Inhibition of pitting corrosion of C-steel in NaCl solution by some inorganic compounds

Abstract

Pitting corrosion potentials of a carbon steel electrode in different concentrations of sodium chloride solutions were measured using potentiodynamic technique. It was found that the increase in chloride ion concentration leads to a decrease in the pitting potential according to S-shaped curve. This curve was explained on the basis of formation of passivitable, limiting active and continuously propagated pits depending on the concentration of chloride ion. Addition of the sodium salts of vanadate, molybdate and tungestate caused a shift of the pitting potential toward the noble direction accounting for increased resistance to pitting attack. The inhibitive properties of these anious were explained on the bases of their strong adsorption on the metal surface as well as formation of insoluble salts by combination with the dissolved metal ions. These insoluble salts resist the penetration power of chloride ion and consequently decrease the rate of pitting corrosion.