Pitting corrosion resistance of coloured oxide films grown on stainless steel in sulphuric acid in the presence and absence of chromic acid

Abstract

In this work, pitting corrosion resistance of coloured oxides films grown on AISI-304 stainless-steel in H2SO4 and H 2SO4 + CrO3 was evaluated. Surface morphology and topography of the films were examined by SEM (scanning electron microscopy) and AFM (atomic force microscopy), respectively. Electrochemical characterizations were conducted by polarization curves and impedance measurements in borate buffer pH 9.2. The pitting corrosion was evaluated by polarization curves carried out in the same solution containing NaCl. All coloured films presented similar values of Epit, but they were higher than those for non-coloured ones. The values of (Epit - Ecor) were in the range of 0.45-0.57 V, 0.78-0.92 V and 0.98-1.12 V for native films and films grown in the presence and absence of chromic acid, respectively. Therefore, the films grown on stainless steel in the absence of chromic acid presented the highest potential range free of pitting corrosion. © 2010 Sociedade Brasileira de Química.