ABSTRACT

In the last three decades, research on the anticorrosion properties of intrinsically conducting (or semiconducting) polymers, denoted throughout this book as conducting polymers (CPs), has flourished and led to the development of a wide variety of CP-based protective coatings with specifically designed properties. CPs are composed of conjugated chains containing π-electrons delocalized along the polymer backbone and combine physico-electrochemical properties that make them unique materials. They exhibit a wide range of conductivities (10−4 to 103 S cm−1) in their p-doped (oxidized) state. The corrosion of metals is an electrochemical oxidative process during which metal releases electrons to an oxidizing species in the interface between metal and corrosive environment, resulting in the degradation or deterioration of the metal. The basic principle behind the idea to apply CPs for metal protection is related with this electron transfer process and passivity, by which nature has predicted the prevention or inhibition of metal degradation. DeBerry (1985) was the pioneer to indicate that polyaniline (PAN) was able to maintain the surface potential of PAN-coated stainless steel in sulfuric acid solutions into the passive state where a protective oxide film is formed on the alloy substrate. The key feature of this process is that PAN-based coatings are pinhole and defect tolerant in a similar way as the protective coatings based on the environmentally hazardous hexavalent chromium. Later on, Wessling (1996) showed how the oxidizing property of PAN is reestablished after metal oxidation by oxygen reduction within the CP layer.