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

Abstract Chromate-free, self-healing protective films were prepared on a surface of zinc electrode previously treated in a solution of cerium(III) nitrate Ce(NO 3 ) 3 by coverage of the surface with a layer of sodium phosphate Na 3 PO 4 . 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 Na 3 PO 4 ·12H 2 O prepared on the electrode previously treated in 1×10 −3 M Ce(NO 3 ) 3 at 30 °C for 30 min and dried at 90 °C 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.