Polarisation studies of the cold rolled mild steel in sulphuric acid containing metallic ions and an inhibitor

The influence of thiourea in association with Cu++, Hg++ or Ce++++ on the open circuit potential anodic and cathodic polarization of the cold rolled mild steel in 2NHH2SO4 has been studied at room temperature. Thiourea at 750 ppm shifts the potential towards active side, indicating its main influence on the cathodic reactions. But, thiourea in presence of different concentrations of Cu++, Hg++ or Ce++++ shifts the potential towards less active direction. Maximum anodic shift in the potential is observed with Ce++++ ions. BH increases with increase in the concentrations of the metallic ions but no such marked change in bFe is observed. At higher concentrations of the metallic cations, bH decreases. Corrosion rates calculated from the polarization curves are in good agreement with the corrosion rates determined from the weight loss.