Synergistic effect of ethyl phosphonate and Zn²⁺ in low chloride media

The synergistic effect of sodium salt of ethyl phosphonic acid (EPA) and Zn²⁺ on the inhibition of corrosion of mild steel in neutral aqueous environment containing 60 ppm Cl^‐ has been evaluated by the weight‐loss method. The formulation consisting of 300 ppm EPA and 300 ppm Zn²⁺ has 88 per cent inhibition efficiency. The nature of the protective film formed on the metal surface has been analysed by x‐ray diffraction, FTIR, uv‐visible and luminescence spectra. The protective film is found to be luminescent and to consist of Fe²⁺ ‐EPA complex, Zn (OH)₂ and a very thin film of oxides of iron.