Rust Formation Research Articles

Possibility of High Phosphorus Pig Iron as Sacrificial Anode

Cathodic protection is an effective method to control the corrosion of underground pipelines and submerged structures. In the present work, high phosphorus containing pig iron was utilized as sacrificial anode for cathodic protection of underground mild steel plates and the results were compared with that of a commercially pure magnesium sacrificial anode. Driving potential and current between the galvanically coupled sacrificial anodes and mild steel plates were continuously monitored in real time for one month. Microstructure and morphology of the corrosion products formed on the surface of pig iron, magnesium sacrificial anodes and mild steel plates were observed with the help of optical microscope and scanning electron microscopy, and phase identification were performed using x-ray diffraction, Raman spectroscopy and Fourier transform infrared spectroscopy. The distribution of phosphorus in the pig iron matrix and soluble rust formation on the surface of pig iron under buried condition were critical from the point of sacrificial effect, indicating the possible scientific reasons for high phosphorous pig iron to be used as sacrificial anode.

Effects of carbon steel corrosion on the methane hydrate formation and dissociation

Pipeline surface corrosion and gas hydrate plugging are two tricky problems with security risks to the oil-gas production and transportation. The surface morphology, induction time, normalized formation rate and percentage conversion of water to methane hydrate were in situ monitored on the carbon steel (CS) coupon inserted in the SDS solution, which was corroded by soaking in the seawater for different times (0–336 h) before use. The water distribution and methane hydrate cages formation on the metal surfaces with different physical structures were also investigated by microsecond molecular dynamics (MD) simulation. Results indicated that the presence of CS coupons could facilitate the hydrate nucleation via reducing the induction time by about 37%. CS corrosion led to 60% decrease in the induction time compared with the pristine CS, but insignificant difference was found for the CS coupons with different corrosion time. Moreover, the CS coupons had insignificant effects on the normalized hydrate formation rate, but were able to significantly enhance the percent conversion of water to hydrate and inhibit the hydrate dissociation. Overall tendency observed from experiments agreed with the MD simulations, which highlighted the contribution of the changes in the physical structure (formation of grooves with different sizes) other than the chemical components (formation of rust) to the hydrate formation.

Modified triazine decorated with Fe3O4 and Ag/Ag2O nanoparticles for self-healing of steel epoxy coatings in seawater

New hybrid nanomaterials based on Fe3O4 and Ag/Ag2O nanoparticles (NPs) supported by 2,4-dihydrazino-6-(methoxypolyethyleneglycol)-1,3,5-triazine (mPEGTH) were successfully synthesized without using reducing agents in both solution and solid phases. The mechanism for Fe3O4 and Ag/Ag2O NPs formation in the presence of mPEGTH, their chemical structures, surface morphologies, crystal structures, thermal stabilities and mPEGTH contents were characterized and identified. The effects of seawater salinity and pH of solutions on the Fe3O4 and Ag/Ag2O NPs surface charges and particle sizes distributions were examined to investigate their performances under aggressive conditions. It was found that, the Fe3O4/mPEGTH, hybrid nanomaterials obtained good dispersed NPs and exhibit a remarkable superiority in enhancing the anticorrosion performance of epoxy coatings more than Ag/Ag2O NPs. The Fe3O4/mPEGTH nanomaterials achieved significant synergistic effect to improve the anticorrosion and self-healing performances for epoxy composite coatings. They achieved higher salt spray resistance up to 1500 h without rust formation. The new self-healing mechanism of Fe3O4/mPEGTH nanomaterials was tentatively discussed.

Innovative Routes for the Fabrication of Advanced Multifunctional Protective Coatings with Combined Improved Barrier, Smart Active Feedback, Self-Repairing, and Antimicrobial Properties for Materials Protection

Due to the massive cost involved in combating corrosion related problems in varied industries, research into the development of new materials that can minimize this loss is a priority area. Although many protective methods have been proposed in recent times for the protection of metallic materials, organic protective coatings are inevitable because of their high adhesion strengths, good barrier properties, cost efficiency and ability to accommodate nanomaterials and active species in their matrix. However, since the strengths of organic coatings are not comparable to those of metals, coating layers can be damaged or scratched during handling and / or when deployed in service due to several environmental factors thereby losing their protective properties. In the present report, active inhibiting agents (benzotriazole and 2-mercaptobenzothiazole) were successfully loaded into clay nanoparticles and embedded into epoxy polymeric coating matrix to (a) isolate the active species from the coating matrix, (b) delay the release of the active agents, and (c) avoid the deactivation of the active agents. This approach yielded good results in delaying the time needed for the exhaustive release of the encapsulated active species following the Peppas and Weibull models, but a continuous outward diffusion of the encapsulated active species was unavoidable even after the corrosion actions have been mitigated in the damaged sites. To overcome this setback and enhance the active protective efficacy of the anticorrosive protective coatings, single/double bilayers of pH-sensitive polyelectrolytes gels based on chitosan cross-linked with epichlorohydrin (CTS-ECH) and glutaraldehyde (CTS-GTA), and complexes of chitosan with polymethacrylic acid (CTS-PMA) and polyacrylic acid (CTS-PAA) were deposited on the loaded nanotubes by layer-by-layer (LBL) methods. The permeability properties of the polyelectrolytes films deposited on the loaded nanotubes were designed to vary with the pH of the solution thereby introducing a smart/intelligent release of the active species. In this way, an innovative route for the fabrication of advanced multifunctional protective coatings possessing multiple functions such as intelligent active feedback, self-healing, antimicrobial (antifouling) and improved barrier properties was proposed. The suitability of the as-received clay nanotubes to encapsulate the active agents, the success of the loading process, and the formations of tube end capping and polyelectrolytes gel multilayers on the loaded nanotubes were confirmed by different spectroscopic measurements (SEM, TEM, FTIR, XRD and TGA/DTG). The improved passive barrier performances of the various innovative coatings were revealed by long-term in-situ impedance spectroscopic (EIS), while their active feedback and self-healing abilities were determined by advanced electrochemical, optical, and spectroscopic techniques. The optical and spectroscopic techniques revealed (a) the degree of pit formation on the steel surface (after the top coat is removed), (b) iron rust formation around the artificially marked defects, and (c) the ability of the marked defects to self-heal over lengthened exposure times. The advanced electrochemical techniques revealed the mitigation of the corrosion process at the defective zones by the released inhibitor molecules that saturate the defective zones and the self-healing of the defective zones by the polyelectrolytes hydrogels used for the nanotube’s interfacial treatments. Furthermore, sophisticated optical / microscopic techniques were adopted to reveal the antimicrobial effects of the innovative coatings. The antimicrobial effects of the innovative coatings were related to the biocidal effects of the polyelectrolyte gel constituents. Various physical and mechanical tests were adopted to compare the physical/mechanical properties of the various protective coatings. The results from the various investigations afforded insights into the effects of exposure time on the protective and failure behaviours of both the reference coatings and the modified coatings. And In overall, an innovative route for the fabrication of protective organic coatings with advanced multifunctional properties for the protection of materials has been proposed.

Effect of bicarbonate on aging and reactivity of nanoscale zerovalent iron (nZVI) toward uranium removal

Bicarbonate, ubiquitous in natural and waste waters is an important factor regulating the rate and efficiency of pollutant separation and transformation. For example, it can form complexes with U(VI) in the aqueous phase and at the solid-water interface. In this work, we investigated the effect of bicarbonate on the aging of nanoscale zero-valent (nZVI) in the context of U(VI) reduction and removal from wastewater. For fresh nZVI, over 99% aqueous uranium was separated in less than 10 min, of which 83% was reduced from U(VI) to U(IV). When nZVI was aged in water, its activity for U(VI) sequestration and reduction was significantly reduced. Batch experiments showed that for nZVI aged in the presence of 10 mM bicarbonate, only 20.3% uranium was reduced to U(IV) after 6 h reactions. Characterizations of the iron nanoparticles with spherical aberration corrected scanning transmission electron microscopy (Cs-STEM) suggest that in fresh nZVI, uranium was concentrated at the nanoparticle center; whereas in nZVI aged in bicarbonate, uranium was largely deposited on the outer surface of the nanoparticles. Furthermore, aged nZVI without bicarbonate contained more lepidocrocite (γ-FeOOH) while aged nZVI in the presence of bicarbonate had more magnetite/maghemite (Fe3O4/γ-Fe2O3). This could be attributed to the formation of carbonate green rust and pH buffer effect of ▪. Primary mechanisms for U(VI) removal with nZVI include reduction, sorption and/or precipitation. Results demonstrate that bicarbonate alter the aging products of nZVI, and reduces the separation efficiency and reduction capability for uranium removal.

Ni-P/Zn-Ni compositionally modulated multilayer coatings – Part 2: Corrosion and protection mechanisms

The Ni-P/Zn-Ni compositionally modulated multilayer coatings CMMCs were electrodeposited from a single bath by switching the deposition current density. The corrosion resistance of the deposits was studied and compared with that of monolayers of Ni-P and Zn-Ni alloys via Tafel polarization, EIS and salt spray tests. Characterization of corrosion products by means of EDS and XRD revealed more details from the corrosion mechanism of the monolayers and multilayers. The corrosion current density of Ni-P/Zn-Ni CMMCs were around one tenth of Zn-Ni monolayer. The CMMC with incomplete layers performed lower polarization resistance and higher corrosion current density compared to the CMMC with complete layers. The electrical circuit that was proposed for modeling the corrosion process based on the EIS spectrum, proved that layering reduces the porosity and consequently improves the barrier properties. Although, layering of Zn-Ni layers with Ni-P deposits increased the time to red rust in salt spray test, the time for white rust formation decreased. The corrosion mechanism of both Zn-Ni and Ni-P (containing small amount of Zn) was preferential dissolution of Zn and the corrosion products were comprised of mainly Zn hydroxychloride and Zn hydroxycarbonate. Also, Ni and P did not take part in the corrosion products. Based on the electrochemical character of the layers and the morphology of the corroded surface, the corrosion mechanism of multilayers was discussed.

INFLUENCE OF SEAWATER ON THE STRENGTH OF RC BEAMS AND CORROSION BEHAVIOR OF STEEL

The effects of seawater on the strength performance of reinforced concrete (RC) beams wereinvestigated. Four RC beams measuring 150 x 200 x 800 mm were constructed. Two beams were constructedwith concrete mixed with freshwater and the other two were constructed with seawater. Center point loadingtest was conducted on the beams specimens. Load, deflection, and strain of each beam were monitored andrecorded. It was found that the difference between the strength test values obtained by using freshwater andseawater were minimal. However, formation of rust in steel when seawater was used was very evident.Hence, the effects of seawater on the corrosion behavior of steel were investigated. Mortar specimens withcold-joint were used as medium to facilitate the investigation of corrosion. Ordinary Portland cement (OPC)Type 1 was used as binder for the mortar and was partially replaced with fly ash at 30% and 50%.Rectangular prism specimens of dimensions 40mm by 40mm by 160mm were cast for macrocell corrosionmeasurements and compressive strength determination. From the test results, the following were observed:(a) Specimens with fly ash were observed to have lower corrosion rates compared with the ones without flyash; (b) Specimens mixed with freshwater resulted to the higher strength both at 7th-day age and 28th-dayage; (c) Regardless of the type of water used in making the mortar, specimens cured in seawater achievedhigher later strength values.

Effect of Corrosion on Flexural Strength of Reinforced Concrete Beam: An Experimental Study

Abstract The main aim of this experimental study is to investigate the effect of corrosion on reinforced concrete beams, particularly on load deflection behavior, load carrying capacity and crack width by using with or without epoxy coating on the steel surface. Accelerated corrosion technique was adopted to corrode the beam experimentally. The corrosion was measured using the Open Circuit Potential (OCP) measurement instrument. A total of 14 simply supported beam specimens with cross section 150 mm×300 mm and 1000 mm length are prepared using M25 grade concrete with a clear cover of 25 mm. All specimens casted are tested in specially prepared loading setup and the load deflection behavior is studied. The load carrying capacity of the beam is more for control beams, but the deflection is less for control beams with respect to other corroded beams (i.e., 2.5 to 7.5% corrosion level with every increment of 2.5%) with or without epoxy coating. Overall, use of epoxy coated specimen shows approximately 35% for higher degree of corrosion (7.5%) for coated specimen when compared to non-coated specimens. Also, epoxy coated specimens behave more ductile than non-coated specimens. Crack width is less at the lower level of corrosion (0 to 5%) after that it increases rapidly (i.e., at 7.5%), but in controlled specimen, the crack is not measurable i.e., at minimum level. Corrosion monitoring and regular maintenance is a viable way to prevent formation of rust on any environment. Keywords: Accelerated corrosion technique, load deflection, corrosion, epoxy coating Cite this Article Muthumari G, Abbas Mohaideen J. Effect of Corrosion on Flexural Strength of Reinforced Concrete Beam: An Experimental Study. Recent Trends in Civil Engineering & Technology . 2017; 7(3): 1–7p.

Engineering failure analysis of corroded R.C. beams in flexure and shear

Abstract In the present paper, a simple model to reproduce the load-deflection response of corroded beams failing in flexure and shear is presented and discussed. Effects of diffused and pitting corrosion on steel bars, compressive concrete strength degradation and concrete bond strength degradation due to rust formation are included in the model. Engineering approach based on limit state theory was here adopted to predict the peak and the residual flexural and shear strength of corroded beams with corresponding deflections and ductility estimation. Calculation of deflection at cracking taking into account of rust formation and deflection at yielding and the ultimate state taking into account also of slippage of steel bars due to rust formation were made. The model was also widely verified against tests available in the literature referred to crack opening, pit depth, attach corrosion penetration, load-deflection curves.

Antimony and arsenic partitioning during Fe2+-induced transformation of jarosite under acidic conditions

Jarosite [KFe3(SO4)2(OH)6] is considered a potent scavenger for arsenic (As) and antimony (Sb) under oxidizing conditions. Fluctuations in water levels in re-flooded acid sulfate soils (ASS) can lead to high Fe2+(aq) concentrations (∼10–20 mM) in the soil solution under acidic to circumneutral pH conditions. This may create favorable conditions for the Fe2+-induced transformation of jarosite. In this study, synthetic arsenate [As(V)]/antimonate [Sb(V)]-bearing jarosite was subjected to Fe2+(aq) (20 mM) at pH 4.0 and 5.5 for 24 h to simulate the pH and Fe2+(aq) conditions of re-flooded freshwater ASS/acid mine drainage (AMD)-affected environments at early and mid-stages of remediation, respectively. The addition of Fe2+ at pH 5.5 resulted in the formation of a metastable green rust sulfate (GR- SO4) phase within ∼60 min, which was replaced by goethite within 24 h. In contrast, at pH 4.0, jarosite underwent no significant mineralogical transformation. Although the addition of Fe2+(aq) induced the dissolution/transformation of jarosite at pH 5.5 and increased the mobility of Sb during the initial stages of the experiment (Sb(aq) = ∼0.05 μmol L−1), formation of metastable green rust (GR-SO4) and subsequent transformation to goethite effectively sequestered dissolved Sb. Aqueous concentrations of As remained negligible in both pH treatments, with As being mostly repartitioned to the labile (∼10%) and poorly crystalline Fe(III)-associated phases (∼10–30%). The results imply that, under moderately acidic conditions (i.e. pH 5.5), reaction of Fe2+(aq) with jarosite can drive the dissolution of jarosite and increase Sb mobility prior to the formation of GR-SO4 and goethite. In addition, repartitioning of As to the labile fractions at pH 5.5 may enhance the risk of its mobilisation during future mineral transformation processes in Fe2+-rich systems.

Understanding the anticorrosive protective mechanisms of modified epoxy coatings with improved barrier, active and self-healing functionalities: EIS and spectroscopic techniques

The present investigation adopted long-term in-situ electrochemical and spectroscopic approaches to study the combined active, self-healing and passive protective mechanisms of a new class of innovative anti-corrosive coatings based on epoxy doped with clay nanotubes impregnated with active species for the protection of carbon steel in 3.5% NaCl solution. The suitability of the as-received clay nanotubes to encapsulate the active agents was confirmed by different spectroscopic measurements. Tube end stopper with Ferric ion and polymer encapsulation with chitosan cross-linked with glutaraldehyde were adopted to tunnel the release of the active agents loaded into the nanotubes. The improved passive barrier performances of the various innovative coatings were revealed by the electrochemical impedance spectroscopic, while their active feedback and self-healing abilities were revealed by the optical and spectroscopic techniques. The optical/spectroscopic techniques revealed the degree of pit formation at the steel/coating interface and the iron rust formation around the artificially marked defects, including the ability of the marked defects to self-heal over exposure times. Adhesion and impacts tests were adopted to compare the physical/mechanical properties of the various coatings. The results afforded insights into the effects of exposure time on the protective and failure behaviours of both the reference and modified coatings.

Influence of Ni(II), Cu(II) and Cr(III) on the formation, morphology and molecular adsorption properties of α-FeOOH rust particles prepared by aerial oxidation of neutral Fe(II) solutions

To elucidate the role of alloying metals such as Ni, Cu and Cr in weathering steels on the formation of α-FeOOH rust by atmospheric corrosion of the steels in industrial and urban districts, influence of alloying metal ions on the formation, morphology and adsorption properties of α-FeOOH particles synthesized by aerial oxidation of neutral FeSO4 solution was examined. The addition of Cu(II) and Cr(III) dramatically suppresses the crystal growth of α-FeOOH and turns the rod-shaped α-FeOOH particles into nano-sized irregular ones. Besides, increase of amount of added Cr(III) forms the iron oxyhydroxysulfate named as Schwertmannite (Fe8O8(SO4)(OH)6). Whereas, the Ni(II) addition shows no noticeable influence on the growth of α-FeOOH crystal and particles. These results imply that the inhibitory effect of crystal and particle growth of α-FeOOH is in order of Cr(III) > Cu(II) >> Ni(II). The adsorption of CO2 gas on the α-FeOOH particles is impeded by adding Cu(II) and Cr(III). Whereas, the formation of Schwertmannite by adding Cr(III) enhances the CO2 and SO2 adsorption. These results suggest that alloying Cu and Cr in weathering steels inhibit the crystal and particle growth of α-FeOOH to accelerate the formation of protective rust layer composed of fine α-FeOOH and/or Schwertmannite rust particles on the steels in urban and industrial atmosphere.

Fe(II) Interactions with Smectites: Temporal Changes in Redox Reactivity and the Formation of Green Rust.

In this study, temporal changes in the redox properties of three 0.5 g/L smectite suspensions were investigated-a montmorillonite (MAu-1) and two nontronites (NAu-1 and NAu-2) in the presence of 1 mM aqueous Fe(II) at pH 7.8. X-ray absorption spectroscopy revealed that the amount of Fe(II) added quantitatively transformed into chloride-green rust (Cl-GR) within 5 min and persisted over 18 days. Over the same time, the reduction potential of all three suspensions increased by 50 to 150 mV to equilibrate at approximately -100 mV vs SHE. The reduction of a model organic contaminant, 4-chloronitrobenzene (4-CINB), also became increasingly slower over time with virtually no 4-CINB reduction being observed after 18 days. There was a strong correlation between reduction potential and the quantity of 4-ClNB reduced by MAu-1, although other factors were likely involved in the decreased redox reactivity observed in the nontronites. It is hypothesized that the temporal increase in reduction potential results from clay mineral dissolution resulting in increased Fe(III) contents in the Cl-GR. These results demonstrate that long-term studies are recommended to accurately predict contaminant management strategies.

Rust distribution and corrosion-induced cracking patterns of corner-located rebar in concrete cover

In this work, the rust distribution patterns and concrete cover cracking behavior of corner-located rebar was studied by means of digital microscopy. The corner-located rebar with various cover thicknesses embedded in concrete specimens was exposed to artificial corrosive environments. The time-dependent evolution of rust distribution profiles around corroded rebar was measured and described by Gaussian models. The results show that for corner-located rebar, when the two side concrete cover thicknesses have the similar value, the onset of rust formation starts simultaneously and its rust pattern can be well described by two or three independent Gaussian functions. At the same level of corrosion, the cracking behavior of corner-located concrete can be considerably different, depending on the rust profiles and dimensional ratio of the two side concrete cover thicknesses.

Determination of the key parameters involved in the formation process of akaganeite in a laboratory-simulated wet-dry cyclic process

To determine the key parameters of akaganeite formation during a wet-dry cyclic process, cyclic immersion tests and simulated experiments were employed under laboratory conditions. The constituents of rust were characterized using XRD and FTIR. According to the results, green rust (FeII4FeIII2Cl2−x(OH)12+x) was a crucial intermediate product during the formation of akaganeite. The evaporation rate of the electrolyte and the amount of Cl− per area played a key role in the formation of the green rust. Additionally, the required amounts of salt for akaganeite formation were determined from simulation experiments in different relative humidity environments.

Development of Pitting Corrosion Monitoring Device under Sodium Chloride Droplet by Means of Wet-Dry Cyclic Method

Pitting corrosion caused by wet-dry cycles under corrosive media droplet is one of the key concerns for passive film of metallic materials, particularly stainless steels and aluminum alloys, exposed to atmosphere during service. In this context, the formation of corrosion can lead to high investment cost dealing with corrosion mitigation strategy, e.g. materials selection, electrochemical corrosion control, etc. Based on materials selection perspectives, it is very necessary to have proper understanding of localized corrosion behaviors of metallic materials under solution droplet. Therefore, the present study aims to develop a methodology for pitting corrosion monitoring that can be suitably used for extending better understanding on corrosion phenomena occurring under wet-dry cycles of droplet. A special liquid handling apparatus controlled by Arduino software was constructed and used for generating NaCl solution droplet at given dimension on the surface of stainless steel specimens based on Pendant drop principle. This was recognized as wet cycle. During dry cycle, such NaCl solution droplet was naturally dried off in various conditions of relative humidity. Pitting initiation was observed through a high-resolution CCD camera. Droplet morphology and evaporation time were evaluated at the temperature of 27°C and relative humidity of 10% and 60%. The research results revealed that pitting corrosion started at 1st cycle without rust formation. Afterwards, the rust formation was clearly noticed when testing cycles of 15 were exceeded.

Insights into Nitrate-Reducing Fe(II) Oxidation Mechanisms through Analysis of Cell-Mineral Associations, Cell Encrustation, and Mineralogy in the Chemolithoautotrophic Enrichment Culture KS.

Most described nitrate-reducing Fe(II)-oxidizing bacteria (NRFeOB) are mixotrophic and depend on organic cosubstrates for growth. Encrustation of cells in Fe(III) minerals has been observed for mixotrophic NRFeOB but not for autotrophic phototrophic and microaerophilic Fe(II) oxidizers. So far, little is known about cell-mineral associations in the few existing autotrophic NRFeOB. Here, we investigate whether the designated autotrophic Fe(II)-oxidizing strain (closely related to Gallionella and Sideroxydans) or the heterotrophic nitrate reducers that are present in the autotrophic nitrate-reducing Fe(II)-oxidizing enrichment culture KS form mineral crusts during Fe(II) oxidation under autotrophic and mixotrophic conditions. In the mixed culture, we found no significant encrustation of any of the cells both during autotrophic oxidation of 8 to 10 mM Fe(II) coupled to nitrate reduction and during cultivation under mixotrophic conditions with 8 to 10 mM Fe(II), 5 mM acetate, and 4 mM nitrate, where higher numbers of heterotrophic nitrate reducers were present. Two pure cultures of heterotrophic nitrate reducers (Nocardioides and Rhodanobacter) isolated from culture KS were analyzed under mixotrophic growth conditions. We found green rust formation, no cell encrustation, and only a few mineral particles on some cell surfaces with 5 mM Fe(II) and some encrustation with 10 mM Fe(II). Our findings suggest that enzymatic, autotrophic Fe(II) oxidation coupled to nitrate reduction forms poorly crystalline Fe(III) oxyhydroxides and proceeds without cellular encrustation while indirect Fe(II) oxidation via heterotrophic nitrate-reduction-derived nitrite can lead to green rust as an intermediate mineral and significant cell encrustation. The extent of encrustation caused by indirect Fe(II) oxidation by reactive nitrogen species depends on Fe(II) concentrations and is probably negligible under environmental conditions in most habitats.IMPORTANCE Most described nitrate-reducing Fe(II)-oxidizing bacteria (NRFeOB) are mixotrophic (their growth depends on organic cosubstrates) and can become encrusted in Fe(III) minerals. Encrustation is expected to be harmful and poses a threat to cells if it also occurs under environmentally relevant conditions. Nitrite produced during heterotrophic denitrification reacts with Fe(II) abiotically and is probably the reason for encrustation in mixotrophic NRFeOB. Little is known about cell-mineral associations in autotrophic NRFeOB such as the enrichment culture KS. Here, we show that no encrustation occurs in culture KS under autotrophic and mixotrophic conditions while heterotrophic nitrate-reducing isolates from culture KS become encrusted. These findings support the hypothesis that encrustation in mixotrophic cultures is caused by the abiotic reaction of Fe(II) with nitrite and provide evidence that Fe(II) oxidation in culture KS is enzymatic. Furthermore, we show that the extent of encrustation caused by indirect Fe(II) oxidation by reactive nitrogen species depends on Fe(II) concentrations and is probably negligible in most environmental habitats.

Shear and flexural strength prediction of corroded R.C. beams

The purpose of the work was the study of the structural safety of R.C. beams subjected to corrosion processes though the derivation of moment-curvature diagrams and moment-to-shear interaction diagrams. Normal-strength reinforced concrete beams with longitudinal bars in the presence of transverse stirrups and subjected to corrosion processed are considered.Experimental results available in the literature related to corrosion processes, for steel bars, crack openings and bond degradation due to rust formation are reviewed. Then analytical laws relating to crack opening, bond degradation with attack penetration depth, through a rearranged form of Faraday’s law, are presented. An analytical model for cross-section analysis and shear strength prediction including the main effect due to rust formation is developed and verified against experimental data. Finally, a case study is added giving moment-curvature diagrams and moment-to-shear interaction diagrams to show the effects of different scenarios of natural corrosion increasing with time on beam elements.

Marine Atmospheric Corrosion of Carbon Steel: A Review.

The atmospheric corrosion of carbon steel is an extensive topic that has been studied over the years by many researchers. However, until relatively recently, surprisingly little attention has been paid to the action of marine chlorides. Corrosion in coastal regions is a particularly relevant issue due the latter’s great importance to human society. About half of the world’s population lives in coastal regions and the industrialisation of developing countries tends to concentrate production plants close to the sea. Until the start of the 21st century, research on the basic mechanisms of rust formation in Cl−-rich atmospheres was limited to just a small number of studies. However, in recent years, scientific understanding of marine atmospheric corrosion has advanced greatly, and in the authors’ opinion a sufficient body of knowledge has been built up in published scientific papers to warrant an up-to-date review of the current state-of-the-art and to assess what issues still need to be addressed. That is the purpose of the present review. After a preliminary section devoted to basic concepts on atmospheric corrosion, the marine atmosphere, and experimentation on marine atmospheric corrosion, the paper addresses key aspects such as the most significant corrosion products, the characteristics of the rust layers formed, and the mechanisms of steel corrosion in marine atmospheres. Special attention is then paid to important matters such as coastal-industrial atmospheres and long-term behaviour of carbon steel exposed to marine atmospheres. The work ends with a section dedicated to issues pending, noting a series of questions in relation with which greater research efforts would seem to be necessary.

In-Situ Electrochemical Monitoring and Ex-Situ Chemical Analysis of Epoxy Coated Steels in Sodium Chloride Environment Using Various Spectroscopic Techniques

The effect of immersion time and chloride ion concentration on the early stage of corrosion behavior of scratched epoxy-coated carbon (SM) and chromium containing low-alloy steel (H5) samples were investigated in an in situ manner using localized electrochemical impedance spectroscopy. The results revealed that, the H5 samples had significantly higher impedance values than the SM, which indicated higher corrosion resistance of H5 samples. The drop in impedance magnitude was observed for higher Cl− ion concentration, which indicated that breakdown of passive film had been initiated by Cl− ion resulting in localized corrosion attack of the surface. The morphological and elemental studies showed the formation of green rust and a very stable hydroxide (CrxFe1−x(OH)2) on SM and H5 surface respectively as a corrosion product. Hence, the H5 could be a hopeful material with extremely high corrosion resistance for the use as steel structures.