Electro-Synthesis of Nano-Colloidal PANI/ND Composite for Enhancement of Corrosion-Protection Effect of PANI Coatings Habib Ashassi-Sorkhabi and Moosa EsÕhaghi (Submitted January 21, 2013; in revised form May 11, 2013; published online August 10, 2013) The polyaniline/nanodiamond (PANI/ND) nanocomposite coating was prepared on mild steel via electro- chemical polymerization using cyclic voltammetry technique. The ultrasonic irradiation was used for effectively dispersing ND particles in electropolymerization solution. The prepared nanocomposite films were found to be nano-colloidal, and very adherent with low porosity. The corrosion performance of the coatings was investigated in 0.5 M H 2 SO 4 solution by electrochemical impedance spectroscopy and polarization methods. The obtained results showed that the presence of ND particles significantly enhanced the corrosion protection performance of the PANI films in 0.5 M H 2 SO 4 corrosive medium. X-ray dif- fraction and FT-IR techniques confirmed the intercalation of the nanoparticles in PANI matrix. Keywords composites, nanodiamond, nanostructured polymer, polyaniline 1. Introduction Nanodiamond particles (NDs) have acquired attention due to their unique properties and inexpensive large scale synthesis with nano-size distribution (Ref 1). More recently, the nano- composite materials have been widely used as a new form of support for electrocatalysts, biosensor, sensor, and thermal applications. Ram and co-workers have developed some metal oxides and conducting polymer nanocomposites which have been extensively used in gas sensors and molecular electronic applications (Ref 2-5). Researchers have focused on the possible use of the conducting polymers as either film-forming corrosion inhibitors or protective coatings (Ref 6-8). Among the conducting polymers, polyaniline (PANI) is one of the most promising conducting polymers because of its high-electrical conductivity, unique electrochemical, chemical, and physical properties, good environmental stability, and ease of synthesis (Ref 9-13). The electronic, optical, photoelectrochemical, photoconductivity, photovoltaic, thermal, sensing, and corro- sion inhibition properties of PANI could be improved by combining with the polystyrene latex, multi-walled-carbon nanotubes, single-walled nanotubes, montmorillonite, TiO 2 , and SnO 2 particles and other nanoparticles (Ref 14-20). It has been shown that PANI and its ring-substituted derivatives possess interesting properties which can make it suitable to be used as protective coating against corrosion of iron and steel (Ref 9, 10). Camalet et al. (Ref 11) synthesized PANI on mild steel by electropolymerization from oxalic acid bath. Sazou and Georgolios (Ref 9) found that the PANI coatings on iron provide good protection against corrosive environments such as sulfuric acid solutions in the absence and presence of halide ions. The postulated mechanisms include the formation of a protective barrier layer and inhibition by the adsorption of organic species, and the anodic passivation achieved as the corrosion potential is shifted to more positive values under the charge transfer from the conducting polymers (Ref 21). In this work, we extended the method of preparation of PANI/ND nanocomposite using cyclic voltammetry (CV) method to obtain adherent and nano-colloidal coating on mild-steel substrate. Also, the ultrasonic irradiation was used to disperse ND particles in electropolymerization solution before polymerization process. Furthermore, the structure, composi- tion, and morphology of the nanocomposite coatings were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), and FT-IR spectroscopy. The effect of ND particles on the corrosion-protection behavior of PANI coating was investigated in 0.5 M H 2 SO 4 solution using electrochem- ical methods such as electrochemical impedance spectroscopy (EIS) and polarization measurements. The PANI/ND nano- colloidal coating on relatively active metals, like mild steel, may provide anodic protection by electronic, chemical, and physical barriers. 2. Experimental Mild-steel electrodes of 0.502 cm 2 surface area were used as the substrates. The composition of the mild steel is given in Table 1. The steel samples were mounted in a polyester resin in such a way that only one side of them remained uncovered. Prior to deposition, the working electrode was polished with different grades of sandpapers up to 1500 grade followed by polishing with alumina slurry, degreased with ethanol solvent Habib Ashassi-Sorkhabi and Moosa EsÕhaghi, Electrochemistry Research Lab, Physical Chemistry Department, Faculty of Chemistry, University of Tabriz, 29 Bahman Blvd., Tabriz 5166614766, Iran. Contact e-mails: habib.ashassi@gmail.com and ashassi@tabrizu.ac.ir. JMEPEG (2013) 22:3755–3761 ÓASM International DOI: 10.1007/s11665-013-0638-4 1059-9495/$19.00 Journal of Materials Engineering and Performance Volume 22(12) December 2013—3755