On the Passivation of Iron in Aqueous Solutions of Zinc 1-Hydroxyethane-1,1-Diphosphonate

Yu. I. Kuznetsov, G. V. Zinchenko, L. P. Kazanskii, N. P. Andreeva, and Yu. B. Makarychev

Frumkin Institute of Physical Chemistry and Electrochemistry, Russian Academy of Sciences, Moscow

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Received June 15, 2006

Abstract — This work is devoted to studying the passivating ability of the zinc complex of the 1-hydroxyethane-1,1-diphosphonic acid (HEDP) in a borate buffer solution. For the first time, we used the in situ ellipsometric method to study the mechanism of formation of a protective film on iron in the presence of HEDP, HEDPZn, and ZnSO₄ in the course of the cathodic polarization of the electrode. The investigations of adsorption of HEDPZn on iron (at E = –0.65 V) in combination with X-ray photoelectron spectroscopy (XPS) have shown that on the metal surface there is formed a multilayer protective film consisting of an internal layer of Zn(OH)₂ and an outer layer consisting of HEDP complexes with Fe²⁺ and/or Zn²⁺. It has been found that the thickness of the passi-vating film does not exceed 60 Å, of which 7–10 Å correspond to the low-soluble zinc hydroxide.