On the passivation of iron in aqueous solutions of zinc 1-hydroxyethane-1,1-diphosphonate

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 passivating film does not exceed 60 ?, of which 7–10 ? correspond to the low-soluble zinc hydroxide. Original Russian Text ? Yu.I. Kuznetsov, G.V. Zinchenko, L.P. Kazanskii, N.P. Andreeva, Yu.B. Makarychev, 2007, published in Korroziya: Materialy, Zashchita, 2006, No. 9, pp. 19–26.