Electrochemical Testing Techniques Research Articles

The effects of ECAP, Mn and Ca elements on the microstructure and corrosion properties of magnesium alloys were investigated

In this study, through reasonable composition design, three elements of Zn, Mn and Ca, which are harmless to human body, were selected for alloying magnesium. The effects of ECAP treatment on the microstructure and corrosion properties of Mg-4Zn-1Mn-0Ca, Mg-4Zn-1Mn-0.2Ca and Mg-4Zn-0Mn-0.2Ca alloys were studied. The corrosion mechanism of Mg-Zn-Mn-Ca alloys with different components in Simulated. Body fluid (SBF) was analyzed by weight loss method and electrochemical test. The grains and the second phase were refined by Equal Angular Channel Pressing (ECAP). It was found that after 8 ECAP deformations, the microstructure of the alloy was refined and more uniform than that of the extruded alloy. The corrosion resistance of the Mg-Zn-Mn-Ca alloy after ECAP deformation in simulated body fluids was studied by electrochemical testing techniques, immersion experiments and observation of the microstructure and morphology of corrosion products. The relationship between microstructure characteristics, the behavior of the magnesium metal matrix and the properties of corrosion products was revealed. The results show that the microstructure of the alloy is refined and the corrosion resistance is improved with the increase in extrusion passes in the SBF solution. The corrosion resistance of magnesium alloy after 8 ECAP deformation is the best, showing small Icorr and large Rt. With the extension of the soaking time, the surface of the alloy will form a passivation film, which will protect the matrix and avoid further corrosion of the alloy. It is found that in SBF, the corrosion of the alloy surface is mainly pitting, which indicates that Ca2+, HCO3- and HPO42- in SBF can reduce the corrosion rate of magnesium alloy.

(General Student Poster Award Winner, 3rd Place) Lithium Niobate Coatings on Lithium Iron Phosphate Cathode Materials for Applications in Lithium-Ion Batteries

Lithium-ion batteries have become a crucial tool in countering global fossil fuel reliance; when paired with electric motors, they provide an alternative to petroleum-based energy storage for internal combustion engines. Typical cathode materials used in lithium-ion batteries present a unique set of challenges. Some of the electrochemical materials that have a relatively high performance also have serious impacts on the environment and human health.1 Other materials that lack these specific drawbacks, such as lithium iron phosphate (LFP), face other issues. For example, LFP suffers from a relatively low electrical conductivity and a relatively slow lithium-ion diffusion, both of which affect the general electrochemical performance of this material. These weaknesses can be addressed using coatings applied to LFP nanoparticles. Carbon coatings have already been shown to improve the performance of LFP nanoparticles, but materials with higher ionic conductivities have remained relatively undeveloped.2 By synthesizing a composite coating of both carbon and lithium niobate, further improvements to LFP nanoparticles were sought to enable a wider range of applications for this cathode material.In this work, lithium niobate coatings on carbon coated LFP nanoparticles were synthesized using a low temperature solvothermal method. Lithium niobate coatings have been shown to improve the specific capacity, rate capability, and durability of other cathode materials for lithium-ion batteries.3 Half-cells were fabricated to examine the effect of adding a lithium niobate coating to the carbon coated LFP cathode materials. Electrochemical testing techniques such as galvanostatic cycling and cyclic voltammetry were used to compare the properties and performance of the composite coated LFP relative to the carbon coated LFP. The composite coatings were also characterized using transmission electron microscopy, energy dispersive spectroscopy, and X-ray photoelectron spectroscopy. This coating method has resulted in the successful synthesis of lithium niobate coatings on carbon coated LFP nanoparticles with an observed improvement in durability. Goodenough, J. B.; Kim, Y. Challenges for Rechargeable Li Batteries. Mater. 2010, 22 (3), 587–603.Wang, J.; Sun, X. Understanding and Recent Development of Carbon Coating on LiFePO4 Cathode Materials for Lithium-Ion Batteries. Energy Environ. Sci. 2012, 5 (1), 5163–5185.Kim, J. H.; Kim, H.; Choi, W.; Park, M.-S. Bifunctional Surface Coating of LiNbO3 on High-Ni Layered Cathode Materials for Lithium-Ion Batteries. ACS Appl. Mater. Interfaces 2020, 12 (31), 35098–35104.

Re-Functionalization of Aged Lithium Iron Phosphate Cathode Materials

As lithium-ion batteries continue to be implemented in everyday technologies, it is imperative to repurpose these battery materials upon their degradation. Carbon-coated lithium iron phosphate (LFP/C) is considered one of the most stable cathode materials for application in lithium-ion batteries. Due to this stability, LFP/C possesses a remarkably long cycle life of greater than 3000 cycles.1 Extended cycling of these cathode materials may result in multiple modes of degradation, including degradation of the carbon coating, and loss of contact between the cathode and the current collector.2,3 In this work, a suitable process and reagents have been selected to isolate and purify the LFP/C from the cathodes of cycled batteries. Isolating and purifying aged LFP/C materials enables the diagnosis of the mode(s) of degradation of these materials and their coatings using a variety of techniques including X-ray diffraction, scanning electron microscopy, and transmission electron microscopy methods.Furthermore, additional work was pursued to give new life to these isolated, spent cathode materials. The addition of a coating with a relatively high lithium conductivity to the aged LFP/C particles was sought to provide a second life to these electrochemically aged materials. Half-cells were fabricated using the coated, aged LFP/C cathode materials to compare their performance to both pristine LFP/C nanoparticles and aged LFP/C nanoparticles without the addition of this custom coating. Electrochemical testing techniques such as galvanostatic cycling, cyclic voltammetry, and electrochemical impendence spectroscopy were used to probe the performance of each type of LFP/C nanoparticle as cathode materials in lithium-ion batteries. The coated, aged LFP/C particles were also characterized using transmission electron microscopy, energy dispersive spectroscopy, and X-ray photoelectron spectroscopy techniques. The techniques developed herein can be used to isolate, purify, and re-functionalize other cathode materials from lithium-ion batteries. Lewerenz, M.; Munnix, J.; Schmalstieg, J.; Kabitz, S.; Knips, M.; Sauer, D. U. Systematic aging of commercial LiFePO4|Graphite cylindrical cells including a theory explaining rise of capacity during aging. Power Sources. 2017, 345, 254-263.Wang, L.; Qiu, J.; Wang, X.; Chen, L.; Cao, G.; Wang, J.; Zhang, H.; He, X. Insights for understanding multiscale degradation of LiFePO4 cathodes. eScience 2022, 2(2), 125-137.

Enhancement of Mass Transport in Catalyst Layers of HT-PEMFC with Tetrafluorophenyl Phosphonic Acid Binder.

The design and development of new and efficient catalyst binder materials are important for improving cell performance in high-temperature proton-exchange membrane fuel cells (HT-PEMFCs). In this study, a series of tetrafluorophenyl phosphonic acid-based binder materials (PF-y-P, y = 1, 0.83, and 0.67) with rigid structures and controllable degrees of phosphonation were prepared and used in HT-PEMFCs using the ultra-strong acid-catalyzed Friedel-Crafts reaction and the combined Michaelis-Arbuzov reaction. The samples exhibited high stability, low water uptake, superior proton conductivity, and cell performance. In addition, the oxygen mass transport properties of the PF-1-P binder were investigated using high-temperature microelectrode electrochemical testing techniques. Compared with the phosphoric acid-doped polybenzimidazole (PBI) binder, the O2 solubility of PF-1-P binder material increased by 30% (5.36 × 10-6 mol cm-3) and the PF-1-P binder material exhibited better cell stability in HT-PEMFCs. After 10.5 h of discharge at a constant current of 0.12 A cm-2, the MEA voltage decreased by 7.1% and 20.8% in case of the PF-1-P and PBI binders, respectively.

Damage characteristics of Cu−Cr−Zr alloy rail of electromagnetic railgun after simulated launch

The damage characteristics of different speed sections of Cu−Cr−Zr alloy rail after simulated launch were studied. The microstructure, morphologies and properties of samples were investigated by using XRD, XPS, EBSD, SEM, hardness test, electrochemical test and DSC techniques. It was found that deposition layers were formed on the surfaces of the simulated launch samples. The thickness and surface roughness of these deposition layers increased with increasing the heat effect, suggesting a launch speed dependent damage degree of the arc ablation. The hardness variation of samples is attributed to the effects of the deposition layer and deformation hardening. The surface deposition layer affects corrosion resistance and crystalline characteristics, leading to changes in subsequent service performances. Additionally, the surface texture and plastic deformation ability of the samples are related to the recrystallization degree and deformation grain amount.

Stability of passive film and pitting susceptibility of 316 L stainless steel in the aggressive oilfield environment containing Cl−-CO2-O2

In this paper, the effects of chloride ions, oxygen, and carbon dioxide on the corrosion resistance of passive films formed on 316 L stainless steel were investigated in the aggressive oilfield environment using electrochemical testing and microscopic characterization techniques. The results showed that Cl− accelerated the anodic dissolution of the metal and compromised the structure and densification of the passive film, thus reducing its corrosion resistance. An increase in the partial pressure of carbon dioxide initially promotes pitting, but subsequently inhibited further corrosion development. The presence of oxygen enhanced the cathodic reaction and passive film formation, effectively preventing the invasion of aggressive chloride ions, thus inhibiting further corrosion. These findings provide a significant scientific basis for material selection and protection of oil extraction equipment in oilfield environments.

Influence of Grain Size and Film Formation Potential on the Diffusivity of Point Defects in the Passive Film of Pure Aluminum in NaCl Solution

The influence of grain size on the corrosion behavior of pure aluminum and the defect density and diffusion coefficient of surface passive films were investigated using electron backscatter diffraction (EBSD) and electrochemical testing techniques, based on the point defect model (PDM). Samples with three different grain sizes (23 ± 11, 134 ± 52, and 462 ± 203 μm) were obtained by annealing at different temperatures and times. The polarization curves and electrochemical impedance spectroscopy results for the pure aluminum in the 3.5% NaCl solution showed that with decreasing grain size, the corrosion current (icorr) decreased monotonously, giving rise to a noble corrosion potential and a large polarization resistance. The Motte–Schottky results showed that the passive films that formed on pure aluminum with fine grains of 23 ± 11 μm had a low density (3.82 × 1020 cm−3) of point defects, such as oxygen vacancies and/or metal interstitials, and a small diffusion coefficient (1.94 × 10−17 cm2/s). The influence of grain size on corrosion resistance was discussed. This work demonstrated that grain refinement could be an effective approach to achieving high corrosion resistance of passive metals.

Construction of unique floating Bi2WO6/g-C3N4 S-scheme heterojunction to promote photocatalytic activity

Inspired by the floating and photosynthesis of algae and corals in the marine ecosystem, a floating photocatalytic system with an S-scheme heterojunction was constructed using melamine sponge as the backbone and Bi2WO6/g-C3N4 as the active components. This system has the advantages of easy availability of raw materials, low cost, simple preparation, easy recovery, and full utilization of solar light, addressing the disadvantages of powdered materials such as difficulty in recovery, susceptibility to external environmental factors, and inactivation. The unique floating structure allows photocatalytic reactions to occur at the interface between water and air, increasing the utilization rate of air O2. Taking BWO/FCN materials as an example, the layered BWO and g-C3N4 were attached to the carbonized melamine sponge backbone using a direct thermal shrinkage method and hydrothermal treatment, forming an S-scheme heterojunction with a suitable band gap. Under visible light irradiation, after 90 min of reaction, the degradation rate of TC reached 98.2 %, with excellent stability and recyclability. Using in-situ XPS, we tested the electron transfer rules in the BWO/FCN heterojunction and demonstrated the successful formation of the S-scheme heterojunction. The structure and properties of the material were characterized and analyzed using SEM, TEM, UV–vis, electrochemical testing, ESR, and other techniques. Finally, the possible ways of TC degradation and the eco-toxicity of intermediate products and the reduction process of product toxicity were analyzed. This study provides a new perspective for researching floating materials and S-scheme heterojunctions, laying a foundation for future environmental governance and energy conversion research in this field.

Corrosion inhibition properties of sweet crude oil for carbon steel 1018 in NaCl solution

Abstract Aged oil pipeline production systems, historically designed without corrosion protection due to predominantly oil-wetted conditions, now face significant changes as increased water content in produced oil arises from field maturation. This work investigates the corrosion inhibition properties of sweet crude oil on carbon steel 1018 in a CO2-saturated NaCl solution using electrochemical testing (open circuit potential, polarization resistance, electrochemical impedance, potentiodynamic polarization) and surface characterization (SEM, EDS) techniques at 50 °C and pH 6. Carbon steel specimens were immersed in crude oil for durations ranging from 0 to 144 h before undergoing corrosion testing. Results showed that a 144-h immersion in crude oil led to an 88 % reduction in corrosion rate, comparable to the efficiency of standard quaternary ammonium-based inhibitors. Furthermore, a semi-empirical model predicting uniform CO2 corrosion rates for varying oil immersion durations is proposed and validated by comparing its predictions with experimental data from the electrochemical tests.

Activation and degradation mechanisms of α-V2O5 cathode materials in Zn-ion battery

Vanadium oxides with high specific capacity have been widely used as cathode materials for aqueous Zn-ion batteries. However, the interactions between the aqueous electrolytes and Vanadium oxides are still unclear. In particular, the intercalation of proton and water which can play a critical role in the degradation process is less well understood. Moreover, the mechanism for the capacity increase during the electrochemical cycling, known as the activation process, is still under debate. In this study, we systematically investigated the α-V2O5||Zn battery system with state-of-the-art characterization tools and electrochemical testing techniques to reveal the activation and degradation processes. It is discovered that the activation can be mainly attributed to the intercalation of protons and water in the first 100 cycles, which destabilizes the overall structural integrity, leading to capacity degradation afterward. It is also revealed that two main cathode electrolyte interface (CEI) components can be formed on the cathode surface, namely Zn3(V2O7)(OH)2·2H2O and Znm(CF3SO3)n(OH)2m-n·nH2O. The formation of Zn3(V2O7)(OH)2·2H2O-based CEI component is irreversible, while Znm(CF3SO3)n(OH)2m-n·nH2O-based CEI component can be reversibly cycled. Different structure-stabilizing charge/discharge protocols are proposed accordingly, which could leverage the structural integrity with thorough phase transition in the activation stage to enhance the cycling performance of the V-based cathodes. We hope to spur further interest in the fundamental understanding of the cathode materials in Zn-ion batteries.

Preparation and corrosion resistance study of a pH-responsive plasma electrolytic oxidation coating modified by halloysite nanotubes

In this research work, pH-responsive halloysite nanotubes (HNTs) microcontainers were utilized to load 2-mercaptobenzothiazole (MBT) corrosion inhibitors by adopting the layer-by-layer assembly method (LbL). Additionally, a pH-responsive composite self-healing coating was fabricated utilizing plasma electrolytic oxidation combined with micro/nano-container loadings in organic coating technology. To study the evolution of the structure and repair performance of the composite self-healing layer under various pH values, and understand the release behavior of the corrosion inhibitor, SEM, TEM, DTA, infrared absorption spectroscopy, and electrochemical testing techniques were employed. The results of the study indicated that poly allylamine hydrochloride (PAH) and poly sodium 4-styrenesulfonate (PSS) displayed efficient encapsulation of HNTs, and the release rate revealed an increase in acidic and alkaline solutions, while it showed a decrease in neutral solutions. Furthermore, scratch tests were conducted on the coated samples, demonstrating that the HNTs-loaded corrosion inhibitors significantly improved the corrosion resistance and repair performance of the coating. Besides, the protonation of the polyelectrolyte coating layer enabled the corrosion inhibitor MBT to gradually release and diffuse into the defects, leading to the formation of an adsorption film, thus inhibiting corrosion and achieving a self-healing effect.

Effects of Welding Techniques on the Corrosion Resistance of Mild Steel

The performance and longevity of welded structures depend heavily on corrosion resistance, particularly when mild steel is used as the primary material. The paper provides an overview of the investigation of the influence of various welding techniques on the corrosion resistance of mild steel. The study combines mild steel specimens using spot-welding, gas metal arc, and electric arc welding techniques. Electrochemical and immersion testing techniques are used to assess the welded samples' resistance to corrosion. The impact of metal microstructure, welded zone surface characteristics, corrosion rates, and filler material selection on corrosion resistance is examined. The results demonstrate that the choice of welding process has a significant effect on mild steel corrosion resistance. Some techniques have a higher level of corrosion resistance owing to the use of heat. As exposure duration rises, both diluted and concentrated hydrochloric acids cause weight loss in the absence of an inhibitor. The temperature increased over time until 190 minutes, which resulted in a decrease in temperature efficiency. In the impact test, adding 3%, 6%, and 9% of the welded components to the metal alloy increased the impact's energy output from 12.32 J to 12.69 J, 12.99 J, and 13.51 J, respectively. The energy effect of the reinforced mild steel was reduced owing to the brittleness of the welded parts relative to the ductile metal matrix. The composite absorbs impact stresses, and the enhanced weight ratio of the welded mild steel thereby increases its toughness.

Oxygen Vacancies Riched PrOx Polycrystalline Nanorods on Graphene Nanosheets as Advanced Oxygen Catalysts for Lithium‐Oxygen Batteries

AbstractThe slow reaction kinetics of Li−O is currently the most pressing technical obstacle to the development of lithium‐oxygen batteries. The Li2O2′s growth/decomposition pathways dominate the battery performance and can be optimized by exploring efficient cathode catalysts. Herein, we prepare regular, polycrystalline, oxygen vacancy (VO)‐riched PrOx uniformly anchored on few‐layered graphene (FLG) nanosheets to boost the Li−O reactions. XRD, TGA, XPS, SEM, TEM, SEAD, and electrochemical test techniques are used to study their chemical composition, microstructure, battery performance, and the effect of FLG on the formation of polycrystalline and VO. It is confirmed that FLG provides a large specific surface area and good electron transport. Moreover, it works as an anchoring substrate to transform PrOx from single crystal to polycrystalline, which is beneficial for exposing catalytic sites and VO and improving the battery performance. This unique composition and structure offer efficient active sites, accelerate electron transport, and regulate the Li2O2′s nucleation to form nanofilms or nanosheets on the catalyst. With this cathode catalyst, the battery achieved an ultralow total overpotential of 0.618 V, with a discharge capacity of 11489 mAh g−1 in the ultimate‐capacity mode and a superior cyclability of 85 cycles under the limited capacity of 500 mAh g−1.

Modification of VPO4 with carbon and 3DG for high performance lithium‐ion battery anode

AbstractLithium‐ion batteries (LiBs) are one of the most promising energy storage devices. However, the large‐scale application of LiBs is limited by their electrochemical properties. In this study, we built a three‐dimensional (3D) conductive network structure with carbon and 3DG coating VPO4 (VPO4@C@3DG) via a one‐pot hydrothermal method with subsequent high‐temperature annealing. The effects of the content of three‐dimensional porous graphene (3DG) on the crystal structure, morphology, and electrochemical properties of VPO4/C are investigated using characterization and electrochemical test techniques. The SEM images show that the size of sphere‐like particles of VPO4@C@3DG composite with 20 wt.% of 3DG (VPO4@C@3DG‐20) is the smallest in all samples. In addition, the electrochemical experimental results reveal that VPO4@C@3DG‐20 exhibits the best cycling and rate performance compared to other VPO4@C@3DG composites. Specifically, VPO4@C@3DG‐20 achieves an initial charge capacity of 601.2 mAh g−1 at 0.2 C (110 mA g−1) and keeps at 354 mAh g−1 at the 100th cycle. This is because the introduction of 20 wt.% 3DG graphene inhibits the growth and aggregation of the particles, thus shortening the diffusion path of Li+. In addition, the 3D conducting network structure boosts the conductivity of the materials and buffers the volume variation resulting from the charging/discharging process.

Combined electrochemical, DFT/MD-simulation and hybrid machine learning based on ANN-ANFIS models for prediction of doxorubicin drug as corrosion inhibitor for mild steel in 0.5 M H2SO4 solution

In this work, Doxorubicin drug was used as mild steel corrosion inhibitor in 0.5 M H2SO4 solution. Herein, standard techniques like gravimetric, electrochemical measurement, density functional theory via DFT/ molecular dynamic simulation (MDS), Scanning electron microscopic (SEM), were used for proper evaluation of Doxorubicin drug as anticorrosive agent. According to the experimental findings, Doxorubicin drug significantly inhibits mild steel corrosion, and its effectiveness increases with an increase in the drug concentration. Maximum inhibition efficiency at 100 ppm was 93.3 %, 91.3 % and 96.8 % for electrochemical impedance (EIS), polarization test (PDP) and gravimetric techniques respectively. The electrochemical study indicates that Doxorubicin is a mixed-type inhibitor. Close scrutiny of the corroded and inhibited metals evidenced that Doxorubicin drug produced a better and more uniform coating on the surface of mild steel. The molecular structure of the drug and its contribution to the inhibition mechanism was further understood using simulations based on density functional theory (DFT) and molecular dynamics simulation (MDS). In addition, artificial neural networks (ANN) and adaptive neuro-fuzzy inference system (ANFIS) were used to predict and model the interactive effects affecting the response. Also, statistical parameters like coefficient of determination (R2), root mean square error (RMSE), mean absolute percentage error (MAPE), and mean absolute deviation (MAD) were used to assess the models' performance. The results demonstrate that the FCM-clustered ANFIS model with 15 clusters perform better than ANN model with RMSE, MAD, MAPE, and R2values of 0.978, 0.642, 4.823, and 0.9925 at the testing phase, and 0.6435, 0.4248, 2.8151, and 0.9998 at the training phase respectively. The best prediction was made using complete FCM-ANFIS model, which had accuracy of 98.4 %. Hence, a robust system prediction can be achieved via ANN and ANFIS algorithms to predict corrosion inhibition of mild steel in acidic environment using drug based corrosion inhibitors.

Growth of mesoporous carbon supported (bimetallic) phosphides derived from Prussian blue for supercapacitors

In the context of supercapacitor energy storage, maintaining high cycle stability while enhancing energy density and coulomb efficiency is crucial. In this investigation, NiCo Prussian blue analogue (PBA) electrode materials were synthesized using the coprecipitation method, and subsequently modified via sulfurization and phosphating to obtain oxides (PBAO), sulfides (PBAS) and phosphides (PBAP) derived from Prussian blue cubes. The microphysical structure of PBA was engineered to enhance conductivity and electrochemical performance, with an in-depth exploration of the effects of sulfurization and phosphating. Additionally, mesoporous carbon (SAC) was doped into the previously prepared PBA, leading to the successful preparation of [email protected] electrode material with exceptional electrochemical performance. By utilizing electrochemical testing and various characterization techniques, the underlying sources of the observed performance differences were analyzed both experimentally and through electrochemical mechanisms. Furthermore, the addition of 0.01 M potassium ferricyanide to the 3 M KOH electrolyte significantly improved the coulomb efficiency of the material under the condition of high current density and long cycle time. Finally, an asymmetric supercapacitor (ASC) was constructed using industrial activated carbon as the negative electrode with the prepared [email protected] electrode material, and its electrochemical performance was evaluated to explore the practical application potential and prospects of this material.

How Do Impurities in Electrolytes Affect the Electrochemical Performance of Oxides in Lithium-Ion Batteries?

The recovery and treatment of spent LIBs has already been studied extensively. On one hand, the hydrometallurgical recovery of cathode materials has aroused widespread attention because of its low energy consumption and benefit to the environment. On another hand, the purification of the materials reclaimed from spent batteries is a challenging process with high probability that, later, some remaining impurities such as transition metal carbonates and sulfates could be released into the electrolyte. In this way the impurity content will have a serious impact on the final performance of the battery. To this point different electrochemical and analytical measurements were conducted to elucidate the effects of impurities in the electrolyte formulation, specifically Li, Mn, Co, Ni, and Al carbonates, sulfates, and acetates. The base LP30 electrolyte was intentionally contaminated with a maximum concentration of selected impurity to study the effects of the contaminated electrolyte on the electrode. Different combinations and varieties were explored correspondingly. Test setups were based on both, NMC811 in half cells (vs. Li) and symmetrical Li||Li cells, and the influence of contaminations was thus exploited on the Li counter electrode and on the NMC811 in Li||NMC811 configuration. A number of standard and advanced electrochemical test techniques such as CC-CV, electrochemical impedance, rate capability tests, GITT, and CV was applied for a fully understanding of the electrochemical characteristics of standard cathode active materials such as NMC811 when electrolytes with (artificially downgraded) low purity levels are present. The presentation will focus on discussion of results regarding the presence of transition metals Ni, Co, and Mn as impurities in the electrolyte which showed a significant impact on the electrochemical performance of the tested cells. When the concentration of the impurities increases, both the overpotentials at the cathode and the rate of capacity decay during cycling increase as well. The data shown will be very helpful for the researchers to understand the impact of impurities on the performance of oxide-based LIB cathode materials.

Research Progress of Macrocell Corrosion of Steel Rebar in Concrete

Macrocell corrosion of steel rebar in concrete induced by corrosive environments has attracted widespread attention in the engineering community due to its rapid corrosion rate, diverse forms, and multiple incentives. Potential differences between dissimilar coupled rebar or different parts of the same rebar mainly cause macrocell corrosion of steel rebar. The more significant the potential difference, the faster the corrosion rate of the macrocell. Based on the existing research reports on macrocell corrosion of reinforced concrete, this review paper comprehensively discusses the macro- and micro-corrosion behavior of various types of steel rebar, and a variety of induction factors, such as dissimilar metals and concentration differences of the service environment, development rules. and electrochemical mechanisms for corrosion of rebar macrocells are summarized. ZRA (zero-resistance ammeter), micro-area electrochemical testing technology and evaluation techniques commonly used in the laboratory, and electrochemical testing techniques used in engineering testing are listed. Common experimental models for corrosion of rebar macrocells are briefly introduced. Based on the internal characteristics of macrocell corrosion of reinforced concrete, this paper further proposes the control strategy of macrocell corrosion, starting from the improvement of the corrosion resistance of the rebar and regulating the service environment of the reinforced concrete structure (RCS). Meanwhile, the future direction of macrocell corrosion of steel rebar is also preliminarily prospected.

Corrosion behavior and mechanism of X80 pipeline steel welded joints under high shear flow fields

The internal-pipeline local corrosion in the welded joint region has been a widely concerning issue, particularly under the synergistic effect of high shear stress and electrochemical corrosion, which can easily result in pipeline rupture. Classical electrochemical testing techniques and wire beam microelectrode (WBE) are used to investigate the local corrosion behavior of X80 steel welded joints in a CO2-saturated NACE solution at different flow rates (velocities of 3 m/s, 5 m/s and 7 m/s), and the corrosion product composition and characteristics are analyzed via scanning electron microscopy (SEM), energy dispersive spectrometry (EDS), X-ray diffraction (XRD), and three-dimensional (3D) measuring laser microscopy. The results show that different welded joint zones exhibit different corrosion degrees. The heat-affected zone (HAZ) shows the worst corrosion resistance, whereas the base metal (BM) and weld metal (WM) show similar corrosion resistances. The HAZ is an anode that corrodes unsatisfactorily at high flow rates, and the enhanced wall shear stresses peel off part of the dense corrosion product film, promoting the development of local corrosion. Therefore, the HAZ zone is a weak link in the X80 steel welded joints. This study provides scientific guidelines for the corrosion protection of long-distance oil & gas pipelines.

Effect of Nb content on microstructure and corrosion resistance of Inconel 625 coating formed by laser cladding

The Inconel 625 coatings with Nb addition of 0 %, 1.5 %, 3 % and 5 % were prepared by laser cladding technology. The effects of different contents of Nb on the phase composition, microstructure and corrosion resistance of the coatings were investigated by XRD, SEM, electrochemical test and other techniques. The results show that with the increase of the Nb content, the surface structure of the coating changes from dendrites to cellular crystals. Because of the consumption of C in γ-Ni phase by forming NbC, more Cr was released from its carbide state and solidly dissolved in γ-Ni phase, which improves its passivation capacity in the electrolyte. The increase of Nb also promotes more Nb and Mo elements to participate in the oxidation process. The plugging of pitting holes by corrosion products reduces the corrosion rate of coatings. The 3Nb coating exhibited the best corrosion resistance in 3.5%NaCl solution. The addition of an appropriate amount of Nb is an effective way to optimize the coating's microstructure, improve its corrosion resistance and microhardness.