Corrosion behaviour of 316L stainless steel coated by amorphous and semicrystalline polypyrrole

Using galvanostatic technique, electrochemical polymerisation of pyrrole on 316L stainless steel substrates was achieved in aqueous solution of oxalic acid and pyrrole. Common amorphous structure was obtained at high current density (1 mA cm^–2). Conversely, semicrystalline polypyrrole coating was achieved at very low current density (0⋅01 mA cm^–2). Using grazing incidence small angle X-ray scattering method, the degree of crystallinity was estimated to be 68%. Corrosion resistance of polypyrrole coatings in 0⋅1M NaCl solution was investigated employing potentiodynamic polarisation and electrochemical impedance spectroscopy methods. Results obtained showed that crystallinity of polypyrrole coating would decrease the corrosion current density and increase the polarisation resistance as well as pore resistance.