Oxidation Of Cr Research Articles

Insights into the role of the Cr and rare element in improving the corrosion resistance of HRB400 rebars in simulated SO2-polluted marine environment

The present work aims to offer insights into the role of Cr and rare element (RE) in improving the corrosion resistance of HRB400 rebar in simulated concrete pore solution (SCPS) containing NaCl and NaHSO3. Electrochemical tests reveal that the increased SO2 concentration reduces the pitting potential and charge transfer resistance. However, the addition of Cr/RE significantly lowers the corrosion current density of HRB400, as confirmed by the corrosion morphology observed after immersion tests. Quantitative analysis of corrosion pits shows that SO2-induced corrosion tends to develop longitudinally, a tendency mitigated by the Cr/RE alloyed rebar. X-ray photoelectron spectroscopy (XPS) results confirm the presence of Cr and RE oxides in the oxide film and demonstrate that SO2 affects the Fe(II)/Fe(III) ratio. Cr and RE doping not only refines the microstructure and modifies inclusions but also enhances the protective properties of the oxide film on the rebar. Therefore, the combination of Cr and RE improves the durability of rebars in SO2-polluted marine environments.

Research on the Corrosion Resistance and Cytotoxicity of Medical Forged Co-28Cr-6Mo Alloy

Co-Cr-Mo alloy as a human body implant material has a long history, because of its excellent corrosion resistance and biocompatibility, and is widely used in human hip joint materials. Co-Cr-Mo alloy in the human body is often in a passivation state; the formation of dense oxide film on the alloy surface prevents further corrosion of the alloy. The main component of the passivation film is the oxide of Cr, so a layer of oxide film formed by Cr on the surface of Co-Cr-Mo alloy is the reason for its good corrosion resistance. In biocompatibility, cytotoxicity is the first choice and necessary option for biological evaluation, and cytotoxicity can quickly detect the effect of materials on cells in a relatively short time. Therefore, this research conducted a comparative evaluation on the corrosion resistance and biocompatibility of forged Co-Cr-Mo alloys produced in domestic and foreign alloys in line with medical standards. Three simulated human body fluids and Princeton electrochemical station were selected for corrosion resistance experiments, and it was found that the corrosion resistance of four alloys in sodium citrate solution inside and outside China would be reduced. All the alloys exhibit secondary passivation behavior in Hanks solution, which improves the corrosion resistance of the alloys. According to the self-corrosion potential Ecorr analysis, the corrosion resistance of domestic B alloy is the best, while that of foreign R31537 alloy is poor. In the biocompatibility experiment, the biocompatibility of Co-Cr-Mo alloy was evaluated through the measurement of contact Angle and cytotoxicity reaction. The experimental results show that Co-Cr-Mo alloy is a hydrophilic material, and the contact Angle of foreign R31537 alloy is smaller, indicating that the surface of R31537 alloy is more suitable for cell adhesion and spreading. According to the qualitative and quantitative analysis of the cytotoxicity experiment, the toxic reaction grade of domestic A, B and R31537 alloy is grade 1, the toxic reaction grade of C alloy is grade 2, and C alloy has a slight toxic reaction.

Effects of varying pH on the passive film formation in high-strength anti-seismic rebar

ABSTRACT In this paper, electrochemical measurements (CV, PDP, M-S and EIS) and surface characterisation techniques (SEM, EDS, AFM, TEM and XPS) were used to study the passivation phenomenon in high-strength anti-seismic rebar under varying pH conditions. The results show that a passive film with a polycrystalline structure with a certain roughness is formed on the surface of the rebar. The passive film is mainly composed of Fe oxides and hydroxides, and there are also oxides of Nb, Mn, Si and Cr. The existence of these oxides builds a dense and stable passive film. The passive film is basically stable at 7d, but the early growth of the passive film at higher alkalinity show instability. After 10 days of passivation, with the decrease of pH, the passive film gradually densifies, the pitting potential increased by about 0.03–0.14 V, the carrier density decreased by 30% on average, the phase angle increased slightly, and the ratios of Fe2+/Fe3+ and O2−/OH− increased, resulting in a passive film thickness of 6.2 nm.

Recovering chromium from electroplating sludge using an integrated technology of bipolar membrane electrodialysis and H2O2 oxidation

Chromium electroplating produces Cr(III)-containing electroplating sludge (EPS) in large volumes, which is easily oxidised to Cr(Ⅵ) and is harmful to the environment and human health. This study recovered Cr(III) as Na2CrO4 from EPS using an integrated bipolar membrane electrodialysis (BMED)–H2O2 oxidation technology. During the treatment process, Cr(III) was oxidised to Cr(VI) using H2O2 in an alkaline environment, BMED was used to separate and recover Cr(VI). Experimental results showed that H2O2 dosage and pH affected Cr(III) oxidation—the highest Cr(III) oxidation ratio of 68.4% was observed when H2O2 dosage and pH were 5.5 mL and 12.0, respectively. The current density, solid/liquid ratio and sludge particle size affected Cr(III) recovery, energy consumption and current efficiency. Under a current density of 20.0 mA/cm2, solid/liquid ratio of 1.0:45 and sludge particle size of 100 mesh, 58.2% of Cr(III) was recovered. When the number of the equipped EPS compartments was increased from one to two and three, the specific energy consumption decreased from 1.04 to 0.87 and 0.81 kW h/g, respectively, but the current efficiency remained almost constant. After EPS treatment, the Cr(III) remaining in the sludge was mainly in the residual state, which is less environmentally harmful. The obtained Na2CrO4 had similar properties according to X-ray diffraction analysis. Thus, the proposed integrated technology effectively recovers Cr(III) from EPS and other chromium-containing solid wastes.

High Temperature Oxidation Behavior of ODS Ferritic Stainless Steel Fe-16Cr-4Al-1Ni-0.4Y<sub>2</sub>O<sub>3</sub>

This study investigates the isothermic oxidation behavior of the new ODS alloy Fe-16Cr-4Al-1Ni-0.4Y2O3 (% by weight) at 700, 800 and 900 °C, with exposure times of 5, 20, 50, and 100 h at each temperature. The purpose is to obtain new data on its high-temperature parabolic oxidation constant for assessing oxidation resistance. The methods used include isothermal oxidation testing, XRD, SEM-EDS characterization, and analysis of oxidation kinetics by monitoring changes in oxide thickness using microscopy and SEM-EDS. The oxide products formed on the sample surface are Fe2O3, Fe3O4, AlFe2O4, and (Fe,Cr)2O3. Al and Cr oxides are located under the dominant Fe oxide layer on the surface of the sample. The oxidation test results showed that the most protective sample was obtained at a temperature of 700 °C for 100 h with an oxide thickness of 263.99 μm. The kinetics analysis correlates strongly with the parabolic equation (R2 ≈ 1). The oxidation rate constants at temperatures of 700, 800, and 900 °C were 681.76, 2957.5, and 12300 μm2 h−1, respectively. The activation energy required by the oxidation reaction in this alloy is 136.5 kJ mol−1. This research enhances understanding and potential applications of the Fe-16Cr-4Al-1Ni-0.4Y2O3 alloy in high-temperature environments.

Investigation of corrosion resistance offered by the Fe-based clad layer under salt spray and electrochemical workstations

The present work aims to evaluate the electrochemical characteristics of the Fe–based alloy coating formed on the 27SiMn steel substrate under neutral salt spray and 3.5 wt% NaCl environments. By adopting the high-speed laser cladding technique, the Fe-based clad layer was fabricated to perform microstructural and electrochemical characterizations. The microstructure and phase of the coating were analyzed using a scanning electron microscope (SEM), electron backscatter diffraction (EBSD) and X-ray diffraction (XRD), and its corrosion performance was also discussed using the salt spray corrosion chamber and the electrochemical workstation. The results show that the microstructure of the coating surface contains equiaxed crystals and long dendritic crystals which arise due to the higher solidification rate after the cladding process. The Fe–based coating was rich in FeCr phase throughout its microstructure without the formation of the intermetallic compounds. Compared to the substrate, the corroded surface of the coating tends to be compact containing a few corrosion pits after different corrosion times, which is attributed to the formation of Cr oxide on it. The electrochemical tests on the potentiodynamic polarization curve (PPC) and electrochemical impedance spectrum (EIS) indicate that the corrosion resistance of the coating is superior to the substrate, presenting a higher corrosion potential (−0.298 V), lower passive current density (1.36 × 10−6 A•cm2), and higher charge transfer resistance (8.23 × 106 Ω·cm2). Additionally, the corrosion mechanism of coating in salt spray and electrochemical tests is the local pitting corrosion due to the autocatalytic effect on the localized region, which facilitates Cl− ions penetrating the coating and leads to the dissolution of Fe and Cr oxides.

Understanding preferential intergranular oxidation in alloy X-750 in 480 °C CO-CO2 environments at the nanoscale

Alloy X-750 was exposed to a 480 °C CO-CO2 reducing gas mixture at an oxygen partial pressure below the NiO dissociation pressure. Post-exposure analytical transmission electron microscopy (ATEM) analysis confirmed the occurrence of preferential intergranular oxidation (PIO) and internal oxidation which resulted in the formation of Ni nodules. Thus, reducing CO-CO2 mixtures can promote PIO in Alloy X-750, similar to Alloy 600 exposed to similar oxygen partial pressure but in H2-steam environment. In Alloy X-750, intergranular oxidation of Ti and Al were observed to occur prior to Cr oxidation, while the presence of intergranular Cr carbides hinders PIO penetration depth.

Chromium cycle in Red Soil Critical Zone constrained by chromium isotopes

Chromium (Cr) isotopic system has been used to trace Cr pollution in the modern surface environment and redox change in the paleoenvironment. However, the transformation mechanism of Cr in soil and the accompanied Cr isotopic fractionation have not been clarified clearly. Here we measured Cr isotopic compositions (δ53Cr) of two paddy field profiles from the Red Soil Critical Zone Observatory in South China. The δ53Cr values of the young paddy fields, which have been cultivated for about 20 years, range from −0.34 ‰ to −0.22 ‰. The old paddy fields have been cultivated for >100 years and have more positive Cr isotopic compositions than the young paddy fields, from −0.20 ‰ to −0.06 ‰. The results of three-step leaching experiments show that iron and manganese oxides are enriched in heavy Cr isotopes, while organic matters have much lower Cr isotopic compositions, likely resulting from back reduction of Cr(VI). Our results suggest that Cr isotopic fractionation during the oxidation of Cr(III) is not the only reason for the depletion of heavy isotopes during oxidative weathering, and the partial back-reduction of generated Cr(VI) by organic matter plays an important role in Cr isotopic fractionation during weathering. Comparison between the old and young paddy fields further indicates that cultivation can significantly affect the Cr cycle in red soils. Paddy fields could be a potential sink for the Cr(VI) contaminant, and soils with a long history of cultivation would be more susceptible.

Binding mechanisms of trivalent chromium on colloidal phases from ultramafic systems: Insights from batch experiments and XAS analysis

Understanding the availability and mobility of chromium is a key factor in gaining insight into the fate of chromium and thus essential for assessing the risk of contamination and developing effective remediation strategies. In the natural environment, such as ultramafic systems, which are natural pools of chromium, chromium occurs mostly in the trivalent state (Cr(III)), which is known to have a high affinity for the solid phases such as particles and colloids. However, since Cr(VI) is more toxic, the vast majority of experimental studies focus on its reduction to Cr(III), which is often considered to form (hydr)oxide precipitates due to its poor solubility. Furthermore, while the oxidation state of Cr dictates its geochemical behavior, its interaction with particles and colloids is rarely controlled or monitored. Therefore, the interaction mechanisms between Cr(III) and particles or colloids require further attention. In this study, ten mineral phases (goethite, hematite, pyrolusite, kaolinite, montmorillonite, chlorite, serpentine, fuchsite, amphibole, and chromite) and one organic phase (humic acid), relevant to chromium bearing and carrier phases in ultramafic soils, were investigated to explore their interaction with Cr(III) species. These phases were first characterized by various techniques (including XRD, XRF, SEM, and BET). Adsorption and desorption experiments of Cr(III) on these phases were then carried out, and the distribution of Cr oxidation states in both the aqueous and solid phases was carefully monitored using UV–vis spectroscopy, geochemical speciation modeling, and Cr K-edge XAS spectroscopy. With the exception of pyrolusite, where partial oxidation of Cr(III) to Cr(VI) occurred, Cr(III) was shown to persist as a single oxidation state in all experiments. Desorption analyses showed significantly low desorbed rates, which further confirmed the prevalence of Cr(III). Experimental sorption isotherm data were interpreted using the Langmuir model and its linearized form, which provides important thermodynamic characteristics of adsorbents related to their structural and surface features. This study will provide better constraints for the understanding and prediction of Cr behavior and fate in the environment, especially in ultramafic systems.

Enhanced high-temperature corrosion resistance of Cr-modified phosphate/aluminum powder composite coatings: Mechanisms and thermodynamic insights

Phosphate composite coatings are regarded as one of the tangible solutions for surface protection in salt spray environments, benefiting from their cost-effectiveness and prominent structure stability upon high-temperature exposure. However, rapid curing of these coatings often leads to crack formation, and the underlying corrosion mechanisms in service conditions remain insufficiently understood, limiting their practical applications. In this study, we developed chromium-incorporated phosphate/aluminum powder composite (Cr-P/Al) coatings and evaluated their corrosion resistance under alternating conditions of salt spray corrosion and oxidation at 450 °C. By integrating experimental results, ab initio calculations, and thermodynamic analysis, we demonstrate that the incorporation of Cr significantly enhances the performance of the P/Al coatings. The structural evolution was first revealed that Cr’s modification reduced tensile stress and prevented cracks in the coating. A mixed layer of amorphous oxides and phosphates forms on the surface of the Al powder, providing robust binding strength. A novel corrosion mechanism was identified that Cl2 and volatile chlorides facilitated the removal of Cl-. This process is more ineffective with Cr-P/Al coating, as amorphous Cr oxide has low reactivity at a high log[p(Cl2)] and low log[p(O2)] compared with amorphous Mg and Fe oxide, thereby enhancing the corrosion resistance of the coating. These coating densification methods and corrosion protection mechanisms provide a critical foundation for the future application of phosphate composite coatings.

Reversible in Situ Control over Monolayer Organization.

Cr2+ and Cr3+ ions are shown to mediate the formation, morphology, and organization of arachidic acid (AA) Langmuir-Blodgett (LB) monolayers. This finding, based on cyclic voltammetry (CV), linear sweep voltammetry (LSV) and fluorescence recovery after photobleaching (FRAP) measurements, show that Langmuir monolayer formation depends on subphase pH and metal ion concentration. Following monolayer deposition on ITO, the LB monolayer organization can be modified reversibly through control of the Cr oxidation state, which has not been shown before by other monolayers formed with other divalent metal ions. The dynamics and the mobility of a chromophore (perylene) incorporated into the monolayer sense changes in Cr oxidation state-dependent organization of the LB monolayer. Demonstrating reversible changes in monolayer organization provides an opportunity to control chemical and electron access to the interface support.

Self-sacrificial hydrogen channel enhances the poisoning resistance of ZrCo-based alloy

ZrCo alloy is considered as a promising candidate for hydrogen isotope storage in nuclear fusion reactors. However, severe poisoning caused by the impurities contained in hydrogen is an inevitable issue in engineering applications. Herein, the effects of Cr-doped ZrCo with segregated the reticular ZrCr2 phase on the activation and oxidation resistance were investigated systematically. Experimental results show ZrCo0·95Cr0.05 can achieve 1.71 wt% hydriding capacity within about 37 min under 1 mol% O2 + 99 mol% H2, whereas ZrCo consumes more than 4 times (150 min) to reach the same capacity. Specifically, the improved anti-poisoning ability of the ZrCo–Cr system could be attributed to the three-step chain effect induced by Cr doping, including the hydrogenation-prone and oxygen resistance character of ZrCr2 phases, sacrificial and catalysis of in-situ formed metallic Cr clusters, and protective effects of Cr oxide layers. Hence, the active sites for rapid hydrogen absorption were obtained and inferior oxygen resistance of ZrCo substrates was alleviated through the self-sacrifice of ZrCr2 and Cr. This work not only proves the feasibility of the multi-component alloying strategy in the field of ZrCo alloy anti-poisoning modification, but also reveals that the core of the multi-component alloying strategy is to realize the modulation of the microstructure through the composition design.

Role of Te-RE alloying on the passive film and pitting corrosion behavior of 316L stainless steel

This work reports the mechanism of corrosion resistance enhancement of 316 L stainless steel after Te-RE alloying. The individual MnS inclusions are replaced by composite inclusions, resulting in a reduced risk of pitting corrosion. The decrease of inclusion amount and Volta potential difference between inclusion and matrix induced by the addition of Te/La promoted the stability of the inclusions and lessened the active sites for pitting corrosion. TeO2 formed in the passive film with Te treatment could be easily reduced by Cr and Mo, and resulting in a significant increasing of MoO2 and Cr2O3 content in the passive film. This enhanced the stability of the passive film. Te and RE exhibited a synergistic effect on the increase of Cr and Mo in the passive film, resulting in a further improvement of the passive film. However, RE could not exist in the passive film stably due to its poor thermodynamic stability of the rare earth oxides, and only acted as a bridge for the formation of Cr and Mo oxides.

Creep fatigue interaction at high temperature in C630R ferritic/martensitic heat-resistant steel

The study investigated the creep-fatigue interaction behavior, fracture mechanism, and microstructure evolution of C630R ferritic/martensitic heat-resistant steel at 630 °C and 1% strain amplitude. The results indicate that C630R ferritic/martensitic heat-resistant steel exhibits noticeable cyclic softening behavior, with a decrease in the softening ratio from 0.46 to 0.40 as loading time increases. Microstructure evolution was examined using optical and scanning electron microscopes, revealing the appearance of secondary cracks on the longitudinal section of the sample. These cracks exhibited a curved expansion trend with multiple deformations and highly bifurcated micro-cracks at a low loading time of 30s. However, when the load holding time was increased to 300s, the fatigue cracks tended to expand in a straight line with fewer branches. Furthermore, the observed crack growth path under different loading times showed enrichment in Fe and Cr, with the crack tip containing Cr oxide, which helped prevent fatigue crack propagation. As the loading time increases, the rise in crack closure resulting from oxidation leads to a decrease in crack propagation. Electron backscatter diffraction observation revealed the formation of numerous substructures and recrystallized grains after varying holding times, enhancing the material's resistance to crack propagation. Moreover, the study found that with increasing load dwell time, the deformed grains decreased, and substructural grains became dominant (57.68% and 62.77% under 30s and 300s, respectively). This increased crack resistance resulted in shorter secondary cracks under prolonged load retention, with the secondary crack length decreasing from 146.36 μm at 30s loading time to 109.09 μm at 300s loading time. Additionally, the kernel misorientation angle value decreased significantly after different loading times, leading to a higher likelihood of cracks or holes forming in regions with high KAM values, where low-angle grain boundaries were formed.

Corrosion behavior and mechanism of 921 A high-strength low-alloy steel in harsh marine atmospheric environments

High-strength low-alloy 921 A steel faces significant corrosion challenges in harsh marine atmospheric conditions, threatening marine and energy industry safety. This study investigates the corrosion behavior of 921 A steel through accelerated tests in a specially developed multi-factor coupled corrosion chamber. Combining the multi-factor coupling cyclic corrosion test method with finite element numerical simulation, the long-term corrosion behavior can be accurately predicted, and the power function relationship between the corrosion rate and time of the test steel is obtained, which is expressed as C=0.2259 t–0.5182. Analysis identified α-FeOOH, Fe3O4, γ-FeOOH, Cl—, and Cr in corrosion layers. First-principles calculations and XPS analysis showed Cr oxidation inhibits Cl— adsorption and diffusion, highlighting the steel’s corrosion resistance. Finite element analysis and outdoor corrosion data confirmed the corrosion rate and time correlation, proving simulation reliability. This research provides crucial insights into 921 A steel’s corrosion resistance in marine environments, benefiting marine engineering.

Formation of heterogeneous microstructure and its effect on corrosion properties of high-silicon stainless steel S38815 weldment

This study aims to clarify the formation of heterogeneous microstructure and its effect on corrosion properties of high-silicon stainless steel (high-Si SS) S38815 weldment. A series of tests about microstructure and electrochemical characteristics were performed, including the electron backscatter diffraction (EBSD) analysis, Mott-Schottky tests, electrochemical impedance spectroscopy (EIS) tests, potentiodynamic and potentiostatic polarization tests. The formation mechanism of heterogeneous microstructure related to high-silicon and its correlation on corrosion was discussed extensively. The results show that the significantly deformed and recrystallised grains were observed at the low temperature heat affected zone (LT-HAZ) and high temperature heat affected zone (HT-HAZ) respectively. The metastable pitting and low impedance values were formed in the above region, despite their low donor density. The deterioration in corrosion resistance of S38815 weldment as a result of high-angle grain boundaries (HAGBs) and carbides is more pronounced than the beneficial impact of Cr and Si oxidation. This study provides valuable references to the manufacturing and enhancing the anti-corrosion properties of this high-Si SS.

Photoinduced oxidation of chromium picolinate to hexavalent chromium in the presence of ferric ions

The occurrence of chromium picolinate (Cr(pic)3) in environment has attracted raising concerns on its fate and the associated risks. Herein, the photoinduced oxidation of Cr(pic)3 in the presence of ferric ions (Fe(III)) under simulated sunlight and natural solar light irradiation were investigated. Cr(pic)3 was stable under dark or without Fe(III). 87.9 % of Cr(pic)3 (C0 = 1.0 μM) was degraded in the presence of 50 μM Fe(III) after 90 min simulated sunlight irradiation at initial pH of 4.0. •OH was the main cause for Cr(pic)3 oxidation, it attacked the chromium center to generate hexavalent chromium (Cr(VI)) and picolinic acid (k = 5.9 ×108 M−1·s−1). Picolinic acid could be further oxidized to NH4+ and small organics. Relative higher Fe(III) content (25 – 75 μM) and Cr(pic)3 concentration (0.5 – 2.0 μM) promoted both of Cr(pic)3 degradation and Cr(VI) accumulation. While, the degradation of Cr(pic)3 decreased with pH at the range of 3.0 – 8.0, more Cr(VI) was accumulated at pH 5.0 and 6.0. The co-existence of inorganic ions and dissolved organic matter (DOM) in river water inhibited Cr(pic)3 oxidation by scavenging the •OH formed and shielding the light. 8.0 – 16.7 μg/L of Cr(VI) was accumulated after 9.0 h simulated sunlight irradiation of Cr(pic)3 in river water matrix ([Fe(III)]0 = 50 – 100 μM). The generation of Cr(VI) under solar light was slower than that under simulated sunlight due to the weaker light intensity (43.2 – 85.0 mW/cm2 vs. 750 – 1300 mW/cm2). These results consistently suggest photoinduced oxidation of Cr(pic)3 in environment generates the toxic Cr(VI), which deserves significant attention.

Morphological Evolution and Dealloying During Corrosion of Ni20Cr (wt.%) in Molten FLiNaK Salts

The dealloying corrosion behavior of the FCC Ni20Cr (wt%) in molten LiF-NaF-KF (FLiNaK) salts at 600 °C under varying applied potentials was investigated. Using in-operando electrochemical techniques and a multi-modal suite of characterization methods, we connect electrochemical potential, thermodynamic stability, and electro-dissolution kinetics to the corrosion morphologies. Notably, under certain potential regimes, a micron-scale bicontinuous structure, characterized by a network of interconnected pores and ligaments riched with the composition of the more noble (MN) element, becomes prominent. At other potentials both MN and less noble (LN) elements dealloy but at different rates. The dealloying process consists of lattice and grain boundary diffusion of Cr to the metal/salt interface, interphase Cr oxidation, accompanied by surface diffusion of Ni to form interconnected ligaments. At higher potentials, the bicontinuous porous structure undergoes further surface coarsening. Concurrently, Cr(II), Cr(III), and Ni(II) begin to dissolve, with the dissolution of Ni occurring at a significantly slower rate. When solid-state transport of Cr is exceeded by the interfacial rates, dealloying depths are limited.

The Influence of Pretreatment of Carbon Support on the Catalytic Activity of Fe–Cr Oxide Systems in the Oxidative Dehydrogenation of Ethane

The Influence of Pretreatment of Carbon Support on the Catalytic Activity of Fe–Cr Oxide Systems in the Oxidative Dehydrogenation of Ethane

Passivation Behavior of Chromium Alloyed High-Strength Rebar in Simulated Concrete Pore Solution

In this study, SEM, AFM, TEM, XPS, and electrochemical tests are used to study the passivation behavior of chromium alloyed high-strength rebar in simulated concrete pore (SCP) solutions with different pH values. The results show that after passivation in SCP solution with different pH values, the passivating film on the surface of the chromium alloyed rebar primarily consists of a layer of nanoscale oxide particles, which makes the passive film exhibit a p-n type semi-conductor, and the passive film presents a rhombohedral crystal structure. As the pH value of the SCP solution decreases, the nanoscale oxide particles on the surface of the rebar become denser, which leads to a reduction in the carrier density (Nq and Na) of the passive film and an increase in film resistance (R2) and charge transfer resistance (R3), thus increasing the corrosion resistance of the passive film. The passive film on the surface of the chromium alloyed high-strength rebar predominantly exhibits a three-layer structure, the outer passive film layer is composed of Fe oxides, the stable layer of the passive film is composed of Fe oxides and Cr oxides, and the growth layer of inner passive film is composed of Cr oxides. Compared with passivation 10 d in SCP solutions with pH 13.5 and pH 12.5, the passive film on the surface of the rebar has good stability at pH 10.5, which indicates that the addition of Cr is beneficial to promote the corrosion resistance of the rebar.