Active protection coatings with layered double hydroxide nanocontainers of corrosion inhibitor M.L. Zheludkevich a, * , S.K. Poznyak a , L.M. Rodrigues a,b , D. Raps c , T. Hack c , L.F. Dick b , T. Nunes d , M.G.S. Ferreira a,e a University of Aveiro, CICECO, Dep. Ceramics and Glass Eng., 3810-193 Aveiro, Portugal b Rio Grande do Sul Federal University, 91501-970 Porto Alegre, Brazil c EADS Innovation Works, 81663 Munich, Germany d University of Aveiro, Department of Environment, 3810-193 Aveiro, Portugal e Technical University of Lisbon, IST, ICEMS, Av. Rovisco Pais, 1049-001 Lisbon, Portugal article info Article history: Received 12 July 2009 Accepted 13 October 2009 Available online 17 October 2009 Keywords: A. Layered double hydroxides A. Nanocontainers A. Corrosion inhibitor A. Protective coating C. Self-healing abstract Novel LDH-based nanocontainers of corrosion inhibitor are developed in the present work. The reservoirs are composed by nanostructured layered double Mg/Al and Zn/Al hydroxides with divanadate anions located in the interlayer regions. The nanocrystalline LDHs (layered double hydroxides) are able to release vanadate ions in a controllable way. XRD, EDS and SEM methods were used in this work to study morphological and structural properties of the synthesized LDH powders. Corrosion protection effect of the LDH powders directly added to corrosive electrolyte or to commercial coatings used for aeronautical application has been studied by electrochem- ical impedance spectroscopy and standard accelerated corrosion tests. Aluminium alloy 2024 was used here as substrate. The results demonstrate that both of the LDH pigments being added to corrosive media confer corro- sion inhibition effect, especially Zn/Al based nanocontainers obtained by the anion-exchange approach. The coatings doped with Zn/Al LDH-nanocontainers provide well-defined self-healing effect and confer corrosion protection properties superior than currently used environmentally unfriendly chromate-based systems. Ó 2009 Elsevier Ltd. All rights reserved. 1. Introduction The application of protective polymer coatings is the most widespread approach used nowadays for corrosion protection of different metallic materials. The main role of the anticorrosion coating is to protect metal forming effective barrier against corro- sive species present in different environments. The aging of the polymer together with various mechanical impacts lead to forma- tion of defects interrupting the barrier and providing direct ingress of the corrosive species to naked metal surface [1]. Also, exposure of these coatings to aqueous electrolyte solutions causes many coatings to swell and to develop conductive pathways not present in the coating before the exposure. After corrosion started the poly- mer coating itself cannot protect the defective zone and is not able to stop propagation of the defect. Therefore, an active ‘‘self-heal- ing” of defects in coatings is necessary to provide long-term pro- tection effect and to prolong the maintenance intervals [2]. The anticorrosion inhibitors are added to polymer coatings in order to provide additional active corrosion protection and to hin- der the corrosion activity in defect sites [3,4]. However, the normal inhibiting pigments are prone to uncontrollable leaching of an ac- tive component leading to fast exhausting of self-healing potential and to osmotic blistering of polymer films [5]. Even chromates, the most used in past, can cause such problems. Moreover, due to very high carcinogenic potential of chromates, they are banned since 2007. Only aeronautical industry is allowed to use chromate-based systems until appropriate solution will be found. Thus develop- ment of new active corrosion protection systems with self-healing ability becomes now a very important challenging issue for many industries. Several new approaches based on encapsulation of inhibiting compounds before addition of them to corrosion protection system have been recently suggested [6]. Porous oxide interlayer applied to the metal surface and doped with organic corrosion inhibitor provides additional active corrosion protection for thin hybrid sol–gel films on an aluminium alloy substrate [7,8]. The inhibi- tor-containing oxide nanoparticles introduced to the hybrid coat- ing were also used as nano-carriers of corrosion inhibitor [9]. 0010-938X/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.corsci.2009.10.020 * Corresponding author. Tel.: +351234370255; fax: +351234378146. E-mail address: mzheludkevich@ua.pt (M.L. Zheludkevich). Corrosion Science 52 (2010) 602–611 Contents lists available at ScienceDirect Corrosion Science journal homepage: www.elsevier.com/locate/corsci