The use of odd random phase electrochemical impedance spectroscopy to study lithium-based corrosion inhibition by active protective coatings

In this work, the study of the time-dependent behaviour of lithium carbonate based inhibitor technology for the active corrosion protection of aluminium alloy 2024-T3 is presented. Odd random phase electrochemical impedance spectroscopy (ORP-EIS) is selected as the electrochemical tool to study the corrosion protective properties of a model organic coating with and without lithium carbonate as a function of immersion time, by examination of the non-linearities and non-stationarities in the system. A dedicated qualitative and quantitative analysis allows linking the presence of non-stationarities in a certain frequency range with the (un)stable behaviour of different electrochemical processes. Monitoring of the system with and without lithium corrosion inhibitors during the first 12 h after immersion in a 0.05 M NaCl aqueous solution and modelling the ORP-EIS data with equivalent electrical circuit (EEC) models revealed a relation between the trends in the parameter evolution and the (un)stable behaviour of the morphological changes taking place. This paper shows that the ORP-EIS based methodology allows us to study the behaviour of corrosion inhibitors in an alternative way; the time-dependent behaviour of corrosion inhibitor containing electrochemical systems is highlighted, proving that this a useful approach for further corrosion inhibitor and active protective coating research.