Coulostatic Perturbation Measurements and the Corresponding Time-to-Frequency Transform Data Analysis for Micro-Electrochemical Study

Abstract

Traditional micro-electrochemical impedance spectroscopy measurement using a capillary cell presents problems such as high ohmic resistance, long test duration and the subsequent possible tip blocking by corrosion products. In comparison, coulostatic perturbation measurements can avoid these issues due to its unique test principle and much shorter test duration. In this work, the coulostatic perturbation tests were performed on microregions of duplex stainless steel (DSS) 2205 immersed in 3.5 wt.% NaCl solution. The micro-electrochemical parameters were estimated by linear fitting the time-domain curve (LFTC), and subsequently by fitting the frequency-domain curve (FFC) obtained through Fast Fourier Transform (FFC-FFT) for comparison. It is shown that FFC-FFT method minimizes the problem of manual error in slope and intercept evaluation during LFTC. In comparison to the traditional EIS tests, FFC-FFT method causes less perturbation to the tested system, less interference of ohmic resistance with shorter test duration, thus can obtain valid low frequency data more efficiently, which is particularly favorable in studying high polarization resistance system or unstable systems. The micro-electrochemical experimental tests of DSS 2205 show that the polarization resistance of the microregion gradually increases with the increase of austenite phase, while the double-layer capacitance shows a decreasing trend.