A Corrosion Monitor Based on Impedance Method

    Published: Jan 1981

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    Theoretical and experimental studies were performed on the impedance characteristics of corroding metal with the aid of a new a-c corrosion monitor. According to the theory of impedance of a mixed potential electrode, the subtraction of the impedance at a high frequency from that at a low frequency yields, in most cases, transfer resistance that is readily reduced to the corrosion rate of the electrode (if an appropriate selection of the two frequencies has been made). By using a superimposed signal of two a-c voltages of 10 kHz and 0.01 Hz, the a-c corrosion monitor was designed to yield either transfer resistance or corrosion current on a recorder in logarithmic scale. The monitor permitted the measurement of the corrosion rate in less-conductive environments, such as tap water, distilled water, and soil. Initiation of localized corrosion was also detected in most cases by a sharp increase in corrosion current. The corrosion currents obtained with the a-c corrosion monitor and by the weight-loss measurement gave a good correlation on various metals under various environments, which cover corrosion rates of 15 to 0.0007 mm/year.


    electrochemistry, corrosion, corrosion monitor, interfacial impedance, impedance diagram, local corrosion, pitting

    Author Information:

    Haruyama, S
    Tokyo Institute of Technology, Faculty of Engineering, Tokyo,

    Tsuru, T
    Tokyo Institute of Technology, Faculty of Engineering, Tokyo,

    Committee/Subcommittee: G01.11

    DOI: 10.1520/STP28032S

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