Cathodic Reactions Involved in Corrosion Processes Occurring in Concentrated Nitric Acid at 100degC

摘要

In order to explain and analyze the corrosion process of AISI 304 L stainless steel in the presence of nitric acid condensates, the reduction mechanism of nitric acid was studied on a platinum electrode in various nitric acid solutions (4- mol centre dot L~(-1) and 12 mol centre dot L~(-1)) at 100degC. Classical electro-chemical techniques were used: cyclic voltammetry, chronoamperometry on a stationary electrode as well as on a rotating disk electrode. A reduction mechanism is proposed; this mechanism is autocatalytic and involves a charge-transfer step and a heterogeneous chemical reactions which regenerates the electroactive species at the electrode surface. The electroactive species is assumed to be nitrous acid which is a soluble species. The other compounds involved in the reduction mechanism are NO and NO_2, which are supposed to be absorbed. The nitric acid concentration influences the major product of the reduction process: NO for concentrations lower than 8 mol centre dot L~(-1) and NO_2 for higher concentrations.