A measurement system based on electrochemical frequency modulation technique for monitoring the early corrosion of mild steel in seawater

The electrochemical frequency modulation (EFM) technique, featuring of obtaining the Tafel constants directly, small polarization and short measuring time, offers a novel way for electrochemical corrosion monitoring. According to current research, the EFM approach should be mostly limited to those corrosion systems with fairly high corrosion rate, such as mild steel or iron in acidic environment. In this paper, a system for EFM measurement was set up with a potentiostat, a laptop, a NI DAQ card and applications developed with LabVIEW 7.0. It was then applied to the mild steel/seawater system. The early corrosion rate for mild steel in Zhoushan seawater was determined in laboratory with EFM technique and another two general electrochemical techniques as well-analysis of the polarization curve in the vicinity of the corrosion potential and electrochemical impedance spectroscopy. The EFM measurements were performed with 0.02 and 0.05 Hz potential perturbation frequencies, and the EFM data were analyzed with activation-controlled equation. It was shown that the corrosion rates determined with EFM technique were higher than the real values, especially at longer exposed times when diffusion-controlled effect became obvious. But they were still at the same order of magnitude as those obtained with polarization curve analysis or weight loss method.