Self-healing mechanism of a protective film prepared on a Ce(NO3)3-pretreated zinc electrode by modification with Zn(NO3)2 and Na3PO4

Self-healing mechanism of a protective film against corrosion of zinc at scratches in an aerated 0.5 M NaCl solution was investigated by polarization measurements, X-ray photoelectron spectroscopy (XPS) and electron-probe microanalysis (EPMA). The film was prepared on a zinc electrode by treatment in a Ce(NO3)(3) solution and addition of aqueous solutions containing 9.98 or 19.9 mug/cm(2) of Zn(NO3)(2)(.)6H(2)O and 55.2 mug/cm(2) of Na3PO4. 12H(2)O. After the coated electrode was scratched with a knife-edge crosswise and immersed in the NaCl solution for many hours, polarization measurements, observation of pit formation at the scratches, XPS and EPMA were carried out. This film was remarkably protective and self-healing against zinc corrosion on the scratched electrode. The cathodic and anodic processes of zinc corrosion were markedly suppressed by coverage of the surface except for scratches with a thin Ce2O3 layer containing a small amount of Ce4+ and the surface of scratches with a layer composed of Zn-3(PO4)(2).4H(2)O, Zn(OH)(2) and ZnO mostly. (C) 2002 Elsevier Science Ltd. All rights reserved.