Electrochimica Acta 56 (2011) 9262–9268 Contents lists available at ScienceDirect Electrochimica Acta j ourna l ho me pag e: www.elsevier.com/locate/electacta Synthesis of tungstate doped polyaniline and its usefulness in corrosion protective coatings K. Kamaraj, V. Karpakam, S. Sathiyanarayanan ∗ , S. Syed Azim, G. Venkatachari CSIR - Central Electrochemical Research Institute, Karaikudi 630 006, India a r t i c l e i n f o Article history: Received 6 May 2011 Received in revised form 1 August 2011 Accepted 1 August 2011 Available online 9 August 2011 Keywords: Mild steel IR spectroscopy EIS XPS Passivity Paint coatings a b s t r a c t A study has been made on the corrosion protection performance of tungstate doped polyaniline contain- ing vinyl coating on steel. The tungstate doped polyaniline was chemically synthesized and characterized by FTIR, XRD, UV-VIS and TGA studies. The corrosion protection performance of vinyl coating containing tungstate doped polyaniline on steel was assessed in 3% NaCl by electrochemical impedance studies (EIS). The coating has been found to offer protection more than 60 days in salt spray and immersion in 3% NaCl. FTIR studies have shown that the formation of iron–tungstate complex along with the passive film on steel. © 2011 Elsevier Ltd. All rights reserved. 1. Introduction Intrinsic conducting polymers were identified as promising candidate materials for chromate free corrosion protection [1–5]. Coatings based on polyaniline have been found to offer superior corrosion protection in comparison to the coatings of conventional inhibitive primers like zinc phosphate primer [6]. Kinlen et al. [7,8] have shown that PANI emeraldine salt dispersed in polymeric matrix is able to protect pinholes due to its redox activity. Further they have shown the importance of dopants such as phosphonate and sulfonate on corrosion protection of iron. Dominis et al. [9] have compared the corrosion protection performance of primer coat- ings containing polyaniline with different dopants using Raman spectroscopy. Silva et al. [10,11] have established the formation of secondary iron–dopant complex protects iron along with the pri- mary passive film formed by the redox processes of PANI. PANI acts as an anion reservoir which releases dopant anions when it undergoes redox transition. Thus, when corrosion manifests at pin holes or at coating damaged areas, PANI undergoes reduction and oxidizes the metal. During this action, PANI releases the dopant anions (corrosion inhibitors) in a smarter way. This facilitates the formation of secondary physical barrier by forming iron-dopent complex which can avoid further penetration of aggressive ions [12]. This warrants the need of a systematic research study on the ∗ Corresponding author. Tel.: +91 4565 227550; fax: +91 4565 227779. E-mail address: sathya cecri@yahoo.co.in (S. Sathiyanarayanan). corrosion protection performance of inhibitive ions doped polyani- line. It has been found that benzoate, sulfonate and oxalate doped polyaniline containing coatings have been found to offer corrosion protection for steel in neutral media [13–15]. Tungstate ions have been reported as good corrosion inhibitor at low concentrations for iron and steel neutral media [17–21]. Sabouri et al. [16] have studied the influence of tungstate dopants in corrosion protection behavior of electropolymerised polyaniline coating on mild steel. They have reported that tungstate ions improved the undercoat passive layer by primary passivation process before polymerization of aniline monomer. It could be a better choice to have tungstate doped polyaniline dispersed in an organic coating instead of elec- tropolymerised coating so that the primary barrier protection of the coating will be achieved. Besides, polyaniline blended organic coating can be used for protection of large industrial structures. In addition, PANI will bring self healing of pinholes by its redox activ- ity and the released tungstate dopant ion is expected to strengthen the passivity. Hence a study has been conducted on the chemi- cal oxidative synthesis of tungstate doped PANI and evaluating its corrosion protection ability for iron in neutral medium. 2. Experimental 2.1. Synthesis of tungstate doped PANI One molar distilled aniline was dissolved in 500 ml of 1 M solution of phosphoric acid or 1 M solution of hydrochloric acid. Pre-cooled 1 M solution of ammonium persulphate was added drop 0013-4686/$ – see front matter © 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.electacta.2011.08.005