Influence of the Temperature on the Reduction Mechanism of Concentrated Nitric Acid on a Silicon-Enriched Austenitic Stainless Steel

Corrosion of silicon-enriched stainless steel in nitric acid strongly depends on the temperature of the electrolyte. Therefore, the reduction reaction of nitric acid on this material was investigated from 40 to 107 degrees C. For the first time, the autocatalytic reduction mechanism of nitric acid reduction is highlighted by coupling electrochemical measurements (LSW, EIS, Chronoamperometry) with chemical analyses (mass spectrometry, ICP-AES, UV-Vis spectroscopy). This study provides further insights into the nitric acid reduction on an oxidized material compared to that reported earlier on noble metals despite slower kinetics of electrochemical reactions due to the presence of a passivating film. Furthermore, it is shown that HNO2 (or NO+) promotes the autocatalytic reactions in concentrated HNO3 and leads to the formation of NOx species released and detected in the gas phase.