ABSTRACT

Inconel-600 and stainless steel-304 were modified electrochemically by formation of hydrous oxide film under potential cycling conditions in alkaline solution. The mechanism of the oxide growth proceeds in an analogy to the growth of oxide films on noble and some non-noble metals,  such  as nickel and iron. The oxide films were characterized by cyclic voltammetry, where  the main oxidation/reduction  processes were attributed to Fe(OH)₂/FeOOH and Ni(OH)₂/NiOOH transitions. Corrosion implications of the present approach of surface modification were shown by anodic polarization and open-circuit potential measurements in acid solution. Modified electrodes exhibited about one order of magnitude lower currents in both active and passive ranges of anodic polarization curves. The breakdown of the oxide films in the presence of hydronium ions was delayed on modified electrodes. The model of enhanced stability presented in this work is based on the formation of a hydrous oxide film in alkaline solution followed by a selective dissolution of nickel and iron when metal electrodes were transferred to an acid solution. Consequently, the enrichment of chromium in the surface layer took place. In this connection, the percolation model for passivation of stainless steels and binary alloys was used here and confirmed experimentally in the case of stainless steel-304 and inconel-600.