Anodic Tafel behaviour of mild steel in presence of inhibitors

The kinetics of mild steel dissolution in 1.0 N H 2 SO 4 and 1.0 N HCl were studied by steady‐state anodic vs potential measurements in presence of varying concentrations of thiourea (TU) and thiosemicarbazide (TSC). An anodic Tafel slope of 38–40 mV/decade was observed in both acids in accordance with the Bockris model. The anodic Tafel slope increases regularly with increasing the inhibitor concentration. A mechanism is proposed – after Kelly – to explain this effect semiquantitatively. A surface complex is assumed to be formed between the adsorbed inhibitor and the dissolution reaction intermediates. A change of the rds for iron dissolution in presence of the inhibitor, is suggested.