Current and potential fluctuations of corroding systems are now currently measured in cells with two working electrodes. In many cases these fluctuations look like background noises, so that determining the corrosion process at the origin of the noise is hardly possible. In this paper, it is shown that the fluctuations of the electrolyte resistance of both working electrodes can be measured simultaneously with the current and potential fluctuations. As illustrated for UNS A92024 T351 aluminum alloy corrosion, the electrolyte resistance fluctuations provide new information on the phenomena involved in the corrosion process.
An experimental arrangement based on two working electrodes (WE) has been introduced by Eden and ~011.? for simultaneously measuring the current and potential fluctuations induced by corrosion of the electrodes, and calculating the noise resistance R, defined as the ratio of the potential and current standard deviations. This arrangement has been widely used in corrosion monitoring applications.* It was experimentally found that the noise resistance was close to the polarization resistance, thus allowing an estimation of the corrosion rate. Recently, a theoretical approach3 confirmed by experimental results4 has specified the conditions under which the noise resistance was equal to the polarization resistance.
In addition to corrosion monitoring applications, the two-WE arrangement has also a great interest for investigating fundamental aspects of corrosion, since both current and potential fluctuations are measurable. The presence of transients in the time records may allow identification of the corrosion process at the origin of the noise. However, ohmic effects which may be of importance in certain corrosion processes, are usually not detected by the current and potential fluctuations since the mean current flowing between the WEs at free potential is rather low.
In this paper, the ohmic effects are analyzed through the measurement of the electrolyte resistance fluctuations simultaneously measured with the current and potential fluctuations. The principle of the measurement scheme will be detailed and illustrated for electrodes undergoing pitting corrosion only or corrosion with hydrogen bubble evolution and exfoliation.
