Influence of nitrate and chloride ions on the corrosion of iron

The effect of nitrate on the general corrosion and pitting corrosion of iron was investigated in sulfate-based solutions with different pH values. Nitrate greatly accelerates the general corrosion of iron in acidic solutions, but has slight influence on the general corrosion in neutral solutions. The pitting inhibition of nitrate is dependent on the pH value of solutions, and nitrate is able to prevent the passivated iron surface from pitting attack only in acidic solutions. This pitting inhibition effect is probably associated with the competition between the passivating action of nitrate and depassivating action of chloride at passivated iron surfaces. The current oscillation characteristics for the iron in pure sulfuric acid (H2SO4) solution and in H2SO4 + NaNb3 + NaCl (sulfuric acid + sodium nitrate + sodium chloride) mixed solution were compared, and the relations between the oscillatory behavior and pitting susceptibility of iron were interpreted.