XPS and EPMA studies on self-healing mechanism of a protective film composed of hydrated cerium(III) oxide and sodium phosphate on zinc

A thin, protective film was prepared on a zinc electrode by coverage with a hydrated Ce2O3 layer and 0.0552 mg/cm(2) of a Na3PO4.12H(2)O deposit layer and by drying the layers at 90degreesC for 23 h, as has been reported in the preceding paper. This film was highly self-healing at the scratched electrode in an aerated 0.5 M NaCl solution for many hours. The present investigation deals with elucidation on self-healing mechanism of this film by X-ray photoelectron spectroscopy and electron-probe microanalysis. The scratched surface was covered with deposits of Zn(OH)(2), ZnO and small amount of Zn-3(PO4)(2). Both cathodic and anodic processes of zinc corrosion were markedly suppressed by coverage of the scratches with the deposits, resulting in the self-healing activity at the scratched electrode in 0.5 M NaCl. (C) 2002 Elsevier Science Ltd. All rights reserved.