Inhibition Behavior of Low Alloy Steel by Sodium Molybdate in Simulated Concrete Pore Solution Containing Chlorine

CHEN Xiaohua; ZHAO Fangchao; ZHOU Kun; SHI Xianfei; CUI Zhongyu; MAN Cheng; WU Dequan

doi:10.16490/j.cnki.issn.1001-3660.2025.12.003

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Surface Technology ›› 2025, Vol. 54 ›› Issue (12) : 37-48. DOI: 10.16490/j.cnki.issn.1001-3660.2025.12.003

Corrosion and Protection

Inhibition Behavior of Low Alloy Steel by Sodium Molybdate in Simulated Concrete Pore Solution Containing Chlorine

CHEN Xiaohua¹, ZHAO Fangchao², ZHOU Kun², SHI Xianfei¹, CUI Zhongyu¹, MAN Cheng^1,*, WU Dequan^2,*

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Abstract

The corrosion of steel reinforcement induced by chloride attack from deicing salts has long been a critical challenge compromising the safety, durability and service life of concrete infrastructure. This deterioration mechanism fundamentally originates from chloride ion penetration through concrete matrices, which disrupts the passive film on rebar surfaces and initiates the corrosion. The chloride resistance of steel reinforcement is intrinsically related to the stability of its surface passive film. To enhance passive film stability and inhibit chloride-induced corrosion, corrosion inhibitors are typically incorporated into deicing salt formulations. Sodium molybdate (Na₂MoO₄), as an inorganic inhibitor, has gained widespread application due to its cost-effectiveness, environmental friendliness and non-toxic characteristics. The work aims to systematically investigate the corrosion inhibition behavior of sodium molybdate on HRB400 steel in chloride-containing simulated concrete pore solutions. The experimental methodology incorporated immersion tests, electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization measurements to evaluate the inhibition efficiency of sodium molybdate and determine critical chloride concentrations for HRB400 steel in solutions with varying molybdate concentrations. Scanning vibrating electrode technique (SVET) was employed to in-situ monitor the corrosion activity evolution on steel surfaces. Post-immersion characterization techniques including X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM) were utilized to analyze the chemical composition and micromorphology evolution of passive films. Immersion tests and electrochemical measurements demonstrated that the sodium molybdate significantly inhibited the corrosion process of HRB400 steel in chloride-contaminated simulated concrete environments. The inhibition efficiency exhibited concentration-dependent enhancement, reaching 90% when the molybdate concentration attained 1.6 mmol/L. The adsorption behavior was calculated based on the electrochemical results, where the adsorption of the sodium molybdate on the iron substrate surface adhered to the Langmuir isothermal adsorption model, and the calculated adsorption equilibrium constant (K_ads) for SM reached 5 966.59, a significantly high value, indicating that SM exhibited outstanding corrosion inhibition efficacy. SVET monitoring revealed that the addition of molybdate effectively promoted passive film formation and improved chloride resistance, leading to substantial suppression of corrosion activity. XPS analysis indicated that molybdate ions adsorbed onto steel surfaces, inducing a notable increase in Fe³⁺/Fe²⁺ atomic ratio within passive films from 4.53 to 7.114, which was about 70% enhancement. AFM characterization demonstrated that molybdate-modified passive films exhibited reduced surface roughness (Ra/R_p decreased from 4.27 nm/3.53 to 20.3 nm/16.3) and enhanced compactness compared to chloride-only systems, with the nanostructured oxide particles showing more homogeneous distribution. It is concluded that the sodium molybdate demonstrates effective corrosion inhibition for HRB400 steel in chloride-containing concrete environments through multiple mechanisms. As an anodic-type inhibitor, it preferentially adsorbs at active sites on steel surfaces, forming protective complexes that hinder chloride adsorption and charge transfer processes. Molybdate incorporation facilitates the transformation of less protective iron oxides (Fe₂O₃/Fe₃O₄) into more stable FeOOH phases, enhancing passive film stability. The optimized inhibitor concentration of 1.6 mol/L achieves 90% efficiency by balancing competitive adsorption between MoO₄^2- and Cl^- ions. Microstructural densification of passive films through molybdate-induced crystallization refinement creates effective diffusion barriers against chloride penetration. These findings provide fundamental insights for developing molybdate-based corrosion mitigation strategies in chloride-exposed concrete structures. This comprehensive investigation establishes quantitative relationships between molybdate concentration, passive film characteristics, and corrosion resistance, offering practical guidance for optimizing inhibitor dosages in concrete durability applications.

Key words

HRB400 steel / simulated concrete pore fluid / passive film / sodium molybdate / critical chloride ion concentration / electrochemical

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CHEN Xiaohua, ZHAO Fangchao, ZHOU Kun, SHI Xianfei, CUI Zhongyu, MAN Cheng, WU Dequan. Inhibition Behavior of Low Alloy Steel by Sodium Molybdate in Simulated Concrete Pore Solution Containing Chlorine[J]. Surface Technology. 2025, 54(12): 37-48 https://doi.org/10.16490/j.cnki.issn.1001-3660.2025.12.003

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Funding

National Key Research and Development Program of China (2023YFB3710300); National Natural Science Foundation of China (U2106216); "Youth Innovation Team" Program of Shandong Provincial Colleges and Universities (2022KJ055); Chongqing Postdoctoral Research Foundation (cstc2021jcyj-bshX0039)