Electrochemical Noise Measurements Part III: Determination of the noise resistance Rn – Corrosion – Application Note 39-3

Abstract

Noise measurements consist of recording the voltage and current fluctuations occurring when two electrodes of the same material (or not) are shorted. These measurements can lead to the determination of corrosion parameters. The fluctuations are of very small amplitude and this is why the choice of the instrument used in this purpose is critical. Efforts have been made by the American Society for Testing and Materials (ASTM) to give a procedure to characterize the measurement ability of the instrument. This second procedure involves a real electrochemical system namely a steel sample in acidic medium. A comparison of the noise resistance obtained using Bio-Logic instruments and by the authors lead to conclude that BioLogic instruments are suitable for noise measurements.

Introduction

The objectives of the first and second parts of this note was to show that Bio-Logic instruments are able to perform reliable noise measurements, compared to ASTM requirements. This third part aims at comparing for a system its noise resistance Rn and its polarization resistance Rp, and using this example to describe the EC-Lab noise analysis tool. There are several ways to analyze noise data, which are discussed in a review paper written by Cottis [1]. As seen earlier, one of them is to calculate a characteristic value of the corroding system called noise resistance Rn. Rn is defined as the standard deviation of the potential divided by the standard deviation of the current:

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