Electrochemical characterization of sol-gel protective ZrO sub 2 coatings on sintered stainless steels

ZrO sub 2 films derived from sol-gel technique were obtained by dip- coating onto commercial sintered AISI 304 and 316 stainless steel compositions. The coatings were processed from a zirconium (4) propoxide precursor solution, sintered at 800 deg C for 2 hours in air. The sintered steel substrates present volumetric residual porosity of approximately 13%. The ceramic coatings aiming at the reduction of the metallic exposed area, give rise to an increase upon the corrosion resistance of these sintered materials. The electrochemical corrosion tests, in acid medium, indicate reductions in the passivation currents at one order magnitude when compared to non-coated substrates. Concerning the corrosion rate, the 304 coated sample presented the best performance by showing a reduction of the corrosion parameters when compared to the non-coated sample. Homogeneity and morphological aspects of the sol-gel densified films are SEM and AFM characterized. The films are generally characterized by irregular and discontinuous structure. Images from AFM indicate that the films are composed of a particulate estructure homogeneously dispersed on the surface, meaning irregular densification/shrinkage.