The role of phosphonates as transporters of Zn²⁺ ions in the inhibition of carbon steel in neutral solutions containing chlorides

Abstract

Phosphonates have shown synergistic effects in combination with Zn²⁺ ions in controlling the corrosion of carbon steel immersed in neutral aqueous environments containing 60‐ppm Cl^‐. The role of phosphonates in the presence of Zn²⁺ ions has been investigated by polarisation tests and weight loss results. It was observed that the phosphonates functioned as transporters of Zn²⁺ ions from the bulk of the solution towards the metal surface. The phosphonate‐Zn²⁺ bond is sufficiently strong to carry Zn²⁺ ions from the bulk solution towards the metal surface, but is weak enough for them to break to form a phosphonate‐Fe²⁺ bond at anodic sites on the metal surface. Inhibition efficiency increases when the phosphonate‐Zn²⁺ complex remains in solution in soluble form. Inhibition efficiency decreased when the phosphonate‐Zn²⁺ complex was precipitated in the bulk of the solution.

Citation

Rajendran, S., Apparao, B.V., Palaniswamy, N., Amalraj, A.J. and Sundaravadivelu, M. (2002), "The role of phosphonates as transporters of Zn²⁺ ions in the inhibition of carbon steel in neutral solutions containing chlorides", Anti-Corrosion Methods and Materials, Vol. 49 No. 3, pp. 205-209. https://doi.org/10.1108/00035590210426472