ZrO2-CeO2 films as protective coatings against dry and wet corrosion of metallic alloys

ZrO2-CeO2 films were deposited on metals by sol-gel processing. The coatings were effective barriers against both corrosion in aggressive electrolytes and oxidation at high temperature. The protective action of the deposited coatings, was mainly dependent on their thickness and above all on the absence of any defects. Coatings withstood up to 80 h in acid environment and up to 18 h at 750 degrees C in air. A strict control of the film thickness and quality could be performed by modifying the solutions of alkoxide precursors of ZrO2-CeO2 used for the deposition. The corrosion behaviour in 0.1 M H2SO4 and in 15 wt.% HCl was studied by electrochemical impedance spectroscopy. The electrochemical test on coated samples in different electrolytes, provided information about the nature and size of the defects with respect to the different preparation procedures. In order to evaluate the protective capacity of films independently of the substrate, superalloy sheets were coated by the same solutions and tested in the same acid environment, and the results were compared with those of 304 stainless steel-coated samples. (C) 1997 Elsevier Science S.A.