Effect of Na₃PO₄ on the corrosion inhibition efficiency of EDTA – Zn²⁺ system for carbon steel in aqueous solution

560-565The synergistic effect of sodium salt of ethylene diamine tetra acetic acid (EDTA) and Zn²⁺ in controlling corrosion of carbon steel in an aqueous environment containing 60 ppm Cl⁻ was evaluated by weight loss and electro chemical methods. A formulation consisting of 50 ppm EDTA and 50 ppm Zn²⁺ was observed to achieve 73% inhibition efficiency. Influence of Na₃PO₄ on EDTA - Zn²⁺ was studied and IE was found to increase from 73 to 98%. A suitable mechanism of corrosion inhibition has been proposed which is based on the results obtained from weight loss method, polarization study, AC impedance spectra and FTIR spectra. The protective film consisted of Fe²⁺ - EDTA, Fe²⁺ - Na₃PO₄ complexes and Zn(OH)₂