中性体系中MoO4^2-对碳钢垢下局部腐蚀的抑制作用

Effect of MoO_4^(2-) on underscale local corrosion of N80 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,采用极化曲线和电化学阻抗方法研究了MoO42-对N80钢在近中性NaCl溶液中闭塞区内化学及电化学状态变化的影响。结果表明,MoO24-能有效地减缓闭塞区内pH值降低及Cl-浓集、减弱酸化自催化效应、抑制垢下局部腐蚀。MoO42-的作用机制在于使水合氧化铁腐蚀膜由阴离子选择性变为阳离子选择性,H+可以从膜下扩散出去,而Cl-难以扩散到膜下富集,抑制了腐蚀反应的阴极过程;同时MoO24-迁入闭塞区后增大了电极表面膜层阻抗,抑制了腐蚀反应的阳极过程。

An occluded corrosion cavity （OCC） simulated cell was designed, and electrochemical impedance spectroscopy （EIS） and polarization curves measurement were employed to study the effect of MoO4^2- on the development of underscale local corrosion of carbon steel in neutral NaCl solution. The results suggested that MoO4^2- could abate pH decrease and Cl^- enrichment, and inhibit the auto-catalyzing acidification effect inside the OCC, so retard the development of underscale local corrosion obviously. The inhibition mechanism of MoO4^2- was that MoO4^2- transformed the hydrate ferrous oxide deposition film from anions selective to cations selective, and the cathodic process of underscale local corrosion was suppressed when it migrated into OCC. Meanwhile, the migrated MoO4^2- resulted in increasing the impedance of the film on the substrate metal and so inhibited the anodic process of the corrosion reaction inside the OCC.