Oxygen Reduction on Mild Steel and Stainless Steel in Alkaline Solutions

摘要

The cathodic polarisation curve of steel in alkaline solutions always shows three regions: (1) oxygen reduction with a Tafel behaviour at potentials cathodic to the open circuit potential followed by (2) a diffusion limited current of oxygen reduction at more negative potentials and (3) hydrogen evolution at very negative potentials. The diffusion limited region of the cathodic current density is controlled both by the oxygen concentration in solution and the flow rate whereas in the Tafel region (charge transfer) the temperature and the pretreatment of the sample determine the intensity of the current density and the slope of the Tafel line. On stainless steels the cathodic reduction currents are lower then on mild steel. It can be concluded that under usual corrosion conditions for steel in concrete the cathodic oxygen reduction is not diffusion limited but charge transfer controlled.