钢铁表面氧化锆转化膜的电化学性能及成膜机理

Electrochemical Performance and Formation Mechanism of Zirconia Conversion Coatings on Iron and Steel

为发展环境友好型表面膜技术,采用浸渍法在45钢表面制备了具有一定耐蚀性能的氧化锆转化膜。用极化曲线研究了转化液主剂Zr4+浓度和pH值对膜层耐蚀性能的影响,并优化了成膜条件;采用电位-时间曲线研究了NO3-浓度对成膜过程的影响;采用扫描电镜(SEM)、能谱、开路电位和电化学阻抗谱(EIS)研究了转化膜的形貌、化学成分、成膜过程电位特性以及成膜过程不同阶段的阻抗谱特性;初步探讨了钢铁表面氧化锆转化膜的成膜机理。结果表明:35℃成膜5 min,最优的Zr4+浓度及pH值分别为0.16 g/L和4;NO3-浓度对成膜过程的影响有限;转化膜主要由Zr,Fe,O组成,为纳米颗粒组成的无定形膜;成膜过程类似于碱性阴极成膜,可以分为基体酸蚀活化、膜快速生长、膜减速生长、膜动态稳定以及膜溶解5个阶段;成膜时间在300 s左右,锆系转化膜耐蚀性较优。

Zirconia conversion coatings with the corrosion resistance were prepared on 45 steel by immersion process.Polarization curves were measured to investigate the effects of Zr4+ concentration and pH value of the conversion fluid on the corrosion resis-tance of the conversion coatings.Potential-time curves were mea-sured,and the effect of NO-3 concentration on the formation of the conversion coatings was explored.The morphology and elemental composition of the conversion coatings were analyzed by means of scanning electron microscopy and energy dispersive X-ray spectrometry.Moreover,open circuit potential and electrochemical impedance spectra were measured to investigate the formation process of the conversion coatings.It was found that the optimized Zr4+ concentration was 0.16 g/L,and the pH value was 4.As-prepared conversion coatings were amorphous and composed of Zr,Fe and O elements.The concentration of NO-3 only had slight effect on the formation of the conversion coatings.Moreover,the formation of the conversion coatings was similar to the local alkalization at cathode and could be divided into five stages,including activation of the substrate by acid etching as well as rapid growth,slow growth,dynamic stability and dissolution of the conversion coatings.The conversion coatings had the best corrosion resistance when the conversion time was 300 s.