Relation between oxidation power of nitric acid solutions containing oxidizing species and corrosion behavior of stainless steel

Motooka, Takafumi; Yamamoto, Masahiro ; Ueno, Fumiyoshi  ; Kato, Chiaki   

The effect of chromium and vanadium ions on corrosion of stainless steels in boiling nitric acid solutions were investigated in terms of valence change with time. The corrosion behavior of type SUS304ULC stainless steel in boiling nitric acid solutions was investigated by corrosion test, measurement of corrosion potential and solution analysis. The formation rates of Cr(VI) and V(V) were also measured in boiling nitric acid solutions. Cr(VI) more severely attacked the stainless steel than V(V). The concentration of Cr(VI) reduced with progress of corrosion and the oxidation ability of test solution weakened. While the concentration of V(V) was constant with progress of corrosion and the oxidation ability of test solution was maintained constant. In boiling nitric acid solutions, the formation rate of V(V) from reducdant was faster than that of Cr(VI). In boiling nitric acid solution with V(V), the formation rate of V(V) was faster than the consumed rate of V(V) by corrosion of stainless steel. This caused the constancy of V(V) concentration and the steady corrosion of stainless steel. In boiling nitric acid solution with Cr(VI), the formation rate of Cr(VI) was slower than the consumed rate of Cr(VI) by corrosion of stainless steel. This caused the decreases of Cr(VI) concentration and corrosion rate of stainless steel.