Inhibitor efficiency inside small crevices investigated by Electrochemical Noise Analysis

Abstract

The Electrochemical Noise Analysis (ENA) is a novel technique employed to investigate dynamic properties of electrochemical systems. The influence of chromate inhibitors on the corrosion activity of an AA 2024 surface in a chloride containing sodium solution was studied by the measurement of current noise under potential control. The noise analysis clearly shows the efficiency of the chromate inhibitor on the crevice corrosion as well as the sufficiency of the ENA as a useful tool as an inhibitor screening process. The measurement under crevice condition was carried out in-situ in an artificial crevice. Die Elektrochemische Rauschanalyse (ENA) ist eine noch junge Methode zur Untersuchung der dynamischen Eigenschaften eines elektrochemischen Systems. Der Einfluss eines Chromatinhibitors auf die Korrosionsaktivität einer AA 2024 Oberfläche wurde anhand der Messung des Stromrauschens unter Potentialkontrolle untersucht. Die Rauschanalyse zeigt die Wirkung des Chromatinhibitors auf die Spaltkorrosion sehr klar und beweist außerdem, dass die ENA ein hilfreiches Werkzeug bei der Suche nach Inhibitoren sein kann. Die Messungen unter Spaltbedingungen wurden in-situ in einem künstlichen Spalt durchgeführt.

Investigation of the initial stage of crevice corrosion on Al99.5 by electrochemical noise analysis

“…from birth and death processes of corrosion nuclei to a stable formation of corrosion nuclei. This transition state can be observed under bulk as well as under crevice conditions and also agrees with the earlier experience on aluminium alloys [10,18]. Figure 5 shows PSD of the current noise, a transformation of the data from the time domain into the frequency domain.…”

“…Under all conditions (bulk and crevice conditions with and without inhibitor), the current density in the passive range was very small (%10 À7 A/cm 2 ). Measurements on AA2024 in a similar electrolyte with lower chloride concentration (0.01 mol/l Na 2 SO 4 þ 0.005 mol/l NaCl) under bulk conditions showed significantly higher current densities in the passive range (%10 À6 A/cm 2 ) [10]. Generally, the passive behaviour of Al99.5 is very good.…”

“…as reflectors in heat exchangers, as packing material and as a clad material in the aircraft industry [8]. In earlier investigations, we focused mainly on crevice corrosion on the aluminium alloys AA2024 and AA6013, which are primarily used in the aircraft manufacturing industry [9,10]. The corrosion processes of these alloys are essentially determined by the microstructure.…”