Corrosion inhibition by phosphonic acid –Zn2+ systems for mild steel in chloride medium

S. Rajendran (S. Rajendran is based at the Corrosion Study Centre, Department of Chemistry, G.T.N. Arts College (Autonomous), Dindigul, Tamil Nadu, India.)
B.V. Apparao (B.V. Apparao is based in the Department of Chemistry, Regional Engineering College, Warangal, Andhrapradesh, India.)
N. Palaniswamy (N. Palaniswamy is based in the Corrosion Science and Engineering Division, Central Electrochemical Research Institute, Karaikudi, Tamil Nadu, India.)

Anti-Corrosion Methods and Materials

ISSN: 0003-5599

Publication date: 1 December 2000


The inhibition efficiencies of 2‐carboxyethyl phosphonic acid (2 CEPA) – Zn2+ system and ethyl phosphonic acid (EPA) – Zn2+ system in controlling corrosion of mild steel in a neutral aqueous environment containing 60ppm CI have been compared. Polarization study reveals that both the systems function as mixed inhibitors. The inhibition efficiencies of these systems decrease with period of immersion due to the dissolution of the protective film as the period of immersion increases. The 2 CEPA – Zn2+ system has a better inhibition efficiency than the EPA–Zn2+ system. This is due to the fact that the amount of Fe2+– 2 CEPA complex present on the metal surface is higher than that of Fe2+– EPA complex, as revealed by fluorescence spectra. The molecular size of the iron phosphonate complex exercises a greater influence than the electronic (inductive) effect of the substituent in controlling corrosion of mild steel in chloride environment.



Rajendran, S., Apparao, B. and Palaniswamy, N. (2000), "Corrosion inhibition by phosphonic acid –Zn2+ systems for mild steel in chloride medium", Anti-Corrosion Methods and Materials, Vol. 47 No. 6, pp. 359-365.

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