Polypyrrole as a protective coating for iron

SILVANA B. SAIDMAN

Corrosion Protection: Processes, Management and Technology

Nova Science Publishers

Lugar: Nueva York; Año: 2009; p. 101 - 123

Abstract Due to the technological importance of iron and ferrous alloys there is a great interest in finding new surface coatings to improve their corrosion protection. One of the approaches to protecting these materials is the electrodeposition of a conducting polymer. Particularly, polypyrrole (PPy) films have several advantages such as its relatively easy electrosynthesis under a wide variety of conditions.   In this chapter results are presented on the electrosynthesis of stable and adherent PPy films onto iron electrodes in the presence of the surfactant sodium bis(2-ethylhexyl) sulfosuccinate (AOT) in a wide pH interval. The characterisation of the formed coatings was done using electrochemical measurements including open circuit potential measurements, cyclic voltammetry and electrochemical impedance spectroscopy (EIS), and also SEM/EDX and IR spectroscopy. As a result of iron dissolution, a gel-like product is formed in parallel to the growth of the polymer. To better understand this peculiar behaviour, the electrochemical response of iron in pure aqueous AOT solutions was also studied. The obtained results allow proposing that the gel-like material is a mixed NaAOT–Fe(AOT)3 lamellar mesophase. The coated electrodes exhibit significant corrosion protection properties in chloride media. The degree of corrosion protection attained after covering the substrate was explained considering the characteristics of the protective oxide film, which depend on the pH of the electropolymerization solution. The beneficial role of the presence of surfactant molecules is also discussed. The surfactant molecules not only alter the electrode surface, facilitating the electropolymerization process, but also act as a dopant, conditioning the properties of the polymer matrix. In addition, the gelatinous material inside the pores of the coating hinders the diffusion of species such as chloride.