Sixteen laboratories have performed electrochemical noise (EN) measurements based on two systems. The first uses a series of dummy cells consisting of a "star" arrangement of resistors in order to validate the EN measurement equipment and determine its baseline noise performance, while the second system, based on a previous round-robin in the literature, examines the corrosion of aluminium in three environments. All participants used the same measurement protocol and the data reporting and analysis were performed with automatic procedures to avoid errors. The measurement instruments used in the various laboratories include commercial general-purpose potentiostats and custom-built EN systems. The measurements on dummy cells have demonstrated that few systems are capable of achieving instrument noise levels comparable to the thermal noise * Corresponding author 1 ISE member 2 of the resistors, because of its low level. However, it is of greater concern that some of the instruments exhibited significant artefacts in the measured data, mostly because of the absence of anti-aliasing filters in the equipment or because the way it is used. The measurements on the aluminium samples involve a much higher source noise level during pitting corrosion, and most (though not all) instruments were able to make reliable measurements. However, during passivation, the low level of noise could be measured by very few systems. The round-robin testing has clearly shown that improvements are necessary in the choice of EN measurement equipment and settings and in the way to validate EN data measured. The results emphasise the need to validate measurement systems by using dummy cells and the need to check systematically that the noise of the electrochemical cell to be measured is significantly higher than the instrument noise measured with dummy cells of similar impedance.

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In-situ impedance-spectroscopy measurements were performed at temperatures between 600 and 1,000°C to investigate ionic transport in oxide scales formed on Kanthal AF alloy. The samples were pre-oxidized at 800, 900 and 1,000°C in air. The impedance spectra of the oxide formed at 1,000°C exhibited essentially one semicircle, whereas samples oxidized at lower temperatures showed an additional semicircle at high frequencies suggesting a more heterogeneous oxide. The ionic-transference number, derived by measuring the voltage across the oxide scale, indicates that the oxide is a predominant electronic conductor. Ionic diffusivity in the oxide scales formed at different pre-oxidizing temperatures was calculated, using the ionic-transference number. The ionic diffusivities obtained in this way are in reasonable agreement with literature data acquired by other methods. The oxide-formation temperature has a significant influence on the conductivity and ionic-transport properties of the oxide scale.

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