中性介质中碳钢腐蚀沉积膜下局部腐蚀行为

UNDERSCALES LOCALIZED CORROSION BEHAVIOR OF CARBON STEEL IN NEUTRAL SOLUTION

设计了一种能够模拟垢下局部腐蚀自催化过程的闭塞电池,并用线性极化和电化学阻抗方法研究了闭塞阳极内电化学行为的变化。研究表明:垢层将加剧微区内的酸化自催化作用,pH值降低,Cl-浓集,闭塞区内外产生明显的耦合电流,内部保持活性阳极溶解,外部受到阴极保护。闭塞微区内阳极溶解受界面电荷传递的电化学过程控制。持续的闭塞效应,使垢层下微区内阳极溶解不断进行,并随偶合时间的延长基体金属界面反应电阻有所降低,阳极反应变得更为容易。

An occluded corrosion cavity （OCC） cell which could simulate the auto-catalyzing process of localized corrosion was designed to study underscales corrosion behavior of carbon steel in neutral NaCl solution in this paper. Electrochemical impedance spectroscopy （EIS） and linear polarization curves measurements were employed to study the variation of electrochemical behavior of the occluded anode. The changes of pH value and Cl^- concentration inside the OCC were determined, and the galvanic current between the occluded anode and the bulk cathode at different area ratio （Sc/Sa） was measured. The results showed that the galvanic current produced between the occluded anode and bulk cathode keep up at a high level steadily when （Sc/Sa） is a proper value. The auto-catalyzing acidification process inside the OCC is exacerbated by corrosion products layer. The solution inside the OCC become more acidic and the CI- is centralized, the occluded anode kept up activation dissolution, while the bulk cathode outside the OCC was partly or fully protected. The active dissolution of the occluded anode is controlled by an irreversible charge transfer process at metal/oxide film interface. The occluded anode dissolution reaction was developed persistently by the occluded effect, and the reaction resistance decreased along with the short-circuited time continually.