A comparative study on the corrosion behaviour of 304 austenitic stainless steel in sulfamic and sulfuric acid solutions

Potentiodynamic polarization and EIS have been employed to compare the corrosion behaviour of 304 stainless steel in NH2SO3H and H2SO4 solutions. Corrosion tests were carried out as a function of the acid's concentration (0.1-0.5 M) and solution temperature (20-60 oC). The corrosion rate is higher in H2SO4 than in H2NSO3H in all concentrations and temperatures. Values of the activation energy (Ea) revealed that the corrosion process is faster in H2SO4 than in NH2SO3H solution. EIS data showed that the display of Nyquist plots, and hence the mechanism of corrosion, depends not only on the acid concentration but also on the solution temperature. In 0.1 M concentration, the equivalent circuits Re(RctQdl) and Re(RctQdl)(RQ)ads describe the corrosion systems in H2NSO3H and H2SO4 solutions respectively. At concentrations ≥0.2 M, the equivalent circuit Re(RctQdl)Qdiff is applicable. Adsorption of the counter ion of the acid on the steel surface and the stability of the surface complex may explain the observed corrosion rates. © 2008 Elsevier Ltd. All rights reserved.