氯离子对球墨铸铁管土壤腐蚀影响机理研究

基于埋片加速腐蚀试验,采用电化学阻抗谱测量和微观分析技术,研究了氯离子(Cl~-)对球墨铸铁腐蚀规律、腐蚀层结构以及腐蚀产物的影响。主要结论如下:(1)球墨铸铁主要发生局部腐蚀,且随Cl~-含量的增加,腐蚀速率增大,出现严重腐蚀坑;其腐蚀坑深与腐蚀时间成幂函数关系,当Cl~-含量高于0.515%时,局部腐蚀情况尤为严重。(2)球墨铸铁腐蚀经历点蚀诱导期、点蚀发展期和稳定腐蚀期3个阶段;在前两个阶段电荷传递为腐蚀速率控制步骤,第三个阶段转变为氧的扩散控制。(3)腐蚀产物主要为铁的氧化物和羟基氧化物;高Cl~-环境下产生的β-Fe OOH和铁的羟基氯化物均能加速球墨铸铁的电化学腐蚀。

Mechanism of the Effect of Chloride Ions on Soil Corrosion for Ductile Iron Pipes

An accelerated buried coupon test coupled with electrochemical impedance spectroscopy and microanalysis was conducted to research the effect of chloride ions (Cl-) on soil corrosion mechanism,corrosion layer structure and corrosion products.The main conclusions are as follows.(1) Localized corrosion was the main corrosion type,and the corrosion rate and pitting depth of ductile iron increased with the increasing of Cl-content;the pitting depth and corrosion time presented a power function relationship,and the local corrosion was especially serious when the Cl-content was higher than 0.515％.(2) Three stages were observed during ductile iron corrosion:pitting induction stage,pitting developmental stage,and stable corrosion stage;charge transfer was the control step in the first two stages and oxygen mass diffusion turned to be the key step in the third stage.(3) Iron oxides and iron oxyhydroxides were main crystal minerals;~FeOOH and ferrous oxychlorides appeared in high Cl-environment accelerated the electrochemical corrosion of ductile iron.