磁场对铁局部腐蚀自催化过程的影响

The effects of magnetic field on auto-catalysis processes involved in typical localized corrosion systems for iron in aqueous solutions will be investigated, aiming at elucidating the effects of magnetic field on element reactions and their coupling systems in localized corrosion growth stage. The effects of magnetic field on typical pitting corrosion and crevice corrosion systems for iron in natural and industrial environments are emphasized. Anodic and cathodic reactions on the bulk and the corrosion cavity surfaces and their coupling systems in auto-catalysis processes in the presence or absence of magnetic field will be measured. Based on the selective effects of magnetic fields on reactions under various types of rate-determining steps, the contribution of interface reactions and rate-determining steps in auto-catalysis process on anodic dissolution will be clarified. The effects of magnetic field on electron transfer and mass transport steps and the resulted change of localized corrosion growth are studied. A new localized corrosion mitigation approach based on improving the penetrating efficiency of inhibitors under magnetic field gradient force will be explored. For getting deterministic results of magnetic field on localized corrosion growth stage, electrochemical measurements, immersion tests, simulating pitting corrosion and crevice corrosion tests, and simulated occluded cells as well as the monitoring of local electrochemical states and solution compositions are designed to exhibit the key features of auto-catalysis process. The research outcome will be used as the theoretical basis for the evaluation of service performance of steel structures under magnetic fields. It is also expected that the results will serve for the development of a new approach for mitigating localized corrosion and the new clues for the fundamental mechanisms of localized corrosion.

研究磁场对铁典型局部腐蚀体系自催化过程的影响，阐明磁场影响局部腐蚀发展基元过程及其耦合体系的科学规律。以铁在自然和工业环境中点腐蚀及缝隙腐蚀为重点，研究磁场对自催化过程中本体、局部环境中阴极与阳极反应的影响，以及对局部腐蚀内、外部反应耦合场的作用。利用磁场对不同类型速率控制步骤的选择性作用，明确自催化过程中界面反应类型与速率控制过程对局部阳极溶解的影响机制，分析磁场作用下局部和宏观体系电子转移与物质传输步骤对局部腐蚀发展的影响，探索利用磁场梯度力效应调控缓蚀剂穿透效率以抑制局部腐蚀的新途径。研究中将采用有、无磁场下的电化学测试、模拟点腐蚀和模拟缝隙腐蚀试验以及局部闭塞电池，配合局部电化学状态与溶液组成监测技术，强化自催化阶段的影响以得到磁场作用的确定性结果。研究结果将为磁场作用下钢铁材料的服役性能评价提供理论依据，为发展应用磁场调控局部腐蚀提供参考，并为解析局部腐蚀机理提供基础信息。

在电磁设备、输电线路和电气化铁路等设施附近的金属构件受到感应磁场和腐蚀环境的共同作用，需明确磁场对局部腐蚀的影响。本工作研究恒稳磁场对金属局部腐蚀基本过程-自催化过程的作用规律，分析阳极反应类型、点蚀形貌以及速率控制步骤与磁场耦合作用的结果。研究了磁场对铁在含氧化剂（钝化剂）或缓蚀剂的氯化钠溶液以及含氯离子的酸性、中性、弱碱性、碱性溶液中阳极反应和局部腐蚀形貌的影响。发现铁电极表面感应磁场的不均匀分布会导致溶解局部加速或减缓，不均匀电极表面会阻碍活化-钝化转变过程。铁电极水平朝上放置时磁场对阳极过程影响最大，竖直放置时其次，水平朝下放置时影响最小。铁在含亚硝酸根或者钼酸根离子中性氯化钠溶液中：磁场降低稳态钝化电流而使钝化膜更稳定，如果电极整体处于钝态只是局部区域出现点蚀，电流主要来自于点蚀处，点蚀坑内部环境相对闭塞自催化效应显著时，磁场会通过加速点蚀坑内外的传质过程，阻碍自催化效应，抑制点蚀发展；而当电极表面点蚀数目多、且连片，且点蚀坑敞开性强有利于蚀坑内外传质过程时，磁场增大电流密度而加速点蚀发展；在点蚀电位区极化时间延长使自催化效应增强时，磁场干扰自催化作用而阻碍点蚀发展的作用更显著。磁场增大车轴钢在含氯离子弱碱性碳酸氢钠溶液中动电位扫描极化曲线中预钝化区的电流密度，但降低其过钝化电位区恒电位极化下时的电流密度；在极化曲线钝化区中恒电位极化时会出现点蚀，且磁场使初始电流密度增大并增加点蚀数目。磁场减小铁在含氯离子碱性碳酸钠溶液中阳极极化曲线中钝化区的电流密度，增大慢速扫描极化曲线中过钝化区的电流密度，而减小快速扫描时过钝化区的电流密度。通过分析磁场对发生点蚀金属的本体表面的宏观磁电化学交互作用作用，与对蚀坑底部微观磁电化学交互作用之间的耦合作用在理论上说明了磁场对点蚀的影响机理。