ABSTRACT

From the results of the three Round-Robin tests on electrochemical noise (EN) measurements with dummy cells performed between 2014 and 2017 by the European Cooperative Group on Corrosion Monitoring of Nuclear Materials, it can be concluded that only very few commercial potentiostats are able to perform valid EN measurements. This paper is aimed at guiding users of the EN technique by providing the minimum knowledge for EN measurements, including the necessary validation of the signals measured at different sampling frequencies by calculation of their power spectral densities. Two practical works performed with a commercial potentiostat are proposed. The first one is devoted to the measurement of the thermal noise of three resistors of equal value connected in a ‘star’ arrangement and used in the conventional three electrode EN measurement setup using a zero-resistance ammeter. This allows the instrumental noise of the equipment to be determined. The second practical work concerns pitting corrosion of two identical aluminum electrodes in potassium chloride to show that the noise impedance is equal to the modulus of the impedance of the electrodes. A bias voltage is then applied between the electrodes to obtain one anode and one cathode which shows the difficulty of analyzing the measured EN in asymmetric systems.

INTRODUCTION

In order to evaluate the capabilities of commercial general-purpose potentiostats for producing reliable and valid measures of potential and current fluctuations generated by electrochemical systems, in particular corroding systems, round-robin (RR) tests have been performed by different groups.1,2 Recently, three new RR tests on electrochemical noise (EN) measurements with dummy cells have been performed by the European Cooperative Group on Corrosion Monitoring of Nuclear Materials (ECG-COMON).3 Using dummy cells, composed of three resistors of equal value connected in a ‘star’ arrangement, with a potentiostat working in a zero-resistance ammeter (ZRA) mode, gives the possibility of measuring voltage and current noise signals of reproducible amplitude, in contrast to corrosion processes that often evolve with time.

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