| The objectives of this research were to gain an understanding of the corrosion characteristics of carbon steel with immersion experiments in seawater and with AV signals superimposed on the existing, DC corrosion potential.;The influence of AV (60 Hz) applied between the carbon steel working electrode and a platinum mesh counter electrode, the corrosion rate increases with applied voltage then decreases as the peak voltage is increased in the range of 100 to 600 mV. However, with a further increase in AV beyond 600 mV, the corrosion is observed to increase exponentially. A similar trend is found when the AV signals are applied between the working electrode and the reference electrode; however, the overall corrosion rates experienced are higher.;Potentiodynamic polarization experiments show that higher pH solutions result in lower corrosion currents. Also, a small passivation region appears on the curves for pH values greater than 8.2. Thus, it is believed that the change in local pH must be responsible for the observed passivation regime for immersion experiments.;The separate effects caused by the positive and negative halves of the AV signals were studied by using rectified AV for some experiments. Generally, these results show that positive cycle rectified AV increases corrosion above that for full wave AV. Negative rectified AV results in corrosion rates less than full wave AV; however, the rates experienced are still higher than with no signal applied.;The effect of frequency of AV signal was also investigated. With increases in frequency, corrosion rates drop quickly to levels near that for no AV. At higher frequencies, metal ions formed during corrosion in the positive half cycle are available for immediate redeposition. Also, at lower frequencies, the time necessary for metal ion diffusion into the solution is less than the time in which the polarity of the electrode is changed. Hence, less metal ions are available for redeposition.;A computer model, based on DC polarization curves, demonstrates that the corrosion rates should increase with applied voltage. The predicted increase in corrosion current by the model is much greater than the actual increases observed. (Abstract shortened with permission of author.)... |
