ABSTRACT

Round-robin (RR) tests on electrochemical noise (EN) measurements with dummy cells have been performed in the European Cooperative Group on Corrosion Monitoring of Nuclear Materials since 2006. Dummy cells are composed of three resistors of equal value connected in a ‘star’ arrangement and employed in the conventional three electrode EN measurement setup using a zero-resistance ammeter. The use of dummy cells has the advantage of measuring voltage and current noise signals of reproducible amplitude contrary to corroding systems. The arrangement provides a well-defined source impedance and noise level, thereby allowing the testing of the noise level and sensitivity of the measuring instrument, which is a potentiostat in most cases. Although the resistors used in the dummy cell generate thermal noise of very low level, as low as for passive electrodes, it is not expected that all instruments will be able to measure this noise. From the results of the three RR tests performed between 2014 and 2017 that are presented, it may be concluded that small improvements could be observed compared to the very first RR campaigns, but that still only few commercially available instruments are able to perform fully valid electrochemical noise measurements and that better guidance to the users of such instruments is needed.

INTRODUCTION

Electrochemical noise (EN) has been widely used since the first paper by Iverson1 to study corrosion processes2-4 and since that time EN is claimed to be a promising technique to detect localized corrosion. However, while random signals can be correctly measured with spectrum analyzers since the eighties, the use of personal computers with data acquisition cards or digital voltmeters since the nineties often led to improper noise measurements due to aliasing occurring during the analog-to-digital conversion.5 This problem is currently ignored in many commercial general-purpose potentiostats and an overview of the EN literature shows that aliasing is almost never addressed in the experimental procedures.

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