The a.c. corrosion of stainless steel—II. The breakdown of passivity of ss304 in neutral aqueous solutions

The effect of alternating current on the corrosion of Type 304 Stainless Steel in aqueous solutions of Na2SO4, NaNO3 and NaCl has been investigated with an alternating voltage (AV) modulation technique, using 60 Hz square wave AV. The anodic and cathodic polarization curves were measured for a range of AV from 0 to 1000 mV and the surfaces of specimens after a potentiostatic coulometry experiment were examined under a scanning electron microscope. It was found that AV shifted the corrosion potential toward the positive direction and the passive-transpassive transitional potential toward the negative direction. AV destroyed the passivity and enhanced the pitting corrosion of the steel in aqueous environments. The behavior was explained with a simple mathematical model. The computer simulated polarization curves for the AV modulation of Type 304 Stainless Steel showed characteristics similar to the experimental curves: good agreement was obtained for the onset of transpassive potentials in the presence of AV.