Influence of Deaeration, Cl⁻ Ion and Strong Oxidizer on the Active Behavior of the High Phosphorus Containing Pig Iron and Subsequent Effect on the Sacrificial Anode Behavior

The effect of deaeration, Cl⁻ ion content and strong oxidizer on the active behavior of the high phosphorus pig iron (HPPI) samples was studied in 3.5% NaCl and 1 N HNO₃ solutions. Deaerating the 3.5% NaCl solution could effectively shift the corrosion potential of the HPPI below the protective potential of the steel in seawater [− 0.778 V vs saturated calomel electrode (SCE)], which has not been observed in the freely aerated 3.5% NaCl solution. Both the Cl⁻ ion content and the deaerated conditions restrict the formation of the stable iron phosphate on the surface and promote the dissolution of the pig iron as soluble iron phosphate hydrate (FePO₄·2H₂O). However, in the case of the freely aerated nitric acid solution, even with deaeration, the HPPI samples have shown more noble behavior as compared to the mild steel due to the strong oxidizing nature of nitric acid and the formation of a stable iron phosphate on the surface.