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 °C 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 °C in the presence of K₂Cr₂O₇ or Na₂O₂ as additives.