Analysis of protective f ilm formed on surface of mild steel immersed in Chloride – HEDPmolybdate – Zn2+ environment

Abstract

The inhibition efficiency of the formulation consisting of 1hydroxyethane-1, 1-diphosphonic acid (HEDP), molybdate and Zn2+ in controlling the corrosion of mild steel in neutral aqueous environment containing 60ppm Cl– has been evaluated by the weight-loss method. The formulation consisting of 50ppm HEDP, 300ppm molybdate and 10ppm Zn2+ has 97 per cent inhibition efficiency. The nature of the protective film has been analysed by using xray diffraction (XRD), FTIR and fluorescence spectra. The protective film is found to be fluorescent and to consist of Fe2+–HEDP complex, Fe2(MoO4)3 complex and Zn(OH)2. A suitable mechanism of corrosion inhibition is proposed based on the results obtained from the weight-loss method, polarisation study, XRD, FTIR, fluorescence and atomic absorption spectra.