Electrochemical Behavior in Na2SO4 of Nanoporous Oxide Films Previously Formed on AISI 304 by Electrocoloring

Thick nanoporous oxide films exhibiting interference colors were grown on AISI 304L stainless steel by triangular current scan method in 5 M H2SO4 + 2.5 M H2CrO4 using different electrolysis times. The nanocrystalline spinel oxide films thus obtained were electrochemically characterized by cyclic voltammetry at 1 mV.s(-1) in 0.5 M Na2SO4. Strong anodic peaks are observed at the potential region where the transpassive peak of stainless steels is expected. Such behavior evidences not only the large active surface area of the films, but also that the cationic species are not fully oxidized. The effect of polarizing in 0.5 M Na2SO4 to a potential in the transpassive region on the morphology and the composition of these films was investigated.