| AVS 65th International Symposium & Exhibition | |
| Advanced Surface Engineering Division | Monday Sessions |
| Session SE+NS+TF-MoM |
| Session: | Nanostructured Thin Films and Coatings |
| Presenter: | Shoshan Abrahami, Vrije Universiteit Brussel (VUB), Belgium |
| Authors: | S.T. Abrahami, Vrije Universiteit Brussel (VUB), Belgium V.C. Gudla, Technical University of Denmark K. Marcoen, Vrije Universiteit Brussel, Belgium J.M.M. de Kok, Fokker Aerostructres T. Hauffman, Vrije Universiteit Brussel, Belgium R. Ambat, Technical University of Denmark J.M.C. Mol, Technical University Delft, Netherlands H. Terryn, Vrije Universiteit Brussel, Belgium |
| Correspondent: | Click to Email |
Anodic aluminum oxides (AAOs) are important nanostructures in many engineering applications. But despite their popular use, the important parameters that control their (dis-)bonding to an organic coating are not fully understood. This study uses an original approach that employs porous- and barrier AAO specimens for both chemical characterization and mechanical tests, thereby enabling the distinction between chemical and morphological contributions to the surface affinity for interfacial bonding. A validation for the cooperative effect of mechanical and chemical bonding mechanisms is given in this study. This was achieved by post-anodizing immersion of AAO’s in sodium fluoride solution after anodizing in sulfuric acid (SAA) or a mixture of phosphoric- and sulfuric acid (PSA). Transmission electron microscopy (TEM) cross-section images show that fluoride-assisted dissolution smoothed the oxide surface, removing the fibril-like top nanostructure of the porous oxides, which are important for dry adhesion. However, chemical surface modifications were dependent on the initial oxide composition, as measured by X-ray photoelectron spectroscopy (XPS) and Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS). Chemical analysis reveals that the surface hydroxyls of AAO are partially replaced by fluorides that do not form interfacial bonding with the epoxy resin. As a result, the peel strength of SAA under wet conditions is severely reduced due to these chemical changes. Conversely, fluoride-assisted dissolution of surface phosphates in PSA compensates for the adsorbed fluorides and the wet peel strength of PSA panels is not further deteriorated.
[1] S.T. Abrahami et al., J. Phys. Chem. C, 119, 19967-19975 (2015).
[2] S.T. Abrahami et al., npj Materials Degradation, 1, 8 (2017).
[3] S.T. Abrahami et al., J. Phys. Chem. C, 120, 19670-19677 (2016).