Corrosion by Alternating Current: A Study of the Anodic Polarization of Mild Steel in Na2SO4 Solution

A study has been made of the anodic polarization of mild steel in Na2SO4 solutions (pH 3-9) in the presence of a sinusoidal electric current. The measurement was carried out over a range of alternating current (AC) densities from 0 to 200 mA/cm2 and AC frequencies from 20 to 6000 Hz. It was found that the corrosion potential of mild steel shifted toward the active direction in the presence of AC. The magnitude of the potential shift increased with increasing AC densities, and decreased with AC frequencies. AC also increased the passivity current density in a way similar to the addition of chloride ions to the electrolyte. The phenomenon was explained with a time-averaging analysis of the mixed potential theory.