abstract
A proper assignment of time constants is important for the correct interpretation of the electrochemical impedance spectra of coated substrates. In this work, several model aluminium samples with different anodic oxide thicknesses were prepared and characterised. The aluminium samples were coated by a hybrid sol-gel formulation and studied by electrochemical impedance spectroscopy (EIS) during immersion in NaCl solution. A hierarchical model containing three R-C elements adequately described the impedance spectra of the coated samples. The R-C elements described the properties of sol-gel coatings, aluminium oxide layers and corrosion process. The contribution of the aluminium oxide layer to impedance was unambiguously proven to be at middle frequencies on the spectra. Furthermore, the real capacitances of oxide layers were obtained from two capacitance-CPE equations and their applicability was scrutinized. The obtained results presented an opportunity to determine the adhesion behaviour of the sol-gel coatings to the oxide layers, which was studied by analysing the ratio of the oxide layer capacitance of the sol-gel coated samples to the capacitance of the uncoated ones. It was demonstrated that the exposed surface area of the oxide to the electrolyte was about 60-68% and was not changing during immersion. Based on these findings, a degradation model of the sol-gel coating on anodised aluminium was proposed. (c) 2021 Elsevier Ltd. All rights reserved.
keywords
ACTIVE CORROSION PROTECTION; OXIDE-FILMS; INTERMETALLIC PHASES; ORGANIC COATINGS; ALLOY; CONVERSION; SURFACE; PRETREATMENTS; SPECTROSCOPY; PERFORMANCE
subject category
Electrochemistry
authors
Yasakau, KA; Starykevich, M; Ferreira, MGS; Zheludkevich, ML
our authors
Kiryl Yasakau
Assistant Researcher
Maksim Starykevich
Junior Researcher
Mário Guerreiro Silva Ferreira
Retired Professor
Mikhail Zheludkevich
Invited Principal ResearcherProjects
Projeto de Investigação Exploratória: Kyril Yasakao (IF/01284/2015)
acknowledgements
KY is grateful to the Portuguese Foundation for Science and Technology (FCT) and a researcher grant (IF/01284/2015). A part of this work was developed within the scope of the project CICECOAveiro Institute of Materials, UIDB/50011/2020 & UIDP/50011/2020, financed by national funds through the Portuguese Foundation for Science and Technology/MCTES.