1993 年 42 巻 479 号 p. 930-933
Corrosion potential fluctuation was analyzed to investigate the stress corrosion cracking of SUS304 stainless steel immersed in 42 mass% MgCl2 solution. A potential difference between the specimen and the Ag/AgCl reference electrode was measured with a precise digital voltmeter at a sampling frequency of 2.56Hz. Elongation of the specimen was measured with a differential transformer at 10s interval, for the computation of elongation rate.
From an electrochemical point of view, the measured corrosion potential was divided into a component of the signal shifted to a more noble potential (Signal of Repassivation) and the one shifted to a less noble potential (Signal of Film Breakdown). These two types of signals were extracted from the sampling data by use of the differential coefficient at each data point. To avoid an errorr in the FFT calculation, the extracted signal was extended symmetrically. Then, a power spectra density (PSD) was calculated by FFT algorithm for each type of signal.
The difference in PSD level between two types of signal showed a good correlation with the elongation rate of the specimen. During the time when the elongation rate increased, the value of PSD for the signal of film breakdown became bigger than that of repassivation in the frequency range 10-100 mHz. Conversely, the PSD level for signal of repassivation exceeded that of film breakdown, when the elongation rate decreased or kept a constant value, in the same frequency range.