ELECTROCHEMICAL STUDIES OF THE CORROSION OF 316L STAINLESS-STEEL COATED WITH SOL-GEL ZRO2 FILMS

ZrO2 sol-gel coatings were deposited on 316L stainless steel by dip-coating techniques, using a sol of Zr(OC3H7)(4) as a precursor and isopropanol, glacial acetic acid and water as the solvent prepared under ultrasound. The coatings were densified at temperatures ranging from 450 to 800 degrees C for 2 h. The influence of the different coatings on the corrosion behavior of steel in aerated aqueous solutions of 30 g dm(-3) NaCl was studied by potentiodynamic polarization curves and by electrochemical impedance spectroscopy using transfer functions from electric equivalent circuits for the fitting of the data. Both techniques showed a significant decrease in the corrosion rate for the coated samples as well as a discontinuity in the behavior of the system for films densified at temperatures above 450 degrees C. From the equivalent circuit analysis it was concluded that the films densified at 450 degrees C are quite porous, acting simply as a physical barrier between the substrate and the solution. For higher densification temperatures extra parameters related to a coating porosity effect must be included in the equivalent circuit; this effect is similar to that observed with paint coatings and related systems.