Influence of substituents on the inhibition efficiency of phosphonic acid – Zn2+ systems

The inhibition efficiencies of ethyl phosphonic acid (EPA) and 2-chloroethyl phosphonic acid (2-Cl EPA) in the presence of Zn2+, in controlling the corrosion of mild steel in a neutral aqueous environment containing 60ppm Cl- have been evaluated by weight-loss method and compared. It is observed that 2-Cl EPA-Zn2+ system has more inhibition efficiency than an EPA-Zn2+ system. It is due to the electron withdrawing power of the Cl atom and its size. The nature of the protective film formed on the surface of the metal has been analysed by X-ray diffraction, UV-visible reflectance and luminescence spectr