Protein–surfactant aggregate as a potential corrosion inhibitor for mild steel in sulphuric acid: zein–SDS system

The corrosion inhibition of mild steel in 0.5 M H2SO4 in the presence of zein (a biocompatible water insoluble corn protein) and sodium dodecyl sulfate (SDS, an anionic surfactant) is studied employing electrochemical techniques and gravimetric measurement. SEM and FTIR techniques are employed to observe the morphology of the corroded surface and the nature of the adsorbed layer. It is revealed that SDS micelles in high concentration exhibit low corrosion inhibition efficiency for mild steel in H2SO4, but inhibition efficiency increases drastically in a zein–SDS mixed system, reaching more than 90% in the presence of 4 mM SDS–500 ppm zein. The dependence of the inhibition efficiency on surfactant–protein ratio is explained by zein–SDS complex formation, followed by SDS induced conformational change of zein.