Progress in Organic Coatings 70 (2011) 91–101 Contents lists available at ScienceDirect Progress in Organic Coatings journal homepage: www.elsevier.com/locate/porgcoat The characterisation and performance of Ce(dbp) 3 -inhibited epoxy coatings J. Mardel a , S.J. Garcia b,c , P.A. Corrigan d , T. Markley d , A.E. Hughes d,∗ , T.H. Muster d , D. Lau d , T.G. Harvey d , A.M. Glenn e , P.A. White d , S.G. Hardin d , C. Luo f , X. Zhou f , G.E. Thompson f , J.M.C. Mol c a CSIRO Molecular & Health Technologies, Clayton 3169, Australia b Delft University of Technology, Department of Aerospace Materials and Manufacturing, Kluyverweg 1, 2629 HS, Delft, The Netherlands c Delft University of Technology, Department of Materials Science and Engineering, Mekelweg 2, 2628 CD, Delft, The Netherlands d CSIRO Future Manufacturing Flagship, Private Bag 33, Clayton South MDC, Clayton 3169, Australia e CSIRO Division of Process Science and Engineering, Minerals, Clayton 3169, Australia f Corrosion and Protection Centre, School of Materials, The University of Manchester, PO Box 88, Manchester M60 1QD, England, United Kingdom article info Article history: Received 14 April 2010 Received in revised form 27 September 2010 Accepted 26 October 2010 Keywords: Cerium Corrosion inhibitors Electron microscopy Organic coatings FTIR Aluminium alloy AA2024-T3 abstract Cerium dibutyl phosphate (Ce(dbp) 3 ) was tested as a replacement for chromate corrosion inhibitors in a two-component epoxy applied to AA2024-T3 aluminium alloy. The interaction of the Ce(dbp) 3 with the epoxy-amine functionalities were investigated using FTIR. Water uptake and Ce release were studied using weight gain and ICP-AES analyses, respectively. Corrosion resistance was assessed using filiform testing. It was found that the filiform corrosion resistance increased with increasing Ce(dbp) 3 load- ing, and the best performance was obtained for the highest loading. The primer also showed improved wet adhesion. It was found using SEM and TEM that the corrosion protection offered by the Ce(dbp) 3 - inhibited epoxy and the improved wet adhesion were due to the development of an interfacial oxide at the metal/primer interface. Crown Copyright © 2010 Published by Elsevier B.V. All rights reserved. 1. Introduction The development of chromate-free primers, particularly for application in the aerospace industry, has been an expanding field for some decades [1–6]. While replacements are now undergoing in-service evaluation for exterior applications [7–9], the develop- ment of primers for interior applications is still an active area of research. This is principally due to the fact that the exterior paint system, which ages within 3 years [10], is relatively easily accessed whereas the interior has occluded spaces which are not easily assessed during standard inspection. Indeed, in many instances the evidence of corrosion can only be confirmed after teardown which might be some decades after manufacture [11]. A broad range of approaches to the development of chromate- free primers have been reported in the scientific literature. These cover sacrificial Mg particles [2,9], inorganic alternatives to chro- mates (with a strong focus on oxyanions such as vanadates [12–15]), cationic inhibitors such as the rare earths (described in more detail below), organic compounds [3,16,17], as well as very low solubility salts of these compounds [1,3,5]. Because of differ- ∗ Corresponding author. Tel.: +61 3 9545 270; fax: +61 3 9544 1128. E-mail address: Tony.Hughes@csiro.au (A.E. Hughes). ences in solubility of some inhibitors to chromate pigments [3,5], a range of delivery systems with a focus on double layer hydrox- ides including hydrotalcites, are being investigated by many groups [13–15]. Additionally, research has also focused on the possibility of merging the conversion or anodised coating functionality with the primer functionality through the development of hybrid sol–gel systems [4,16–23]. Rare earth compounds features frequently in the development of chromate-free coatings. The first reports of the effectiveness of rare earth metal salts, for example CeCl 3 , as cathodic corrosion inhibitors appeared in the literature some decades ago, indicating their potential as replacement inhibitors for chromates in corro- sion prevention for a number of metals [24–32]. Indeed, rare earth replacements have been identified for all of the chromate-based components of the coating system used in aircraft manufacture including deoxidisers, conversion coatings and inhibited primers [33]. The emergence of rare earth organophosphates as corrosion inhibitors has been an expanding area of research in recent years [34–43]. Interest in this area is based on the development of bi- functional inhibitors that incorporate the good cathodic inhibition qualities of the rare earths as well as the potential for anodic inhi- bition from the organophosphate functionality which is an anion in solution. Rare earth dibutylphosphates, for example, show good inhibition properties for a range of metals [34–41] and are rel- 0300-9440/$ – see front matter. Crown Copyright © 2010 Published by Elsevier B.V. All rights reserved. doi:10.1016/j.porgcoat.2010.10.009