Effect of Cetylpyridinium chloride on corrosion inhibition of mild steel in chloride environment

With the objective of developing a new environmental friendly inhibitor formulation for corrosion of mild steel, Cetylpryidinium chloride (CPC) was chosen as inhibitor in 3.5%NaCl environment. Zn2+ was chosen as a synergist. The inhibition efficiency (IE) of various concentrations of a CPC-Zn2+ system in controlling corrosion of mild steel immersed in 3.5% NaCl solution was evaluated by a weight-loss study, electrochemical impedance spectroscopy and potentiodynamic polarization method. The result showed that when CPC alone was used the IE was less but in combination with Zn2+ as a synergist, IE increases. The most effective inhibitive effect was shown by 250 ppm of CPC and 5 ppm of Zn2+ as 54%. Polarization study reveals that the inhibitor formulation was a mixed type inhibitor. The protective film formed on the metal surface was confirmed by electrochemical impedance spectroscopy (EIS). The nature of the protective film has been characterized by FTIR and FESEM. The protective film is found to consist of Fe2+- Cetylpyidinium chloride complex. The alkyl chain of the surfactants is directed to the metal surface and covers the larger areas at the interface and thus increases the density of the protective layer on the metal surface. Based on the above studies a suitable mechanism has been proposed for the corrosion inhibition.