Dissolution susceptibility of the oxide species formed on mild steel during its oxidation in molten NaNO3-KNO3 eutectic mixture

Mild steel was oxidized in pure molten NaNO3-KNO3 eutectic mixture at temperatures of 300, 375, and 450 degreesC and in the presence of 0.05 molal KH2PO4, K2Cr2O7, or Na2O2 as additives. The dissolution susceptibility of the formed oxide species was evaluated in H2SO4 acid solution using the potential-time and current-time measurements under the open-circuit conditions. It was found that the rate of dissolution depended on the composition of molten nitrate bath, used for oxidation of mild steel, and its temperature. This was attributed to the effect of the previous conditions of the nitrate bath on the nature and composition of the oxide species formed on the metallic surface. The more resistant to dissolution in H2SO4 solution were those electrodes that were oxidized in nitrate melt at 450 degreesC in the presence of K2Cr2O7 or Na2O2 as additives.