基于电化学噪声研究模拟海洋大气环境下304不锈钢的点蚀行为

基于电化学噪声技术建立了不锈钢海洋大气点蚀监测系统,利用该系统对处于干湿循环环境下不锈钢的点蚀行为进行监测.使用时域谱图、时域统计、频域谱图和散粒噪声理论等分析方法对采集到的电化学噪声数据进行处理分析,并结合动电位极化法,形貌分析法共同研究不锈钢的点蚀行为.研究结果表明,304不锈钢在模拟海洋大气环境下的点蚀行为分为钝化、亚稳态点蚀和稳态点蚀三个阶段.在钝化阶段,电位电流噪声信号出现少量的同步异向波动,腐蚀事件发生频率高,平均电量低;在亚稳态点蚀阶段,电位电流噪声信号出现大量的同步同向波动,腐蚀事件发生频率降低,平均电量上升,通过扫描电镜观察蚀点;在稳态点蚀阶段,电位电流噪声信号不仅存在大量的同步同向波动,还出现了同步异向波动,腐蚀事件发生频率较低,平均电量大幅度上升,通过扫描电镜观察到电极表面出现小而浅的蚀点.而动电位极化法可以证实304不锈钢点蚀的发生.两种分析方法所得结果具有较好的一致性,证明该监测系统很好地实现了对模拟海洋大气环境下304不锈钢点蚀行为的连续监测,并能判断点蚀的发生.

Pitting Behavior of Stainless Steel in Simulated Marine Atmosphere Based on Electrochemical Noise

A measurement system for detecting the atmospheric corrosion of stainless steels was built based on electrochemical noise technology. The electrochemical noise data have been collected for 304 stainless steels which were exposed to the simulated marine atmospheric environment. The pitting behaviors of 304 stainless steels were studied by analyzing the electrochemical noise results with the time domain spectrogram, statistic, frequency domain spectrogram and shot noise theory. Meanwhile, potentiodynamic polarization and morphological analysis were also used as assistant measurements. It has shown that the 304 stainless steel in the whole wet-dry cycle could be divided into three stages, including passivation stage, metastable pitting stage and stable pitting stage. During the passivation stage, the electrochemical current noise and electrochemical potential noise exhibited minor synchronous-perikinetie fluctuations. The corrosion events occurred at high frequencies with the low average electric quantity. During the metastable pitting stage, the electrochemical current noise and electrochemical potential noise increased exponentially and at the same time decayed abruptly, and the frequencies for corrosion events decreased with the increased average electric quantity. However, no pitting spots were observed from the SEM micrographs. During the stable pitting stage, the electrochemical current noise remained an exponential increase and abrupt decay, corresponding to the pulse in electrochemical potential noise which is characterized by an exponential decay following by an abrupt recovery. Meanwhile, the lifetimes of fluctuations in electrochemical current noise and electrochemical potential noise were longer. The frequencies for corrosion events became lowered with the significant rise of average electric quantity. In addition, some small and flat pitting spots could be found from the SEM micrographs. The potentiodynamic polarization technique can be applied to verify the nucleation of stable pitting. The pitting potential decreased sharply when the stable pitting was formed at the 304 stainless steel surface. The results obtained by the two methods were consistent with each others, proving that the measuring system can continuously monitor the pitting behaviors of 304 stainless steels in the simulated marine environments, and judges the occurrence of stable pitting.