A study has been made of the effect of 60-Hz sinusoidal, square, and triangular alternating voltages (AV) on the corrosion of aluminum in dilute nitric acid, sodium nitrate, sodium sulfate, and sodium chloride solutions. The anodic polarization curves and the pitting behavior of aluminum were examined with an AV modulation technique over a range of AV magnitudes from 0 to 2000 mV rms. The results revealed that AV reduced the passive potential regime of aluminum by shifting the passive-transpassive transition potential toward the negative direction and the active-passive transition potential toward the positive direction. AV destroyed the passivity of aluminum in the nitrate solutions and caused the pitting corrosion to occur at more negative DC potentials. The effect of AV on the pitting corrosion of aluminum in nitrate solutions was much greater than that in sulfate solutions, but less severe than that in chloride solutions. The pits generated by AV in nitrate solutions were perfect hemispheres, in contrast to the irregular shaped pits in chloride solutions, and shallow elongated pits in sulfate solutions.

Subject
Pits, Anode potential, Aluminum, Sulfates, Oxide films, Chloride solutions, Acidity, Nitric acid, Nitrates, Pitting, Corrosion potential, Passivity, Electrode potential
Keywords:
AC corrosion, destruction of passivity, pitting, polarization
National Association of Corrosion Engineers
1989
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