Self-healing mechanism of an organosiloxane polymer film containing sodium silicate and cerium(III) nitrate for corrosion of scratched zinc surface in 0.5 M NaCl

A highly protective and self-healing film of 1,2-bis(triethoxysilyl)ethane (C2H5O)(3)Si(CH2)(2)Si(OC2H5)(3) polymer containing sodium silicate (water glass) Na2Si2O5 and cerium(III) nitrate Ce(NO3)(3) was prepared on a zinc electrode previously treated in a Ce(NO3)(3) solution. The film was examined by polarization measurement of the electrode in an aerated 0.5 M NaCl solution after the electrode was scratched and immersed in the solution for 4-72 h. Self-healing mechanism of the film was investigated by X-ray photoelectron spectroscopy and electron-probe microanalysis for the coated electrode surface after scratched and immersed in the NaCl solution. A passive film composed of Zn(OH)(2), ZnSi2O5 and Ce3+-Si2O52- salt or complex was formed on the scratched surface and preferential deposition of Si2O52- pounds occurred at a defect of the passive film where Cl- accumulated, resulting in suppression of pitting corrosion at the scratch. (C) 2002 Elsevier Science Ltd. All rights reserved.