Corrosion kinetics of type 310 EHP stainless steel in nitric acid with Cr(VI)

Corrosion kinetics of a stainless steel in nitric acid at elevated temperature has been investigated with special emphasis placed on its correlation with reduction rate of Cr (VI) in the solution. Extra High Purity (EHP) stainless steel, which is immune to intergranular corrosion in trans-passive potential range in nitric acid solution, has been employed to examine the dominant factor of corrosion rate. The results indicate that dissolution amount of the alloy agrees well with the stoichiometric value of dissolution based on the reduction amount of Cr (VI). This fact means that the dissolution kinetics of the stainless steel is simply dominated by reduction rate of Cr (VI) in the boiling nitric acid including Cr(VI). Reduction rate constant of Cr (VI) follows the identical Arrhenius equation including all the data with and without boiling, although oxidation rate constant of Cr (III) to Cr (VI) is strongly affected by boiling. A dominant factor of corrosion rate has been cleared based on the reduction rate constant of Cr (VI) and the oxidation rate constant of Cr (III).