Influence of a cationic surfactant on the inhibition efficiency of calcium gluconate – Zn²⁺ system

The influence of a cationic surfactant, N‐cetyl‐N, N, N‐trimethyl ammonium bromide (CTAB) on the inhibition efficiency (IE) of calcium gluconate (CG) – Zn²⁺ system in controlling corrosion of mild steel in a neutral aqueous environment containing 60ppm Cl^‐ has been evaluated by weight‐loss method. The formulation consisting of 200 ppm CG and 50ppm Zn²⁺ has 86 per cent IE (immersion period = three days). Addition of various concentrations of CTAB to the above system improves the IE to 99 per cent. Presence of CTAB facilitates the transport of CG and Zn²⁺ from the bulk of the solution to the metal surface. The nature of the protective film formed on the surface of mild steel has been analysed by FTIR and fluorescence spectra. The protective film is found to be fluorescent and to consist of iron‐CG complex, iron‐CTAB complex and Zn(OH)₂.