Preparation of chromate-free, self-healing polymer films containing sodium silicate on zinc pretreated in a cerium(III) nitrate solution for preventing zinc corrosion at scratches in 0.5 M NaCl

Self-healing protective films of 1,2-bis(triethoxysilyl)ethane (C2H5O)(3)Si(CH2)(2)Si(OC2H5)(3) (abbreviated to BTESE) polymer containing sodium silicate Na2Si2O5 (water glass) and cerium(Ill) nitrate Ce(NO3)(3) were prepared on a zinc electrode previously treated in a 1 x 10(-3) M Ce(NO3)(3) solution at 30degreesC for 30 min. After the surface of coated electrode was crosswise scratched with a knife edge, the electrode was immersed in an aerated 0.5 M NaCl solution at 30 degreesC for many hours and polarization measurements of the scratched electrode were carried out for estimating the self-healing effects of the films on zinc corrosion at the scratches. The optimal quantities of Na2Si2O5, Ce(NO3)(3) and BTESE in the films were determined by polarization measurements and observation of pit formation at the scratches, No pitting corrosion occurred at the scratches on the zinc electrode covered with a film composed of their optimal quantities after immersion in the solution for 72 h. (C) 2002 Elsevier Science Ltd. All rights reserved.