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Current interruption, potential pulse methods, and the AC impedance technique are well accepted means of measuring the ohmic potential drop to an electrode for ohmic resistance compensation. An interpretation of the measured quantities is given, and the relationship between the measured and true parameters is established. Theoretical calculations indicate that a significant discrepancy may exist between the measured and the true corrosion rate, although the data are corrected for the ohmic resistance in the solution by conventional means. The cause of the error is a nonuniform ohmic potential drop to the electrode surface, and its magnitude is determined by geometry, position of the reference electrode, solution conductivity, and corrosion rate. Such errors in practice are specific to low-conductivity media and occluded cells with gaps or crevices. The magnitude of expected error is calculated for a few typical geometries. Possible ways of correcting the error are discussed. These include probe design, measurement technique, and methods of data analysis.
current distribution, nonuniform ohmic drop, polarization resistance, disk electrode, crevice corrosion, current interruption, AC impedance, corrosion monitoring, probe design
Professor, Laboratories of Industrial Electrochemistry, Norwegian Institute of Technology, Trondheim,