Cathodic reactions involved in corrosion processes occurring in concentrated nitric acid at 100 degrees C

In order to explain and analyze the corrosion process of AISI 304 L stainle ss steel in the presence of nitric acid condensates, the reduction mechanis m of nitric acid was studied on a platinum electrode in various nitric acid solutions (4 mol.L-1, 8 mol.L-1 and 12 mol.L-1) at 100 degrees C. Classica l electrochemical techniques were used: cyclic voltammetry, chronoamperomet ry on a stationary electrode as well as on a rotating disk electrode. A red uction mechanism is proposed; this mechanism is autocatalytic and involves a charge-transfer step and a heterogeneous chemical reaction which regenera tes the electroactive species at the electrode surface. The electroactive s pecies is assumed to be nitrous acid which is a soluble species. The other compounds involved in the reduction mechanism are NO and NO2, which are sup posed to be adsorbed. The nitric acid concentration influences the major pr oduct of the reduction process: NO for concentrations lower than 8 mol.L-1 and NO2 for higher concentrations.