Abstract
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.
Highlights
Corrosion protection by the application of inhibitor doped organic coatings or the addition of inhibiting species to aqueous corrosive solutions is amongst the most common means of corrosion control strategies for metal applications in aggressive environments
Multiple studies applying a variety of electrochemical characterization techniques exist to study Cr(VI)-free corrosion inhibitors and investigate their performance for a given metallic substrate
Potentiodynamic polarization (PP) experiments describe the kinetic behavior of an inhibitor-containing electrochemical system by decoupling the anodic and cathodic reactions on the surface under investigation
Summary
Corrosion protection by the application of inhibitor doped organic coatings or the addition of inhibiting species to aqueous corrosive solutions is amongst the most common means of corrosion control strategies for metal applications in aggressive environments. Multiple Cr(VI) containing compounds, added as active corrosion inhibitors in many polymer formulations because of their exceptional performance, have been or are prone to be phased out in the near future even for demanding applications because of their toxic and carcinogenic nature.[1] The replacement of these Cr(VI) based inhibitors by eco-friendly, Cr(VI)-free inhibitors is challenging, since there is a significant performance ‘gap’ between them.[2] Different alternatives to the hexavalent chromium technology have been studied, including rare-earth-, vanadate- and lithium- based inhibitors but are not universal and experience some technical constraints, such as upscaling and cost adjustments, to date.[3] These corrosion protective substances or mixtures, added in low concentration, prevent or minimize the corrosion rate of a variety of metal substrates. Through linear polarization resistance (LPR) measurements using a small amplitude excitation potential and measuring the current density
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