Synergistic inhibition of anionic and nonionic surfactants on corrosion of mild steel in acidic solution

Sodium oleic sulfonate (SOS), polyoxyethylene (20) sorbitan monooleate (Tween 80 or T₈₀) and their mixtures have been studied as acid corrosion inhibitors for mild steel in 1M HCl using adsorption and gravimetric techniques. All the data reveal that the compounds act as inhibitors in the acid environment. The adsorption and inhibition efficiency are discussed as a function of the concentration and the nature of mixing the two surfactants. T₈₀ + α_SOS mixtures show a better inhibition effect than SOS + α_T80, that increases with the value of α_SOS. The interaction and synergism of the investigated mixtures are studied by calculating the interaction parameters (β) and the degree of synergism (S) from surface tension‐concentration and corrosion data. The degree of synergism for T₈₀ + α_SOS is higher than that of SOS + α_T80. This is believed to be due to the presence of the small amount of the co‐surfactant SOS which serves as an anchor molecule for the nonionic molecules.