金属/土壤界面液膜分布及其与局部腐蚀相关性研究

Soil corrosion of metal material is an urgent problem of underground engineering. The pore structure with air and thin electrolyte film is formed at metal/soil interface, and all environment factors influencing electrochemical corrosion function through the thin electrolyte film at metal/soil interface. Soil granularity and water content can result in the change of distribution characteristic of the thin electrolyte film. When the thickness and the distribution of the thin electrolyte film become uneven, the oxygen concentration cell will give rise to the occurrence and development of the local corrosion. Therefore, it has the very important scientific value to investigate the distribution characteristic of the thin electrolyte film and its correlation with local corrosion. This project intends to use the thin electrolyte film (TEF) technology to acquire the relation curves between electrolyte film thickness on surface of carbon steel or copper plate electrode and electrochemical parameters of oxygen reduction reaction (ORR). The location changes of cathodic and anodic reaction corresponding to the induction and growth period of local corrosion are investigated using wire beam electrode (WBE) technology accompanying with the appearance and component analyses of corrosion products. Finally the thickness and distribution of thin electrolyte film at metal/soil interface are obtained, and then the influence on electrochemical reaction process of soil corrosion, the correlation and the action laws of the electrolyte film distribution with local corrosion can be got by combining the TEF with WBE technology. These can provide the theoretical basis for the fast evaluation for a tendency to local corrosion and the effect on cathodic protection from local corrosion by testing the electrolyte film distribution.

金属材料的土壤腐蚀是地下工程建设急需解决的难题。金属与土壤接触界面上有大量由空气和液膜构成的孔隙，影响电化学腐蚀过程的各种环境因素都要通过界面液膜起作用，土壤粒度和含水量的变化会导致液膜分布特征改变。当金属表面液膜厚度和分布不均匀时，氧浓差电池将引起金属局部腐蚀的发生和发展。因此，研究液膜分布及其与局部腐蚀的相关性具有非常重要的科学价值。本项目拟利用薄液膜（TEF）技术，研究液膜厚度与氧阴极还原反应（ORR）过程电化学参数之间的关系；采用丝束电极（WBE）技术辅以腐蚀形貌和产物成分表征，探索局部腐蚀诱导期和发展期对应的阴、阳极反应区的位置变化；结合两种技术获取金属/土壤界面的液膜厚度和分布，研究液膜分布对土壤腐蚀电化学反应过程的影响、与土壤局部腐蚀的相关性及其作用规律，为建立利用液膜分布测量来快速评价土壤局部腐蚀倾向性和局部腐蚀阴极保护效果的分析方法提供理论依据。

研究金属在土壤这一气/液/固多相、多界面复杂体系中的腐蚀问题意义重大。液膜不均匀分布易引发局部腐蚀,研究金属/土壤界面内液膜分布的影响十分必要。首先，本项目利用丝束电极（WBE）技术结合薄液膜厚度测试和控制技术研究了大气液膜厚度对金属腐蚀速度的影响和腐蚀倾向性。结果表明，减小液膜厚度使电偶电流增大和腐蚀速度加快，当厚度减为约40微米时，电偶电流最大和腐蚀速度最快。此外，针对金属在土壤中的腐蚀过程，本项目采用传统电化学方法研究了整体腐蚀特征，又用丝束电极连续监测了腐蚀诱导期和发展期金属/土壤界面处的电偶电流、局部电位、腐蚀形态变化等。结果表明湿度增加，金属表面液膜整体变厚且分布均匀，阳极反应速率增加，易于发生均匀腐蚀；而土壤粒度更易影响到孔隙结构和液膜分布的变化，粒度增加其不均匀程度增加，微区阳极电流明显较大，易于诱发局部腐蚀。因此，丝束电极技术可以准确、快速地反映出孔隙结构及气/液分布的变化，进行薄液膜下的腐蚀特征及速率预测。最后，本项目开展了一些旨在对埋地管线进行腐蚀防控的研究，发明了一种长寿命、低成本的金属氧化物涂层电极，并在环氧树脂涂料中添加纳米钛黑进行改性使其力学性能和防腐性能大为改善。