The influence of phosphate ion dopants in corrosion protection properties of polypyrrole coating on mild steel

Polypyrrole (PPy) and polypyrrole-phosphate (PPy − PO³⁻₄) coatings were electrodeposited on mild steel electrodes from aqueous oxalic acid solution using cyclic voltammetry (CV) technique. Electrodeposition of PPy − PO³⁻₄ was carried out with addition of tri-sodium phosphate dehydrate compound to the supporting electrolyte. The obtained coatings were characterized using scanning electron microscopy (SEM) and line-scan EDX techniques. In addition, comparison between their abilities to control corrosion of mild steel were done with application of open circuit potential (OCP) monitoring, polarization and electrochemical impedance spectroscopy (EIS) methods in 3.5% NaCl solution. Corrosion studies indicate that phosphate dopants can improve corrosion protection properties by taking part in: (i) the passivation processes occurred prior to electrodeposition processes, (ii) the electrosynthesis processes and incorporation into the polymer chain.