A SPECIFIC ASPECT OF IMPEDANCE MEASUREMENTS IN LOW CONDUCTIVITY MEDIA - ARTIFACTS AND THEIR INTERPRETATIONS

Impedance measurements in the high frequency range beyond the electrolyte resistance, Re, currently exhibit one or several loops irrelevant to the electrode process. For low conductivity media encountered in spreading corrosion studies these relaxations appear in a lower frequency range (10-100 Hz) and can overlap the faradaic frequency range, thus leading to possible misinterpretation of the data. This aspect was investigated in concentrated acetic acid solutions using two different kinds of reference electrode. Solution resistivity as well as nature of the reference electrode and the distance between working electrode surface and reference extremity were extensively investigated. The parasitic contributions of the different elements of the experimental setup on the measured impedance was modelled by a unique electrical circuit which reproduces with an excellent precision the experimental data. This allowed us to underline the various contributions of the electrical couplings occurring in the electrochemical cell, especially between the reference electrode and the other elements. © 1990.