Efficiency of corrosion inhibitors in aqueous solutions depends on several interfacial parameters, which may vary over time. Therefore, reliable electrochemical techniques are demanded for screening the efficiency of corrosion inhibitors and monitoring their performance over time. Here, we evaluate corrosion inhibition efficiency of imidazole-based compounds on bare Cu surfaces and highlight the importance of electrochemical evaluation of the inhibitor over time, characterized by linear polarization resistance techniques as a reliable, instantaneous and non-invasive method for assessing intrinsic inhibitor performance in lab screening studies.

In previous work, the importance of taking the time-domain into account when studying corrosion inhibitor-containing electrochemical systems was highlighted. In this work, odd random phase electrochemical impedance spectroscopy (ORP-EIS) is applied as the electrochemical tool to study the time-effect by the evaluation of the non-stationarities per frequency decade over time for the screening of different silica- and phosphate- based corrosion inhibitors for hot-dip galvanized steel and possible corrosion inhibitor synergism. This serves as the basis for the interpretation of the results obtained from different macroscopic electrochemical techniques such as potentiodynamic polarization (PP), open circuit potential (OCP) with superimposed linear polarization resistance (LPR), electrochemical impedance spectroscopy (EIS) and electrochemical noise (EN) measurements. The analysis of the time-domain shows that all systems have a system-specific ‘stabilization’ time which affects the interpretation of the results obtained from the macroscopic electrochemical techniques. Furthermore, these results indicate that all corrosion inhibitors tested exhibit corrosion protective action and that the combination of both silica-based corrosion inhibitors show synergistic action on hot-dip galvanized steel.

In this paper, different macroscopic electrochemical techniques are applied to study the corrosion inhibitor efficiency, protection mechanism and stability of a calcium aluminum polyphosphate silicate hydrate inhibitor on hot-dip galvanized steel in the time-domain. Potentiodynamic polarization (PP) measurements are applied to study the anodic and cathodic mechanistic behavior as well as inhibitor efficiencies at discrete and single times of exposure. Open circuit potential (OCP) with superimposed linear polarization resistance (LPR) measurements are applied as a faster, non-invasive alternative to PP, characterizing the overall performance of the system in terms of the polarization resistance. Electrochemical impedance spectroscopy (EIS) measurements are applied to detail both the overall performance of the system as well as the corrosion inhibition mechanism related to the electrochemical system’s physicochemical representation over time. Electrochemical noise (EN) measurement are used to evaluate the inhibition efficiency as a function of exposure time, represented by the electrochemical noise resistance. Odd random phase electrochemical impedance spectroscopy (ORP-EIS) is selected as the electrochemical tool to study the system’s instability, by evaluation of the non-linearities and non-stationarities over time. The non-stationarities present in the inhibitor-containing electrochemical system are shown to cause the overall instability of the system and should be taken into account when interpreting results from the different techniques over time.

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.

A common approach to investigate chemical interactions at the polymer/metal oxide interface is by monitoring ultrathin polymer films onto a metal oxide substrate by a variety of surface analysis techniques. The deposition of this nanometer-thin overlayer is frequently carried out by reactive adsorption from dilute polymer solutions. However, the influence of the solvent on the metal oxide chemistry is seldom taken into account in interface studies. The overall amount of available adsorption sites on the metal oxide surface might decrease due to competing adsorption of the solvent and the polymer adsorbate. Therefore, in this work, the adsorption of a common organic solvent (methanol) onto a physical vapor-deposited aluminum oxide surface is monitored in situ by an integrated attenuated total reflectance Fourier transform infrared spectroscopy in the Kretschmann geometry and odd random phase multisine electrochemical impedance spectroscopy system. It is shown that methanol immediately physisorbs onto the aluminum oxide surface and replaces the initial adventitious carbon layer. This process is followed by methanol chemisorbing onto the oxide surface to form methoxide species at the liquid/solid interface. Additionally, chemisorption is validated ex situ by X-ray photoelectron spectroscopy.