Sonoelectrochemical synthesis, optimized by Taguchi method, and corrosion behavior of polypyrrole-silicon nitride nanocomposite on St-12 steel

• Synthesis of PPy and PPy-SiN nanocomposite coatings using sonoelectrochemical method.
• Optimization of nanocomposite synthesis was performed through Taguchi design.
• The presence of SiN nanoparticles improved the corrosion resistance of PPy coatings.
• Characterization of prepared coatings was investigated by FT-IR and SEM techniques.

This work describes a new sonoelectrochemical synthesis method of novel composite materials based on silicon nitride (SiN) nanoparticles and intrinsically conducting polypyrrole (PPy). The sonoelectrochemical synthesis of polypyrrole coating and polypyrrole-silicon nitride (PPy-SiN) nanocomposite performed and corrosion behavior of these coatings on St-12 steel was studied by electrochemical methods. A design of experiment (DOE) technique using the Taguchi method has been applied to optimize the affecting factors on the sonoelectrochemical synthesis of PPy-SiN nanocomposite such as current density, synthesis time and amount of nanoparticles.The corrosion protection of St-12 steel by polypyrrole and polypyrrole-SiN nanocomposite coatings were investigated by open circuit potential (OCP) time trends, potentiodynamic polarization technique and electrochemical impedance spectroscopy (EIS) in NaCl 3.5% solution. The Kramers–Kronig transformation (KK) was applied to evaluate the validity of the experimental impedance data. The results prove that the addition of nanoparticles increased corrosion resistance of coatings and improved the surface morphology. Scanning electron microscopy (SEM) images reveal that the nanocomposite coatings form compact, homogenous and dense films on the St-12 steel surfaces.