteristics of bridge weathering steel Q345qDNH and low alloy steel Q345qD were compared. The corrosion characteristics were identified and underlying corrosion inhibition mechanism of bridge weathering steel Q345qDNH were analyzed. The experiment and analysis results show that the rusting coat on the exterior of standard carbon steel is relatively loose and porous, and the main component is Fe3O4. The rusting coat of weathering steel is divided into internal and external layers under atmospheric corrosion, the outer rusting coat is loose primarily composed of γ – FeOOH and the inner rusting coat is uniform and dense, principally containing α – FeOOH. During the evolution of the rusting coat, the addition of trace alloy elements in weathering steel effectively promoted the transformation from γ – FeOOH to α – FeOOH, forming a more stable and condense inner rusting coat. It can potently isolate the corrosive medium from penetrating in and enhance the electrochemical corrosion resistance of rusting coat, so it possesses better corrosion resistance in atmospheric corrosion environment and has a promising application prospect in bridge engineering construction.
A contrastive study about ultraviolet light (UV) illumination on Na2SO4, NaCl induced Q450 weathering steel was qualitatively and quantitatively studied. The corrosion rate was calculated from mass losses and the order was as following, coupons deposited with Na2SO4 under UV illumination (238.18 μA·cm⁻²) > with NaCl under UV illumination (213.77 μA·cm⁻²) > with NaCl under Dark condition (71.98 μA·cm⁻²) > with Na2SO4 under Dark condition (43.26 μA·cm⁻²). The influence of UV illumination on metal corrosion followed this sequence: Na2SO4> NaCl, and which was on account of corrosion products film on metal depositing Na2SO4 with a larger carrier density on metal depositing Na2SO4 with a larger carrier density (9.32×10²⁰ cm⁻³) and stronger electric conductivity ability than NaCl (8.93×10²⁰ cm⁻³). Electrochemical impedance spectroscopy studies revealed charge transfer resistance Rct value, suggesting that smaller resistances gained on the rusted samples due to UV illumination, and an accelerated corrosion effect on rusted sample was also obtained under UV illumination. The improved corrosion performance by UV illumination was due to corrosion products of semiconductor property and photovoltaic effect.
Non-painted bridge were weathering steel was built and exposure test panels were installed on it on the highway of the Tohoku mountainous area. Twelve years having passed since then, investigations were made on conditions of rust layers formed on those surfaces.It was found that rust on the bridge was deep reddish brown in general and protective rust seemed to have been formed steadily but ion properties resistance value was so low as 0.34 kΩ on average. On the other hand, in the investigations of rust layers of exposure test pieces, it was recognized there were almost uniform non-polarizing layers containing condensed Cr and Cu.But many cracks were found on those rust layers and condensed Cl existed along them. It is supposed this may be the cause which made the ion properties resistance value low.This Cl was supposedly produced from antifreeze agent spread on the road in winter time, and its mist may have accumulated and penetrated into the rust layers. In the future, it must be studied what effect this Cl will give to formation protective rust.
The corrosion product formed on weathering steel exposed in a rural environment in the United States for 16 years has been investigated using Mossbauer spectroscopy, X-ray diffraction and Raman spectrometry. Mossbauer spectroscopy was used to measure the fraction of each oxide in the rust layer and micro-Raman spectrometry was used to locate and map the oxides to 2 microns spatial resolutions. The protective innerlayer closest to the steel substrate consisted of nano-sized goethite ranging in size from 5-30 nm. The outer-layer close to the rust layer surface, consisted of lepidocrocite and goethite with the former oxide being most abundant. Comparison of the goethite in the rust layer was made with synthetic chromium substituted goethite with nearly identical microstructural characteristics being recorded. It can be said that most of the so-called X-ray amorphous substance, generally considered as mixture of nano-phase oxides of crystal size less than about 15 nm and actual amorphous phase with very short-range ordered atomic arrangement, possesses goethite structure with particle size less than 15 nm. Considering this nano-phase goethite, new quantitative determination method of total goethite in rust layer is proposed. It is concluded that chromium-substitution in the goethite is important for formation of a nano-phase oxide layer which may help protect the weathering steel from further corrosion.
The Raman spectra of the passive films formed on iron in a neutral borate solution at various potentials were measured for evaluating its composition without any enhancement technique. The ex-situ spectrum measured in air after removal from the aqueous solution corresponds to the composition of disordered Fe3O4, i.e., Fe3−δO4. The passive film in the aqueous solution, which could not be measured in this paper due to a large background scattering light intensity from surrounding water around the iron electrode, may be a compositional framework same as the ex-situ passive film, although it is expected to be hydrated under the in-situ condition. For the in-situ measurement of the passive film, it is speculated that much accumulation will be required to decrease the noise level of the background light scattering relative to the signal from the thin film.
A new standard laboratory test (SAE J2334) for evaluation of the cosmetic corrosion resistance of autobody steel sheet has been developed through the joint efforts of the Society of Automotive Engineers Automotive Corrosion Prevention Committee (SAE/ACAP) and the Auto/Steel Partnership (A/SP) Corrosion Task Force. Results from this test gave an excellent correlation with those of on-vehicle tests conducted for 5 years in Canada at St. John`s, Newfoundland, and Montreal, Quebec. To determine how results of the Canadian tests related to environments in the United States, racks of identical materials were mounted on the front license plate brackets of cars driven in various locations in the US snowbelt, including Bethlehem, Pennsylvania; Detroit, Michigan, and Chardon, Ohio. After 4 years to 5 years, these tests showed the US environments produced less scribe creep and more red rust than those conducted in Canada. Similar rankings were obtained for the scribe creep resistance of the various coated steel sheet products when compared at equivalent amounts of corrosion. However, the ranking of materials changed at longer exposure times in Canada, and for that reason, it was concluded that the 5-year Canadian results used in the development of the SAE J2334 test provided a better real-world performance standard.
DNA sensing protocols, based on different modes of nucleic acid interaction, possess an enormous potential for environmental monitoring. This review describes recent efforts aimed at coupling nucleic acid recognition layers with electrochemical transducers. It considers DNA hybridization sensors for sequences related to microbial or viral pathogens, and DNA-modified carbon electrodes for monitoring low molecular weight priority pollutants interacting with the surfaceconfined DNA. Carbon strip or paste electrode transducers, supporting the DNA recognition layer, are used with a highly sensitive chronopotentiometric transduction of the DNA analyte recognition event. Factors influencing the performance of these new environmental biosensors are discussed, and their environmental utility is illustrated. While the use of DNA biosensors is at a very early stage, these and similar developments are expected to have a profound effect on environmental analysis.
Understanding of short crack behaviors is essential to construct lifetime prediction models for light water reactor components. There is, however, no established method of directly measuring short crack behaviors. Therefore we need some interpolation or extrapolation technique to precisely evaluate the short crack growth rate. In this study, constant load tests were conducted to investigate a short crack growth rate on primary water stress corrosion cracking (PWSCC) for different mill annealed alloy 600 samples in primary water at 350°C. Maximum crack length was measured for each sample and then divided by relevant test duration to evaluate its crack growth rate. On the other hand, to determine the accurate crack growth rates, a crack growth simulation model which allowed for mechanical effects of grain boundaries on a crack kinked at the grain boundary triple point was developed. With this simulation model, the crack growth processes in the tests were reproduced using a computer and thereby the crack growth rate was evaluated.
The corrosion products of carbon steel and weathering steel exposed to three different types of atmospheres, at times ranging from one to three months, have been identified. The steels were exposed in an industrial site, an urban site (São Paulo City, Brazil), and a humid site. The effect of the steel type on the corrosion products formed in the early stages of atmospheric corrosion has been evaluated. The corrosion products formed at the various exposure locations were characterized by Raman microscopy, X-Ray diffraction (XRD) and their morphology was observed by Scanning Electron Microscopy (SEM). Three regions of different colours (yellow, black and red) have been identified over the steel coupons by Raman microscopy. Analysis carried out on each of these areas led to the characterization of the correspondent oxide/hydroxide phases. The main phases present were lepidocrocite (g-FeOOH) and goethite (a-FeOOH). Small amounts of magnetite (Fe3O4) were also eventually encountered.
Laser Raman spectroscopy has been applied for detection and characterization of thin corrosion films formed on iron in air. In situ ellipsometric measurements have also been conducted for quantitative estimation of film growth kinetics. Oxidation leads to formation of a surface oxide film composed primarily of magnetite. The water vapor in air accelerates the formation of hematite. The ratio of magnetite to hematite in the film appears to increase with increasing water vapor pressure, ascending temperature, and oxidation time.
The oxidation products of Fe (OH)2 formed in the presence of Co2, Cu2 and Cr3 were characterized by various means. Co2 and Cu2 produced pure Fe3O4 by inhibiting the generation of a-FeOOH, whilst Cr3 promoted the a-FeOOH formation and interfered with the Fe3O4 formation. The Fe3O4 particles produced with Co2 exhibited high Fe2 content, electrical conductivity and stability to oxidation. Mössbauer spectroscopy demonstrated that the excess Fe2 replaced for Fe3 in B-sites of Fe3O4. A small quantity of metal Fe formed in addition to Fe3O4 on adding Co2.
Corrosion behavior of zinc coatings produced from ammonium chloride + zinc chloride + potassium chloride bath (ACB) and zinc chloride + potassium chloride + boric acid bath (BAB) was studied using weight-loss and electrochemical techniques. It was established that the zinc coatings electrodeposited in ACB performs better than the electrodeposited coatings produced from BAB. The zinc deposition reactions in baths having ammonium chloride polarized to a greater extent than the bath blended with boric acid. Alternating current (AC) impedance studies demonstrated that the coatings produced in both types of solutions formed unstable film in corrosive media. This was corroborated by weight-loss as well as direct current (DC) polarization techniques. The presence of boric acid in the plating bath had little influence on charge-transfer resistance of zinc deposition. However, the electrochemical double-layer capacitance decreased with the increase of boric acid concentration in the bath. Scanning electron microscopy (SEM) and electrochemical impedance spectroscopy (EIS) studies revealed that the coating produced in ACB has amorphous-type grains whereas the BAB coating showed a crystalline structure. It was concluded that improved corrosion resistance of the zinc coating deposited in the ACB was caused by the stronger complexing tendency of ammonium chloride with zinc cations, which resulted in a slow discharge of this ion during the deposition process.
ASTM G 1-90 solution, also popularly known as Clarke solution, which contains concentrated hydrochloric acid (HCl, specific gravity [sp.gr.] = 1.19) + 2% antimony trioxide (Sb2O3) and 5% stannous chloride (SnCl2), shows considerable variation in its corrosive effect toward steels having different chemical compositions. Plain carbon steels (PCS) and some low-alloy steels (LAS) experience faster dissolution in comparison to LAS having copper, manganese, silicon, chromium, etc., as alloying elements. The presence of phosphorous in steels has an accelerating effect on corrosion rate. An attempt has been made to bring down the corrosion rate of different types of steels to an equal level by modifying the composition of the ASTM-recommended cleaning solution. Addition of 0.5% copper salt (cuprous chloride [CuCl]) to the Clarke solution has dramatically improved the performance of the solution, and an almost identical rate of corrosion is recorded for all the studied steels. This addition also accelerates the dissolution rate of oxide of steels with variations in their chemical compositions. Electrochemical direct current (DC) polarization and alternating current impedance spectroscopic (EIS) studies have been performed to understand the mechanism of the action of the original and modified solutions in controlling the corrosion of steels.
The atmospheric corrosion performance of carbon steel (SS400) and high phosphorus weathering steel (Acr-Ten A) exposed indifferent atmospheric environments was studied and compared after exposure for various periods (up to 6 years) in Taiwan, In an industrial atmosphere, the corrosion kinetics of weathering steel was found to deviate from the behavior predicted by the well-known bilogarithmic law after 3 years' exposure. The results of atmospheric exposure tests, rust structure analyses and electrochemical impedance measurements were integrated in this study to investigate the abnormal corrosion behavior, of weathering steel deviating from the bilogarithmic law. Furthermore, this deviation phenomenon was adequately simulated by an accelerated laboratory test under cyclic wet/dry conditions with the addition of SO2.
Metallic substrates and rust layers of several hundred year old (y.o.) ferrous artefacts were characterised. Composition, structure and porosity of the rust were analysed by different methods: OM, SEM, EDS, EPMA, XRD, μXRD, SAXS, BET and mercury porosimetry.Several important parameters to describe an old rust layer were determined and measured. These parameters will be used for the modelling of long-term indoor atmospheric corrosion.
The rust layers formed on weathering and mild steels by atmospheric corrosion in an industrial region for a quarter of a century have been characterized using various analytical techniques. In particular, analysis of a local portion of the rust layers by means of Raman spectroscopy gives important information on the structure of the layers. It is elucidated that the inner stable and protective rust layer which covered the surface of weathering steel mainly consists of nano-particles of α-FeOOH containing a considerable amount of Cr. The relative change of the amount of rust constituents for low alloy steels supports well a newly proposed schematic progress of long term alteration in stable and protective rust layer formed on a weathering steel in an industrial environment, i.e. the γ-FeOOH, as an initial rust layer, is transformed into a final stable rust layer of α-FeOOH, probably via an amorphous oxyhydroxide substance, during the long term atmospheric corrosion of a weathering steel.
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.
In einer früheren Arbeit wurde die Wirksamkeit von punktförmigen Ansammlungen von Eisen(II)-sulfat beim atmosphärischen Rosten beschrieben.
Der elektrochemische Mechanismus dieser Eisen(II)-sulfat-Nester kann nur in groben Zügen angegeben werden, da es bisher nur überraschend wenige experimentell belegte Arbeiten über das atmosphärische Rosten gibt. Anhand einer schematischen Darstellung eines Nestes werden die Vorgänge an der Anode und der Kathode sowie die sich ergebende Bedingung der Elektronenleitfähigkeit der beteiligten Eisenoxyde erörtert.
Die Initialphase, der Wachstumsvorgang, die Stabilitätsfaktoren und die Beziehungen zu den bisherigen Anschauungen über das atmosphärische Rosten werden diskutiert.
Veröffentlichungen über die Zusammensetzung des Rostes, seine Redoxfunktion sowie über bestimmte, für die Theorie der Nester bedeutsame Eisenoxydhydroxyde werden referiert bzw. Angeführt.
Theoretical interpretation of the ferrous(II) sulphate concentrations in atmospheric rust–part II
In an earlier article, the effect of point-shaped concentrations of ferrous(II) sulphate on atmospheric corrosion was described.
The electro-chemical mechanism of these ferrous (II) sulphate concentrations can only be indicated in broad outline, since atmospheric corrosion has so far been the subject of surprisingly few publications supported by experimental research. On the basis of a schematic presentation of such a concentration, the phenomena at the anode and cathode and the resulting condition of the electronconductivity of the iron oxides concerned are discussed.
The discussion then extends extends to the initial phase, the growth phenomena, the stability factors and the relationship with previous theories on atmospheric corrosion.
Reference is made to publications on the composition of the rust, its redox function, and certain iron oxide hydroxides which have an important bearing on the theory of these concentrations.
Raman spectra of FeO, Fe3O4, α-Fe2O3, α-FeOOH, and γ-FeOOH, the common products of iron oxidation, have been measured. The spectra of FeO and Fe3O4 appear to be identical. Armco iron oxidized in air
at 250°C was examined by Raman spectroscopy after varying periods of exposure and the surface film was found to contain Fe3O4 and α-Fe2O3.
Storage of ferrihydrite in aqueous suspensions at 24oC and pHs between 2.5 and 12 for as long as three years resulted in the formation of goethite and hematite. The proportions and crystallinity of these products varied widely with the pH. Maximum hematite was formed between pH 7 and 8, and maximum goethite at pH 4 and at pH 12. We relate the proportions of goethite and hematite to the activity of the Fe(III) ion species in solution; conditions favorable for the formation of goethite are unfavorable for that of hematite and vice versa. -from Authors
The possible use of Raman spectroscopy for studies of anodic corrosion film formation on Fe-Cr and Fe-Cr-Mo single crystals has been elucidated. The study shows that Raman spectra from passive films (thickness range 5-6 nm) and from 'transpassive films' or films grown during secondary passivity (thickness range 5-25 nm) can be detected and interpreted. The results from Raman spectroscopy have been obtained in 1M KOH and combined with complementary results from x-ray photoelectron spectroscopy and nuclear microanalysis. Identified phases in the passive film are alpha -(Fe, Cr)//2O//3 and in the transpassive film alpha -(Fe, Cr)//2O//3, Fe-Cr spinel, and amorphous FeOOH.
A simple analytical theory is presented to explain the measured roll over and cross over behaviour of the IV characteristics of thin film CdTe solar cells. It involves a classical description of the CdS/CdTe junction and the CdTe/back contact structure and is extended with a new description of minority carrier current in the CdTe contact region. This extension is crucial in describing the light dependence of the forward IV curves, and hence cross over. The same model also explains the measured CV curves. It is shown that analysis of the capacitance measurement can yield additional information about the doping density of CdTe in the vicinity of the contact. A relationship between the fill factor of the solar cell and the barrier height of the back contact is derived; this relation is useful as a new, practical criterion for the quality of the back contact. The results of this simple analytical model are confirmed by full numerical calculations of the dc and ac characteristics. © 1997 American Institute of Physics.
Die Summe der kristallinen Phasen ist bei der quantitativen, röntgenographischen Phasenanalyse immer kleiner als 100 Prozent. Es wurde deshalb versucht, mit einem kombinierten Verfahren aus quantitativer, röntgenographischer Phasenanalyse und chemischen Extraktionsversuchen in mehreren charakteristischen Proben der verschiedenen Rosttypen röntgenamorphe Beimengungen nachzuweisen, Der Industrie-, Wald- und Seerost enthält keine amorphe Beimengung. Die kristallinen Fehlbeträge bei der Phasenanalyse werden durch Gitterstörungen der kristallinen Phasen α-FeOOH, γ- FeOOH und Fe3O4; hervorgerufen. α-FeOOH besitzt die stärksten, Fe3/O4, die geringsten Störungen. Der Wasserleitungs- und der Meerrost besitzen z. T. röntgenamorphe Beimengungen. Es besteht jedoch die Möglichkeit, daß diese erst durch die Bearbeitung der Rostproben an der Luft entstehen und daß die betreffenden Roste in Entstehungsmilieu ebenfalls keine amorphe Phasen enthalten.
X-ray amorphous phases in rust
The sum of the crystalline phases found during a quantitative X-ray analysis of rust is always below 100%. An attempt was therefore made to identify amorphous phases in several characteristic Of different types Of rust; to this end a combination was used of quantitative phase analysis by X-rays and chemical extraction. Rust from industrial, forest and lake environments does not contain amorphous components. The crystalline deficit found during phase analysis is due to lattice distorsions in the crystalline Phase α-FeOOH, γ-FeOOH and Fe3O4; the distorsions are greatest in the α-phase and smallest in Fe3O4. Rust from water ducts and maritime environments sometimes contains X-ray amorphous components. It is possible, however, that these components are formed only by the treatment Of rust samples in the air and that rust of this type does not contain any amorphous phase in its original environment.
Die Hauptkomponenten des Rostes sind Lepidokrokit (γ-FeOOH), Boethit (α-FeOOH) und Magnetit (Fe3O4). Von diesen bildet sich als erste Kristallphase, evtl. über (FeOH)2, Lepidokrokit. Dieser kann sich in Geothit und in Magnetit umwandeln.
Pseudomorphosen von Goethit und Magnetit nach Lepidokrokit werden beschrieben. Während Magnetit, der sich bei höheren Temperaturen direkt auf dem Eisen bildet, epitaktisch aufwächst und eine Schutzschicht darstellt, die weitere Korrosion verhindert, ist dies bei aus Lepidokrokit umgewandeltem Magnetit nicht zu erwarten. Die notwendige Haftfestigkeit und Porenfreiheit ist durch die Epitaxie einer Schutzschicht bedingt.
Phase conversions in rust
The principal components of rust are lepidocrocite (γ-FeOOH), göthite (α-FeOOH) and magnetite (Fe3O4). The first crystal phase, possibly via (FeOH)2, is lepidocrocite. This may later be transformed into göthite and magnetite.
The paper describes pseudo-morphoses of gothite and magnetite after lepidocrocite. Magnetite, which at higher temperatures is formed directly on the iron, grows epitactically and forms a protective layer which prevents further corrosion. In contrast, magnetite transformed from lepidocrocite cannot be expected to have such an effect. The necessary adhesion and freedom from pores is conditioned by the epitaxy of a protective layer.
The atmospheric corrosion of a few common metals has been studied at more than twenty sites in Nigeria and at some others under various conditions of atmospheric humidity and salinity. Contrary to general belief, corrosion is not generally higher under tropical conditions than in temperate climates. Where there is no industrial pollution, the governing factor is airborne salt and while in very saline atmospheres steel may corrode as much as 8 g./dm.2/month, in very humid areas free from high salinity the rate may be less than 0.1. The rate of corrosion of ferrous metals varies little between wet and dry seasons or between day and night. Atmospheric salinity has been measured by various methods and at many places; the corrosion of ferrous metals and zinc is proportional to the rate of deposit of salt on a damp textile surface. The corrosion of steel in tropical tidal waters is twice as fast in tidal as in continuous immersion, and in the former case can be as high as 12 g. dm.2/ month.
Measurements of the complex impedance of the interface between a single crystal or a sintered disc of β alumina and a gold electrode have been made in the frequency range 1–104 Hz. The electrolyte surface was polished to differing extents, and the variation of the slope of the plot in the complex impedance plane investigated. Deviation from the vertical line expected from a pure double layer capacitance is due to pits on the surface of the sintered material. This does not occur with the single crystal. The double-layer capacitance increases with polishing, but the values are not readily reproducible. Possible explanations are considered.
Goethite, hematite and intermediate products of goetite thermal decomposition were studied by IR and Raman spectroscopy to identify these products used as catalysts of some chemical reactions. The presence of a small number of OH-groups in the products of the decomposition up to 900–1000 C was supposed to hinder the formation of perfect hematite structure. The hypothesis concerning C
3v
6
space group of protohematite indistinguishable from D
3d
6
space group of hematite by X-Ray diffraction was suggested. This hypothesis explains both the additional lines in IR and Raman spectra compared to hematite spectra and the same position of peaks in X-Ray diffraction picture.
Atmospheric rusting of mild and low alloy steels was studied by means of infra-red and far infra-red spectrophotometries, X-ray and electron diffraction methods and scanning electron microscopy. The rusting process can be interpreted on the basis of a previously reported diagram for rust formation in aqueous solution. A large amount of amorphous matter in rust formed in semi-rural atmosphere was identified by infra-red and far infra-red spectra as amorphous ferric oxyhydroxide, FeOx (OH)8-2x. The amorphous ferric oxyhydroxide rust on low alloy steel was dense and uniform, and contained a considerable amount of bound water. From these results it can be concluded that the amorphous ferric oxyhydroxide rust acts as a protective barrier against atmospheric rusting of the steels. Cu, P and Cr in low-alloy steels are inferred to favour the formation of crack-free, uniform rust layer and help to produce uniform amorphous ferric oxyhydroxide.
Materials Transactions
- Ohtsuka