STP1188

    Specific Aspects of Impedance Measurements in Low Conductivity Media

    Published: Jan 1993


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    Abstract

    Impedance measurements in the high frequency range, namely f > 1 kHz, often exhibit one or several loops irrelevant to the electrode process. For low conductivity media, encountered in corrosion studies such as in natural waters or in organic solvents, these relaxations also appear at a lower frequency range. This may lead to a possible misinterpretation of data by mistaking them for faradaic relaxation phenomena. The influences of the solution resistivity, the position of the Luggin capillary tip, and the nature of reference electrode were extensively studied. The corrosion of austenitic stainless steel in acetic acid was used as a model system. The conductivity of acid was changed by varying the water content. The reference electrode was either Ag/AgCl or the tip of a platinum wire embedded in a glass capillary. The results allowed us to propose an equivalent electrical circuit. The circuit is described as a capacity divider bridge (due to the stray capacitances between reference/working and reference/counter electrodes) and by the electrolyte resistance inside the capillary tip. The numerical simulations fit the experimental data well.

    Keywords:

    electrode impedance, acetic acid, low conductivity media, electrolyte resistance, potential distribution, Luggin capillary, equivalent electrical circuit


    Author Information:

    Chechirlian, S
    Research engineer, Centre de Recherche, Rhône Poulenc, Décines,

    Keddam, M
    Directeur de recherche, CNRS, Physique des Liquides et Électrochimie, Laboratorie de l'Université P&M Curie, Paris,

    Takenouti, H
    Directeur de recherche, CNRS, Physique des Liquides et Électrochimie, Laboratorie de l'Université P&M Curie, Paris,


    Paper ID: STP18061S

    Committee/Subcommittee: G01.11

    DOI: 10.1520/STP18061S


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