Chloride Environment Research Articles

Life performance of 40-year-old RC beams with different concrete covers and bar diameters in natural corrosion environments

This study entailed an experimental evaluation of the life performance of 40-year-old reinforced concrete (RC) beams with different concrete cover depths and tensile bar diameters. Beams that were naturally corroded in a marine environment were used in this study, and no artificial process was employed to accelerate the corrosion. Most existing evaluations of beams employ electrical acceleration, admixture, or exposure to designed chloride environments to aid corrosion. Given the paucity of studies on naturally corroded beams, this study is of significance regarding the design, service, and life assessment of RC structures. Two-point load bending test was employed to examine the residual mechanical performance. The corroded bars were extracted to assess the corrosion properties, while the mechanical properties were evaluated via a tensile test. The focus of this study was on evaluating the progress of deterioration and capacity loss in naturally aged beams. The results indicated that a concrete cover of 50 mm satisfies the requirements of a design service life of 50 years. Furthermore, the cross-sectional loss–ultimate capacity loss relationship is consistently linear for the RC beams. Thus, the estimation of ultimate capacity loss based on cross-sectional loss is acceptable in case of natural corrosion of the RC beams. Hence, the findings can contribute to the prediction of the life performance and maintenance of existing structures as well as to designing new structures.

Accelerated corrosion testing of cold spray coatings on 304L in chloride environments

Cold spray is an advanced metal manufacturing technique applied across many fields for a wide range of functions. Low heat input and compressive stresses induced into the substrate by the cold spray process makes it a promising choice for protective corrosion resistant coatings. One potential application for cold spray is as a protective coating against corrosion for spent nuclear fuel (SNF) interim dry storage canisters. As these canisters are currently stored at interim storage locations longer than originally intended, chloride induced stress corrosion cracking has been identified as a high priority knowledge gap, specifically with respect to prolonging or extending canister lifetimes (Teague et al., 2019). The high deployability of cold spray, for which nozzles have been developed for application in constrained spaces, in conjunction with beneficial properties inherent to cold spray makes this a good candidate for a corrosion protection coating on SNF canisters. This work explores a pathway to rapidly down-select cold spray coatings for canisters by focusing on the corrosion properties. Specifically, this study examines the corrosion protection abilities of nickel and nickel-based alloy cold spray coatings on 304 L stainless steel in chloride rich environments through electrochemical scans and ferric chloride pitting tests (ASTM G48 Method A). It was shown that the porosity of the coating, the processing gas, material selection, and deformation in the substrate all impact the corrosion behavior of cold spray coatings and are areas where optimization could reduce potential materials degradation, enabling enhanced coatings development.

Compressive, flexural and corrosion permeability resistance properties of concrete with bauxite tailing as supplementary mineral admixtures

This paper investigates the compressive and flexural properties and corrosion permeability resistance of concrete, using bauxite tailing as supplementary mineral admixtures. The concrete mixes, curing and testing for mechanical properties were conducted in accordance with BS EN 12390, 2019. Chloride permeability test was conducted in accordance with ASTMC 1202, 1997. The results depicted that at the optimum composition of 20% replacement, the compressive strength, flexural strength and static modulus of elasticity increased by 22%, 28% and 13% respectively over the control concrete specimen. These results showed that, generally, there was an increase in the strength properties and subsequently the modulus of elasticity when cement was replaced with bauxite tailing at the latter age. Again the presence of silicate and aluminum in the bauxite tailing might have consumed Ca(OH)2 which was liberated from cement hydration, enriching the microstructure of the concrete (AS2 +3CH+6H=C2ASH8 +C-S-H) with C-S-H gel and crystalline calcium alumino-silicate (C2ASH8) at the latter age than at the earlier age. The mixes with bauxite tailing replacement had low permeability and very low chloride penetration as compared to the control concrete specimen. This study recommends that bauxite tailing should be used as a mineral admixture to concrete not exceeding 20% replacement and in a chloride environment.

Effects of the heat treatment on the microstructure and corrosion behavior of 316 L stainless steel manufactured by Laser Powder Bed Fusion

Additively manufactured AISI 316 L stainless steel samples were heat treated at temperatures from 400 °C to 1100 °C, and the corrosion behavior in chloride environments was electrochemically studied. Heat treatments at 400 °C and 650 °C increased the grain size and the treatment at 1100 °C formed MnCr2O4 inclusions. Also, these postprocessing techniques reduce the hardness and increased the porosity. Heat treatment at 400 °C increased the polarization resistance and maintained the pitting corrosion mechanisms of the additively manufactured samples. Heat treatments at higher temperatures reduced the polarization resistance but changed the corrosion resistance mechanisms.

Electrochemical Behavior of Additively Manufactured 7050 Aluminum Alloy in Chloride Environments

The benefits of additive manufacturing (AM) process combined with the high-strength, corrosion resistant and fracture toughness properties of the 7xxx series aluminum alloys make them promising candidates for the aerospace and defense industries. However, these alloys undergo unconventional thermal cycles during additive manufacturing process like laser powder bed fusion (LPBF) as well as during post-processing treatments like hot isostatic pressing, resulting in microstructures different from equivalent wrought alloys.In our work, we investigate how the effects of microstructural differences in a modified LPBF 7050 aluminum alloy compared to an equivalent wrought alloy, results in differences in electrochemical behavior. A series of AM 7050 aluminum alloy samples with different post-processing treatments and subsequent microstructures are tested for polarization and electrochemical impedance behavior in varying chloride ion concentrations. The effects of underaging and overaging treatment on the electrochemical behavior is also studied. Localized corrosion behavior of the alloys is investigated using immersion tests and scanning vibration electrode technique (SVET), which showed differences in pitting behavior and pit stability. The results indicate that AM 7050 alloy in general, showed less corrosion susceptibility compared to an equivalent wrought alloy.

The Combined Action of Organic Inhibitors on Copper and Aluminium Metals and Aluminium Alloy Containing Copper

The approach used in the present work involves investigating the corrosion protection properties of mixed inhibitors for copper and aluminium substrates in chloride-containing solutions, which serve as a benchmark for studies of the alloy AA2024, with Cu and Al being the main culprits for localized corrosion. A synergistic mixture of inhibitors could find potential applications in novel blending combinations, such as in cooling water as an inhibitor in closed systems or incorporated in various protective coatings as additives, nano-containers, etc. If possible, the protective inhibitor film should show irreversibility of inhibition which can be defined as the ability to, once formed, retains its protective properties when the concentration of the corrosion inhibitor decreases. This irreversibility of the protective properties is essential for long-term protection.Inhibitory action of organic molecules, 2-mercaptobenzimidazole (MBI) and octylphosphonic acid (OPA) and their binary combinations on aluminium, copper and aluminium alloy 2024-T3 was investigated in chloride environments by conventional electrochemical methods and surface-analytical techniques [1,2]. In addition, the influence of pre-treatment of the metal surface and the choice of solvent for liquid-phase deposition on adsorption of MBI and OPA was studied on individual metals, Al and Cu [3]. Although OPA is not an inhibitor for Cu, it can synergistically boost corrosion inhibition of copper when added to MBI. In contrast, a synergistic effect between MBI and OPA as corrosion inhibitors was not observed for AA2024-T3. The mechanism was proposed where the thickness and structure of the surface layer are dependent on the pH. For the sample exposed to MBI at pH 5.5, where the Cu2O is stable, a thin Cu(I)MBI film is formed.In contrast, when exposed to the mixture of MBI and OPA at a pH of 4, the amount of produced Cu+ ions is boosted, and a much thicker Cu(I)MBI film forms by dissolution-precipitation mechanism. This layer exhibits high inhibitory effectiveness on copper substrate. At even lower pH, the thick compact Cu(I)MBI film does not form due to intensive dissolution of the Cu2O underlayer, resulting in a voluminous product. The postulated mechanism is confirmed by electrochemical data and composition of the layer by X-ray photoelectron spectroscopy, time-of-flight secondary ion mass spectroscopy and focused-ion beam scanning electron microscopy with chemical analysis.Immersion of AA2024 in an OPA-containing solution caused significant localized corrosion, while no local electrochemical activity on AA2024 was detected in an MBI-containing solution, indicating that the MBI inhibitor was very effective against pitting corrosion. Figure shows FIB/SEM (cross-section) analysis of local corrosion induced by Al2CuMg phase after 24 h immersion of AA2024 in 3 wt.% NaCl containing 1 mM MBI. The chemical analysis employed at the cross-section (yellow rectangles) of the Al2CuMg revealed that the MBI layer reduces the dissolution rate of dealloying of this phase and the rate of oxygen reduction on the copper remnant sites.This study shows that the behaviour of each combination of inhibitor and metal substrate is unique and cannot be translated to the more complex system such as alloy. Therefore, a profound understanding of the inhibition mechanism of individual metals is a prerequisite for further investigation of the corrosion inhibition of aluminium alloys. Acknowledgements: The financial support of the project by the Slovenian Research Agency is acknowledged (grants No. P1-0134, P2-0393 and BI-US/22-24-140) is acknowledged. Barbara Kapun, BSc, is acknowledged for FIB-SEM-EDS analysis.

The Effect of [Cu(EDTA)]2− on Crevice Corrosion of Type 316L Stainless Steel

Alloyed Cu is known to inhibit the growth of pitting corrosion on stainless steels after pitting initiation. The Cu2+ dissolved from the stainless steel matrix acts as an inhibitor in acidic chloride environments which is formed in pits. The Cu2+ suppresses active dissolution rate inside the pits1. This suppression effect is supposed to be also effective for active dissolution which promotes crevice corrosion. Therefore, if it is possible to introduce Cu2+ to the inside of a crevice from the outside, introduced Cu2+ is supposed to inhibit crevice corrosion on stainless steel. However, diffusion of ions between inside and outside of the crevice is restricted by its geometry, and Cu2+ does not migrate to inside of a crevice according to the electroneutrality principle. [Cu (EDTA (ethylenediaminetetraacetic acid))] 2− is a chelated Cu2+ which has negative charge, and is expected to migrate to inside of a crevice from the outside by electrochemical migration. In addition, it is reported that Cu2+ in [Cu(EDTA)]2− could be easily substituted by Fe2+ in low pH2. Therefore, Cu2+ is considered to be introduced to the inside of the crevice as [Cu(EDTA)]2−, and to affect crevice corrosion of stainless steel. In this study, in situ observation of an inside of the crevice3 was performed to analyze the effect of [Cu(EDTA)]2− on crevice corrosion. Type 316L stainless steel was used as specimen. The crevice corrosion tests were conducted in a flow cell3. 0.1 M NaCl or 0.1 M NaCl-10 mM [Cu(EDTA)]2− was flowed through the flow cell. The crevice was made by pressing the glass plate on the specimen surface. The specimen surface was perfused with 0.1 M NaCl before the glass plate was pressed. Therefore, inside of the crevice was filled with 0.1 M NaCl. The specimen was polarized at 0.35 V (vs. Ag/AgCl, Sat. KCl). After the crevice corrosion initiation, the different propagation morphology was observed between 2 conditions. In the case of 0.1 M NaCl, the gas bubbles were observed with corrosion propagation. On the other hand, little gas bubbles were observed in the case of 0.1 M NaCl-10 mM [Cu(EDTA)]2−. The gas bubbles observed in 0.1 M NaCl were considered to be H2 generated by the H+ reduction reaction inside the crevice. It was reported that the reduction reaction inside the crevice was changed by migrated anions which reacted with H+ inside the crevice3. Therefore, the results indicate [Cu(EDTA)]2− migrated to the inside of the crevice from the outside, and affected the crevice corrosion morphology.References T. Sourisseau, E. Chauveu, and B. Baroux, Corros. Sci., 47, 1097-1117(2005).W. Guan, B. Zhang, S. Tian, and X. Zhao, Appl. Catal. B, 227, 252-257 (2018). T. Aoyama, Y. Sugawara, I. Muto, and N. Hara, J. Electrochem. Soc., 166, C250-C260 (2019).

Evaluating Localized Corrosion Susceptibility of Austenitic Stainless Steels Exposed to Varying Nitrate to Chloride Ratio Droplets

Austenitic stainless steels (SS), utilized extensively in coastal environments due to their enhanced corrosion resistance, are susceptible to localized corrosion and stress corrosion cracking (SCC) when exposed to chloride environments. One potential scenario under which SCC may pose a concern is the interim storage and the eventual transport of spent nuclear fuels (SNF) in SS canisters. The SS canisters may be subjected to marine sea-salts and elevated temperatures; however, assessing the current damage state on the surface of these canisters is difficult due to high radiation levels dictating confinement within a limited-access overpack. Hence, accelerated tests are needed in order to help predict potential materials degradation on the surface of these canisters. Another important factor related to SNF storage is the fact that the canisters are located in a variety of climates across the United States. Salt compositions and daily fluctuations of relative humidity (RH) and temperature differ widely by location. Of particular interest, inland sites have a higher nitrate concentration in comparison to coastal locations. One governing brine property for corrosion is the amount of nitrate present in the brine as this can serve to passivate a corroding alloy. Herein, we evaluate the influence of nitrate to chloride ratios on the pitting susceptibility of SS304L under full immersion and cyclic RH conditions. The results of this study are discussed in terms of potential canister degradation. Acknowledgements SNL is managed and operated by NTESS under DOE NNSA contract DE-NA0003525. This document is SAND2022-3796 C.

Combination of Galvanic Interaction and Acoustic Emission Measurements on Damaged Painted Al Alloys: Towards Instrumented Witness Coupons for Outdoor Corrosion Testing

After real environmental exposures, the presence of corrosion damages on aircraft structures may be detected by means of non-destructive techniques (NDT). However, corrosion initiation and mechanism behind the defect cannot be distinguished by currently used physical methods. Therefore, aircraft industry needs sensors able to detect both corrosion initiation and its propagation.Few years ago, a new test sample design providing accelerated response during atmospheric corrosion tests was reported by G.S. Frankel research group [[1],[2]]. A painted Al alloy panel, uncoated through-hole noble fasteners and scribes, was specially designed to measure the galvanic current between fasteners and scribes during exposure in a salt fog chamber using a zero-resistance ammeter.But galvanic current measurement remains an electrochemical technique which could be difficult to be implemented in environments expected to be encountered in service, even if some attempts were described in literature [[3]]. More robust NDT methods, like acoustic emission was suggested to evaluate corrosion damage on Al alloys [[4]] but their application has not been yet transferred to instrumented witness coupons.Recently a European program [[5]] was launched to validate the application of ultrasonic corrosion sensors for real time detection of early stages of localized corrosion on Al alloys. Following our previous work on laboratory-scale tests based on mass transport control from inhibitors leaching from primer exposed at scribes [[6]], this talk describes the laboratory validation of acoustic emission combined with galvanic corrosion current measurements to evaluate the role of depletion of available corrosion inhibitors in the paint on scratched plates, mimicking riveted aircraft panels, exposed to chloride environments, in various conditions, i.e. immersion and salt spray conditions. [1] C.A. Matzdorf, W.C. Nickerson,B.C. Rincon Troconis,G.S. Frankel, Longfei Li, R.G. Buchheit, Galvanic Test Panels for Accelerated Corrosion Testing of Coated Al Alloys: Part 1—Concept, Corrosion, 69 (2013) 1240-1246. [2] Z.Feng and G.S. Frankel, Galvanic Test Panels for Accelerated Corrosion Testing of Coated Al Alloys: Part 2—Measurement of Galvanic Interaction, Corrosion,70 (2014) 95-106. [3] Z. Feng, G.S. Frankel,W.H. Abbott,C.A. Matzdorf, Galvanic attack of coated al alloy panels in laboratory and field exposure, Corrosion, 72 (2016) 342-355. [4] A. Prateepasen, C. Jirarungsatian, Implementation of acoustic emission source recognition for corrosion severity prediction, Corrosion, 67 (2011), 056001/1-056001/11. [5] Early detection and progress monitoring and prediction of corrosion in aeronautic Al alloys through calibrated Ultrasonic-CorROSion Sensor application, EU H2020 Grant agreement ID: 864905, https://cordis.europa.eu/project/id/864905 [6] R. Oltra and F.Peltier, Laboratory-scale testing of the anti-corrosion effectiveness of a primer coating on a bare AA2024 surface, Surface Interface Analysis, 48 (2016) 775–779.

Improving the adhesion properties of cement/epoxy interface using graphene-based nanomaterials: Insights from molecular dynamics simulation

The cement/epoxy interface is a critical component in a repair system. Normally, the adhesion properties of the epoxy coating are negatively affected by the presence of moisture or the ingress of harmful species to the interface. In this paper, the interfacial properties between the cross-linked epoxy and hydrated calcium silicate (C–S–H) using graphene (GR) and graphene oxide (GO) nanomaterials were investigated utilizing molecular dynamics (MD) simulation. Various reinforcement schemes were adopted, including adding the GR or GO layer and modifying the epoxy with GR or GO nanomaterials. In addition, three exposure systems (dry, wet, and salty) were considered. The results indicated that introducing a GO sheet at the epoxy/C–S–H interface enhanced the adhesion energy as the oxygen-containing functional groups in the GO provided better tight-binding patterns with the C–S–H surface as well as the epoxy overlay. Modifying the epoxy by GR nanosheet also increased the adhesion energy due to its suitably-oriented conformation inside the epoxy matrix. Moreover, the introduction of graphene reinforcement effectively mitigates the diffusion of moisture and chloride ions. The reported results will certainly enhance our understanding of the sustainability and durability of the epoxy-bonded concrete systems under aggressive moist and chloride environments.

Electroless Nickel Phosphorus Coatings to Mitigate the Corrosion of Construction Steel

Reinforced concrete is widely used in structures and construction, but its durability is limited due to corrosion of the embedded steel rebars. Thus, mitigation of corrosion of construction steel rebars is an important area of research. The present work reports the ability of electroless nickel phosphorus coating for corrosion protection of Fe-600-grade steel rebars used for construction purposes in chloride and sulphate environment. The coating deposited on Fe-600 rebar was Ni-P and was subjected to electrochemical tests in 3.5% NaCl and 0.5M H2SO4. Severe corrosion pitting and cracking were observed for the uncoated rebar while Ni-P coating showed nobler corrosion potential and low corrosion current density in the corrosive environments.

Corrosion resistance of 6061-T6 aluminium alloy and its feasibility of near-surface reinforcements in concrete structure

Abstract The durability of concrete structures is often reduced owing to the corrosion of reinforcement in an aggressive environment. Ordinary reinforcement methods, such as wrapping section steel or steel plate, are also vulnerable to corrosion. Using 6061-T6 aluminium alloy as near-surface reinforcement of the concrete structure is a feasible method. In this study, the corrosion resistance of 6061-T6 aluminium alloy bars was studied by simulating the coastal environment, atmospheric environment, and concrete internal environment with chloride solution, simulated acid rain solution, and saturated Ca(OH)2 solution. The corrosion rate of the 6061-T6 aluminium alloy in the above environments was tested using a weight loss method, and its corrosion resistance was evaluated using the metal corrosion resistance classification standard. Based on the electrochemical reaction mechanism, the polarisation properties and AC impedance spectra of steel and 6061-T6 aluminium alloy were compared, and the corrosion resistance mechanisms of steel and the 6061-T6 aluminium alloy in the above corrosive environments were obtained. The results show that the 6061-T6 aluminium alloy has better corrosion resistance than steel bars in chloride and atmospheric environments, with corrosion currents of 0.012 and 0.037 µA·cm−2, and 8-day corrosion rates of 0.051 and 0.031 mm·a−1, respectively. However, owing to the activity of the aluminium alloy, its corrosion resistance in an alkaline environment inside concrete is poor; the corrosion current is 0.22 µA·cm−2 and the 8-day corrosion rate is 16.166 mm·a−1. The research results can provide a reference for applying aluminium alloy bars as external prestressed concrete bars and near-surface steel bars.

A two-step approach for calculating chloride diffusion coefficient in concrete with both natural and recycled concrete aggregates

This paper presents an analytical approach to calculate the effective diffusion coefficient of chlorides in concrete with both natural and recycled concrete aggregates. In the approach the concrete is treated as a composite consisting of three phases, namely mortar, natural aggregate plus interfacial transition zone, and recycled concrete aggregate plus interfacial transition zone. The effective diffusion coefficient of chlorides in the composite is calculated through two steps. The first step is to calculate the effective diffusion coefficients of chlorides in the natural aggregate plus interfacial transition zone and in the recycled concrete aggregate plus interfacial transition zone by using multilayer spherical approximation, the results of which provide the information about the quality of recycled concrete aggregate in terms of chloride penetration resistance. The second step is to calculate the effective diffusion coefficient of chlorides in the three-phase concrete composite by using effective medium approximation, the results of which provide the information about the influence of recycled concrete aggregate on the diffusivity of recycled aggregate concrete. The analytical expression of the effective diffusion coefficient is derived and carefully compared with the results obtained from both the experiments and numerical simulations, which demonstrates that the present analytical model is rational and reliable. The analytical expression presented can be used to predict the service life of recycled aggregate concrete exposed to chloride environment.

Macro-cell corrosion between crossed steel bars in cracked concrete

• Macro-cell corrosion current I g included crack-induced macro-cell current I g s and current between two crossed steels I g d . • Both I g s and I g d increased in varying degrees with wider crack and the I g s / I g d ratio was always around 2. • Crack location was proved to influence the value and the direction of I g s and. I g d . To investigate the corrosion behavior of coupled crossed steel bars in cracked concrete, a study on the influence of crack width W and crack location L on the microcell and macro-cell corrosion of coupled crossed steels in cracked concrete is presented. The corrosion process of crossed steel bars in concrete specimens with crack widths of 0, 0.1, 0.2, 0.5 and 1.0 mm, respectively, were continuously monitored in an artificially created chloride environment for 26 weeks. The results showed that the corrosion of steel bars in cracked areas was much severer than that of steel bars in uncracked areas. Both microcell corrosion current ( I c o r r ) and macro-cell corrosion current ( I g ) of coupled active steel bars in a cracked area increased with the increase of the transverse crack width, and I c o r r was found to be more sensitive to the change of crack width. The I g / I c o r r ratio decreased with time, which meant that while macro-cell corrosion made a fair contribution, microcell corrosion played a dominant role in the whole corrosion period. In addition, the distance between the concrete crack and the intersection of the crossed steel bars, defined as the crack location L in the study, was proved to have a significant impact on the value and the direction of total macro-cell corrosion current I g .

Investigation of distinct welding parameters on mechanical and corrosion properties of dissimilar welded joints between stainless steel and low carbon steel.

The tensile strength and corrosion behavior of dissimilar welded joints are currently a subject of concern. In this work, gas metal arc welding (GMAW) and distinct welding parameters (welding current, arc voltage, and welding speed) were used to join 304 stainless steel (SUS304) and SS400 low carbon steel, and the ultimate tensile strength (UTS) of the dissimilar welded joints was investigated. A corrosion test was conducted by immersion in 3.5 wt.% sodium chloride (NaCl) solution for 7, 14, and 21 days. Based on tensile strength and Tafel testing, the welding parameters "Item 4" (welding current: 170 A, arc voltage: 20 V, welding speed: 40 cm/min) yielded good mechanical strength and low corrosion characteristics. The microstructure characterization showed that the area around the welded joints and SUS304 had more granular corrosion and corrosion tubercles with increasing immersion time. The chromium content gradually decreased. When exposed to the chloride environment, these welded joints easily underwent corrosion due to the loss of passivity. However, high-velocity oxygen-fuel (HVOF) spray used on the welded joints reduced the corrosion current density. Compared with the non-thermal spray sample (corrosion current density:7.49e - 05 A/cm2) while the corrosion current density (7.89e - 10 A/cm2) is five orders of magnitude lower. This spray effectively slowed down the corrosion rate of the welded joints and gave the structural objects good protection in the sodium chloride solution.

Self-healing recovery and micro-structural properties of slag/fly-ash based engineered cementitious composites under chloride environment and tidal exposure

Self-healing behavior of Engineering Cementitious Composites (ECC) has received a lot of attention due to its influence on the durability and mechanical performance of composite structures exposed to marine environment. However, very few studies have reported mechanical recovery of self-healing ECC under marine environmental exposure conditions. This paper reportes an experimental study of self-healing induced mechanical recovery of pre-damaged slag/fly ash based ECC and chloride transport behavior in ECC exposed to simulated marine environmental for up to 120 days. The results show obvious regaining of tensile properties of pre-damaged slag/fly ash based ECC due to self-healing. At the micro-scale level, the presence of abundance fly ash particles facilitates the stress transfer between the fiber and the matrix after self-healing, leading to fiber-bridging strength recovery to roughly the same level as that of the control specimen. Furthermore, the ultimate tensile strength shows a slight recovery for all ECC specimens under tidal and submerged environmental conditions, as compared to the 28-day result. However, as the slag replacement level increases, some inconsistencies emerge. Because of high chloride content and oxygen content, as well as the action of tidal impact, concrete deterioration and corrosion are more intense in tidal and splash zones.

Electrochemical corrosion and passive behavior of a new high-nitrogen austenitic stainless steel in chloride environment

In this work, the electrochemical corrosion and passive behavior of a high-nitrogen austenite stainless steel named QN2109 in different NaCl solutions were studied by potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), Mott-Schottky analysis and X-ray photoelectron spectroscopy (XPS). QN2109 stainless steel exhibited a wide passive region and high impedance value in the chloride environment. The high ratio of O2−/OH− made the passive film better self-repair effect, and the passive film is mainly composed of Mo-oxides, Fe-oxides and Cr-oxides, providing excellent pitting corrosion resistance at room temperature. The passive film with p-type and n-type semiconductor characteristics showed a double-layer structure. In addition, the influence of CrN and NH3/NH4+ in passive films was also discussed.

Influence of ammonium sulfate on the corrosion behavior of AZ31 magnesium alloy in chloride environment

Electrochemical corrosion of AZ31 magnesium alloy in the NH4+-SO42−-Cl− environment is studied. Effect of NH4+ overshadows that of Cl− as the (NH4)2SO4 concentration is 0.005 M or higher, yielding an evolution from localized corrosion to uniform corrosion. Acceleration effect of NH4+ can be attributed to that (i) NH4+ dissolves the inner MgO and hinders the precipitation of Mg(OH)2 and (ii) the buffering ability of NH4+ provides H+, enhances the hydrogen evolution, and expedites the corrosion process. The latter is demonstrated as the dominant factor with the results in unbuffered and buffered environments. The severe corrosion and hydrogen process in NH4+-containing solution results in a high Hads coverage and yields an inductive loop within the low frequency. Meanwhile, SO42− is helpful in generating cracked but partially protective corrosion products, while Cl− could broaden the corrosion area beneath the corrosion product.

Nanoindentation and Corrosion Behaviour of 410 Stainless Steel Fabricated Via Additive Manufacturing

This study investigates the microstructural, nanomechanical, and corrosion behaviour of different sections of 410 steel fabricated via directed energy deposition technique. The morphology exhibited by the longitudinal and transverse sections of the specimens was examined under a scanning electron microscope (SEM), while micro-computed tomography technique (micro-CT) was used for examination of the internal structure of the specimens. Nanomechanical properties were assessed using a nanoindenter, while potentiodynamic polarization technique was adopted to investigate the corrosion resistance of the specimens in a chloride environment. The SEM micrographs revealed minimal pores in the specimens which confirmed the improved density in the layer-by-layer built specimen. Micro-CT images confirmed the presence of tiny pores in the specimens sectioned from the top layer of the 410 stainless steel rod in comparison with the middle- and bottom-sectioned specimens. The corrosion and post-corrosion analyses confirmed that the top specimen exhibits the least corrosion resistance in comparison with the other specimens.

Mineral Katkılı Çimento Bulamacı Kaplanmış Betonarme Donatıların Korozyon Performansının İncelenmesi

Reinforcement corrosion is considered as one of the most important parameters determining the service life of reinforced concrete structures. In this study, an alternative method that protects reinforced concrete reinforcements against the effects of corrosion has been examined. Within the scope of the study, in addition to the traditionally produced reference reinforced concrete samples, reinforced concrete samples produced with mineral additive cement slurry coated reinforcements were prepared. In addition to silica fume at 30% of the cement amount by mass, blast furnace slag at 25% and 50% of the cement amount was used in mineral added cement slurries. According to the test results, it was determined that the slurry coating application decreased the corrosion potential values and the corrosion current density values of the reinforcements in the samples exposed to the wetting and drying cycles in the sodium chloride environment.