目的 以纯铁和12Cr铁素体/马氏体（F/M）钢为研究对象,针对液态铅铋共晶（LBE）环境中常用的腐蚀后表征方法难以连续反映其氧化膜动态演化的问题,探讨电化学阻抗谱（EIS）在LBE环境下氧化膜生长行为及保护性能表征中的应用可行性。方法 本研究采用EIS结合扫描电镜（SEM）和能谱分析（EDS）的方法,系统研究了200 ℃ LBE中氧化膜的结构特征与保护性能,并将EIS参数估算结果与SEM实测膜厚进行对比分析。结果 结果表明：在LBE中浸泡的8 d内,纯铁的Nyquist图容抗弧半径和低频阻抗模值随时间逐渐增大,膜电阻持续升高、等效电容逐渐减小,说明表面氧化膜不断增厚并趋于致密稳定;浸泡8 d后,纯铁表面形成以FeO和Fe3O4为主的氧化膜,SEM测得平均厚度为58.92 μm,基于EIS参数估算的膜厚为84.90~119.60 μm。而F/M钢的24 h预氧化样品因氧化膜生长不充分、连续性较差,表现出明显的短路特征;48 h预氧化样品容抗弧半径最大、膜电阻最高,氧化膜平均厚度约为6.03 μm,保护性能最佳;72 h预氧化样品阻抗仍较高,但膜层增厚至21.66 μm且局部疏松和开裂,保护效果较48 h预氧化样品略有下降。结论 EIS计算得到的氧化膜厚度与SEM截面观察结果在趋势上具有较好的对应关系,说明基于电化学参数的阻抗分析能够为评估LBE环境下氧化膜的演化过程提供参考。
Abstract
This study evaluates the applicability of electrochemical impedance spectroscopy (EIS) for characterizing the growth behavior and protective performance of oxide films formed on pure iron and 12Cr ferritic/martensitic (F/M) steel in liquid lead-bismuth eutectic (LBE). In LBE corrosion studies, conventional post-corrosion characterization techniques, such as scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS), can provide detailed ex situ information on the morphology, thickness, and composition of oxide films after exposure. However, because these techniques require specimen removal from the corrosive medium, they cannot continuously monitor the dynamic evolution of oxide films during exposure. Therefore, in this work, EIS was used to evaluate the oxide-film behavior in LBE at 200 ℃, while SEM and EDS were employed as complementary ex situ methods to characterize the film structure and composition after exposure, so as to discuss the feasibility of applying electrochemical impedance spectroscopy (EIS) to characterize the growth behavior and protective performance of oxide films in the LBE environment.
The results showed that, during immersion in LBE for up to 8 days, the radius of the capacitive arc in the Nyquist plots of pure iron gradually increased with exposure time. Meanwhile, the impedance modulus in the low-frequency region also increased continuously. The fitting results further indicated a sustained increase in film resistance and a gradual decrease in equivalent capacitance. These changes suggested that the oxide film formed on the surface of pure iron continuously thickened during immersion and gradually became denser and more stable. After 8 days of exposure, an oxide layer mainly composed of FeO and Fe3O4 was formed on the surface of pure iron. The average oxide-film thickness measured by SEM was 58.92 μm, while the thickness estimated from EIS parameters ranged from 84.90 to 119.60 μm. Although the EIS-estimated values were higher than the SEM-measured value, the two results remained within the same order of magnitude, indicating that EIS could reasonably reflect the relative change in oxide-film thickness.
For 12Cr F/M steel, the pre-oxidation duration had a significant influence on the integrity and protective performance of the oxide film in LBE. The specimen pre-oxidized for 24 h exhibited obvious short-circuit characteristics, which could be attributed to insufficient oxide-film growth and poor continuity of the surface film. As a result, the film failed to provide effective barrier protection against the LBE environment. In contrast, the specimen pre-oxidized for 48 h showed the largest capacitive arc radius and the highest film resistance among the tested F/M steel specimens, indicating the best protective performance. SEM observations showed that the average oxide-film thickness of this specimen was approximately 6.03 μm, suggesting that a relatively thin but compact and continuous oxide film could offer effective protection. For the specimen pre-oxidized for 72 h, the impedance remained relatively high; however, the oxide layer thickened to about 21.66 μm and exhibited local looseness and cracking. These defects weakened the barrier effect of the film, leading to a slight decrease in protective performance compared with the 48 h pre-oxidized specimen.
In conclusion, the oxide film thickness estimated from EIS shows good agreement with the SEM cross-sectional observations in terms of the overall trend, indicating that impedance analysis based on electrochemical parameters can provide a useful reference for evaluating oxide film evolution in an LBE environment.
关键词
铅铋共晶 /
电化学阻抗谱 /
纯铁 /
F/M钢 /
氧化膜 /
厚度
Key words
lead-bismuth eutectic /
electrochemical impedance spectroscopy /
pure iron /
ferritic/martensitic steel /
oxide film /
thickness
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基金
国家重点研发计划（2022YFB1902502）; 国家自然科学基金企业创新联合基金（U22B2064）; 国家自然科学基金（52201097,52401132）; 广东省基础与应用基础研究基金（2024A1515011362,2025A1515012093）
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