氯离子浓度对Ni-P合金涂层失效过程影响的SECM实验和COMSOL模拟研究

The Effect of Chloride Ion on Corrosion Behavior of Ni-P Alloy Coating Using SECM Experiment and COMSOL Simulation

目的发展具有空间分辨的腐蚀电化学研究方法。方法用电沉积方法在铜基体上制备Ni和Ni-P涂层,应用扫描电镜和XRD检测涂层表面形貌和晶体结构,采用扫描电化学显微镜(SECM)研究Ni和Ni-P涂层在不同浓度Na Cl溶液中的失效行为,并结合COMSOL多物理场软件建立二维和三维模型,模拟量化活性点大小和反馈机制。结果低浓度Cl-对于纯Ni涂层具有活化作用,增加Cl-浓度会促进腐蚀发生。Ni-P合金涂层在低浓度Na Cl溶液中,短时间内保持良好的稳定性,浸泡6 h后,低P合金涂层出现典型的活性点和腐蚀产物,而高P合金涂层在浸泡24 h后出现腐蚀产物和活性区域。0.1 mol/L的Na Cl溶液促进低P合金涂层局部腐蚀的发生,而涂层在0.3 mol/L Na Cl溶液中则以发生均匀腐蚀为主。逼近曲线及其模拟结果表明,腐蚀产物对于Fc Me OH的电化学过程完全失活,而新鲜Cu表面对Fc Me OH氧化还原过程受扩散控制。三维模拟结果显示,低P合金涂层失效过程中活性点大小接近10μm。结论 Ni和Ni-P合金涂层的失效过程中活性点的形成、腐蚀产物的生成和累积过程与SECM面扫描图谱中正负反馈效应相关,Cl-促进腐蚀发生,其浓度影响腐蚀类型。COMSOL多物理场模拟明确反馈效应与探针和基底的距离有关,Ni-P涂层失效活性点大小在微米级。

Objective To develop corrosion electrochemistry method with spatial resolution. Methods Pure Ni and Ni-P alloy coatings on copper substrates were fabricated by electrodeposition. Scanning Electron Microscopy （SEM） and XRD wereapplied to check surface morphology and crystal structure of the alloy coatings. Scanning Electrochemical Microscopy （SECM） research was applied to monitor the failure behavior of typical Ni and Ni-P coating in different concentration of NaC1 solution. Combined with COMSOL Multiphysics simulation, 2D and 3D models were built to quantify activity point size and feedback mechanism. Results The low concentration of chloride ion had the activation effect for pure Ni coating, while higher chloride ion concentration promoted corrosion occurrence. Ni-P alloy coating maintained good stability in a short immersion time in low concentration of chloride in the solution. After 6 hours soaking, there were typical active points and corrosion products for low P alloy coating, while after 24 hours soaking for high P alloy coating. The corrosion type for low P alloy coating in 0.1 mol/L NaC1 solution was localized corrosion and uniform corrosion in 0.3 mol/L NaC1 solution. The simulation results of approaching curve showed that the electrochemical process of corrosion products for FcMeOH was completely inert and fresh Cu surface was electrochemical activity. 3D simulation results showed that active points of Ni-P coating failure process were close to 10 micron. Conclusion The failure process including the formation of active points, the generation and accumulation of corrosion production of Ni and Ni-P coating in NaC1 solution is dependent on the positive and/or negative feedback effect of SECM map- ping. Chloride ion promotes occurrence of corrosion process, and its concentration has a strong effect on the corrosion type for Ni-P coating. COMSOL multiphysics simulation results indicate that the feedback effect is strongly dependent on the distance between the tip and the substrate, and the size of active point for Ni-P coating is micron level.