(Keynote) Anodized Oxide Films As an Important Interface in Different Aluminum Applications
Authors: Terryn Herman Albert 
Published: December 2020

In several applications such as aerospace, automotive, lithography, porous anodized aluminium substrates are coated with organic coatings. Interfacial interactions between PAO and organic coatings are mainly determining the durability of the entire organic/inorganic hybrid systems. However, analyzing this solid/solid interface is challenging. Since this region is covered by a µm-thick polymer layer on one side and a porous aluminium oxide matrix on the other. The use of conventional surface analysis techniques to probe this region is often hindered and is therefore often referred to as the buried interface. In a first part we introduce model interfacial interactions of several polymeric films on modified aluminum oxides discussing in situ analytical methods for the characterization of a realistic model interface exposed to environmental. The use of Ambient Pressure X-ray Photoelectron Spectroscopy (APXPS) is employed to describe the behavior of interfacial interactions in the presence of water vapor [1]. Furthermore, combined ATR-FTIR Kretschmann with EIS is utilized to obtain a near-interface infrared spectrum while simultaneously, the influence of an above-the-polymer electrolyte (such as water) on the interface is characterized. The local deposition of organic molecules we try to probe by Nano IR or TOF-SIMS/AFM approaches. The relevance of these approaches is demonstrated in the case of Cr(VI)-free anodizing for adhesive bonding applications. It is well known that two fundamental characteristics are critical for bonding: the oxide chemistry and morphology. To separate between these two contributions, either barrier-type or porous-type oxide specimens were applied. The investigated Cr(VI)-free anodizing electrolytes are phosphoric- (PAA), sulfuric- (SAA) and mixtures of phosphoric- and sulfuric acid anodizing (PSA). Experimental results show that the incorporation of PO43- and SO42- species from the electrolytes significantly changes the oxide surface composition [2]. Bond performance using an epoxy resin is highly affected by the ingress of water, with its strength linearly increasing with the hydroxyl fraction, as quantified by X-ray photoelectron spectroscopy (XPS) on barrier-type anodic oxides [3]. The next part explores the effect of porous oxide morphology. Mechanical tests show that the anodizing conditions such as the electrolyte combination and temperature, rather than the pore size and oxide layer thickness are critical for moisture-resistant adhesion [4]. In the last part is will be shown that it is possible to modify both the chemical and morphological oxide film properties even further by applying a post-treatment.

S. Pletincx, L. Trotochaud, L.L. Fockaert, J.C.M. Mol, A.R. Head, O. Karslıoğlu, H. Bluhm, H. Terryn. T. Hauffman, Scientific Reports. 7, 2017, p45123.

2.S.T. Abrahami, T. Hauffman, J.M.M. de Kok, J.M.C. Mol, H.A. Terryn. Journal of Physical Chemistry C 119 (34), 2015, p19967.
3.S.T. Abrahami, T. Hauffman, J.M.M. de Kok, J.M.C. Mol, H. Terryn. Journal of Physical Chemistry C, 120, 2016, p19670.
4.S.T. Abrahami, J.M.M. de Kok, V.C. Gudla, R. Ambat, H. Terryn, J.M.C. Mol npj Materials Degradation, 1(1),2017 p8.