Self-healing protective films prepared on zinc by treatments with cerium(III) nitrate and sodium phosphate

Chromate-free, self-healing protective films were prepared on a surface of zinc electrode previously treated in a solution of cerium(Ill) nitrate Ce(NO3)(3) by coverage of the surface with a layer of sodium phosphate Na3PO4. The self-healing ability of the film was examined by polarization measurements of the electrode after scratching the surface with a knife-edge crosswise and immersed in an aerated 0.5 M NaCl solution for many hours and by observation of pit formation at the scratches. A thin film containing 0.0552 mg/cm(2) of Na3PO4 . 12H(2)O prepared on the electrode previously treated in 1 x 10(-3) M Ce(NO3)(3) at 30 degreesC for 30 min and dried at 90 degreesC for 23 h was highly self-healing and protective against corrosion of zinc in 0.5 M NaCl at the scratches. No pit was detected at the scratches on the electrode coated with this film after immersion for 72 h. (C) 2002 Elsevier Science Ltd. All rights reserved.