Improvement in the self-healing ability of a protective film consisting of hydrated cerium(III) oxide and sodium phosphate layers on zinc

A self-healing protective film prepared on a zinc electrode by previous treatment in a Ce(NO3)(3) solution and coverage with a Na3PO4 layer was improved by the addition of Zn(NO3)(2). The protective and self-healing abilities of the films against corrosion of zinc in an aerated 0.5 M NaCl solution were examined by polarization measurements and observation of pit-like anodic dissolution feature (plf) and pit formation after the electrode was scratched with a knife-edge crosswise and immersed in the solution for many hours. The film prepared on the pretreated electrode coated with 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 was significantly protective and self-healing against zinc corrosion on the scratched electrode. The protective efficiency of the film was more than 96% in the region of the immersion time between 72 and 360 h. No plf was observed at the scratches after immersion for 120 h. Results of Fourier transform infrared reflection and X-ray photoelectron spectroscopies revealed that the film was composed of Na3PO4, Zn-3(PO4)(2) and Ce2O3 layers. (C) 2002 Elsevier Science Ltd. All rights reserved.