Progress in Organic Coatings 72 (2011) 653–662 Contents lists available at ScienceDirect Progress in Organic Coatings jou rn al h om epage: www.elsevier.com/locate/porgcoat Improving the corrosion protection properties of organically modified silicate–epoxy coatings by incorporation of organic and inorganic inhibitors A.C. Balaskas a , I.A. Kartsonakis a,∗ , D. Snihirova b , M.F. Montemor b , G. Kordas a a Sol-Gel Laboratory, Institute of Materials Science, NCSR “DEMOKRITOS”, 15310 Agia Paraskevi, Greece b ICEMS, Instituto Superior Tecnico, Technical University of Lisbon, Portugal a r t i c l e i n f o Article history: Received 6 April 2010 Received in revised form 15 July 2011 Accepted 20 July 2011 Keywords: ORMOSIL AA2024-T3 Corrosion Inhibitors Impedance a b s t r a c t Organically modified silicate (ORMOSIL)–epoxy coatings were formed on aluminium alloy 2024-T3 in order to protect the substrates from corrosion. Organic and inorganic compounds, all known for their cor- rosion inhibition ability, were incorporated into the polymer matrix for the improvement of the corrosion resistance. The ORMOSIL–epoxy coatings were deposited via the dip-coating process. The properties of the coatings were investigated after 24 h of curing at 90 ◦ C. The morphology of the coatings was examined by scanning electron microscopy (SEM). Their composition and structure were investigated by Fourier transform infrared spectroscopy (FT-IR) and energy dispersive X-ray analysis (EDX). The corrosion resis- tance of these coatings was investigated using electrochemical impedance spectroscopy (EIS). The results showed that the most effective corrosion protection ability was provided by the inorganic inhibitors and that an important role can be attributed to the cation in the nitrate salt. © 2011 Elsevier B.V. All rights reserved. 1. Introduction Corrosion of aluminium alloys (AA) has an enormous economic impact. Chromate surface treatments and chromate-containing epoxy primers are often used for corrosion control of AA. How- ever, many efforts have been focused on the development of new techniques for the replacement of hexavalent chromium. Alter- native protection of AA is urgent since hexavalent chromium provokes human diseases [1,2] and many environmental prob- lems. ORganically MOdified SILicates (ORMOSILs) are promising coatings for corrosion protection of AA. These compounds are hybrid organic–inorganic materials, formed by sol–gel method, via hydrolysis and condensation of organically modified silanes with traditional alkoxide precursors [3]. ORMOSILs coatings can be used to mitigate corrosion activity on AA due to their improved adher- ence to the substrate, since they form stable covalent bonds, and very good barrier properties [4–8]. In addition, these coatings can be loaded with organic and inorganic inhibitors, which will enhance their protection ability. Yang and collaborators synthesized and used a sol–gel conver- sion coating for aluminium corrosion protection. The sol–gel coat- ing consisted of SiO 2 and ZrO 2 . They concluded that their coating inhibited local dissolution of the aluminium surface in Harrison’s solution [9]. Addition of SiO 2 nanoparticles was also reported by ∗ Corresponding author. Tel.: +30 2106503302; fax: +30 2106547690. E-mail address: ikartsonakis@ims.demokritos.gr (I.A. Kartsonakis). Montemor et al. [10] as beneficial additives in silane coatings for the protection of galvanized steel. Pathak and co-workers prepared a 3-glycidoxypropyltrimethoxysilane, methyltrimethoxysilane and hexamethoxy-methylmelamine sol–gel solution. Aluminium sub- strates were dip coated in those solution and the results revealed that the coatings act as a protective barrier in the corrosive elec- trolytes [11]. Khramov et al. synthesized a sol–gel derived hybrid coating including corrosion inhibitors and they examined the developed coatings on AA 2024-T3. They concluded that the corro- sion protection could be improved by means of direct addition of the corrosion inhibitors [12] to the protective coating. The anti-corrosion resistance properties of ORMOSIL coat- ings on 2024-T3 aluminium alloys were studied by Metroke et al. and have been reported as a promising treatment for aluminium alloys. They prepared coatings with different concen- trations (up to 16.6 vol.%) of alkyl-modified silane, X n · · ·Si(OR) 4-n , where X = methyl, dimethyl, n-propyl, n-butyl, i-butyl, n-hexyl, n- octyl, or i-octyl. They concluded that the best overall corrosion resistance was observed for coating systems containing ≥10.4 vol.% alkyl-modified silane [8]. Furthermore, Metroke et al. synthe- sized spray and dip-coated 3-glycidoxypropyltrimethoxysilane (GLYMO)-tetraethoxysilane (TEOS) ORMOSIL films. Films prepared from high organic contents (25 and 67 mol% GLYMO) and low hydrolysis water content values exhibited the best corrosion resis- tance when applied by dip coating. These coatings comprise a dense network structure with organic groups dispersed through- out the film, providing a hydrophobic barrier coating capable of repelling water and corrosion initiators. Generally the coating 0300-9440/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.porgcoat.2011.07.008