交流电对X70钢表面形态及电化学行为的影响

EFFECTS OF ALTERNATING CURRENT ON X70 STEEL MORPHOLOGY AND ELECTROCHEMICAL BEHAVIOR

采用动电位极化曲线、电化学阻抗谱(EIS)、浸泡实验等方法研究了交流电流密度(0—100 A/m^2)对X70钢电化学行为的影响,采用OM和SEM观测了X70钢交流腐蚀产物及蚀坑形貌,探讨了交流电诱发金属腐蚀的机理.结果表明,在交流电影响下,X70钢的腐蚀电位向负向偏移,偏移量和腐蚀速率随着交流电流密度的增大而增大.低电流密度下,X70钢的EIS特征为容抗弧,没有出现明显的感抗特征及扩散特征,在低电流密度下X70钢表面发生了均匀腐蚀.当交流电流密度增大时,EIS低频区出现Warburg阻抗特征,表明试佯表面的腐蚀过程由扩散控制,局部腐蚀特征明显.交流电对金属极化作用产生重要影响,交流电正,负半周期内的极化效果不对称诱发了金属腐蚀.

Alternating current （AC） corrosion is a significant problem to metal structures in close proximity to alternating current carrying conductors. While for direct current （DC） interference there is large agreement on protection criteria to be used for corrosion mitigation, but the mechanism and relationship between AC density and corrosion rate are still not clear, although some studies have been carried out for many years. In this work, electrochemical methods, including open curves, polarization curves and electrochemical impedance spectra （EIS） on X70 steel samples, were performed in soil-simulating conditions at various AC current behavior and mechanism were discussed based on densities from 0 to about 100 A/m2. The corrosion the electrochemical, XRD, stereo microscope and SEM results. The simulation experiment was set up to predict the effects of AC current density on corrosion potential and corrosion rates. The results indicate that the corrosion potential and corrosion rate increases with the rise of AC current density. When the alternating current goes across the X70 steel, its surface suffers from an obvious corrosion potential accompanied with the bubble crop up. It＇s because the hydrogen and oxygen reduction reactions happened on the surface of X70 steel. There is only one capacitive reactance arc on EIS at the corrosion potential under a low current density interference. Warburg impedance appears in a higher alternating current density of the low frequency area. It shows that the corrosion process of surface is controlled by diffusion. The amount of AC corrosion can be generally expressed as a percentage of the amount of DC corrosion with the equivalent corrosive effect. Alternating current causes less than 1% of the corrosion caused by the equivalent direct current. The X70 steel is corroded uniformly in the early AC interference, but corrosion pits appear gradually on the surface of X70 steel with the extension of＇ time. Especially in the high current density interference, the pitting is more likely to occur. Furthermore. tile higher current density increases pitting tendentiousness and depth. Alternating current has a major impact on metal polarization, and tile asymmetry of positive and negative half cycle induces corrosion at alternating current interference. Alternating current could generate an ＂oscillating＂ effect in the metal/medium interface.