Corrosion Behaviour of Electrodeposited Nanocrystalline Cobalt

Abstract. The room temperature corrosion behaviour of sulfur-containing nanocrystalline Co (12nm grain size) produced by electrodeposition has been studied using potentiodynamic polarization in a 0.25 molar Na2SO4 solution at a pH of 6.5. The results were compared with measurements on conventional polycrystalline Co prepared by different methods and annealed nanocrystalline Co. None of the samples showed passivity in this environment and grain size had only a minor effect in the overall corrosion performance. In as-deposited nanocrystalline Co, the S impurities were found to accumulate on the surface of the sample after potentiostatic polarization and resulted in slightly enhanced corrosion current. However, after grain growth in this material to an average grain size in the order of 10µm by annealing, extensive intergranular corrosion was observed which is likely due to S segregation to the grain boundaries