Progress in Organic Coatings 70 (2011) 16–22 Contents lists available at ScienceDirect Progress in Organic Coatings journal homepage: www.elsevier.com/locate/porgcoat In situ studies of conversion coated zinc/polymer surfaces during exposure to corrosive conditions Maria Öhman ∗ , Dan Persson, Dan Jacobsson Swerea KIMAB AB, Drottning Kristinas väg 48, Stockholm, Sweden article info Article history: Received 1 July 2008 Received in revised form 7 September 2010 Accepted 9 September 2010 Keywords: ATR-FTIR Spectro-electrochemistry Interface Conversion coating Zinc abstract This work investigates the hidden interface between a conversion-coated zinc surface and a polymer coat- ing upon exposure to an electrolyte by simultaneous in situ ATR-FTIR and EIS. Various system properties were distinguished, such as the ingress of electrolyte constituents, and an active process of water-induced alterations of the conversion layer. The interface between a polymer film and a surface treated metal sur- face is of considerable fundamental and technical interest in many areas of application, and the results obtained open up the use of this method for a wide range of important applications. © 2010 Elsevier B.V. All rights reserved. 1. Introduction The environmental stability of hidden metal/polymer interfaces is important in many metal applications, such as organically coated and adhesively bonded metal structures in automotive applica- tions, coil-coated metal sheets. Organic coatings applied to a metal surface suppress electrochemical reactions by excluding water and other corrosive constituents. Nevertheless, water will move within a polymer film [1–7]. Several analytical techniques exist to describe separate parts of this process, but the transport of water and ions to a hidden metal/polymer interface and the subsequent processes at the metal surface are complicated to analyse in-situ and at ambient pressure conditions. Various chemical pre-treatments may be applied to the metal surface in order to further increase the resistance to corrosion and to enhance the adhesion between the metal and the protective organic coating. While coupling agents such as silanes normally require a polymer top-coat for corrosion protection, conversion coatings provide a better corrosion resistance by also acting as a passivating inhibitor. Although chromium conversion coatings are superior to other surface treatments on metals [8], the use of chro- mates has been legally restricted due to their harmful effects on human health and environment. Today, efforts are made to develop green inhibitors of similar interfacial stability as these traditional systems. Conversion coatings with a low environmental impact ∗ Corresponding author. E-mail address: maria.ohman@swerea.se (M. Öhman). may be based on for instance zirconates and titanates, which form transparent colourless films by interfacial precipitation of metal oxides and hydroxides [9]. In order to obtain improved corrosion resistance, some systems also contain organic components that may act as complexing agents for the inorganic components and also assist in the formation of a barrier layer. Although crucial for the development of new systems, thin interfacial surface films formed between a metal and a polymer film are hard to detect and its protective behaviour is difficult to evaluate. In order to gain a deeper understanding of changes in the metal/polymer interfacial region in the presence of a conversion coating upon exposure to an electrolyte, this work used an exper- imental set-up based on two complementary techniques; in situ attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) in the Kretschmann configuration and electrochemical impedance spectroscopy (EIS). This set-up was recently developed in our laboratory and used for in situ studies of aluminium/polymer interfaces exposed to water and electrolyte solutions [10,11]. To our knowledge, surface-treated metal/polymer interfaces have not previously been studied using this ATR-FTIR technique. 2. Experimental A zinc film with a thickness in the order of 100 nm, as deduced by quartz crystal microbalance, was deposited on a ZnSe internal reflection element (IRE) by high-vacuum evaporation (99.9% zinc, Goodfellow Cambridge Ltd.) using a Univex 300 vacuum evaporator (Leybold Vaccum). The zinc surface was further converted by spray application of a 10% (pH 3) aqueous solution based, according to the 0300-9440/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.porgcoat.2010.09.012