2002 Volume 51 Issue 12 Pages 549-554
Nitrous acid affects the corrosion of metals such as stainless steels in nitric acid. However nitrous acid is not particularly stable in nitric acid and the analytical methods available are quite involved. Accordingly, the calculation of nitrous acid concentration from redox potential was tested in the HNO3-H2O system as a convenient in situ analysis method. The calculation process is based on Nernst's equation and the required thermodynamic data were obtained from published values. The available thermodynamic data allow calculation of nitrous acid concentration from 273K to 373K for 0%-100% HNO3. The redox potential was measured in 8kmol·m-3 HNO3 under NO bubbling and the nitrous acid concentration was determined by a Colourimetric method. The calculated data were compared with the measured data and a good agreement was found. It was found that the corrosion potential of stainless steel is influenced by nitrous acid concentration in nitric acid solution. The calculation process is useful for in-situ analysis of nitrous acid species in HNO3-H2O system and understanding the behavior of the cathodic reaction associated with nitric acid corrosion.