1988 WHITNEY AWARD LECTURE - DONT BE AFRAID OF ELECTROCHEMICAL TECHNIQUES BUT USE THEM WITH CARE

It is pointed out that neglecting the effects of the uncompensated resistance (ohmic drop) can cause distortions of polarization curves, underestimation of corrosion rates, and changes in the true scan rate of a potentiodynamic curve. Positive feedback and the interrupter technique can be used to eliminate such errors. The choice of the correct scan rate is an important factor in the performance of potentiodynamic tests. Electrochemical impedance spectroscopy (EIS) has broadened the range of corrosion phenomena which can be studied using electrochemical techniques. Examples of EIS applications include the evaluation of corrosion behaviors of polymer-coated metals and anodized Al alloys. EIS can be used as a quality control test for anodized Al surfaces and for chromate conversion coated Al alloys. It is only possible to use the full power of the EIS technique if suitable models for the impedance behavior and fitting programs for the analysis of EIS data are developed. Examples of such models and software are given for polymer-coated steel and anodized Al. A model which describes the localized corrosion behaviors of Al alloys and Al-based metal matrix composites is also presented.