Effect of molybdate, nitrite and zinc ions on the corrosion inhibition of mild steel in aqueous chloride media containing cupric ion

摘要

An investigation has been conducted on the corrosion inhibition of mild steel by molybdate, nitrite and zinc ions in aqueous chloride media containing cupric ion. Molybdate inhibits mild steel corrosion in near neutral and alkaline (pH 6 and above) chloride media and accelerates corrosion in acidic media (below pH 6) both in the presence and absence of cupric ion. Nitrite inhibits mild steel corrosion in chloride media at pH 4.5 and above, but accelerates corrosion below pH 4.5 both in the presence and absence of cupric ion. Molybdate and nitrite act as a synergistic corrosion inhibitor in chloride media with or without cupric ion at pH 4.5 and above. In the acidic region between pH 3 and 4.5, the combination can decrease corrosion with a low concentration of molybdate and high concentration of nitrite. These concentrations depend on the relative amounts of molybdate and nitrite present in the system. Zinc ion inhibits mild steel corrosion only in acidic chloride media. Based on the experimental results, mechanisms of action of molybdate, nitrite and zinc ions on mild steel corrosion in aqueous chloride media with or without cupric ion have been proposed.