Corrosion resistant sol-gel ZrO 2 coatings on stainless steel

Abstract

Corrosion resistant ZrO 2 coatings on 316L stainless steel sheets have been fabricated utilizing sonocatalysis of precursors sols. The solutions were prepared from zirconium alkoxide Zr(OC 3H 7) 4, isopropanol alcohol, glacial acetic acid and water, and submitted to ultrasonic agitation. Their composition varied between 0.025 and 0.9 mol/l ZrO 2. Single thin films were thermally treated between 40 and 1100°C in unoxidizing atmosphere. The coatings characteristics were determined by X-ray diffraction, optical reflection, ellipsometry and scanning electron microscopy. At temperatures higher than 700°C, the films are polycrystalline with a tetragonal structure and show a blue-green color. Depending on the composition, the thickness varied from 5.5 to 35 nm. When treated under a slow and controlled heating rate, the ZrO 2 films with the smallest thickness show outstanding corrosion resistance to acid attack and to oxidation as no weight change was observed after 30 h treatment in H 2SO 4 at 81°C or 10 h treatment in air at 800°C. The thicker films as well as the films treated with a rapid heating rate tend to crack during the densification process and are less corrosion resistant.