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

E-mail: kuznetsov@ipc.rssi.ru

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.

DOI: 10.1134/S0033173207070065

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