CORROSION-RESISTANCE OF ARTIFICIAL PASSIVATION FILMS OF FE2O3-CR2O3-NIO FORMED BY METALORGANIC CHEMICAL-VAPOR-DEPOSITION

A series of thin Fe2O3-Cr2O3-NiO films were formed on Pt by an MOCVD technique using Fe(III), Cr(III), and Ni(II) acetylacetonate. The corrosion resistance of the films was examined in H2SO4 and HCl by measuring the film thickness using ellipsometry and the chemical analysis of test solutions with ICPS. The dissolution rate of Fe2O3-Cr2O3 composite films decreases exponentially with an increase in the cationic mass fraction of Cr3+ ions, X(Cr), of the films, and at the values of X(Cr) larger than 0.7 it becomes two orders of magnitude lower than that of Fe2O3 films. The same type of changes in the dissolution rate with X(Cr) was observed for the NiO-Cr2O3 composite films. Therefore, the addition of Cr2O3 to Fe2O3 and NiO films effectively improves the corrosion resistance. The addition of NiO to Fe2O3-Cr2O3 composite films containing an adequate amount of Cr2O3 does not bring an effective improvement in corrosion resistance. Therefore, the corrosion resistance of Fe2O3-Cr2O3-NiO composite films is determined primarily by the Cr2O3 content of the films.