Short-term electrochemical tests were performed on iridium-activated Al alloy anodes in ASTM seawater, using an impressed anodic current density of 0.62 mA/cm2. Uniform behavior was not obtained, even though all test samples were taken from the same parent anode, The electrochemical behavior of all samples could be readily classified into one of two distinct categories. Samples which underwent general corrosion and achieved closed-circuit potentials more active than -1.1 V (SCE) were arbitrarily termed Type-I samples, while samples which underwent pitting corrosion and did not achieve closed-circuit potentials more active than -0.945 V (SCE) were classified as Type-l samples. Faradaic efficiencies were determined to be higher for Type-I samples than for Type-II samples. Previous testing on other anode samples from the same heat had revealed only Type- I behavior. The presence of Type-II behavior in the current work can be attributed to the fact that the exposed surface area of the test samples ( 1 cm2) is much smaller than that utilized in the previous work (-39 cm2). It is demonstrated that the presence of small Type-II regions on the larger surface area samples would not be detected by the short-term electrochemical method.
Keywords: aluminum, sacrificial anodes, iridium-activated, cathodic protection, seawater